Thread: 2-Speed vs 1-Speed drivetrain
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Unread 13-05-2014, 15:57
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Re: 2-Speed vs 1-Speed drivetrain
Quote:
Originally Posted by themccannman View Post
Yes, stall current is stall current. Ideally your low speed gear ratio in your 2 speed drivetrain should be as fast as possible while still being traction limited. That gives you a higher speed in low gear without sacrificing any pushing power.
Well....stall current is kinda stall current. The stall current per motor for 4 motors is slightly different than the stall current for 6 motors. Stall current for a 6 CIM system is about 75 Amps/motor and the stall current for a 4 CIM system is about 87.5 Amps/motor. This is because when you add more CIMs, the motor voltage will decrease. This voltage can drop to about 7.5-8 volts when stalling. The stall current cited in the CIM motor documentation (~131 Amps) is assuming the voltage is a constant 12 volts (not what we see in robots). It is correct that friction is what limits the stall current. Also, note that there's a difference between the static friction and kinetic coefficient of friction. In fact, you can even have just as much pushing power with a 4 CIM drive as a 6 CIM drive (if geared properly).