Specing motor

So I am looking at spacing a motor for my first custom 3d printer design. I am using a CoreXY based system.

Now I have a few questions:

1. If I get a high torque nema 17 and run it at low power without skipping steps, would that be quieter than running a mid torque motor at a higher power?

2. What dictates the noise made by a motor?

I am looking to use these [robotdigg.com] with A4988 drivers.

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greghoge.com

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For a given load, the current needs to be at a certain level in order to not miss steps. These things are consequently to one another, so its not so much liberty in setting current to a low level. That would be the place to aim at when adjusting the current anyway, so it goes without saying.

If you want to avoid the audible noise, get a driver which has "more knobs" than just vref. For example drivers which let you also set decay in whatever mode you want. Also some other drivers let you adjust some parameters related to frequency. For example if you try to use a driver like "stepper motor driver 3.3" that will let you adjust much more than a pololu. Better chances to have it run least audible when you can adjust almost everything. I dont think they make that driver version anymore, but i think would be a good one for the purpose.

The nema size is just the faceplate of the motor, i dont think the external geometry of the motor would matter, e.g. be it nema17+extra long or nema23 normal. But i would personally go for nema23 if you want to run a higher load, just coz you can replace it later whereas the nema17+long probably wont have a direct replacement, for being already at the extreme of its category (that status usually has some implications of some sort).

I've noticed that you can get surplus NEMA-23's cheaper than the NEMA-17's sometimes. Probably because the surplus dealers KNOW that the 17's are wanted by the reprap builders.
If you can modifiy your design to work with the 23's you could save money. The 'short 23's might not weigh much more than the 'extended 17's.

(I just bought 5 surplus NEMA-23 motors rated at 2.7v 1.8A 1.5ohm for $5 each at a hamfest.)

Thanks for the responses guys!

The reason I am looking at NEMA 17s over 23s (I actually have some 23s from my old rapman) is because I am planning on concealing them in a corner joint with aluminum extrusions. I havent actually drawn my design up in CAD yet, but it would definitely make the joint larger.

Also, I am planning on going with a Bowden extruder and a printed guide on aluminum extrusion for a carriage. So I dont think it will be very heavy. However, I would like to have interchangeable tools so I can switch from an extruder to a laser to a Dremel. But I think that might be a future upgrade once I get it built...

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