Stepper Motors

Apologies for this slightly disconnected haven't read-all-the-posts-above reply, but I am at a conference in Boston at the moment typing this on the laptop that is also running Darwin at the conference exhibition...

1. None of the motors use the back shaft - we specified that as it didn't make any difference to the price (for us at least) and it gave us a lot more potential design freedom.

2. There is untested (and probably wrong) code in the firmware for half-stepping the motors. But this should be easy and modular to fix. Then any 200-steps-per-rev bipolar motor that will physically fit, has the same torque as the Nanotech one, and can be driven by 12v/2A through the coils should work.

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best wishes

Adrian

[reprap.org]
[reprapltd.com]

Argh! Looks up and checks the machine beside him using actual glasses: Zach's right - the Z motor does use the back shaft. Sorry. But 2-shaft motors shouldn't be much more difficult to find than one-shaft ones. Most manufacturers offer both options.

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best wishes

Adrian

[reprap.org]
[reprapltd.com]

I haven't read the design docs for a while, so I may just be asking the obvious, but is there any particular reason to use the back shaft? How hard would it be to modify it for front shaft only? Most cheap steppers are single shaft, so that's my reason for asking.

Obviously if someone found the holy grail stepper with 2 shafts, 400 steps, tons of torque, and only $10, the question would be pointless.

-Samuel

[cgi.ebay.com]

can anybody comment on these?
what kind of size restrictions are we looking at?

Jon Wrote:
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> [cgi.ebay.com]
> ER-MOTOR-425-OZ-IN_W0QQitemZ120176572930QQihZ002QQ
> categoryZ78196QQcmdZViewItem
>
> can anybody comment on these?
> what kind of size restrictions are we looking at?

Jon i am using these but the dual shaft version. 60.00 is very good i paid 100.00 with shipping. I would like to see what they end up at. I bought them from the same vendor and they came in a week. My machine is 95% done I just have end stops and some more tweaking to go mostly with my extruder but they seem to work with the present electronics and very well with the new adruino circuit which i bread boarded this weekend..

Bruce

NEMA 23 is the size that Darwin uses... so it would definitely fit. the torque on that thing is total overkill, although it would probably still work. having extra room is nice, but you can also get by with $20-30 motors from automation direct, etc . as well.

How about these $29 stepper motors, will they work?

[web2.automationdirect.com]

leggazoid Wrote:
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> How about these $29 stepper motors, will they
> work?

Nothing to work. No stock.

How about these $39 steppers, they draw 2.8 amps. Can you limit the current with the reprap driver boards to 2 amps, if so will they work with the reprap stepper driver electronic board?

[web2.automationdirect.com]

leggazoid Wrote:
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> How about these $39 steppers, they draw 2.8 amps.
> Can you limit the current with the reprap driver
> boards to 2 amps, if so will they work with the
> reprap stepper driver electronic board?
>
I'm working with smaller, linear steppers which use a driver board that I designed myself that is nothing like what Darwin uses. I'd say that you ought to direct this sort of question directly to Zach, who designed the Arduino driver board, iirc, and/or Nophead, who seems to know more about steppers than just about anybody here, saving Dr Bowyer.

> Can you limit the current with the reprap driver
You can with Zach's driver board by adjusting a preset. You can't with the PIC version of the electronics.

If you reduce the current you reduce the torque by the same factor of course.

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[www.hydraraptor.blogspot.com]

In the Host software presets you can set the torque for each stepper... So for the PIC electronics there is a setting..

I do not know if this setting will change anything on the Arduino electronics.

I have to set mine to 70% using the kelinger steppers and the PIC electronics.

Bruce W.

Skeinforge greatly improves the quality of prints by using many properties of plastics and the extrusion process.

Nophead gets excellent results with his accurate off-the-shelf XY table, at metalab they get excellent results using an existing CNC machine with very high accuracy.

For some time now, I have the impression that the quality of prints is currently being limited by the positioning accuracy, which is bigger (=worse) than 1/8 mm for 200 step motors. With a 400 step motor like the ST5709S1208-B you will have 1/16 mm.

They have a new 400 step stepper motor: ST5909M1008. A bulk order of these nanotec steppers could be in the 20 euro's price range (a discounted sample price, nevertheless a very decent price). I've attached the datasheet for the dual output shaft version.

I think the maximum movement speed is really a non-issue. If it's above 50 mm/s that's well enough and I'm sure that that can be reached with any stepper motor, also 400 step motors (you're still only driving it at under 1kHz).

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

I doubt the stepper motors limit accuracy. I only output my STL files with 0.1mm resolution normally.

I don't know where you get 1/8mm from. With 200 step motors, half a step is 0.1mm on my Darwin. Perhaps my pulleys are smaller.

I think delays in the firmware are the biggest problem. At 16mms/s 0.1mm is 6ms so to maintain accuracy your firmware has to be substantially faster than that.

The next biggest factor, I would guess, is mechanical slop in the structure and give in the belts.

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[www.hydraraptor.blogspot.com]

I think that indeed my pulleys are bigger. I use the moulded pulleys from BfB that were initially offered. With this I need about 8 steps per milimeter. I could check the radius. I just have this impression that the positioning needs to be about an order of magnitude more detailed than the width of the filament. I will soon try to do a comparative test, since I have both 200 and 400 degree steppers.

I noticed that the curved part of the pot you printed consists of many short straight lines (4 mm long) that make up the circle. Do you think this is due to the resolution of the STL file? (don't worry, I still think that it's very pretty!)

I'm not sure how close we are to the maximum step frequency that the firmware can currently generate. I have the impression that there's even some room for optimization when we get too close. Especially when we decide to use the step as the unit and not the mm or inch and solve the conversion in the host software instead of the firmware. It could still use G-Code, just with support for one unit (a single 'step'). This room could be used to use microstepping for more quiet movement and less resonance in the Darwin frame. Reducing wear, noise and energy usage. It also keeps you form having to re-fasten nuts & bolts all the time. A sinoidal+PWM chopper+microstepping board doesn't need to be more expensive than the current board.

Delays in the firmware are indeed a problem, but I'm looking a bit beyond that since buffering can solve that (or a more powerful chip than the atmega) such as PIC32 or motorola. I'm all in for PIC, though. Running data from an SD card could perhaps also help...

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

When I make STL files in CoCreate I can specify the linear accuracy and the angle accuaracy seperately.

When you make a circle with line segments you need surpisingly few to stay within 0.1mm accuracy but you can easily still see the facets. To remove them I can set the angle accuracy to somthing small like 1 degree. That causes the triangle count so shoot up from say several hundred to 10's of thousands. Even the you would probably only get 360 line segments, which would still be visible on a large circle.

Maybe I will do some tests to see how many lines look good.

I think the only efficient way to make aesthetically pleasing circles is to fit arcs to the data after slicing and send arcs instead of lines to the firmware.

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[www.hydraraptor.blogspot.com]

Erik, I'm half stepping 200 step Kelling steppers using Zach's driver boards and BfB pulleys, and getting 8 steps/mm. Very occasionally I can detect a slight offset in one raft filament relative to another, but it's not big. It's probably a resolution thing between STL, Skeinforge and Darwin, but it's not a problem.

I actually get better accuracy running at 8 mm/s and slowing down my extruder, but I usually run it at 16 mm/s just to keep the production rate up. There's some software issues with the firmware for sure; I've included Shane's feedrate compensation hack, but that hasn't taken care of all the delay. I'm using a very hacked version of Zach's Experimental Gcode, and I just realized that my extruder encoder interrupts are probably messing with my stepper timing; that might cause one problem. The faster I go, the more the delays start to mess with things.

I don't get actual blobs of plastic, I just get slightly more plastic in the areas that have a lot of short moves.

My current scope doesn't have the memory to pick up the timing pulses on the stepper controllers at the moment, but I've got a cheap logic analyzer on order; that should help me sort out the timing issues.

All of my curves look the same way; the limit is the fact that we have to use discrete straight line segments to describe a curve at the moment. Too many segments bogs down the Arduino firmware, so you have to keep them long. The slight comms delays I have compared to Nophead's rig means that the joints of my curves are slightly more pronounced.

[picasaweb.google.com]

You can see the exaggerated joints in that photo.

Curves supported in Skeinforge and Gcode would be cool, but I know it's not there yet. Up for some trig?

Oh, and vibration is always an issue; I use nylock nuts wherever I can, and loctite everything else.

If you want more accuracy without microsteping you could get .9deg/step motors. I got three motors from Alltronics.com at $17.95 each. They're very powerful .9 deg/step motors. below is description:

Lin Engineering Model 5709M-05S-04, Nema 23, stepper motor. This is a High Torque, Highest Step Accuracy, High Resolution, 2.25" stepper motor. Shaft is 3/16" X 3/4". Number of Leads 4

Alltronics part number 28M005

^^ Do those Lin Engineering motors work well? I found those a little while ago, and have been trying to decide what motors I want to go with. Those look like decent motors at a good price.

In Europe it's slightly more expensive to get the Lin Engineering motors than the Nanotec ones.

It depends on where you're located and your order quantities, though.

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

I'm in the U.S. I haven't seen any motors with similar specs for any less than those Lin Engineering ones. I just ordered three of them, so I'll see how they work. I'll let you guys know!

Check your pulley bore diameters, the Kelling steppers have a 1/4" shaft, while the Lin has 3/16.

Are there any plans to sell the Kelling motors on the rrrf store again?