[Patrick Wang]

The electric motors exert a constant force relatively speaking on the system.

Basically, as the speed of the robot increases, the internal friction (friction in the gears/sprokets/bearing) increases directly proportional to the increase in speed.

So basically if comes down to this.

(Force from motor)-Friction (energy lost to heat/sound) = remaining force left to accelerate your robot.

Remember the force from the motor is constant, but the force of friction increases with increasing speed. So as you accelerate there is less and less energy in reserve left to accelerate your robot. At some point, the

force of friction = force put out by motors.

at this point, the robot has reached a dynamic equilbrium and can no longer accelerate because all of the force is being used to overcome the fraction in your system.

If you think about it, the drill motor drive train is relatively noisy, (loss of energy) and the drill motor heats up considerabally after use (loss of energy).