Some nema 17 are short and some are longer...

Some nema 17 are short and some are longer… Does anyone know what’s the difference?

The longer the motor. Has a bigger magnet. Thus more torque

Nema 17 just means it is a 1.7" square faceplate. Voltage, deg/step, holding torque, current limit, etc may all vary…

Nema 23 means it’s a 2.3" square faceplate, and so on…

@Taylor_Landry While that might be where the name comes from, the specification includes more than that. Namely, the hole spacing/arrangement and size, dimensions of the pilot (the raised section around the motor shaft), and the dimensions of the shaft (length is specified as a maximum value, some are shorter). The idea is that you should be able to mount any NEMA17 motor in place of any other, though in some cases, a longer motor body (which is not part of the specification at all) or shaft may be a problem in a particular machine.

In terms of the length of them, there is a difference of holding torque. Oddly enough, even though their names are done using the imperial system, their holding torque rating seems to be in metric (from what I have seen at least). Most are measured with a holding torque from one cm from the center of their shafts. The longer the motor, typically the higher the torque, but you should always check the motor specs to compare them based on torque rather than just on their length.

@Griffin_Paquette I’ve seen stepper motors with their torque ratings in ozin, mNm, Ncm, gcm and kgcm. The last two, though probably the most common these days (I used to see mostly ozin, but it seems to have become less popular), are technically incorrect because grams/kilograms are measures of mass rather than of force. They should really be written as gfcm and kgfcm, but I’ve never seen anyone bother to do so.

@Whosa_whatsis couldn’t agree more. I don’t get why they use a unit of mass. Some things just don’t make sense but get overlooked haha

@Branden_Coates That’s an oversimplification. I had NEMA17 steppers that are under 10mm and over 100mm long. There are a couple of common sizes that are built that way, though.

As many have said before, there is typically a correlation with length of stepper motor length and holding torque (though there may be exceptions). Another thing that may change is motor current/voltage and inductance. A longer motor may operate at a lower current and/or higher drive voltage and will typically have greater inductance because of a larger solenoid. This may mean your step rate may be limited or a higher drive voltage may be needed for larger motors.

@Ishaan_Gov In my experience, larger motors are generally rated for more current (which makes sense for several reasons), but you can get a wide variety of voltage ratings/inductances/resistances depending on the way they’re wound.

Because 3D printing has made them popular, most of the motors you see today are designed to work with a current-limiting driver at 12-24V (which means a voltage rating in about the 2-4.5V range), but the motors that MBI used for the CupcakeCNC were smallish NEMA17s (about 30-35mm long, IIRC) that were rated for 14V. The resistance was 35 ohms and the inductance was also way too high, making them really underpowered and incapable of high speed/acceleration.

In those days, it was tough to self-source motors because the specs were all over the chart, but now you almost have to go out of your way to find NEMA17 motors that aren’t being sold specifically with 3D printing in mind, so they all have windings that are appropriate for that purpose.