0.9 degrees stepper motor?

I am in the process of researching and sourcing parts for my first build. I am currently looking for stepper motors and came across these stepper motors at Sparkfun. These stepper motors have a 0.9 degree step angle or 400 step/rev.

Has anyone used these before? Will they work with existing firmware/software?

Surely the extra resolution would be an advantage? Advice?

Cheers,
Dane.

I think I found what I need. I haven't been having much success using the search function in the forum, however I found this forum topic using Google which pretty much answers my question.

Any other comments welcome.

Cheers,
Dane.

0.9 degree steppers will work perfectly fine. I used 0.9 degree NEMA 23's in my RepStrap with RAMPS.

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You will have a finer resolution, but slower operation as twice as many steps are needed to travel the same distance.

.9deg/step is unnecessary for x/y and especially Z, and in many cases a bad thing. Most firmwares still have some issues outputting very high step rates needed to fully micro-step at 16x for quietest operation, and still achieve high speed. Of course, there are always exceptions.

It would be useful for .9/step for a direct drive extruder though, as below .15mm layer height the 1.8deg/step becomes quite coarse.

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Andrew Diehl Wrote:
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> .9deg/step is unnecessary for x/y and especially
> Z, and in many cases a bad thing. Most firmwares
> still have some issues outputting very high step
> rates needed to fully micro-step at 16x for
> quietest operation, and still achieve high speed.
> Of course, there are always exceptions.

You can just use 8x micro stepping. Same resolution, speed, etc. as a 1.8 degree motor with 16x stepping, and 8x isn't much louder than 16x. There's no real reason to choose a 0.9 degree motor over a 1.8 degree motor however unless you can get an especially good deal on some 0.9 degree step motors.

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Ok, I have been reading up on stepper motors and this is what I have found.

This article was good, it seem that micro stepping increases the resolution but the accuracy will suffer. This is due to micro stepping affecting torque. The article talks about 'Incremental torque' and basically says the more micro steps the less incremental torque. To me this means that if you have a load on your motor it could be driven several microsteps before the shaft starts to move ie. until the accumulated (incremental) torque is sufficient to overcome the load. Obviously during this process the motor shaft is not where it is expected to be, at least until the accumulated torque has overcome the resistance of the load, therefore poor accuracy.

It is interesting to look at the colour phasor diagram about half way down in this article and compare the light green and dark green vectors which show the difference in torque between full stepping and 1/8 stepping.

So what does this mean?
If I use a 0.9 degree stepper with 1/8 micro stepping it should be more accurate, possibly a bit more torque, a bit noisier and a little harder on the drive train than if I used 1.8 degree with 1/16 stepping.

I am not sure if they would run at the same speed? A 0.9 degree stepper with 1/8 micro-stepping will have the same number of micro steps as a 1.8 degree stepper with 1/16 micro-stepping therefore should run at the same speed shouldn't it?

I'm guessing that steppers will have a maximum speed and that a 1.8 degree stepper will run faster that a 0.9 degree stepper, however are the steppers in RepRaps running at near maximum speeds? Is this an issue to take into account?

My reason for considering a 0.9 stepper is that there is not many options that I can find in Australia, and I would like to buy from within Australia to avoid costly shipping. One option is a 'Mercury Motor' which a couple of retailers sell. It seems to be a bit light on with its torque, however the wiki says that they have been used successfully (comments?), and then there is this 0.9 degree model that I have been considering.

It seems to me that the 0.9 degree stepper would be an acceptable option and should work fine. I do like the idea of greater accuracy too.

Quote

It is interesting to look at the colour phasor diagram about half way down in this article and compare the light green and dark green vectors which show the difference in torque between full stepping and 1/8 stepping.

That is a common misconception. If you set the current on a microstepping driver to give the same power dissipation you get the same torque. I.e. set the single coil on current to 1.4 times the two coil on rating. The circle of the phasor diagram then runs through the corner. Otherwise you are comparing apples and pears because the inner circle is putting less power into the motor and running it cooler, so of course there is less torque.

Edited 2 time(s). Last edit at 11/09/2011 08:08AM by nophead.

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