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Author Topic: where to find 4-wire suitable steppers?  (Read 498 times)
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Im making an installation where ill use 6 steppers to each lift a load of 300-500g. Im looking for motors which have a RPM of 500-600 (if you measute steppers in that way!?). If the motors are dirt cheap thats a big plus! The idea is to drive each stepper with the A4988 Stepper Motor Driver Carrier (http://www.pololu.com/catalog/product/1182).

Or will the steppers from old printer work? Might be hard to find 6 of them tho…

Best
/g
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Massachusetts, USA
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If you want cheap, look for surplus.

Steppers are usually rated for torque and maximum step rate. 

Conversion of 'load' to 'torque' depends on how you are doing the lifting. For example if your motor is winding a string around a 10mm rod:  10mm diameter = 5mm radius.  500 gm lift at 5mm radius required 2500 gm mm (or 250 gm cm) torque.

The maximum steps per minute divided by the steps per revolution will get you the maximum rotation rate.
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With bipolar steppers driven from a chopper drive like the A4988 you'll get faster maximum
step rates with a higher supply voltage - steppers with low inductance windings will be necessary
to get the fastest performance - something like 600 RPM isn't impractical for motors with
winding resistance of an ohm or so - low resistance windings have low inductance because
there are fewer turns. 

Make sure the hold-in torque is substantially larger than your load torque too.

I've got cheap sets of NEMA17 bipolar motors from eBay before.

Finding ex-equipment steppers rated for 600rpm might be rather hit and miss...
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For steppers, try eBay as mike said, there is a fair few of them with all sorts of ratings. Yes it might be a bit more, but it is less headache if they are the correct size you need, and all six are the same. Try looking under CNC stepper......
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Don't forget that the faster you go, the less torque you get.
The rotation speed doesn't really matter IMO, you should consider the desired lift speed and adapt the diameter of the wheel winding the rope if that's what you intend to use.
If you need bigger motors to achieve your goal, the A4988 may not be strong enough.

I've got a few nema 17 bipolar steppers from Lexmark forms printers, I've measured their holding torque to be around 40N.cm

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