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Unread 22-09-2003, 10:52
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Paul Copioli Paul Copioli is offline
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FRC #3310 (Black Hawk Robotics)
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Torques do not Combine

jNadke,

OK, I was wrong about the differential not being like the CCT, but I know I am right about the torques NOT combining. The calculations are done in my whitepaper. Conservation of energy dictates that the torques DO NOT combine.

Put simply,

The second motor acts like the housing on the drill transmission: all it does is REACT the load of the input motor. To be exact, its reaction torque is (Torque of output carrier - torque of sun motor). The backdriving phenomenon you are describing is as if the housing breaks. If the ring gear motor does not have enough torque, then it can't react the load and is backdriven or put to stall and pops breakers.

The latter is exactly what happened to us at Great Lakes in 2002. I, like you, thought the motors combined torques and that got us in a lot of trouble. We popped breakers constantly. When we got home and I actualy sat down and did the calculations required (in the whitepaper), I discovered that the torques did not combine and the ring gear motor was merely a speed increaser. This is the biggest disadvantage of the CCT: add a motor and get speed, not torque.
However, the cool part is that you get more speed with the same output torque. In 2002 that was a big advantage, because we could move both goals at high speed.

If you are not convinced, you can e-mail me and I will discuss the details with you.

-Paul