CHEAP Linear Motor/Actuator

In article <9bko61th4it3t3qi1j4o1uq425oqq86v9f@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:

I'm gravitating toward
stepper-motor/belt-drive/ball-bearing-drawer-slide/
some-kind-of-sensor approach.
Click to expand...
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.

--
Tony Williams.
 
On 25 Apr, tonyw@ledelec.demon.co.uk wrote:

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.
Click to expand...
Followup.

American Standard 25-1 chain has a 0.25" pitch.
A standard 9-tooth sprocket would be 2.25" per
turn. A Spectrol 533-series 3-turn potentiometer
would have measuring range of 6.75", with 0.25%
linearity.

--
Tony Williams.
 
On Mon, 25 Apr 2005 02:58:14 GMT, Tim Hubberstey <bogus@bogusname.com>
wrote:

Jim Thompson wrote:

On Wed, 20 Apr 2005 20:27:01 -0400, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:


On Wed, 20 Apr 2005 16:39:49 -0700, the renowned Jim Thompson
thegreatone@example.com> wrote:


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


"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?

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
36" long). Use a nut welded/soldered to a pushrod as an actuator or
drill and tap your actuator directly. 0.25" rod has 20 threads/inch -
0.05"/revolution. Your 0.010" resolution only requires 60-degree steps.
Measured backlash on a random sample of 0.25" bolts and nuts from my
junk drawer appears to be around 0.004".

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.
Click to expand...
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
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
"Jim Thompson" <thegreatone@example.com> wrote in message
news:r0vp615iafa5fd7nf1n0s84cnm4ducq0as@4ax.com...
On Mon, 25 Apr 2005 02:58:14 GMT, Tim Hubberstey <bogus@bogusname.com
wrote:

Jim Thompson wrote:

On Wed, 20 Apr 2005 20:27:01 -0400, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:


On Wed, 20 Apr 2005 16:39:49 -0700, the renowned Jim Thompson
thegreatone@example.com> wrote:


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


"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?

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
36" long). Use a nut welded/soldered to a pushrod as an actuator or
drill and tap your actuator directly. 0.25" rod has 20 threads/inch -
0.05"/revolution. Your 0.010" resolution only requires 60-degree steps.
Measured backlash on a random sample of 0.25" bolts and nuts from my
junk drawer appears to be around 0.004".

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.
Noise, is dependant on slop in the gear, and how you drive the stepper. If
Click to expand...
you micro-step (even to a 'simple' level like 8 steps), and the gear has
some form of spring bias, the result can be smooth and quiet. Some 'Type
N' stepper motors are sold with an internal nut, and a hole right through,
to drive exactly this configuration.

Best Wishes
 
I read in alt.binaries.schematics.electronic that Jim Thompson
<thegreatone@example.com> wrote (in
<r0vp615iafa5fd7nf1n0s84cnm4ducq0as@4ax.com>) about 'CHEAP Linear
Motor/Actuator', on Mon, 25 Apr 2005:

Hi Tim, I thought about that, too. Doesn't that get a bit noisy?
Click to expand...
Put some thick grease on it.

Although I thought of nylon-nut-steel-screw (or vice versa) as a
possible solution.
Click to expand...
Screw needs to be rigid, so make that the steel bit.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
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