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Suitable motors for i3?

Posted by kscharf 
Suitable motors for i3?
August 30, 2014 12:01PM
I've found a source for some low cost Nema-17 motors but they might be a little on the feeble side for an i3.
The spec's are:
5.6v, 0.85A, 6.3 ohm, 7mh, 4 wire bipolar. These are a custom variant of a type made by SEI. Other 4 wire motors in this series of motors, have a rated torque of 50oz/in, the 6 wire motors in the series are rated at 38oz/in. The sizes of all of these motors are standard Nema-17 width and height (42mm), the depth of these are 1.5".

This motor actually appears to be the same as a similar bipolar motor rated at 2.8v and 1.68A, with 50oz/in torque. ie: it is double the voltage and half the current of the model it was derived from.
(http://www.sei-automation.com/StepHybrid.html model 17H150-168-4A is the original motor this model was based on.)

Assuming the motors in question are somewhere between 38-50oz/in torque would they be suitable for the standard sized i3 design? I will be using 1.75mm filament, so the extruder doesn't need as high a torque motor as it would for 3mm.

Edited 2 time(s). Last edit at 08/30/2014 12:08PM by kscharf.
Re: Suitable motors for i3?
August 30, 2014 04:31PM
Imho, the 2.8v and 1.68A would be better. Eyeballing, the 5.6v and 0.85A is probably going to have poor performance at 12v, it would need something more like 24-32v power source.
Re: Suitable motors for i3?
August 30, 2014 04:43PM
Well, I can get the 5.6v ones for under $5 each. At that price I suppose I can give them a try, and I can probably run the steppers on 24V easily enough. It's actually easy to isolate the heaters and fans on the ramps board from the stepper motors since the MOSFETS switch the cold lines. You don't HAVE to connect the 12v ends of those back to the ramps board, they can go though their own fuses to the 12v rail. Just have to remove the LED's from the ramps and rewire them off board. But you don't really need the fan and heater LEDS at all.
Re: Suitable motors for i3?
September 01, 2014 07:46AM
Yes at that price you can surely give the motors a try, and probably would work.

Regarding the mosfets yes, they interrupt the gnd line so you can have a load with a different voltage. But it has to have the same ground, e.g. both 24v for stepper and 12v for heaters would come from same power supply so all the gnd returns to same psu. This is because the microcontroller gnd has to correspond to the heater gnd in order to operate the mosfet gate. Otherwise the mosfets would have to be optoisolated (which are not).
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