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How fast do the treads move? Post a Video.
What were your calculations for the motor/gear requirements (a link to a previous thread is good).
Exactly what are the full motor specs, link the data sheet.
What is the motor's current draw when trying to move and when you are holding the bot from moving?
Does the threads move freely? if they are too tight then this will rob power for the motors.
Thus, the first thing to do: Measure the voltage across the motor when it is stalled! It may be you're seeing less than the nominal battery voltage.
Second: 24V times 25A is just barely above the rated 400W of motor power. The motor may want to draw much more than that temporarily, as the rating may be an average or sustained rating. If the controller chops the current, that will lead to less torque in the motor. Look for motor drivers that can give you more amps, and that have built-in current sensors, so you can get a sense of the current draw without having to have your multimeter in the loop!
Fourth: Hook up both treads/tracks, and drive both motors forward at the same time. If it's still simple to stop the robot, then perhaps you're getting too much loss in the tread system. If the first motor has enough oomph to get the bot moving, then the second motor should be able to add significant additional force when both are driving.
Fifth: Try getting some wheels instead, with a diameter similar to your driving pinion. See if that works better! That would indicate losses in the track/tread system.
If you measure 12 volts when stalled then either the controller is chopping the current or your battery is too weak. (I'm assuming you're not actually seeing 120 volts?)If you can't use both motors at the same time, battery is the most likely culprit. Power is proportional to voltage squared, so 12V instead of 24V means 1/4 the available power. Get controllers and batteries that are up to the task and your robot will probably have lots of life in it
I was actually seeing 120 volts when I stalled it.