I have asked the seller for a torque curve for the motor and they tell me they don’t have one. Can I make my own torque curve for the motor without testing it? I was thinking a linear fit between the stall torque and the no load RPM. Would this work? Should I use a different fit? Any help would be awesome.

Actually, linear interpolation does work (Adam - I actually took the time once and worked through all the equations and theory you mentioned, and it works out very nicely - at least for the drill motor, which is what I compared my theoretical results to).

Anyways, don’t take my word for it - Joe Johnson posted a spreadsheet a couple of years ago which asks you for a few simple parameters (voltage, stall torque, stall current, free speed, free current) and comes up with plots of speed, torque, power, and efficiency. It also has a sheet of information on FIRST motors (although be careful; the Fisher-Price motor is certainly out of date, and others may be as well).

Sorry your right. It will work. I have a picture of one of those graphs in my book and it has the relationship between motor torque and RPM. Definately linear. Its just one of those duh moments.