.9 degree steppers. Do I need to change settings anywhere?

Phidgets.com has .9 degree NEMA 17s for the same price as 1.8 degree.

Will I have to make any changes to the firmware or software?

Edit: I should say, I KNOW i'll need to make changes, but can't find where.

I'm using redsnapper (for now) and gen6 electronics

Edited 1 time(s). Last edit at 10/14/2010 04:20PM by Buback.

Typically, there are STEPS_PER_MM_... settings in the firmware source code (some .h file) awaiting your care. Type in double the value than for 1.8 deg steppers. I don't know which type of firmware mendel-parts uses, though.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thanks!
I kept looking for steps per rev or degrees per step.
The firmware is standard fiveD with a couple adjustments, according to mendel-parts.com

The coil resistance on the linked 0.9 steppers is only 1 ohm. Are you using standard reprap electronics? I think they need a resistance of at least 6.2 ohms

Someone correct me if I'm wrong, but nophead is using a 6.2 ohm resister for heating the hot bit

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My blog's Reprap feed: [blog.markbova.com]
I'm currently working on a stock Mendel build with a Seeeduino Mega and four Pololu A4983 stepper controllers.

I couldn't figure out the wiki, frankly. Yes, it does say 6 ohms min, but then most of the tested NEMA 17's on the stepper motor page are ~1.6 ohms per phase

In particular, i'm using the Mendel-parts gen6, and the motors they sell are 1.65 ohms.

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I think they need a resistance of at least 6.2 ohms

It doesn't matter how many Ohms a motor has, the stepper driver is designed compensate for that. For low Ohm motors, you just don't turn up the current potentiometer as far as with higher Ohm motors.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I added your comment to the wiki, as it explicitly states 6 Ohms and i don't want others going crazy trying to track down just the right NEMA 17

Good to know, but I was sure that I've read that someone blew out a stepper board thanks to that oversight. Maybe that was adjusted wrong or something. I see that 12.4 volts = 2 amps x 6.2 ohms.



Traumflug Wrote:
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>> I think they need a resistance of at least 6.2
>> ohms
>
> It doesn't matter how many Ohms a motor has, the
> stepper driver is designed compensate for that.
> For low Ohm motors, you just don't turn up the
> current potentiometer as far as with higher Ohm
> motors.

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My blog's Reprap feed: [blog.markbova.com]
I'm currently working on a stock Mendel build with a Seeeduino Mega and four Pololu A4983 stepper controllers.

Ohms on steppers don't matter, as long as it's low enough. Unless you're using the H-bridge chips on the older-style extruder controller to drive a stepper. That hack works, as long as you don't turn the potentiometer up too high. Then it overheats the H-bridge chips and burns them up.

On the stepper drivers (pololu or otherwise) the driver limits the *current* and so doesn't get overloaded. Also the driver chips have over-temperature protection, so you won't burn them out by overloading them. You *can* destroy your stepper motors by getting them to hot if you set the current too high, though most steppers are rated for more amps than the chips can handle without serious heatsinking. You may want to look at the amp rating of the motors. You can run them under the rated current and it's fine (just less torque) but running them over that will mean eventual overheating. Just not right away, it takes some time for them to get really hot. Steppers are generally designed to run almost to hot to touch anyway, so don't burn out until they get really, really hot.

If there's too many Ohms (i.e. it's designed for running off 24V directly, or something) then the current won't rise fast enough for the chip to do it's "limit the current" thing, and you essentially don't get microstepping (which limits the current to get the in-between steps). Or even the full rated torque or speed in some cases.

You'll notice that the motor you linked to doesn't even specify the voltage. Just the amps. That's not uncommon. In theory, 2.4A at 1Ω means it's designed to run on 2.4V. But we'd run it at 12V. The trick is that the coils in the motor act as inductors, current can't rise instantly to the maximum of 12V/1Ω=5A, and before it gets above whatever you've set the limit as, the chopper circuit in the stepper controller starts cutting the voltage in and out, limiting the current to whatever you've set the max current to, or whatever fraction thereof that corresponds to the current micro-stepping position.

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I'm building it with Baling Wire

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Steppers are generally designed to run almost to hot to touch anyway, so don't burn out until they get really, really hot.

Most of the motors I have seen specs for give the current for two coils on that gives an 80C rise. I.e. they can run at 100C! When using them on plastic brackets you need to under-run them to stop the brackets melting. With PLA you have to seriously under-run them! Fortunately temperature rise is proportional to the square of current, but torque is directly proportional so you can lose a lot of temperature without losing too much torque.

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[www.hydraraptor.blogspot.com]

That part in wiki needs to point to some ideal values +/- something.

In a better / clearer way than it is now. Like amps ohms ~x,~y, the resulting voltage should be ~y (~z times lower than 12v and why), and how to choose a stepper that:
- wont burn your extruder chip (like mine) and
- will have acceptable temperature.

The only orientative information there puts emphasis on torque, and that may mislead peoples.

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The only orientative information there puts emphasis on torque

Well, torque _is_ the only meaningful thing a motor provides. Sending more current to the motors than to get axes running reliably is a waste of electricity, makes motors louder and even increases wear of the bearings a bit.

If you look for the maximum current allowed, this depends on the motors you use. The value is usually found on the motor's type shield. No idea how this is measured, though.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Is there any downside to having a .9 degree stepper? The drivers can run them fast enough, right?

The only downside IMO is that you have twice as many steps to cover for a particular distance, assuming both steppers are being driven at the same step rate.

This itself shouldn't be a problem, except...

The values for how many steps to cover (and indeed, how many steps from home) are usually stored somewhere in the firmware. If these values exceed the max value allowed in the firmware, you will probably have issues when that occurs. By halving the step angle, you're effectively doubling the current max value, which may be too much.

Given that we have people using 1/16th step with 1.8 degree motors, there should be no problem at all using 1/8th step with 0.9 degree motors. As long as you can adjust the amount of steps your stepper driver does, you will at least end up with something that works. You can then try 1/16th with a large part and see if your firmware has issues.

There isn't really much (if any) of a downside to .9 degree steppers. There is, however, an upside - greater accuracy.

You can use microstepping settings to make a 1.8 degree stepper behave like a .9 degree stepper, but the accuracy of the stepper is always 1/2 of a real step. So a .9 degree stepper will always be more accurate.

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I'm building it with Baling Wire

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Is there any downside to having a .9 degree stepper? The drivers can run them fast enough, right?

In conjunction with 1/16 microstepping, you'd probably go beyond the performance limits of the ATmega. jgilmore is right, a 0.9 deg stepper with 1/8 microstepping is more accurate than a 1.8 deg stepper with 1/16 microstepping.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I use 0.9 deg stepper motors with 1/8 stepping and very small pulleys, giving me something like 80 steps per mm. I have no issues with it at all.

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yes mine work just fine as well.

I started this topic a while ago, so I'll give an update. gen6 only does 1/8 microstepping, so i just doubled the numbers in the firmware.

The only thing i notice, which is not really related to .9 deg steppers, is that i had to up my baud rate because the printer kept pausing, waiting for commands. I assume it has to do with the large number of steps, and would be the same if using 1/16 and 1.8 deg. i increased the baud rate to 38400 and the problem went away.

I'm not sure I'm seeing much benefit from the .9 deg steppers yet, although i don't have any other point of comparison. But i just think my machine needs more refining and calibration before I actually get to a point where the finer resolution matters. I am glad i went with the .9, though, since i know down the road i will have even better prints, without having to buy anything else.