CHEAP Linear Motor/Actuator

The leadscrew-stepper combination on floppy drives looks pretty cheap. Does it have to be fast? Do you have enough volume to support really cheap? Is there a holding force requirement?

Do you plan to drive this with a 10 bit DAC? Where does such an accuracy requirement for position versus voltage come from? (just curious)

LVDT's can be built cheaply. Would there be any opportunity to calibrate each unit for accuracy, or does it have to be accurate as first built?

FWIW, you're welcome.

How much force? There are some electrical cylinder replacements that kinda look like a hydraulic cylinder (all enclosed). They are pricey new, but maybe surplus or on eBay...

There were some used in satellite positioning, but the accuracy might be a bit iffy and the ones I've seen were pretty big. Some used a reed capsule/magnet for incremental feedback.

Best regards, Spehro Pefhany

Have you thought about a car window motor. Maybe a bit too much travel - but maybe adjustable.

Cheers.

Model airplane servo's are cheap. Some mechanical linkages could be rigged to get your travel. Input is pwm, not sure if it will have

Thers also the maybe of a long throw speaker plus lever, all depends what youre doing. I cant remember the trade name, but someone sells IIRC 3" wide speakers with ultralong throw, they fit into tiny spaces and give decent sound supposedly.

NT

I've used the ones formerly from Airpax that are stepping motor/ acme screw types. They come in various force ranges from an ounce to several pounds. Airpax was part of Philips and was sold to Thomson.

or

Another is HSI

Hope this helps. Least I could do in return for some of the material you have supplied.

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This is almost what I call an "arithmetic argument".

On my calculator, 2 raised to the 8th power is 256. I allowed an extra bit for the sake of precision. We could argue about that if I was willing, but I am not.

Also Google for "linear actuator"

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"Jim Thompson" schreef in bericht news: snipped-for-privacy@4ax.com...

The obvious solution is a stepping motor with a lead-screw - you can buy these as a unit from broadline distributors. Farnell sell a Burgess unit for

When I've used this sort of gear, I put a neodynium-iron or a samariun-cobalt magnet on the moving part and a Hall effect sensor nearby, and use the output of the Hall sensor as a check (and if necessary as a reset) for (micro-) step-counting logic. The hysterisis in the Hall sensor means that it detects the magnet in slightly different positions if the carriage is coming or going.

There are loads of other solutions - chart recoders used to use DC motors driving a windlass around which you wound five or six turns of stainless steel wire.

Cheap chart recoders relied on a potentionmeter on the windlass shaft for position feedback, better units put a linear potentiometer on the on the pen carriage. I once worked on a capacitative position sensor where a grounded plate (in a flexy) shielded a variable length of a driving plate from a receiving plate.

-------- Bill Sloman, Nijmegen

I happened to see this on Ebay just yesterday:

Ken

Really old hard drives (PC-XT vintage) used a taut band driven by a

For 10-mil accuracy, you can probably use a good-quality ball bearing drawer slide as a stage. At power-up, drive the motor to one end and let it stall, so you know where you are, then step to your desired position.

Cheers,

Phil Hobbs

Good idea!

I also thought of going to Pep Boys and buying a power radio antenna ;-)

...Jim Thompson

"Pricey" is right!

I'm gravitating toward

stepper-motor/belt-drive/ball-bearing-drawer-slide/some-kind-of-sensor

approach.

Looks like I need about a ft-lb or so of torque, 3.6° would do.

Sources, suggestions?

(Like all new things I get involved in, I don't know rat-s*it, but I'm a quick learner... like the Bosch EC motor controller design... I just breadboarded a circuit in parallel with their discrete design, observed where it was struggling, immensely improved it, then swapped in my breadboard... tweaked it, then integrated it ;-)

...Jim Thompson

How about a stepper motor with a direct-drive connection to a piece of Redi-rod (that's what it's known as in Canada - threaded steel rod up to

This is a very standard way of converting rotary motion to linear (lathes, old floppy drives, etc.). You might even be able to salvage the head positioner out of an old 8" floppy drive. Newer floppy drives use taut-baud positioners which wouldn't be as easy to hack.

Hi Tim, I thought about that, too. Doesn't that get a bit noisy? Although I thought of nylon-nut-steel-screw (or vice versa) as a possible solution.

...Jim Thompson

A chain and two sprockets. Nut and bolt through one link of the chain to get the linear output. Drive one sprocket with a dc motor+gearbox. Put a potentiometer on the other sprocket to sense the position. 0.030" in 6" is 0.5% linearity required off the pot.