Choosing a Battery

[Ether]

Originally Posted by Al Skierkiewicz

Eric,
Please keep in mind that in a two wheel configuration, the motors will need to be capable of accelerating to a higher speed than your target in order to accomplish balance.

@Eric: In other words, when you're cruising along at your desired 3 m/s, you need some headroom to increase the voltage.

Suppose you leave 2 volts headroom, so you're operating at 10 volts at 3 m/s (I have no idea if 2v headroom is enough or too much, this is just for sake of discussion).

CIM free speed at 10v is 4425 rpm. To go 3 m/s at that motor rpm with 12.5" dia wheels, you'd need a gear ratio of 24.5:1, not 34:1.

Of course, at free speed a motor is producing no torque output. So let's say 90% of 10v free speed, or 3983 rpm CIM speed (again, I do not know if that is sufficient¹). Now you need a gear ratio of 22.1:1.


¹At 10v and 3983 rpm, each CIM produces about 28.6 ozin torque. Run this through the 22.1:1 geartrain and assume 10% torque loss in the drivetrain and you've got about 3 ft-lb torque at each wheel. For a 12.5: dia wheel this translates to about 5.7 lb motive force per wheel, or 11.4 lb total for both wheels. Is that enough to move your 100 lb robot+payload at 3 m/s up a 5% incline on a gravel surface?