Surplus steppers I won't be using!

Philldapill

I'm working on a prop project involving about 10 stepper motors. However, they are quite expensive(usually), but found a guy on ebay right in town that is selling a huge lot of 225 assorted steppers. I think I can get him to sell them all for $450. That's $2 each for anyone who has trouble dividing. I don't plan on using all of these and want to pawn some off on people to re-coop some money. This post wasn't meant to be a FOR SALE post, but anyone interested, PM me. Like I said, a large assortment. Big ones small ones, and everything in between. I'm willing to sell them off in quantities as small as only one motor, plus shipping.

Now, for my question. I want to use these motors in a high-torque, possibly·mechanical shock-prone enviroment. If a stepper is in the process of moving to the next phase, and it recieves a large WHACK, will it be moved backwards and screwing up the movement? If so, how? How to prevent this?

stevenmess2004

Depends on the torque that the motor is able to provide. If the shock produces more torque than the motor can supply then it will move and this could screw up the movement. To prevent it you could either get a big enough motor or put an encoder on the shaft so that you can check the actual movement.

Steven

Philldapill

If I understand steppers correctly, if the motor is "locked" in a phase, i.e. no power given to any phase, it will not move. This is why you cannot move a stepper when no power is supplied?

stevenmess2004

Only to a certain point. All steppers have a maximum holding torque that you can find in their data sheets. If you get a small stepper you will be easily be able to move the shaft if you can get a grip on it.

Philldapill

Oh... I thought they were mechanically "locked", like gear teeth locked against the housing or something.

James Long

Philldapill said...
Oh... I thought they were mechanically "locked", like gear teeth locked against the housing or something.

Only if they have a brake, but it is rare to fine a stepper with a brake on it from ebay. The brake usually has separate wires coming out. They are easy to spot.

James L

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James L

Partner/Designer
Lil Brother LLC (SMT Assembly Services)

stevenmess2004

I believe that the holding torque is generated by the shape of the magnets in the motor. There are a lot of north and south poles that line up with gear like projections on the coils. This allows the motor to stay in one place and also to make a lot of small steps. If you want something that can't be moved, look at a worm drive. These are self locking of the output side. Just make sure that you get on that won't break.

You may want to move this to the sandbox so that others can see about the motors.

Philldapill

Thanks Steven. Er... how?

stevenmess2004

Just click on the sandbox item in the Forum Quick Jump drop down box at the top of the page.

Sawmiller

phila phil,

you need to know what kind of steppers he has. and thier holding torque.

there are lots of steppers in printers that are nice and small , but i wouldnt pay $2 each for. on the other hand the nice steppers that i am using on my big cnc rig are 425 oz that sell for $40 ea.

if you just want some steppers lots of people will give you old printers, basic rule of thumb is the older the printer the more torque in the stepper... paticularly the big old dot matrix and i think the laserjet 4's

i probally have in the neighborhood of 20 small steppers that i have scavenged laying in my spare parts boxes, i try to take the stepper driver chips also. one of these days i will make one of those marble kinetic sculptures out of some of the smaller ones just for the heck of it.

dan

Phil Pilgrim (PhiPi)

Just to clarify: the "holding torque" spec for a stepper motor is the amount of torque required to rotate the shaft externally when full power is applied statically (i.e. not stepping). With no power applied, the shaft can rotate freely except for a slight "detent" force.

-Phil

Graham Stabler

I don't want to be negative but I wouldn't bother with them. You can now get stepper motors fairly cheaply especially from Chinese suppliers and you will get the ones YOU NEED. At least price up the cost of 10 steppers suitable for your project.

I don't know who is good for steppers outside the UK but arc eurotrade here in the UK are doing a deal on some of their steppers, only 10GBP each, in my experience that would mean you could get them for $10-$15 in the US. It would be worth asking on the CAD_CAM_EDM_DRO yahoo group.

Are you able to tell us more about the application? You may be able to use some form of elastic element to take the shocks, even though you can't back drive worm gears you don't want to hit them with a hammer either [noparse]:)[/noparse]

If you short out the windings then that will increase the power-less breaking force but it still won't be massive.

Graham

rjo_

I would encourage you to take the deal...seems like you could always repackage them in small kits...

BUT I have stepper motors all over the place... and many of them have little info stamped on them to indicate what I've got.

How do you know what you've got?... let's assume that the part labeling leads you no-where... is there a flow sheet somewhere that will lead you to a proper ID or do you just have to experiment?

Graham Stabler

A multimeter can tell you what sort of stepper motor it is, uni-polar, bipolar, both, 5-phase then you can apply a small voltage to the windings and see how hot the motor gets turning up the voltage bit by bit, when it's getting too hot to touch (steppers can be run pretty hit by design) you have just gone beyond the rated current and voltage. You can drive at higher than the rated voltage as long as you current limit, up to 20X is often quoted.

For low performance applications just play it safe and run at just warm currents.

Graham

Philldapill

Well, many of these steppers look pretty big. Here is the ebay link to what he is selling. I figure I can at least re-coop my money by selling the ones I don't use in lots of 2-3 for $10 or so. This is just judging by the current prices on ebay. As you can see from the ad, many of these are big, and brandnew.

Philldapill

Oops! Here's the link...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110217746972

rjo_

Graham,

You are the most productive and least quoted expert on the forum... which be proof of some basic problem in statistical mechanics.

My guess is that my multimeter isn't going to tell me as much as your multimeter tells you[noparse];)[/noparse]

I'm thinking I need something more along the lines: "stepper motors for idiots." But I'm in the playing mode this weekend and my multimeter is within a 10 yard radius[noparse]:)[/noparse]


Thanks,

Rich

Philldapill

With the link to the auction up, suggestions in regards to this purchase are welcome. I've asked him how many of these still have some sort of ID stamp on them. Judging by the long list of items he posted, it seems many of them do so it shouldn't be TOO difficult to track down datasheets/info on them.

Philldapill

By the way, I don't think I was clear. If anyone is interested in these steppers, I'll part with them AT COST. Well, maybe a little less than $2 each for the small ones, probably $5 for the huge ones. Either way, I'm not looking to turn a profit. I usually like to buy in bulk, keep a few, sell the rest, maybe break even and keep MY parts for free. Once, I bought 800 75A mosfets for $50 off ebay and was hesitating when it came to paying beause I thought it might be TOO good to be true. Nope. Ended up selling 700 of the MOSFETs for about $1 each and kept 100 for "free". Not this time. Like I said, anyone interested, PM me or post a reply.

Eck, better yet, just PM me. I'd like to keep this forum post on topic and not a for sale ad. I appreciate Parallax's generocity in giving us a forum in the first place and I don't want to abuse it. [noparse]:)[/noparse]

rjo_

These would be great as items to put into grab bags at the up coming unofficial NE prop convention ... contact Oldbitcollector see if he is interested. If he wants to do it give me a private post and I'll see what I can do.

Graham Stabler

They actually look pretty good, go for it! I don't want to get lynched but do sell them at more than cost, your time is worth something!!


Rich,

www.cs.uiowa.edu/~jones/step/types.html Look at the diagrams for bipolar and unipolar, notice that the unipolar could be wired as a bipolar by ignoring two wires. The whole website is an education!

Bipolar uses two coils and th driver must be able to push current through in either direction. Unipolar uses effectively 4 coils but they are working in pairs, each has a "this way" coil and a "that way" coil so the driver circuit has four outputs and it never has to reverse polarity (simple transistor rather than a bridge), the central point is the common.

I hope that suitably educates your multimeter.

I would not consider myself an expert, I have contributed to some pretty esoteric discussions and done some small difficult things but my spin is terrible and I have never even used an sd card yet, as for all this computer science stuff they talk about I'm clueless [noparse]:)[/noparse]

Cheers,

Graham

Philldapill

Haha, thanks Graham! It's good to hear from someone who knows a thing or two that this is a fair deal. Whenever I buy large lots, I'm always a little unsure whether or not I'm going to get screwed. I told the guy I'll take the lot. I mentioned that PayPal is going to keep about $15-20 and maybe he could knock that much off if I pay in cash. We'll see.

As for selling them for a little more, maybe. I might just keep 20 or so of the smaller ones, a couple big ones, and then sell the rest to re-coop my money. That way, free steppers for me only costing me some time in shipping the rest.

By the way, Graham, that site is also very good info. Thanks.