Aero - I've got a motor I'm dealing with (the one I emailed about) that produces 8.5 inch pounds of torque. The limited data I have gives a current of 16 Amps. I'm assuming that's stall current, but it doesn't say.
One of the challenges for me is translating the weight of a robot into power required to move it. It would have to consider weight, rolling resistance, desired acceleration a dn any amount of slope I might want. I suppose I qould emperically determine how much force it takes to move something, but that means I can't really design it until after I've designed and built it.
I'm not sure about a plastic adapter (from 4mm square shaft to something round). I don't know how well the plastic would hold up. Short of getting a piece of metal machined, I just had another thought. I could get a pair of flat L brackets and bolt the together suchb that they have a 4mm square in the middle and four ends sticking out that I could then bolt to a wheel or something. Does that sound workable?
No worries. I really love DC and BLDC electric motors. I have dedicated some amount of study to them. DC electric motors are easier to understand and easier to control, but BLDC motors offer more power density and usually they have better efficiencies. This is not always the case, but it is a good generalization.
One thing, though that I have found by creating the simple chart that I described is that you can then you can back out how much torque you are actually using and then size your next round of motors more appropriately. If you take your current motor and make that chart, and then you put the motor under the worst load that you are expecting, you can then measure the RPM of the motor (assuming that you have an encoder and some way to record this). Once you have this RPM, you can go back to the chart you created and just fine on the line the value of the RPM. You then read on the Y axis the torque. Now you have a better estimate for your next round of motors.
Oh and did you get my email on how to solve your motor adaptor problem? I think that it will work for you. Let me know if you need any help getting that drawn up. I can help out with that.