A question from a stepper noob: I have steppers on hand from Massdrop, with current, voltage, and holding torque specs. For the purposes of designing and selecting related mechanical components, I need an estimate of the largest torque the stepper will deliver at common 3D printer voltages and current. Is it as simple as multiplying the holding torque by the ratio of rated electrical power to planned electrical power?
The current rating is the maximum current the motors are rated to take (so that they will start radiating heat as fast as they produce it before before exceeding a safe temperature), and they should not be driven above this amperage. The rated voltage is the voltage that, given the phase resistance of the motor, will produce the rated current at 100% duty cycle, and the holding torque is how strongly they will hold their position when the rated current is applied.
Does that answer your question?
I learned a thing or two, so thanks.
I was able to parse your answer after a couple readings. I think I can sharpen my question to this: Given a common 12V (or 24V) RAMPS setup, is the maximum torque the stepper may exert in the system simply the rated holding holding torque multiplied by the ratio of operating to rated voltage?
Or do I need to get myself educated on some more complex topics?
No. The maximum holding torque that the motors can safely achieve is the holding torque on the datasheet. You don’t multiply it by anything. Your stepper driver has to drop the duty cycle of the supply voltage down to maintain a constant current, so the motor should never see a net voltage (averaged across the time of the on-off cycle) greater than its rated voltage. The reason you want a supply voltage greater than the rated voltage is because when the motor starts turning, it produces it’s own voltage, and your stepper driver needs enough excess voltage to overcome that induced voltage and maintain the current that it is supposed to be supplying, or the torque will start to drop.
OH, OK. So if I understand this correctly, 24V is only helpful if the controller can emit step pulses faster than the driver can maintain current at 12V. A clock-limited controller like the Arduino may not be able to deliver enough steps at 1/16 microstepping to justify higher voltage. So I would probably need to be willing to use 1/8 or lower microstepping if I want to take advantage of the speeds enabled by 24V.
Since force on a wire (and thereby holding torque) is dependent on current and geometry only (EE principles is seeping back into my head from 20 years ago as I type), selecting supply voltage is a non-issue for my structural design phase. Perfect. Thanks tons.