In my current project I’m running this Nema 17 motor which works fine as all I’m doing is slowly turning a geared drum.
I’m looking to see if I can put a larger motor in its place so I can use the same machine as a semi high speed to high speed rock tumbler by switching setting (The code isn’t the issue).
My limitations are:
12v power source (Battery)
2Amp max draw
Motor being driving from an Easydriver
I’m thinking about replacing the motor with this one:
But I’m confused buy how this motor gets such a higher holding torque with a similar amount of power as the Nema 17 (How I understand it is that torque is liner to the amount of power provided to it).
Do you think this motor would work? Any recommendations?
All I’m really looking for is some more torque at higher RPM’s without changing the gearing.
Is there a semi easy formula to use to calculate the torque for a provided Voltage and Amperage to the motor?
An Easydriver has a max current of 0.75 amps. A BigEasydriver or a Pololu A4988 can provide about 1.2 amps without a heat sink and a Pololu DRV8825 can provide about 1.5 amps without a heat sink. A TB6560 can deliver up to 3 amps. Above that you need more expensive industrial stepper drivers.
For high speeds you need a motor with a low coil resistance and a higher current. I don't think that large Nema23 motor is intended for high speeds. A low coil resistance goes with a low nominal voltage. That motor has a 10.5 volt nominal voltage which means it has lots of turns of wire in its coils. That's how it gets high torque with a lowish current. Also it is longer so it can have longer coils and magnets.
The nominal voltage of stepper motor is largely irrelevant. The important factor is the current. For higher speeds you need to drive the motor with a higher voltage. if you are limited to a 12v power supply you should choose a motor with a low nominal voltage. But be careful to stay within the limits of your stepper driver - or buy a more powerful driver.
So initially i'm going to get a TB6560 so i know i am getting most current from my battery to the motor without buying a more expensive driver.
As for the high speed i am also going to need to keep the same torque i'm using currently at the slow speed to continue driving everything (so i will need to find what that is).
before this I have just been looking at the Ncm holding weight to size my motor as i figured that was the max torque for the motor and that's why i was looking at the big Nema23.
But if i'm understanding correctly, if i can find a Nema 17 with a 3Amp rating i will be able to get my highest torque value (for my 12v source and driver limitations) and i would want a lower voltage motor for higher speeds.
Wouldn't the lower voltage motor ultimately lower my torque as well or would the driver over power the motor?
If so wouldn't the motor burn up if run for long periods of time under those conditions?
What do you think could be a happy medium?
If it has more Oz.in than your existing motor than your existing motor it is going in the right direction. And it has a low resistance coil. I wonder if the 2.8 amps is too close to the limit for the TB6560. Personally I would like to have a driver that can deliver (say) 50% more amps than I need.
But if i'm understanding correctly, if i can find a Nema 17 with a 3Amp rating i will be able to get my highest torque value (for my 12v source and driver limitations) and i would want a lower voltage motor for higher speeds.
Nema17 just defines the size of the front of the motor - 1.7 inches. The only important factors are the torque and the current.
The proper way to select a stepper motor is to look at the manufacturer's graphs showing the torque at different speeds. Unfortunately many of the cheaper motors do not have such graphs.
The holding torque is the max and only applies when the motor is stationary.
Kirkg:
But I’m confused buy how this motor gets such a higher holding torque with a similar amount of power as the Nema 17 (How I understand it is that torque is liner to the amount of power provided to it).
Wrong I'm afraid, torque is mainly limited by motor rotor volume(*) and the properties of iron and copper.
NEMA23 motor has much higher rotor volume so you'd expect much higher max torque.
The magnetic gap size (and magnetic circuit in general) is very important in determining how much
magnetizing force is needed for a given magnetic field strength, and thus the static power consumption.
But it also affects the back EMF and thus max speed of the motor. There is a trade-off to be made.