- #1
Cosmoneer
- 7
- 0
Hi all,
I am not a physics major and have spent some time learning via the university of Google. I would really appreciate a second set of eyes on what I am calculating and tell me if I am correct, or if I have done something wrong along the way. I am trying to calculate MOI and need results in milliNewtonmeters. After that, since I am working on a small Control Moment Gyro, I need to calculate the velocity producible by the CMG gimbal rates and the RPM of the gyro wheel.
I have a gyro flywheel with a mass of 8.84 grams @ radius of 8.55mm. As I understand it, one of the formulas used to calculate MOI is simply
I=MR^2
(I = moment of inertia, M = Mass, R is radius to center of mass)
So...
I = 8.84 * (8.55)^2
I = 8.84 * 73.1025
I = 646.2261 gmm^2
At this point I am confident in my result, but now I need to convert this into mNM. I found I needed to first convert to KgM^2, so I used this converter:
http://www.endmemo.com/sconvert/gmm2kgm2.php
Which is basically:
I = 646.2261 * 0.000000001
I = 0.0000006462261 KgM^2
Then to convert to NM I found that I need to multiply by a simple conversion factor:
I = 0.0000006462261 * 0.101971621298
I = 0.0000000658967231420834778
I = 6.589672314208348e-8 Nm
And then convert to mNm:
I = 6.589672314208348e-8 * 1000
I = 6.589672314208348e-5 mNm
I = 0.0000658967231420834778 mNm
At this point I feel rather confident that I haven't made a mistake. It's this next part where I get fuzzy.I now need to know how much torque I will derive from the CMG when I apply torque on the Gyro via the gimbal. From what I can find, the formula for that is this:
L = I * w
(L = torque, I = Moment of Inertia, w = angular velocity)
So, I found that w can be represented as:
w= RPM * 0.10472
This gives radians per second of the gyro wheel. Which, if given an RPM of 1000, I would get this:
L = (0.0000658967231420834778mNm) * (1000 * 0.10472)
L = (0.0000658967231420834778mNm) * (104.72 rads/sec)
L = 0.0006900704847438981795216 mNm rads/sec
Does this looks ok? What I don't see is how much gimbal angle produces this? What else am I missing?
Thanks for any input and or insight you provide!-Andrew
I am not a physics major and have spent some time learning via the university of Google. I would really appreciate a second set of eyes on what I am calculating and tell me if I am correct, or if I have done something wrong along the way. I am trying to calculate MOI and need results in milliNewtonmeters. After that, since I am working on a small Control Moment Gyro, I need to calculate the velocity producible by the CMG gimbal rates and the RPM of the gyro wheel.
I have a gyro flywheel with a mass of 8.84 grams @ radius of 8.55mm. As I understand it, one of the formulas used to calculate MOI is simply
I=MR^2
(I = moment of inertia, M = Mass, R is radius to center of mass)
So...
I = 8.84 * (8.55)^2
I = 8.84 * 73.1025
I = 646.2261 gmm^2
At this point I am confident in my result, but now I need to convert this into mNM. I found I needed to first convert to KgM^2, so I used this converter:
http://www.endmemo.com/sconvert/gmm2kgm2.php
Which is basically:
I = 646.2261 * 0.000000001
I = 0.0000006462261 KgM^2
Then to convert to NM I found that I need to multiply by a simple conversion factor:
I = 0.0000006462261 * 0.101971621298
I = 0.0000000658967231420834778
I = 6.589672314208348e-8 Nm
And then convert to mNm:
I = 6.589672314208348e-8 * 1000
I = 6.589672314208348e-5 mNm
I = 0.0000658967231420834778 mNm
At this point I feel rather confident that I haven't made a mistake. It's this next part where I get fuzzy.I now need to know how much torque I will derive from the CMG when I apply torque on the Gyro via the gimbal. From what I can find, the formula for that is this:
L = I * w
(L = torque, I = Moment of Inertia, w = angular velocity)
So, I found that w can be represented as:
w= RPM * 0.10472
This gives radians per second of the gyro wheel. Which, if given an RPM of 1000, I would get this:
L = (0.0000658967231420834778mNm) * (1000 * 0.10472)
L = (0.0000658967231420834778mNm) * (104.72 rads/sec)
L = 0.0006900704847438981795216 mNm rads/sec
Does this looks ok? What I don't see is how much gimbal angle produces this? What else am I missing?
Thanks for any input and or insight you provide!-Andrew