I'm trying to determine at what speed my brushed dc motor will run at, given a certain power dissipation. The background is I've built a lathe, using this motor, and for a given depth of cut and feed rate (which is dependent on motor speed and how fast I turn the z axis handle), there is a certain power requirement to remove that much material. Calculating the power is easy, if I make an assumption about the motor rpm, but if I'm running the motor at 12v, I don't have direct control over the speed, just the range of speeds, correct?
So, if I set the voltage, then attempt to stall the motor (huge depth of cut or very high feed rate), I will draw max current, and have zero speed, or I can take no cut, and have essentially the no load speed. For a given cut though, I can find the power, but there are two points along the torque speed curve (other than max power) that give that power, so how do I know which point I'm at? The high torque low speed point, or the high speed low torque point?