CHEAP Linear Motor/Actuator

[Jim Thompson]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

Thanks!

...Jim Thompson

 

[John Fields]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

 

[Larry Brasfield]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

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?

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

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)

If necessary I'm sure I could devise my own position feedback, if
necessary.

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?

Thanks!

FWIW, you're welcome.

 

[Ken Taylor]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

Thanks!

...Jim Thompson
--

I happened to see this on Ebay just yesterday:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11726&item=5767073198&rd=1&ssPageName=WDVW
Even if this doesn't suit in itself the idea may be what you're after. Check
out satellite TV dish accessories.

Ken

 

[Spehro Pefhany]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

Thanks!

...Jim Thompson

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

 

[Chris]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

Thanks!

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

Cheers.

 

[Bill Sloman]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

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
66 euro (about $90) under order code 318-7603, and RS Components offer six
alternatives at similar prices.

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.

 

[Eric Pearson]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

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 <1%
accuracy, but that does'nt sound too bad.
Eric

 

[Oppie]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

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.
http://www.thomsonmotors.com/Sectio...L2=10600000&L3=&L4=&L5=&L6=&IT=Descrip&lang=1

or
http://www.thomsonmotors.com/Sectio...?PC=8999400&CL=1&L1=8999400&lang=1&IT=descrip

Another is HSI http://www.hsimotors.com/linear-actuators/index.htm

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

 

[Oppie]

Also Google for "linear actuator"

 

[[email protected]]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

Thanks!

...Jim Thompson

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

 

[Genome]

Anyone know of a CHEAP Linear Motor/Actuator?

I'd like at least 4-5" of travel.

Ideally I would simply feed this device a voltage and it would go to a
position accurate to 0.010", although realistically I could probably
live with 0.030" position accuracy.

If necessary I'm sure I could devise my own position feedback, if
necessary.

Thanks!

...Jim Thompson

Oooooh Oooooooh Oooooooooh

Buy a $30 300dpi printer and kick the shit out of it.

Or, maybe not.

DNA

 

[John Fields]

..
..
..

Do you plan to drive this with a 10 bit DAC?

5"/0.01" = 500, so 8 bits ought to be plenty.

 

[Larry Brasfield]

5"/0.01" = 500, so 8 bits ought to be plenty.

This is almost what I call an "arithmetic argument". <g>

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.

 

[Genome]

This is almost what I call an "arithmetic argument". <g>

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.

I think what Larry was trying to say was.

'You stupid dipfuck Fields.

8 bits gives you 256. I can't buy a 9 bit converter so I'll use a 10 bit
one.'

To which you might have responded

'Whoops.'

And 'That Folks' would have been the end of the conversation.

In the meantime,

**** off Barry.

DNA

 

[Larry Brasfield]

news:[email protected]...

[Inconsequential, unheated "arithmetic argument" cut.]

I think what Larry was trying to say was.

'You stupid dipfuck Fields.

No, I was not trying to say that. We all flub sometimes
and it should not be an occasion for name calling among
adults. You can speak for yourself, but not for me.

8 bits gives you 256. I can't buy a 9 bit converter so I'll use a 10 bit
one.'

To which you might have responded

'Whoops.'

He still might, but acknowledging an obvious error
is hardly worth the bandwidth.

And 'That Folks' would have been the end of the conversation.

One could hope.

 

[John Fields]

This is almost what I call an "arithmetic argument". <g>

On my calculator, 2 raised to the 8th power is 256.
I allowed an extra bit for the sake of precision.

---
Yup. brain fart on this end...

We could argue about that if I was willing, but I am not.

Suits me.

 

[Phil Hobbs]

Really old hard drives (PC-XT vintage) used a taut band driven by a
200-step/rev stepper motor to position the head. They come apart
easily, too. Taut band drives give zero backlash.

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

 

[Jim Thompson]

Really old hard drives (PC-XT vintage) used a taut band driven by a
200-step/rev stepper motor to position the head. They come apart
easily, too. Taut band drives give zero backlash.

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

 

[Jim Thompson]

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

"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-shit, 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