Stepper motor torque question

So I sourced a batch of stepper motors that ended up having 39oz/in of holding torque. The listing didn’t have the specs but I ended up finding out on the interwebs. I currently have them powering my MP3DP and a Piper printer. My question is, if I get higher torque motors, say like the 84oz/in jobs I have on my MPCNC, can I run the printer faster with less chance of skipping steps? The current ones occasionally skip, I think, but then they don’t have a flat spot on the shaft so it could bee the shaft spinning in the pulley on hard jerky moves. I searched the other topics and couldn’t really get a definitive answer from any of them. Just wondering. TIA

More torque comes from more current, and more torque at higher speed comes from voltage. None of that will matter if you’re skipping on the shaft.

What the driver does is turn on and off the voltage while trying to reach a set current. When the motors are moving, they resist the current. So when you are moving fast, they might be “on” 100% of the time, and not reaching their set current. That can lead to skipped steps. This is why 24V is popular in faster printers. Having more voltage really helps push current, even if the motor is moving really fast. At slow speeds a 12V PSU is just going to be “on” twice as long as a 24V PSU, so it doesn’t matter. Where the cutoff is depends on a lot of things. But my gut is you wouldn’t see a difference under about 50mm/s on an MP3DP.

Or, if your printer is just sitting still, you can just grab a pulley and twist it. That is because of the stepper rating, and the current setting. If you installed those bigger motors, and you set the current up to give them full power, they definitely would need more to make them skip. You might then hit another limit, like driver current, or heat.

The new motors would have a flat spot on the shaft. So that is a definite plus. You can easily install them on the X, Y, Z and not worry about the weight. They wouldn’t make it worse.

Thank you for the help Jeff. I think I understand better now. I’ll probably just swap out the X and Y, as the Z doesn’t seem to be effected by high speeds at this time. But swinging around that MK8 and my heavy bed I think I’ll get better results at higher speeds. I’m currently running a RAMPS board with 8825s so I’ll look into if I can run it at 24v or if I’ll need a new controller. Thanks again.

The ramps can, but IIRC it needs to disconnect the 5V regulator. I know there are some guides to setting it up as 24V.

Oh cool. Yeah, I already cut the diode out or the ramps and power the 2560 via USB. Already burned one up before reading about that.

Don’t take my word for it. But I am confident it is possible.

I guess this pretty much covers it.

Driving RAMPS at 24v

84 oz/in motors arrived today. Swapped out the X and Y motors on my MP3DP. Blew through half a benchy at 100mm/sec then realized my problems now are cooling related. But no skips!

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