Good info! The same thing is happening in our motors: the magnetic field generated by typical permanent and electromagnets is inversely proportional to temperature. So as a motor heats up, it needs more current to produce the same amount of power, and at 56% efficiency, that means more heat, which means less power... You get the idea.

Compounding this is the fact that the motor relies on a fan attached to the armature for internal cooling, which makes its effectiveness proportional to speed.

These factors, along with battery drain, explain why a robot which might have good power in testing and early in the match, might have a hard time getting up the ramp after a lengthy pushing battle.

The strength of the magnetic field of a motor going down is a direct result of the internal resistance of a motor skyrocketing.

As we all know, the force of a magnetic field is proportional to current as:
Force = I*B*L = I^2 * C
I = Current
C = N * L * u0 * Xm / l

I've shortened this equation because the things in the constant C, are never changed during the operation of the motor. Some are, but they are very small. If you want to know what this equation means, or how I got it, or think it is wrong, PM me first. If you still think it's wrong, then you may argue your point here. Now, the current draw of a motor is related by the equation:

Current = Voltage / ( R + Rz )
R = Internal Motor Resistance
Rz = Motor Impedance (Resistance to Current)

Now, as a motor approaches stall, it's impedance becomes 0, because the windings aren't moving and there is no magnetic field to resist a change in current, so the current draw of a motor can be accurately represented as I = V/R.
R of Drill Motor = 94.5 milliOhms
R of Chiaphua = 105.3 milliOhms

Now, V, for the most part, remains constant at 12V. The only thing that is able to change is the resistance of the material. So, lastly, the Resistance of a Material, R, is affected by temperature according to the equation:

R = R0 + aT
R0 = Resistance of alloy at 0 Degrees C
a = Material-Dependant Constant
T = Temperature

As with every other equation above, there is only one varible that is really changed, and that is T, Temperature. All the other symbols are constants.



As you can see, comparing this equation with the first equation, any increase in temperature is SQUARED as a magnetic field decreases. Furthermore, as said above, it is inversely proportional, in that:
Force = C / (Temperature)^2

Now you might just think twice about how important it is to cool your motors....