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As part of a project, I am designing a reaction wheel system for a nano-satellite. I am now researching on how to determine the nominal speed of the reaction wheel. I have characterized the deadzone of my motor with the flywheel attached, and found that I would be optimal to not have the nominal speed at zero to avoid the problems cause by the zero-speed crossing. I have tried searching for some research papers on how to determine the nominal speed and I wasn't able to find anything useful.

Here are my thoughts on how the nominal speed should be chosen:

My motor has a speed range of 100-4800RPM, if you factor in the deadzone region. I think it should be sufficient to set the nominal to set the speed in the middle, ( (4800-100)/2 + 100 = 2450RPM ). As this would allow the same amount of torque to be generated in either direction, and desaturation in both directions would be required equally as frequently as each other. However, although this logic does sound correct, the justification sounds too weak.

Are there any other methods to determine the nominal reaction wheel speed?

Thanks!

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  • $\begingroup$ This is highly dependent on the mission. What are you trying to achieve here? $\endgroup$ – Schlusstein Mar 2 '17 at 3:57
  • $\begingroup$ @Schlusstein I'm trying to achieve a sun tracking mode with my satellite. $\endgroup$ – John Mar 2 '17 at 3:58
  • $\begingroup$ How much precision do you need? Is this just for keeping your solar panels oriented? $\endgroup$ – Schlusstein Mar 2 '17 at 4:13
  • $\begingroup$ About 15-20 degrees maximum error $\endgroup$ – John Mar 2 '17 at 4:14
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    $\begingroup$ This isn't a full answer, but the higher you set your nominal speed, the more power you'll burn on average. If your nano-satellite has a tight budget, it might be worth it to set the nominal speed relatively low, but still out of the dead zone. You'll have to deal with a little jitter during the transition through zero speed during some occasional maneuvers, but the trade might be worth it. $\endgroup$ – aerocooper Mar 2 '17 at 20:39
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Since you only need 15-20 degrees of precision, you don't need to set a nominal zero for your reaction wheels. You'll need to use pulse width modulation even if the motor is voltage controlled and the movement may be a little jittery, but if you have a halfway decent control algorithm and put minimal effort into characterizing the response of the motors at low speed it should be fine.

Unless of course you have other mission needs that require smooth, precise pointing.

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  • $\begingroup$ My motor is pwm controlled with digital speed feedback. I need a non zero nominal speed or there will be a delay in the actuation due to the dead zone though. $\endgroup$ – John Mar 2 '17 at 4:50
  • $\begingroup$ I've measured the max acceleration to be about 900rpm/s. Which means if I set it at the mid point of the speed range, I can get the maximum torque in either direction. And equal desaturation would be required for both directions of torque $\endgroup$ – John Mar 2 '17 at 4:51
  • $\begingroup$ How much delay? Is that a problem for your mission? $\endgroup$ – Schlusstein Mar 2 '17 at 12:42

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