Buying the right motor in the UK?

Hi, thanks everyone for your input about stepper motors so far. I am based in the UK, so MakerBot is out!

I have found this from Digikey: [search.digikey.com]
would this be suitable?
Basically bi-polar stepper motor, 5.7V, 1.8 deg,holding torque 75 / 0.53 (oz-in / mNm).

Please can you confirm if this is OK, or if not, what needs to be different.
Thanks,
Hazel.

Expensive.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Someone mentioned Astrosyn [www.astrosyn.com]

They sell steppers on ebay, e.g.
[cgi.ebay.co.uk]|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50

- £35 for four, + £12 postage

I've seen a lot of 4 Nema17 steppers a week or so ago - I think they post pretty much constantly.

I've not used them myself, but it might be worth a look...

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

I've got some of the AstroSyn NEMA 17s. They are nice motors but low torque, so not sure how suitable they'd be for moving the axes of a Darwin. Probably fine for extruders though, which is what I plan to use them for.

I'm building a CNC router table/RepStrap, so wanted as much torque as I could get. I got a set of these 3Nm NEMA 23's: [www.motioncontrolproducts.co.uk]

which seem to do the job nicely, but they are quite big! Alternatively, I know that company also do some slightly smaller, lower torque (and cheaper!) 23's which might be more appropriate for a Darwin.

Good Luck!

Yep, that was me. The caveat is that I have not tried to use them in a reprap yet - have not got that far; but as far as I can see they fit the spec.

They do have a D-Cut shaft though, which I am not sure the standard reprap couplers will cope with, but that would be simple to fix.

The also have lots of 3 available, but with £12 postage per order I bought 2 lots of 4 as I am sure I will find a use form them.

The seller was excellent, they shipped the next day and I had them the day after that - well packed, so no damage in transit.

I thought so, too. I was expecting around £30 each.
Unfortunately, the MakerBot site doesn't give the specs of the motors.
I'll keep looking. Is this the right kind of spec though?
Cheers, Hazel.

I hadn't expected eBay to have such things!
Do you know, if you search "stepper motor" these don't come up. Anywhere. Although a lighthouse does!

I am now searching "stepper motorS" instead. Ah I wish eBay had a better search facility!

Thanks,
Hazel

Thanks for the link - I'll take a look there.
Hazel

So.... what exactly IS the spec?
Bipolar I know. 1.8 deg I know.
What about voltage & holding torque?

Do you know if these specs would be alright?
"Voltage: 4V
Current (phase): 1.2A
Inductance (Phase): 6mH
Holding Torque: 45Ncm"

Or do you know where I can find the right specs documented somewhere?Thanks,
Hazel.

@Matt Darley

I looked at motioncontrolproducts also, but have not bought anything from them - any issues when dealing with them?

I'm looking at going the same route as you, with a basic router table; do you really think you are going to need that much torque, or are you planning something big?

Also, what are you using for the lead screws and rails? The standard DIY threaded rod and aluminium channel, or did you get real ones from motioncontrol? Their prices for the lead screws does not seem that bad, but the ball nuts are not cheap!

@Lee

I ordered direct from MCP and the motors arrived in about a week, no problems. Shipping was around £10 and that was for 3 motors. They all work fine, although I haven't finished the table yet to test them simultaneously under load.

The table I'm building is relatively large and based on the JGRO plans listed on cnczone. I modified things a bit for metric, and enlarged slightly to cope with a standard quarter sheet of MDF or Ply (1220 x 610 mm). The rails are pretty much as described in the JGRO plans - steel tube, angle aluminium and skate bearings. For the lead screws, ballscrews were well out of my price range so I went with 12mm trapezoidal screws: [www.worldofcnc.com]
and made a tap from an off-cut of one the screws, so that I could make my own anti-backlash nuts from some Acetal.

@Hazel

There is a decent amount of information here [reprap.org]

However I don't think there is a definitive spec per say, rather you need one that is compatible with your electronics and power supply that has enough torque.

The original ones used were 0.9 degree rather than 1.8, but I believe there is a firmware switch to use 1.8s with half stepping - its what most people seem to be doing given the high price of 0.9 degree steppers.

@Matt

Thanks for the info and the URL, had not seen that supplier, looks like they have a good range at reasonable prices. I was not planning anything as big as yours, so the 1Nm 23s I have will hopefully be fine - I can always use 2 lead screws for the x axis if I need more torque.

Edited 1 time(s). Last edit at 04/30/2009 10:23AM by Lee Freyberg.

Hazel,
The problem is nobody has produced a spec for the motors for Darwin, just a list of motors that have been found to work. [reprap.org]

I built mine with the Keling NEMA23's from the RRRF. The dollar was better then so it was cheaper than buying locally. I connected them in bi-polar parallel, which needs 3.4A for full power, but found 1A was plenty of torque. They are rated at 1.2Nm so I conclude that 0.35 Nm is enough torque. That brings it into the range for NEMA17, but I haven't tried that. I think Vik Olliver may have built a Darwin with NEMA17's though.

One thing to bear in mind is that a stepper run at its maximum rating without a heatsink will get very hot and possibly melt the plastic parts of a Darwin. That is why I like to underrun them.

The voltage does not matter much because the driver boards are constant current choppers. Lower voltage and inductance means higher top speed though.

I think the assumption is that for the McWire repstrap people would use the same motors and transfer them to Darwin they made with it. They are not the ideal motors though as the McWire needs far less torque and resolution than Darwin because one rev is only the screw's pitch, rather than 40mm. It is really difficult to get threaded rod drive to go fast enough for extruding with steppers.

15 degree per step motors are probably better for threaded drive, but no good for belt drive. I will be playing with some this weekend to see how fast they go compared to the NEMA17s and NEMA23s that I have.

Edit: sorry got your name wrong first time!

Edited 1 time(s). Last edit at 04/30/2009 08:45AM by nophead.

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[www.hydraraptor.blogspot.com]

@Hazel

a holding torque of 45Ncm (0.45NM) as you quoted seems a bit low - the original steppers specified were around 1.0NM so twice the torque. I'm not sure how much a Darwin actually requires, but I would go for at least as much as the original.

These are what I bought:

[cgi.ebay.co.uk]

And they seem pretty close to what other people have, and to what makerbot / RRRF are selling though YMMV.

What sort of reprap are you building and what electronics are you using?

Hi Lee,
I am building a McWire-alike. I have nothing beyond parts as yet, not even enough to call it mechanics at the moment, and certainly nothing remotely electrical! I have just started out (literally, just last week) and here is my blog on progress so far:
[http://copycatbot.blogspot.com/]

I'm delighted to have access to so much input from others, and that people are willing to give of their experience. Thanks for being one of these people - the help is invaluable.
Cheers,
Hazel

Hey Hazel,

I'm in a similar situation to you, although I have been following reprap for about a year now, I have not actually got a huge amount done. I've learnt a lot though, and I generally like to research things up front rather than dive in, saves on the 'oh damn, did not think of that' moments.

I was originally going to build a McWire too, but after working out the cost of pipe etc, and realising that a chunk of the cost would be throw away, I changed to routing table similar to what Matt and other are building. Seems easier to me, and there is far more information online, including full plans. Also, being able to route / mill wood and plastic seems like a useful thing to have, and will just require a different toolhead.

If you have not already I'd spend the time to read though both Nophead's and Forrest's blogs - I learnt a hell of a lot, just doing that, and I am amazed at the depth, detail, and clarity of material that they put up!

Hi Nophead, thanks for the Reprap workable motors link. That's just the info I needed.

According to the data sheet for the Lin NEMA 17 listed there, the holding torque for that one is 41 oz in. By my calculations that works out as just 0.3 Nm. (I think - please can someone check my maths? I've never used these combined units before.)

So it looks like torque isn't really the issue.

So is this OK for a repstrap stepper motor spec then? Bear in mind my stages are 6 mm MDF.....
Voltage: 4V
Current (phase): 1.2A
Inductance (Phase): 6mH
Holding Torque: 45Ncm

(This is one of the NEMA 17s - at only just over £9 each.)

Hazel

Yes I get 41 oz in is a shade less than 0.3Nm. I have just received some of those Lin motors, so I will be able to tell you how fast they can go at the weekend.

The motor spec you have will certainly have enough torque for McWire but a cheap tin can motor my be faster. Again I can publish some figures at the weekend.

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[www.hydraraptor.blogspot.com]

farnell have a decent selection of stepper motors if you can fight through the website to find them. they will probably have teh equivalent of a nema 23/17 on there

the specs on the back of my stepper motors (nema 23) that i got from makerbot are:

keling KL23H251-25-8B
Rated Current: 2.8A, Rated Voltage: 4.17V (in Bipolar Parallel)

farnell have a nema 17 motor for £28.34
and a nema 24 motor for about £40
and farnell dont charge for postage

sugest that you get them from makerbot when you get your electronics though as they ar only about $30 for the nema 24s from there (not sure how much teh 17s cost if they do them)

Hi Simon,
I've been stung ordering electronics from the States before - the import tax was not accounted for on the ordering side, and then the courier added on their admin cost to claiming the import tax.... = ouch!

Thanks to Matt who gave me the weblink,I have plumped for 3 NEMA 17s from [www.motioncontrolproducts.co.uk] at ~ £9.25 each, which seems much more reasonable. They're heavy, but i don't think I can quibble for that price.

Cheers,
Hazel.

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Hazel

[copycatbot.blogspot.com]

Yes when I got the NEMA17s from MakerBot I was stung for 15% VAT + £8 handling.

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[www.hydraraptor.blogspot.com]

Sligtly off subject but:-

I was also stung by the Post office for the extra £8 handling on my MakerBot order.

Im not botherd by the VAT just the extotionate handling charge.

Please note that the Post office is only £8 compared to Parcelforce £13.50 handling charge

Parcelforce are the EMS delivery service for DX.

I'm still waiting for 1kW inverters for my Solarpowerd Workshop via Parcelforce

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