How To Calculate Moment Of Inertia Of Motor

It represents how difficult it overcomed to change its angular motion about that axis. Adding the moments of inertia of the components of the disk/shaft/spool system, calculate the value (with uncertainty) of the moment of inertia of the system, for both orientations of the disk. The concepts of “rotation” and “translation” are explained. 44 Reinforced Concrete 2. Thus the load inertia may be reduced so much that it is actually less than the motor's own inertia J m. • That means the Moment of Inertia I z = I x +I y. I know the motor's torque and the moment of inertia of the disk it will be turning. Suspend the quad by one arm and give it a little push and time the period. Then i want to add weight to the boat like a motor or some other elements and see how the boat trims. \$\endgroup\$ – Neil_UK Apr 23 '17 at 6:52 2 \$\begingroup\$ If you have (or can make) an accurate model of the rotor something like Solidworks will calculate the moment of inertia about the centroid of mass. The bending moment in a beam can be related to the shear force, V, and the lateral load, q, on the beam. It is calculated the same way you would calculate the inertia. Calculate the angular velocity of a rotating system when there are energy losses due to nonconservative forces. • To investigate and characterize the the rotational friction characteristics of the motor shaft and bearings. s (Ke) electromotive force constant 0. It is always considered with respect to a reference axis such as X-X or Y-Y. That means in the first second of applying that torque, the tip of your 7 meter long arm will move about 3. ANSWER: 0 T. GD Square is unit of Moment of Inertia of the rotor shaft. Apply the parallel axis theorem to each cutout. Gear Drive System. Select a motor type from AC Motors, Brushless DC Motors or Stepping Motors based on the required specifications. The formula for moment of inertia for a circle is the product of pi over four times the radius to the power of four. The equation for this is JL/JM = 50, or a ratio of 50:1. 5m to 3m in diameter. To calculate the moments of inertia about the solid rectangular block, the known equations below were used: 𝐼 = I( 2+ 2) 12 𝐼 = I( 2+ 2) 12 𝐼 = I( 2+ 2) 12 4. Moments of inertia: ( kilograms * square meters ) Taken at the output coordinate system. For my first example I will use a load with an inertia ratio of 50:1, meaning that load inertia is 50 times greater than the motor. Ball hits rod angular momentum example. Moment of Inertia, General Form. The "inertia mismatch" is a rule of thumb indicator for good controllability of the axis. The moment of inertia for a disk, or solid cylinder (see chart provided below), equals ½mr 2. And Moment of Inertia X Angular Velocity = Angular Momentum. • To measure the motor torque constant K m. Estimated Motor and Transmission Inertia and Drive Requirements. This reduction in load inertia makes it much easier to find a suitable motor. The J is. (3) Mass Radius of Gyration The Radius of Gyration k xx of a Mass (m) about an axis (x) is defined as: equ. does the starting torque of the motor give any indication about the motor moment of inertia? cheers. Calculating Joint Moments in the Squat By Andrew Vigotsky. Because I usually use >>: that for water hammer analysis. Calculate relevant pattern properties (area, centroid, moments of inertia). Moment Of Inertia Cylinder Equation Tessshlo. †Calculate the inertia applied to each element to calculate the total load inertia of the motor shaft conversion value. Using work energy. Method for Calculating Moment Loads on Linear Actuators. For many years, people in the fitness industry have calculated joint moments in the squat using the floor reaction force vector (FRFV) method or by assuming the external load is the only force inducing a moment (Figure 1). First, you calculate the moment of inertia at the centroid of the bar and aligned along the bar's local coordinate system (i. Cross-Product MOI is really just an indication of the symmetry of the object. Calculate the moment of inertia of the steel plate of mass m = 900 g in the figure below for rotation about a perpendicular axis passing through the origin. NInformation from the motor manufacturer includes a. 5 meter outside diameter tube with a 0. I know the moment of inertia is integer(r^2*dm). > my handbook of formulas has a myriad of entries for the moment of. INSTRUCTIONS: Choose units and enter the following: (m) This is the mass of the ellipsoid (b) This is the length of axis 1. The moment of inertia is the quantitative measure of rotational inertia, just as in translational motion, and mass is the quantitative measure of linear inertia—that is, the more massive an object is, the more inertia it has, and the greater is its resistance to change in linear velocity. sum of the torque necessary to deform the sample and the torque to overcome the inertia as shown in figure 2 (*). It is quite common to have gear ratios of 40, 50, or 100. 352 kg ⋅ m 2. – Calculate torque and angular momentum – Plug in to T net = dL/dt Repeat, using mass's lowest point as origin Wooden board falls off table – Mass m, starting from rest – Using edge of table as origin: – Calculate T net and a right edge of board at t=0 – (Assume board stays rigid → v proportional to r) Why does a helicopter need a tail rotor? m θ d. The moment of inertia, otherwise known as the mass moment of inertia, angular mass or rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis; similar to how mass determines the force needed for a desired acceleration. The moment of inertia calculates the rotational inertia of an object rotating around a given axis. 2 m diameter flywheel for the total system inertia. Thus the load inertia may be reduced so much that it is actually less than the motor’s own inertia J m. 0001 kg-m 2 The WR 2 of motors can be found on page 47 u To calculate WR 2 (GD 2) of single reduction integral gearmotor : WR 2 = WR 2 motor + WR 2 reducer EXAMPLE : Find WR 2 of B11-87-1MHH Motor = 1 hp, WR 2 = 30. This simple, easy-to-use moment of inertia calculator will find moment of inertia for a circle, rectangle, hollow rectangular section (HSS), hollow circular section, triangle, I-Beam, T-Beam, L-Sections (angles) and channel sections, as well as centroid, section modulus and many more results. NInformation from the motor manufacturer includes a. Calculate the moment of inertia of each of the following uniform objects about the axes indicated. For tests with a simulated moment of inertia, it is only necessary to adapt the acceleration at each time to step. If you apply a torque of 20000Nm to an object with the moment of inertia of 20000Nm2 you will get a fairly decent acceleration of 1 radian/s2. Gearboxes can reduce the inertia ratio,enabling higher-speed operation and/or the use of smaller, cheaper motors. , the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force). FACT: For a system of objects you will need to add the rotational inertia of each object to find the rotational inertia of a system. The load inertia has been reduced by a factor of n2 due to the gear train. The moment of inertia of the motor and all connected parts is 10, Calculate the time required for the motor with the speed-torque characteristic shown by curve (1) in Fig. There are three factors to calculate when sizing a motor; Moment of Inertia, Torque, and Speed. An 8 inch propeller has to compare a moment of inertia of 1,9 E-05 kg*m2. Reduce the inertia of the table by six times the value found in step 3. If there are others group of additional parts, do the same method. Total Moment of Inertia, [I total or ∑MK 2] = 5. Its also known as low Inertia motors. 01 V/rad/sec (Kt) motor torque constant 0. The rotor inertia can be estimated from measurements of the mechanical time constant, kt , and R. Sort By: Name | Popularity. High Inertia Loads. To calculate the equivalent circuit parameters, the speed-torque characteristic may be determined experimentally, as we described it or given by reference (by. That is the angular acceleration depend not only on the torque τ but also on the moment of inertia I of the body about the given axis which is determined by using the equation. The rotational constants are given in $\pu{MHz}$. calculate, as well as the moment of inertia of bearing units rotating masses. The motor having an initial angular speed of ! 0 = 1:06 102 rev/min will come to a stop when its angular speed goes down to zero:! = ! 0 + t 0 = 1:06 102 2ˇ 60 1:96t t = 0 21:06 10 2ˇ 60 1:96 = 5:66 s b) The radians covered between switching o and stopping is = 0 = 0 + ! 0t+ 1 2 t2 = 1:06 102 2ˇ 60 t 1:96 2 t2 = 1:06 102 2ˇ 60 5:66 1:96 2 5:662 = 31:43 rad 4. To properly size a motor you will need to calculate both torque and inertia. The trade-off of a gearbox is that it reduc-es the output speed of the motor/gear-. Then the total moment of inertia of the entire rocker box and secondary assembly is just the sum of these moments: I=∑ miri 2 (Equation 5) To estimate the moment of inertia about the azimuth axis we break the moment of inertia sum into two sections. About the Moment of Inertia Calculator. I don't need linear inertia calculations, but instead to calculate rotational motion inertia for an object rotating on itself over an axis. Rotational Motion: Moment of Inertia and check that your slope is consistent with your mass value (m1 + m2) thus verifying Eq. Relationship between Torque and Moment of Inertia. the formula to calculate the rotor motor inertia for 3 phase induction motor. Determine the moment of inertia of the shaded area with respect to the x axis. Using work energy. If inertia matching is the only concern, then the gear ratio can be calculated as: N = √ (J Load / J Motor) where N is the gear ratio, J Load is the inertia of the driven load, and J Motor is the inertia of the motor. Calculating vehicle inertia Knowing the inertia of a vehicle, especially around the yaw axis is very useful for dynamic simulations such as ChassisSim. Full load torque = 26470 lb-ft Synchronous speed = 1800 rpm Full load speed = 1785 rpm The moment of inertia of the load and the motor rotor are combined numerically to give the total lb-ft2 of the mass to be accelerated. The moment of inertia is defined for a molecule as it would be for any other solid: you consider the nuclei as points with mass, ignore the mass of the electrons, and you can then calculate either the scalar moment of inertia or the tensor of the same name. The moment of inertia is the weight multiplied by the radius of the gyration squared and divided by 32. Non-excited Motor. Note: Another way to calculate gear ratio is by reference to the individual gears. The equation is shown here as a reminder. I = 1/3 m L^2. It is determined from the cross-sectional area of the beam and the central axis for the direction of interest. where t is your torque, I is your moment of inertia, and a is your angular acceleration. The calculator can use any two of the values to calculate the third. Calculating Joint Moments in the Squat By Andrew Vigotsky. This reduction in load inertia makes it much easier to find a suitable motor. (5) can be rewritten in the following form,. (Refer to the below sections on calculations for each. The motor having an initial angular speed of ! 0 = 1:06 102 rev/min will come to a stop when its angular speed goes down to zero:! = ! 0 + t 0 = 1:06 102 2ˇ 60 1:96t t = 0 21:06 10 2ˇ 60 1:96 = 5:66 s b) The radians covered between switching o and stopping is = 0 = 0 + ! 0t+ 1 2 t2 = 1:06 102 2ˇ 60 t 1:96 2 t2 = 1:06 102 2ˇ 60 5:66 1:96 2 5:662 = 31:43 rad 4. Definition of Mass Properties Terms: Mass vs. A small moment is then applied to the aircraft to measure its period of oscillation, which allows further calculation of its angular frequency, as denoted by omega (⍵). (II) Calculate the moment of inertia of the array of point objects shown in Fig. This reduction in load inertia makes it much easier to find a suitable motor. This article presents methods by which pump and motor moment of inertia may be estimated. Self learning tutorials on the calculations based on numbers for you. • To investigate and characterize the the rotational friction characteristics of the motor shaft and bearings. The body is a collection of six circles, so the momentum of inertia should be calculated as a sum of six (in this case equal) terms. Then the total moment of inertia of the entire rocker box and secondary assembly is just the sum of these moments: I=∑ miri 2 (Equation 5) To estimate the moment of inertia about the azimuth axis we break the moment of inertia sum into two sections. down of reciprocating compressor. Knowledge of the moment of inertia of a pump, motor and associated components is typically required for transient analysis of a pumped system. The rotational motion does obey Newton’s First law of motion. Polar Moment Of Inertia Hollow Cylinder Equation Tessshlo. Last visit: 4/19/2020. Calculate axial and shear loads acting on individual bolted joints in the pattern. Figure 3: The values of moment of inertia of the forearm were similar to the value from Winter [6]. Solve the equation to find the moment of inertia of a triangle about an axis through its center of mass, in terms of M and L. Moment of inertia tensor. A helicopter rotor blade can be considered a long thin rod. The use of radians is introduced. A vessel's "Mass Moment of Inertia" also called "Roll Moment of Inertia" is a way of expressing resistance to being put into motion by a force. sum of the torque necessary to deform the sample and the torque to overcome the inertia as shown in figure 2 (*). NInformation from the motor manufacturer includes a. Moment of inertia and Its calculation. The processor 317 calculates the moment-of-inertia and the center-of-gravity of the part at positions 316a, 316b and causes a display unit (not shown) to display the calculated values. When a torque is applied to body the angular acceleration α is given by. Moment of Inertia Metric Conversion Calculator. Area moment of inertia - double pipe beam? I'm trying to calculate the Area Moment of inertia of a beam that consists of two same size pipes welded one on top of the other. The moment of inertia of the load and the motor rotor are combined numerically to give the total lb-ft2 of the mass to be accelerated. This behavior can also be seen in the transfer function of Equation 16. cm²], the component of the motor shaft is - If converted to SI units of the inertia moment, the inertia moment is expressed as I in SI units and this is represented as an equation below. I = 1/3 m L^2. Right now you show that the LCB is ~ 1 foot forward of the LCG (assuming you are measuring from the forward perpendicular), which means that the trimming moment would 1 ft* lbs displacement. If you apply a torque of 20000Nm to an object with the moment of inertia of 20000Nm2 you will get a fairly decent acceleration of 1 radian/s2. Rotational version of Newton's second law. For exam- ple a 25:1 gear ratio will reduce the effec- tive load inertia by 252 , or 625 times. 3 Note: where b effective width of compression flange bw average width of web Use actual b if it is less than the calculated b using the above formulae. Hence, torque, T = I = (51. Rotational kinetic energy. It can be written as. For the identification of friction parameters an energy analysis is performed considering the effects of cogging and white noise on phase currents and a solution to avoid those disturbances is proposed. Its inner radius is 100 mm. The weight may be of significance in connection with transportation and installation. J L = inertia of load reflected to motor. Making statements based on opinion; back them up with references or personal experience. Not pictured but also available: wood planks to roll these objects down. Moment of inertia or second moment of area is important for determining the strength of beams and columns of a structural system. By multiplying the velocity constant by the nominal motor voltage, obtain the theoretical no-load speed of the motor (zero torque and no-load speed) and plot it on the left vertical axis. 352 kg ⋅ m 2. Where, Δ D is the maximum deflection, the uniformly distributed load on the beam is w D, the length of the beam is L, E is the modulus of elasticity, and I X is the moment of inertia along X axis. The torque can be affected by an opposing force that results from a resistant surface. That is, for a specific motor, if load inertia reflected to the motor shaft can be made to match the motor inertia, disregarding added inertia and inefficiency of the reducer, power transfer will be optimized and maximum acceleration of the load will result. A generic expression of the inertia equation is. Find the distance between the neutral axis and the centroid. The moment of inertia I of the rotor can be calculated by using the method of superposition. This tool helps to draw any open, closed, cut, holed 2D cross section, extrude to 3D geometry and then calculate mass moment of inertia properties. Of course, the part to be tested also has inertia. Low Inertia motors have advantage of precise position accuracy at lesser time. automatic weight calculator for rectangular, square, round, or hexagonal, plate, tube, bar, beams, sheet, rod and other engineering material shapes. The rotational constants are given in $\pu{MHz}$. The value is given as, C s =0. Polar moment of inertia will be calculated from the following equation. We know that mass of the weight is m=12. The total moment of inertia for the capsule would be the sum of its constituent moments of inertia, so it would be Rectangle's + 2 * (Semicircle's). moment of inertia conversion factors provided by unitconversion. long and has a mass of 160 kg, calculate the moment of inertia of the three rotor blades about the axis of rotation. Polar Moment Of Inertia Hollow Cylinder Equation Tessshlo. Now if we talk about a DC motor which also works on the same principle since it is also a rotational machine. From oscillation frequency and the value of the position to current gain you used, you can calculate the effective rotor inertia. Calculating the moments of inertia of various objects, even symmetrical ones, can be a lengthy and tedious process. A low inertia ratio (e. For very small motors, when the moment of Inertia of the rotor and the mechanical load are desirably small, they can start without any starting methods. To do this, I need the engine's moment of inertia. 55 meter per second. Thus, (1a,b,c). Since the greater the rated output moment of the servo motor is, the greater the moment of inertia of its rotor is, so it is meaningless to simply discuss the magnitude of the motor's moment of inertia. Its size and shape d. The total inertia to be overcome is the sum of J(load) and J(screw) = 1. 4 The motion equation Let us call J the moment of inertia of the wheel and the motor rotator. Rotational Motion: Moment of Inertia and check that your slope is consistent with your mass value (m1 + m2) thus verifying Eq. Calculating vehicle inertia. • To investigate and characterize the the rotational friction characteristics of the motor shaft and bearings. m is the motor torque, and the inertia J eff is the e ective inertia \felt" by the motor. θ = Angle of twist in radians on a length. An 8 inch propeller has to compare a moment of inertia of 1,9 E-05 kg*m2. Functionally, by applying a step angular speed set point (ω2-ω1), measuring the time required to achieve the new speed (ΔT) and the torque (τ), to calculate the rotor inertia. Polar moment of inertia will be calculated from the following equation. The trade-off of a gearbox is that it reduc-es the output speed of the motor/gear-. We want to replace the weight with a motor and we need to calculate its moment of force. This measurement is obtained using the rated motor amps and sufficient weight placed radially on the motor shaft. 8–43 about (a) the vertical axis, and (b) the horizontal axis. Angular Acceleration and Moment of Inertia in Machine Design. Rolling without slipping problems. The speed at which the motor rotates is independent of inertia. Find moment of inertia of a uniform hollow cylinder Home Problems and Answers Classical Mechanics Find moment of inertia of a uniform hollow cylinder We know that the moment of inertia for hoop with radius R is mR2. angular speed 2. I = k m r 2 (2c). The method of calculating radius of gyration. This reduction in load inertia makes it much easier to find a suitable motor. Then, use that same factor in the equations below to calculate the required simulation flywheel polar moment of inertia. – Calculate torque and angular momentum – Plug in to T net = dL/dt Repeat, using mass's lowest point as origin Wooden board falls off table – Mass m, starting from rest – Using edge of table as origin: – Calculate T net and a right edge of board at t=0 – (Assume board stays rigid → v proportional to r) Why does a helicopter need a tail rotor? m θ d. The Rotating Earth: The earth's rotation is a prominent example of rotational kinetic energy. m/Amp (R) electric resistance 1 Ohm (L) electric inductance 0. I think this is very similar to calculations for a car but only with 2 wheels (or for a bike) except that the inertia of each component is easy to calculate but I am getting very confused with how to calculate my total inertia and if parallel axis theorem applies here. From Torsion Equation we can consider. MEASUREMENT OF MOMENT OF INERTIA The aim of this measurement is to determine the moment of inertia of the rotor of an electric motor. But there is an additional twist. Angular momentum. In the second case, because of the moment of inertia of the flywheel along with the moment of inertia of armature, the time taken by the system for slowing down is more. If known, enter motor inertia (else, enter "0"), Jm (kg-m 2, g-mm 2) Enter motor inertia in g-mm 2 if different than above Motor operating efficiency, etamotor. Inertia Force F I. does the starting torque of the motor give any indication about the motor moment of inertia? cheers. Using energy methods, calculate the moment of inertia of the can if it takes 1. The formula for moment of inertia for a circle is the product of pi over four times the radius to the power of four. 125568 N or 125. Because I usually use >>: that for water hammer analysis. Heavier objects have a greater moment of inertia and roll more slowly. If there are others group of additional parts, do the same method. Now let us find out the rate of change of speed with respected time at the normal speed of the motor for both the cases from the curves. diameter, connected through a 3:1 gear set, first use equation 1 to determine the load inertia. Apply the parallel axis theorem to each cutout. This is the information from the software I think is required to do the calculations. A parameter that is sometimes overlooked is the load moment of inertia or simply put load inertia. Not pictured but also available: wood planks to roll these objects down. To calculate the moment of inertia of such a continuous distribution of mass at various distances, we use calculus, due to its dexterity with continuous variables. Its size and shape d. J L = inertia of load reflected to motor. does the starting torque of the motor give any indication about the motor moment of inertia? cheers. 00767V/rad/s (often ≥. It represents how difficult it overcomed to change its angular motion about that axis. Knowledge of the moment of inertia of a pump, motor and associated components is typically required for transient analysis of a pumped system. And Moment of Inertia X Angular Velocity = Angular Momentum. It consists of dial plate diameter, thickness, density for calculate mass, the number of stations, station mass, station radius to rotation center, etc. The Rotating Earth: The earth's rotation is a prominent example of rotational kinetic energy. As you may have noticed, the images update in real time as the dimensions are adjusted. Find moment of inertia of a uniform hollow cylinder Home Problems and Answers Classical Mechanics Find moment of inertia of a uniform hollow cylinder We know that the moment of inertia for hoop with radius R is mR2. Since the greater the rated output moment of the servo motor is, the greater the moment of inertia of its rotor is, so it is meaningless to simply discuss the magnitude of the motor's moment of inertia. TAKEAWAYS: High load-to-motor inertia ratios push resonance and anti-resonance peaks to lower frequencies, shrinking the operating bandwidth of the machine. This simple, easy-to-use moment of inertia calculator will find moment of inertia for a circle, rectangle, hollow rectangular section (HSS), hollow circular section, triangle, I-Beam, T-Beam, L-Sections (angles) and channel sections, as well as centroid, section modulus and many more results. angular speed 3. It is always considered with respect to a reference axis such as X-X or Y-Y. In the system below, a torque, τ a, is applied to gear 1 (with moment of inertia J 1). Cross product and torque. 0001 kg-m 2. Secondly if the square you cut out is not centred on the axis you need to calculate its moment of inertia using the parallel axis theorem. The one that calculates torque due to inertia has the form: T=I α which says that torque required (T) is equal to moment of inertia (I) times the angular acceleration (α). Note that although the strict mathematical description requires a triple integral, for many simple shapes the actual number of integrals worked out through brute force analysis may be less. Inertia Force F I. 0 rotations. is the mechanical losses at the rated speed, from equation (2) , the equation for moment of inertia is given by (3). This reduction in load inertia makes it much easier to find a suitable motor. The bending moment in a beam can be related to the shear force, V, and the lateral load, q, on the beam. Speed ramps on the AUT require a start velocity, an end velocity, and a set-point for the acceleration. I don't need linear inertia calculations, but instead to calculate rotational motion inertia for an object rotating on itself over an axis. This is because the smaller the ratio of load inertia to motor inertia, the less compliance will affect the system. It represents how difficult it overcomed to change its angular motion about that axis. The load inertia has been reduced by a factor of n2 due to the gear train. Moment of Inertia, as I was explained, is treated by some to be mass itself in Linear motion. Motors can be equipped with an mechanical integrated holding brake and/or a wide variation of feedback devices. Calculate relevant pattern properties (area, centroid, moments of inertia). It can be found by integrating over the mass of all parts of the object and their distances to the center of rotation, but it is also possible to look up the moments of inertia for common shapes. A 25-hp motor, based on rated torque and inertia, and with no other inertia attached to the shaft, could accelerate at 20,020 rpm/sec. The body is a collection of six circles, so the momentum of inertia should be calculated as a sum of six (in this case equal) terms. Details to perform each of these steps are provided in the following sections. The product of the mass of a particle and the square of its distance from an axis of rotation. Motor Shaft Conversion Moment of Inertia Z 1 : Teeth number of the motor-side gear Z 2 : Teeth number of the load-side gear R : Gear ratio Z 1 /Z 2 J A : Moment of inertia of load[kg・m 2 ] J 1 : Moment of inertia of the motor-side gear[kg・m 2 ] J 2 : Moment of inertia of the load-side gear[kg・m 2 ]. I think this is very similar to calculations for a car but only with 2 wheels (or for a bike) except that the inertia of each component is easy to calculate but I am getting very confused with how to calculate my total inertia and if parallel axis theorem applies here. 28*10^-38 gm-cm^2. Moment of inertia of a same object will change against different axis. r = distance to axis of rotation. Angular momentum of an extended object. The motor has axle whose radius is r. Method for Calculating Moment Loads on Linear Actuators. Figure 8 – Motor torque and current. The moment of inertia of an object is a numerical value that can be calculated for any rigid body that is undergoing a physical rotation around a fixed axis. The mass for engine is 5200kg. For example, in a hoist calculation allowance should be made to include the motor, brake disc, gearbox, winding drum, ropes, load etc. Total Moment of Inertia, [I total or ∑MK 2] = 5. what u can do is split the I beam in to. Ball hits rod angular momentum example. Thanks for contributing an answer to Worldbuilding Stack Exchange! Please be sure to answer the question. 00 radians/s 2, what is the torque? Answer: The torque can be found using the torque formula, and the moment of inertia of a. Determine the relationship between the applied force, frictional force (of the brake) and the torque. For a rotary load, it's the product of its mass and the square of the perpendicular distance of the mass from the axis. where t is your torque, I is your moment of inertia, and a is your angular acceleration. But there is an additional twist. For my first example I will use a load with an inertia ratio of 50:1, meaning that load inertia is 50 times greater than the motor. Intuitively, if a large enough mass is attached to the motor, the motor won't be able to turn. The formulae for the calculation of the moment of inertia is given by: J = (Tn 2…)2 mgR2 L (1) where 1. In the second case, because of the moment of inertia of the flywheel along with the moment of inertia of armature, the time taken by the system for slowing down is more. Finally, the Parallel Axis Theorem is expounded. Obtaining the moment of inertia of the full cylinder about a diameter at its end involves summing over an infinite number of thin disks at different distances from that axis. Part I of Rotations. In the illustrated 11-inch propeller from carbon the entire moment of inertia: 5,7 E-05 kg*m2. The torque due to acceleration is found by multiplying the total inertia of the system (J t) by the angular acceleration (α). does the starting torque of the motor give any indication about the motor moment of inertia? cheers. Below is a review of understanding torque curves and understanding power curves. 2 The specifications on the DCMCT system model parameters are given in Table A. The yardstick by which this is judged is the inertia ratio, which is defined as the inertia of the driven component(s) divided by the inertia of the motor. 5 rev/s in 9. • To investigate and characterize the the rotational friction characteristics of the motor shaft and bearings. I = m L^2 = 110 kg * (3. You can calculate the moment of inertia of a pendulum by measuring the period of oscillation for small amplitudes. 0 m apart on a light rod (whose mass can be neglected). r = distance to axis of rotation. The Moment of Inertia of an Ellipsoid rotating about the Axis 3 calculator computes moment of inertia for axis 3, the (the long axis, a, in the picture) based on the mass an the length of axis b. >>The formula's are just the same as they always were - integral of >>mass times distance squared. The formula for moment of inertia is the "sum of the product of mass" of each particle. Obtain the turning moment and hence find the mean torque Calculation of the Moment of Inertia of the Flywheel to limit the speed fluctuation to given value Design of the flywheel with the required Moment of Inertia 2/14/2006 ACR/ME209/2006 Design of a Flywheel: Procedure Calculation of torque due to inertia forces x =(n+1)r−[rcosθ−nrcosα] r. The processor 317 calculates the moment-of-inertia and the center-of-gravity of the part at positions 316a, 316b and causes a display unit (not shown) to display the calculated values. This paper investigate the moment of inertia as a significant factor on the performance of PSO algorithm utilizing the weighted transient response index (WTRI) based fitness function. To simplify the calculation, we neglect the small hub at the centre and the rounding of all sharp edges. length of moment arm and magnitude of force Why is the radius of gyration instead of the radius of rotation used to calculate the moment of inertia? The radius of gyration for any rotating body is the radius of the axis about which it rotates , and this axis may / may not be passing through the centre of mass. J = Polar moment of inertia. Not pictured but also available: wood planks to roll these objects down. (longer acceleration time) The moment of inertia is a measure of the "inertia" of the load moving in a. More on moment of inertia. 4 kg m2 and angular acceleration, = 5. 125568 N or 125. MATLAB/SIMULINK based modeling is adopted to compare the transient performance of three-phase induction motor including main flux saturation with and without the moment of inertia (MOI) of the system attached to the motor. i saw pump and motor inertia in hammer help but their unit is Kg. Calculate the moment of inertia of the cylinder about a longitudinal axis through its center in terms of M and R. We want to replace the weight with a motor and we need to calculate its moment of force. >>The formula's are just the same as they always were - integral of >>mass times distance squared. The moment of inertia of the astronaut and her equipment about the axis of rotation is 45 kg-m2. For a value of 165778, selecting 4. pdf Available via license: CC BY-NC-ND Content may be subject to copyright. The needed formulas are outlined below. 8 kg and M=3. inertia of the motor. Direct current Excited. Moment of inertia is determined as the numerical value of the added load divided by the difference in. in kg-m2 There is no special way to calculate motor rotor inertia. It is used to determine the moment of inertia. , the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force). separated so that inertia can be calculated for each part that moves as the Servo Motor rotates. Therefore, the moment of inertia is only concerned with the design of the blade itself and the magnitude of the wind force. An inertia ratio that is too low means the motor is likely oversized, leading to higher than necessary cost and energy usage. Thus there are errors that do not allow evaluating the level of mechanical losses in an electric motor and determining the moment of inertia of its rotating masses with high accuracy. Note that the instantaneous power P delivered by the motor is directly proportional to ω,. Moment of inertia and Its calculation. Without getting too technical, the diagonal elements of theses matrices always represent Moments of Inertia about the primary axes of an established coordinate system. Equally important, are the switching torque of the electrical motor and the. shaft, damper as well as the compressor resistance torque are extremely important in simulating start-up and shut. I am making a very simplified model of offshore propulsion systems (electric motors specifically), and I was wondering if there is any (easy) way to guesstimate weight and/or moment of inertia for propellers ranging from 1. This study aims to generalize and propose an optimal combination of different methods to calculate total components of the added mass matrix with computer. Need to quickly calculate and convert speed, torque, and power?. It depends on the body's mass distribution and the axis chosen, with larger moments. Moment of Inertia, as I was explained, is treated by some to be mass itself in Linear motion. That is the angular acceleration depend not only on the torque τ but also on the moment of inertia I of the body about the given axis which is determined by using the equation. Reduce the inertia of the table by six times the value found in step 3. Calculate the mass moment of inertia required for the flywheel of the punching press machine. m2 unit, instead of Newton meters. x-y axes: x and y are the coordinates of the element of area dA=xy Ixy = ∫xy dA • When the x axis, the y axis, or both are an axis of symmetry, the product of inertia is. In the second case, because of the moment of inertia of the flywheel along with the moment of inertia of armature, the time taken by the system for slowing down is more. asked by birju on May 10, 2013; physics. Some learners will enjoy performing the calculations manually, (we will briefly illustrate and describe some of the calculations later on in this lesson), while others prefer, utilizing one of the many online programs available to help you with all the necessary specifications of the servo motor required for your project and expediate you through the servo motor selection process. The Momentum Calculator uses the formula p=mv, or momentum (p) is equal to mass (m) times velocity (v). The units in any choice of notation system are… Time Force Length Time Force Length Time Time v Jpu = ∗ × ∗ ∗ ∗ × = ( ) ( ) ( ) (Re ) A convenient unit of time is Seconds. I know the motor's torque and the moment of inertia of the disk it will be turning. -This distance is from the axis of the motor to each element?. formula updated in v1. The moment… Read More; rigid bodies. Easy to experiment, understand and learn. Infant Growth Charts - Baby Percentiles Overtime Pay Rate Calculator Salary Hourly Pay Converter - Jobs Percent Off - Sale Discount Calculator Pay Raise Increase Calculator Linear Interpolation Calculator Dog Age Calculator Ideal Gas Law Calculator Euler Number Formulas Calculator Torque Equations Formulas Calculator Engine Motor Horsepower. 13-2 (a) to accelerate the centrifuge to 98 per cent of its ultimate speed. 5 meters, in two seconds it would have moved 10. 28*10^-38 gm-cm^2. The Excel spreadsheet requires several calculations to arrive at values for the angular acceleration and torque that are used to calculate the moment of inertia. Moment of Inertia - WR2 (GD2) WR 2 of Integral Gearmotor (excluding motor) unit = lb-in 2 GD 2 of Integral Gearmotor (excluding motor) unit = 0. Self learning tutorials on the calculations based on numbers for you. (a) If each of the three rotor helicopter blades is 4-m long and has a mass of 120 kg, calculate the moment of inertial of the three rotor blades about the axis of rotation. More on moment of inertia. Inertia Force F I. ⑤ Go to motor selection from movement pattern It links to the motor selection from the movement pattern when clicking. The units are far from simple, so here the ones easiest to use with oz · in: T (oz·in) = I (oz· in· sec2 ) · α (radians). Need to quickly calculate and convert speed, torque, and power?. A typical example may be a precast T-beam. Simulator , May 13, 2019 , in forum: Hydrodynamics and Aerodynamics Replies:. Hence, torque, T = I = (51. Unlike F AD and F RR, F I can be positive or negative. Consider 500mm to be the max size of the flywheel dia. The torque acts in the direction of θ 1. A specific axis of rotation must be defined to calculate the moment of inertia since it measures an object's resistance to a change in rotational direction. The moment of inertia of an object is a calculated measure for a rigid body that is undergoing rotational motion around a fixed axis: that is to say, it measures how difficult it would be to change an object's current rotational speed. We can improve comfort, and we can improve safety by increasing the "Roll Moment of Inertia" of the vessel. High Inertia Loads. Table 1 Comparison of measurements and calculations by means of Catia V5 software for mass moments of inertia in selected car engines No Type of engine Measured weight [kg] Mass moment of inertia I z, kg ·m 2 Crank-shaft flywheel assembly connecting rod. We want to replace the weight with a motor and we need to calculate its moment of force. ) Once you've calculated the inertia, torque and speed for the motor you'll select the type of motor based on. Inertia ratios are typically given for stepper or servo motors, and they are calculated by dividing the total amount of load inertia (or reflected load inertia if geared) by the rotor inertia of the motor. It is based not only on the physical shape of the object and its distribution of mass but also the specific configuration of how the object is rotating. It depends on the body's mass distribution and the axis chosen, with larger moments. The moment of inertia is a value that describes the distribution. 3 Nm is applied to the object in 5s. Equation: Motor Speed. To calculate the moments of inertia about the solid rectangular block, the known equations below were used: 𝐼 = I( 2+ 2) 12 𝐼 = I( 2+ 2) 12 𝐼 = I( 2+ 2) 12 4. Mass moment of inertia is critical for mechanical, rotation, dynamics performance prediction. Moment of inertia of a same object will change against different axis. Knowledge of the moment of inertia of a pump, motor and associated components is typically required for transient analysis of a pumped system. Move the shape so that its centroid is at 0, 0. To calculate the moment of inertia of such a continuous distribution of mass at various distances, we use calculus, due to its dexterity with continuous variables. The axis of rotation is at the center of the rod. For very small motors, when the moment of Inertia of the rotor and the mechanical load are desirably small, they can start without any starting methods. Torque, T = I , where moment of inertia I = 51. Attach a pulley o. N-m^2 is indeed a unit of rotational inertia and you can use a unit conversion program such as FlexUnits to convert. For any change in rotation speed, the load inertia will reflect back through the gears to the motor. Calculate the moment of inertia of the steel plate of mass m = 900 g in the figure below for rotation about a perpendicular axis passing through the origin. In addition to the breakaway and running torque the inertia of the load must be considered when selecting a motor or drive. This is the way to find the moment of inertia for cubes, boxes, plates, tiles, rods and other rectangular stuff. Calculate Angular Deflection of Cylinder. To achieve such a force, we. The torque due to acceleration is found by multiplying the total inertia of the system (J t) by the angular acceleration (α). Abstract: In order to increase the measuring range of the moment of inertia, a new measurement equipment with triple torsion bars based on torsion pendulum was designed. The overall moments of inertia are calculated using the parallel axis theorem. Generally, most servo motors will choose the motor with small inertia, so as to satisfy the high responsiveness of the servo system. The torque acts in the direction of θ 1. Inertia Units Conversion Calculator. The total torque exerted on a body is 81 N-m and mass moment of inertia is 9 kg-m 2. • To investigate and characterize the the rotational friction characteristics of the motor shaft and bearings. s (Ke) electromotive force constant 0. Get a piece of string 1 m long with a weight (lets say 1 kg - use a strong string) on. For a rotary load, it's the product of its mass and the square of the perpendicular distance of the mass from the axis. It also includes an inertia calculator tool which helps you calculate it. Hence, torque, T = I = (51. The diameter of the drum, D = 0. , the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force). (4) k: equ. The results can be sorted depending on various parameters (e. The calculation of the real moment of inertia of a set of loads is of high relevance as a miscalculation can lead to an oversizing, undersizing or simply an invalid solution. The equation is shown here as a reminder. 3 Nm is applied to the object in 5s. It simplifies the design process to help you build a better machine. Horsepower to Torque Converter is an online tool used in electrical engineering to calculate how much torque will be generated according to the input power value either in horsepower or watts. It's possible to calculate how long it will take for a given motor to come up to speed with a given rotational moment of inertia flywheel. For exam- ple a 25:1 gear ratio will reduce the effec- tive load inertia by 252 , or 625 times. The moment of inertia of a pump is its resistance to changes in angular velocity as it rotates about its shaft. K_theta of the steel connecting rod is GJ/L. Select a motor type from AC Motors, Brushless DC Motors or Stepping Motors based on the required specifications. The moment of inertia is used for calculating the acceleration torque. Posts: 1381. does the starting torque of the motor give any indication about the motor moment of inertia? cheers. The area moment of inertia is also called the second moment of area. Estimated Motor and Transmission Inertia and Drive Requirements. The values of moment of inertia of the forearm were similar to the value from Winter [6], although the obtained values from the proposed method showed a tendency depending on the angular velocity (Figure 3). For a BLDC/PMSM motor this length represents the number of turns of wire in the stator armature which interact with the 'flux' provided by the rotor. For this calculation if only rim, spoke cables, cabin/rider weight is required then you can make rough estimate what might be the weight of spindle, hub, bearing, etc. For the same area, the further away the material of a cross-section is away from the axis about which it twists, the greater the Polar Moment of Inertia. Time Master II - Time Calculator for Pilots, Accounting, Broadcasting Ultra Measure Master - Most Complete, Easy-to-Use Metric Conversion Calculator Measure Master Pro - Feet-Inch-Fraction Calculator for Do-It-Yourselfers. Rating: (133) Load vs rotor inertia is an important parameter. If the moment of inertia of its molecules is 8. – Calculate torque and angular momentum – Plug in to T net = dL/dt Repeat, using mass's lowest point as origin Wooden board falls off table – Mass m, starting from rest – Using edge of table as origin: – Calculate T net and a right edge of board at t=0 – (Assume board stays rigid → v proportional to r) Why does a helicopter need a tail rotor? m θ d. Now let us find out the rate of change of speed with respected time at the normal speed of the motor for both the cases from the curves. The formula can be used to build up moment of inertia for complex shapes like cylinders. 2 The specifications on the DCMCT system model parameters are given in Table A. >I'm looking for not the definition of moment of inertia but empirical. ( b) How much torque must the motor apply to bring the blades up to a speed of 5. For simple understanding, we can imagine it as Newton's Second Law for rotation. The diameter of the drum, D = 0. Integration over the whole domain is not the easier option nor the recommended one. A uniform rod of length L and mass m, rotating about its end, has moment of inertia. The motor data sheet is given in Table A. The pull-up torque Torque and starting of high inertia loads, part 1 This is the first part of a two-part series. >>The formula's are just the same as they always were - integral of >>mass times distance squared. Relationship between Torque and Moment of Inertia. Calculate the mass and inertia of each cutout. In the second case, because of the moment of inertia of the flywheel along with the moment of inertia of armature, the time taken by the system for slowing down is more. 60 s by a motor exerting a constant torque. This measurement is obtained using the rated motor amps and sufficient weight placed radially on the motor shaft. (5), the moment of inertia depends on the axis of rotation. I don't need linear inertia calculations, but instead to calculate rotational motion inertia for an object rotating on itself over an axis. For a solid sphere I = 2/5 (m x r²). The use of radians is introduced. cm²], the component of the motor shaft is - If converted to SI units of the inertia moment, the inertia moment is expressed as I in SI units and this is represented as an equation below. G is the shear modulus of the spring material, J is the polar moment of the spring - if it's a circular cross-section this would be (pi/32)*d^4, and L is the length of the spring. Gearboxes can reduce the inertia ratio,enabling higher-speed operation and/or the use of smaller, cheaper motors. Reduce the inertia of the table by six times the value found in step 3. Generally, horsepower is a unit for measuring the power of various electrical motors, piston engines, steam turbines etc and it is equal to 746 watts or. This selector does not request any data nor provide any calculations related to the actual moment of inertia (or inertia mismatch) of your particular Load. The moment of inertia of the load and the motor rotor are combined numerically to give the total lb-ft2 of the mass to be accelerated. controldesign. 27 in 4 I xy = 6. Input required: kinetic energy of the system- to. Objects with their mass focused closer to the axis of rotation have a lower moment of inertia and thus roll faster. In the second case, because of the moment of inertia of the flywheel along with the moment of inertia of armature, the time taken by the system for slowing down is more. Industries and applications High Dynamic Performance series are ideal for: DC motor replacement Plastic & rubber Extruders. This involves an integral from z=0 to z=L. The calculator can use any two of the values to calculate the third. It is now more common to use inertia than GD2. This Video explains how to calculate the moment of inertia for a rotating disc system and hoe to determine the motor's torque required. Visit Stack Exchange. If known, enter motor inertia (else, enter "0"), Jm (kg-m 2, g-mm 2) Enter motor inertia in g-mm 2 if different than above Motor operating efficiency, etamotor. Speed, torque, safety ratio, etc. A vessel's "Mass Moment of Inertia" also called "Roll Moment of Inertia" is a way of expressing resistance to being put into motion by a force. (1) from above it can be shown that: equ. Total Moment of Inertia, [I total or ∑MK 2] = 5. AGN 183 - Rotor Inertia MOMENTS OF INERTIA The moment of inertia, otherwise known as the angular mass or rotational inertia, of a rigid body is a tensor that determines the torque needed for a desired angular acceleration about a rotational axis. the formula to calculate the rotor motor inertia for 3 phase induction motor. The mass for engine is 5200kg. The formulae for the calculation of the moment of inertia is given by: J = (Tn 2…)2 mgR2 L (1) where 1. Step 2: Calculate load parameters. Attach a pulley o. 2 Experimental Determination The configuration, measurements, and calculations for the test to determine the block's moment of inertia can be found below. Substitute into equation above and you will get an approximation of the Inertia. Before starting this process, the following application informa-. More on moment of inertia. Constant angular momentum when no net torque. Ball hits rod angular momentum example. Calculate the load torque, loading moment of inertia and rotational speed of the motor driving shaft. hi[:)] i use hammer7. Motor inertia Jm = 3. However, if the mass is initially at rest torque is required to get it spinning, and the mount of torque needed is dependent on (a) the rotational moment of inertia of the mass and (b) how quickly you want it to get up to speed. Unlike breakaway torque, if a load has a high moment of inertia it may take a significant period of time to accelerate or decelerate. One of the features is the moment of inertia tensor - Unity3D one, PhysX one. All mass properties and dimesions are known, but I don't know how to account for the chain mass in the inertia calculation. Generally, most servo motors will choose the motor with small inertia, so as to satisfy the high responsiveness of the servo system. where Ig is the MI at the CG of section. In mechanical engineering terms, knowing how to calculate the load inertia of a mechanical system is very important. Thus there are errors that do not allow evaluating the level of mechanical losses in an electric motor and determining the moment of inertia of its rotating masses with high accuracy. Since the moment of inertia of an ordinary object involves a continuous distribution of mass at a continually varying distance from any rotation axis, the calculation of moments of inertia generally involves calculus, the discipline of mathematics which can handle such continuous variables. The moment of inertia, otherwise known as the mass moment of inertia, angular mass or rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis; similar to how mass determines the force needed for a desired acceleration. Reduce the inertia of the table by six times the value found in step 3. This selector does not request any data nor provide any calculations related to the actual moment of inertia (or inertia mismatch) of your particular Load. This is the currently selected item. I've got a small DC brush-type gear motor, and I don't know the moment of inertia. Tip: Grossly inflate your RPM-C inertia entries to see the effect. Integration over the whole domain is not the easier option nor the recommended one. From Torsion Equation we can consider. I know the moment of inertia is integer(r^2*dm). CONVERT: (Select units then press Calculate button) Motor Testing Software. The moment of inertia of a figure is the sum of moments of inertia of its parts. Jt = total inertia of the system (kgm2) a = angular acceleration (rad/s2) The total system inertia includes the inertia of the motor (because the motor has to overcome its own inertia), coupling, pulleys, and load. Calculate the moment of inertia of the inertial load which is made of aluminum Also, evaluate the motor total moment of inertia. It also includes an inertia calculator tool which helps you calculate it. If the mecahnism is frictionless, the answer is: zero. Brushless dc motors (BLDC) are 3 phase synchronous. We can improve comfort, and we can improve safety by increasing the "Roll Moment of Inertia" of the vessel. It does work better for larger aircraft, measuring the period of a quad-pendulum will be tricky. This function can calculate inertia of various load shapes such as cylinder, square block, variable speed, linear movement, hanging, conical, and conical base. 40 in 4 I y = 6. When a motor and a load are coupled together, the ratio of load inertia to motor inertia determines how well the motor can control the load during acceleration and deceleration. As you may have noticed, the images update in real time as the dimensions are adjusted. Figure P10. This paper presents a comprehensive analysis for the analytic and experimental calculation of the inertia moment of a squirrel-cage induction motor. Motor Sizing Calculations. First, it is directly proportional to the size of the wind, and second is proportional to the windward area of the blade surface; third is proportional to the maximum power. 1 meter diameter shaft with a mass of 1000 kg is done in the exact same manner. Calculate the inertia of the table as it would be if there were no cutouts. For a value of 165778, selecting 4. The Rotating Earth: The earth's rotation is a prominent example of rotational kinetic energy. The premier tool for sizing and selecting motor and drive solutions. What is a typical ratio of the application load inertia to the motor inertia ? It is not unusual that the application load is in a range of 1:1 to 5:1 to allow highest loop bandwidth and dynamic response. Moment of Inertia, General Form. The rotational motion does obey Newton's First law of motion. Now let us find out the rate of change of speed with respected time at the normal speed of the motor for both the cases from the curves. 0 × 10−5 kg-m2 Motor constant Km ≈. In theory, a "perfect" inertia match of 1:1 (load inertia equals motor inertia) should be the goal, but in the real world, this may not be achievable or practical. Moment of Inertia. Moment of Inertia conversion table and factors: List of abbreviations: Unit of measurement : Abbreviation : gram square centimeter g cm² kilogram force centimeter sq. SOLUTION : • Compute the moments of inertia of the bounding rectangle and half-circle with respect to the x axis. The moment of inertia I of the rotor can be calculated by using the method of superposition. More on moment of inertia. Gearboxes can reduce the inertia ratio,enabling higher-speed operation and/or the use of smaller, cheaper motors. 44 Reinforced Concrete 2. 2 Symbol Description ale Unir Motor: NmA k Motor Terqae Constant 00502 R. Relationship between Torque and Moment of Inertia. The pull-up torque Torque and starting of high inertia loads, part 1 This is the first part of a two-part series. 4:1 or 1:1) indicates that the motor will do a very effective job of controlling the load but it also reveals that the motor may be oversized. Calculating the moments of inertia of various objects, even symmetrical ones, can be a lengthy and tedious process. Generally, most servo motors will choose the motor with small inertia, so as to satisfy the high responsiveness of the servo system. Integration over the whole domain is not the easier option nor the recommended one. Moment of inertia of a same object will change against different axis. For a ratio of 1:1 the necessary torque during. 00­ rod of length 65. Rating: (133) Load vs rotor inertia is an important parameter. The flywheel consists of a heavy circular disc or wheel with a strong axle mounted on ball bearings on two fixed supports. Also, explore many other unit converters or learn more about moment of inertia unit conversions. The sum of the products of each mass element of a body multiplied by the square of its distance from an axis. Generally, horsepower is a unit for measuring the power of various electrical motors, piston engines, steam turbines etc and it is equal to 746 watts or. solid bar. J = Torsional constant for a thin-walled closed section. 0 rev/s in 8. automatic weight calculator for rectangular, square, round, or hexagonal, plate, tube, bar, beams, sheet, rod and other engineering material shapes. s (Ke) electromotive force constant 0. To calculate the moments of inertia about the solid rectangular block, the known equations below were used: 𝐼 = I( 2+ 2) 12 𝐼 = I( 2+ 2) 12 𝐼 = I( 2+ 2) 12 4. Thus, (1a,b,c). I P= I cm( ) +M pd 2 (14) I R = X P∈R I P (15) where I R is the moment of inertia of the rocket about a given axis through the rocket’s centre of mass, I P is the component of the rockets moment of inertia about the selected axis that is due to a given part P. The mass moment of inertia equation for a point mass is simply: I = mr 2. The approach involves finding an expression for a thin disk at distance z from the axis and summing over all such disks. x-y axes: x and y are the coordinates of the element of area dA=xy Ixy = ∫xy dA • When the x axis, the y axis, or both are an axis of symmetry, the product of inertia is. For a body of mass distributed continuously within volume V , the movement of inertia of the mass about the X axis is given by either or , where dm is the mass included in volume element dV at whose position the mass per unit volume is ρ (see illustration). Moment of Inertia. 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