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Unread 13-04-2014, 09:33
gpetilli gpetilli is offline
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Re: Torque Calculation/Determination-Urgent

Quote:
Originally Posted by Ether View Post
At 12V, a 775-18 motor draws 45 amps at 6385 RPM

At 12V, a MiniCIM motor draws 45 amps at 3008 RPM.

But if you have them geared 20:1 and 6:1, respectively, they can't simultaneously be at those speeds.

6385/20 = 319 RPM
3008/6 = 150 RPM


That's an interesting way to look at it. Since I don't yet have a spreadsheet to dynamically calculate operating points, I used JVN table - which does include voltage droop (which looked like about 7.5V).

We did intend for the RS775 to reach max RPM when the MiniCIM was at 1/2 max RPM, so your estimates make sense. Clearly the wheel RPM will be the same for both and currents will split accordingly. The biggest concern I have is what happens after the RS775 exceeds it free RPM. I know it will behave like a generator and load the MiniCIM.

I do have some serious unanswered questions with this configuration. If we put the ESC in coast does that sufficiently break the generator current path such that it does not significantly load the driving motor? I don't think anyone has tried coasting the motor after it exceeds free RPM but instead continue to drive at full voltage. If we back-drive the RS775 to twice it's free RPM (coast or driven) will the generator blow the ESC?
 


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