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Unread 11-12-2011, 22:30
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Re: 2 motor drive VS 4 motor drive

Quote:
Originally Posted by JamesCH95 View Post
I was assuming that the 4-motor drive would accelerate about twice as quickly as a 2-motor drive, spending about half the time in the 'near stall' regime but drawing twice the current over that time, resulting in the same number of A*s (electrons) being used.

Is this a poor assumption to make?
I modeled a drivetrain with a 10:1 ratio, 3-stages of reduction at 90% efficiency, 150 lbs, 4" wheels and 2/4 CIMs. Timestep of .01 seconds, calculated colloumb use per timestep by multiplying timestep by current draw. This was done by modifying JVN's 2004 design calculator, under drive modeling (so that anyone can repeat these results).

With 2 Cims Total
-5.4 Amps per CIM at steady state (fully accellerated).
-1.41 seconds to reach 9 fps (9 fps was picked as a value just below it's steady state speed).
-45.4 C used per side in this 1.41 seconds, 90.8 Total.

With 4 Cims Total
- 8.1 Amp per side at steady state (4.05 per CIM). This difference is likely from the motors not having zero current draw at free speed.
-.58 seconds to reach 9 fps.
- 43 C used per side in this .58 seconds.

I was a bit surprised by these results, the difference in energy use exist, but isn't huge. I imagine this difference would be larger the higher the gearing.

I'm curious how well this data matches the real world.