oh generalized relationships
I'm not sure of any general ones.... hmmm it would depend on the gearing of the motors as well....
the only one I can think of is y = K(x) where y = volts, k > 1 and x = torque, speed, or current
also there would be a limit to y before the motor broke
A better idea is to get motor readings or look for similar motors online and get their readings from online. I understand this is all theoretical, but general relationships that apply to all motors should not exist ( each motor has different gearing , different ga. wire windings, diff. # of windings, etc.)
Then again , I would love to be proved wrong , because I would also benefit from a general equation.