AM-0915a for Drive Motors?

[AlisAquilae]

I am working on another project and would like to use the AndyMark PG27 Gearmotor (AM-0915a) as the direct drive motor for the drivetrain.

Using a quantitative analysis I found that the margin of safety between the stall torque of this motor and the theoretical needed torque to drive a 40lb, four-wheeled robot is approximately 0.3.

I'd like to know if anyone has used this motor in the past to drive the wheels on a robot or if the forum believes that it will have the power to drive a 40lb robot.

Two of these motors will be used to drive each of the 6" rear wheels. We are using a 4mm key and the AM-0985 hub to drive a 6" AM wheel.


Thanks!

[Ty Tremblay]

The gearmotor with the gearbox will drive the 40lb robot no problem. If you're just driving it around like an RC car, you shouldn't have a problem. If you're pushing/pulling a lot, those motors can't handle heat very well and you could run into issues if you're operating at high torques for long periods of time.

[GeeTwo]

The stall torque of the motor is 6.3 ft-lb. Two of these driving 6" wheels can generate a net force of 6.3 ft-lb x 2 x 12in / 1 ft / 3 in = 50.4lb. Unless you have a CoF of better than 1.25 and put all of the weight on those two wheels, you can't stall them with carpet traction. As you will probably be putting only half of the weight over these driven wheels (you did not mention any chains or belts to drive the other wheels), losing traction could be a real problem if you aren't careful. Several solutions exist to inhibit loss of traction, or to recover from it quickly. Any of these would also help reduce the chance of overheating. Ranked approximately from simplest to best the obvious ones are:

limit the voltage ramp. That is, do not allow voltage to change by more than x volts in y milliseconds. This is the only "open loop" idea given here.
monitor the current. Limit voltage increase to keep the current below a threshold.
monitor speed using an encoder. Limit the angular acceleration. If you do this, you may want to make your joystick inputs be related directly to the target speed, rather than the applied voltage.