... For those who wouold study the characteristics ... it is good to note that this write-up is for (as they say at the begining) permanent magnet motors. Series-wound ones (which are used in virtually all conversions) have a different (non-linear) characteristic. Theirs is almost like 1/x function - see below. In theory, at no-load speed would go to infinity. Practically, applying rated voltage to unloaded series wound motor makes the motor go crazy fast until rotor starts coming apart. I still have memmories of my students running for a cover when that accidently happened during a demonstration in a class I held.
Similarly, stall torque (at rated voltage) is extremely high. It causes motor current to shoot so high that it would likely damage the commutator in seconds if not even sooner than 1 sec.
http://www.engineersedge.com/motors/dc_series_wound_motor.htm
