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'[OT]: Small linear actuators'
2000\09\20@061356 by Mark Willis

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Well, I'll hope someone here knows <G>

I'm looking for some small linear actuators for a future project;  say
1" contracted length, 2" extended length?  Something pretty (relatively)
inexpensive would be good, almost NO precision is necessary, say 1
second for full travel is fine.  1 pound of force max., or so?  Haven't
used THESE before <G>  H bridges to drive them, probably.  I'm planning
to look at the HexaPod web pages in the AM, expect to maybe find
something there.  If someone has a favorite supplier who treats them
well, that'd be good to know.  Off-List is fine.

And:  Yes, I know, "Cheap, Fast as you want, Low MTBF - Pick One."  <G>

 Mark

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2000\09\20@070718 by Michael Rigby-Jones

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ISTR that linear servos (for RC planes etc) used to be available that had
that order of magnitude of travel.  Not seen them recently but then, I've
not been building models for a long time.

Mike

> {Original Message removed}

2000\09\20@071301 by Andy Howard

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You might want to look at shape-memory alloys, the kind robotics folk use
for musculature.



----- Original Message -----
From: "Mark Willis" <spam_OUTmwillisTakeThisOuTspamFOXINTERNET.NET>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Wednesday, September 20, 2000 11:13 AM
Subject: [OT]: Small linear actuators


{Quote hidden}

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2000\09\20@080236 by Mark Willis

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Michael Rigby-Jones wrote:
> ISTR that linear servos (for RC planes etc) used to be available that had
> that order of magnitude of travel.  Not seen them recently but then, I've
> not been building models for a long time.
>
> Mike

Hmmm.  I was thinking of getting an RC airplane magazine today, I'll
look - Thanks!  Those might be dearer than I'd like, well, more research
to do <G>

Andy Howard wrote:
> You might want to look at shape-memory alloys, the kind robotics folk use
> for musculature.

On those, I'm a little concerned about cooling, those IIRC use a fair
amount of power - am I recalling correctly?

I will ask the SRS folks, they're semi-local.  (Probably a really good
resource for this one <G>)

Other possibilities are pneumatics & hydraulics, those are possibles for
this project.  I'd rather not use those, pneumatics would be better than
hydraulics (Need more force control than position control!)  Lots lower
MTBF though, I'd think.  I want a well over 2000 hour MTBF on this thing
<G>

 Mark

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2000\09\20@082305 by Michael Rigby-Jones

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{Quote hidden}

Cheap and nasty:
Modify a normal RC servo by removing the rotary pot and the stops, attach
some threaded bar to the output shaft and use a nut/threaded block to get
the linear motion.  A linear pot can be used to provide feedback.  I did
this for a robot arm I made in high school, can be made to apply a lot of
force, but quite slow response.

Cheap and a bit better:
As above, but scrap the servo control electronics and use a pic in
conjuction with an optical encoder on the shaft to increase reliability
(linear pots aren't very good unless you are willing to pay $$$$'s)

Not exactly of the shelf, but it depends on how much money you ned to save.
You can get smallish linear actuators for use with satelite dish
positioners, but I suspect even the smallest one will be too large for your
application.

I guess if "force control" is more important you could use an open loop, but
current limited control scheme?

Mike

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2000\09\20@083551 by Andrew Kunz

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I don't know of any RC airplane companies still making linear outputs on their
servos.

Using them to run a ball-screw setup is a great idea, imho.

Andy

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2000\09\20@133912 by Lawrence Glaister

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Hi Mark
depending on  the actual motion you need, I would recommend model airplane
servos.... they come in a lot of different sizes and torque ratings. If you
can tolerate the rotary to linear conversion in a pushrod, they should do
the trick. They take 4.8-6v dc for power and the control signal is a logic
level pulse between 1 and 2 ms in duration repeated every 20ms or so (not
critical). Cost per device is about $15us to $50us depending on size and
type of output bearings.
=======================================================
Lawrence Glaister VE7IT             email: EraseMElgspam_OUTspamTakeThisOuTjfm.bc.ca
1462 Madrona Drive                  http://jfm.bc.ca
Nanoose Bay BC Canada
V9P 9C9
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{Original Message removed}

2000\09\20@165327 by gwaiche

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Hi all!

Some time ago when I was on model making, I remember
seeing servos giving a translation. They were made for
lifting small cable in sails boats. I think it was Robbe
Graupner products.

Gael

Lawrence Glaister wrote:
{Quote hidden}

> {Original Message removed}

2000\09\20@171205 by Russell McMahon

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>I'm looking for some small linear actuators for a future project;  say
>1" contracted length, 2" extended length?  Something pretty (relatively)
>inexpensive would be good, almost NO precision is necessary, say 1
>second for full travel is fine.  1 pound of force max., or so?  Haven't
>used THESE before <G>  H bridges to drive them, probably.  I'm planning
>to look at the HexaPod web pages in the AM, expect to maybe find
>something there.  If someone has a favorite supplier who treats them
>well, that'd be good to know.  Off-List is fine.

>And:  Yes, I know, "Cheap, Fast as you want, Low MTBF - Pick One."  <G>

Usually it's any TWO of Soon / Cheap / Quality.


Small solenoids are not good at long travel and moderate force across the
range. All the surplus houses have various solenoids but they are
'bang-bang" in operation and draw high current when stalled.

Consider the possibility of a small motor with either worm drive (easy to
get high ratios) or driving a fine pitch screw thread with a nut running on
it as the actuator drive. (I'm hoping to try the latter as as parachute
release mechanism for water rockets using a pager vibrator motor :-) !)




     Russell McMahon
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2000\09\20@194938 by Ricardo Seixas

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Mark,

Maybe you can use door locks (used in cars), there are several types, i'm
pretty sure
you'll find one that fits your needs, they are strong, cheap and high MTBF
(maybe someone will disagree here, pick one <G>).
Comes in various packages and flavours, Motorized, Vacuum, Solenoid...


Ricardo Seixas


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2000\09\22@063617 by Jinx

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How about the small stepper head positioner on a 3 1/2" floppy ?
You should be able to get dead drives for nothing from a service
centre. Of all the ones I've pulled apart the motor has never been
faulty, and they aren't too puny. Wouldn't take an arm off but you
may get something useable. Besides, they'd be better in a parts
box than at the tip

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2000\09\22@072444 by Peter L. Peres

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Look for RC servos designed for rocket gliders. There are 2 or 3 makers. I
think Robbe or Hitec or someone like that will have some. These you can
drive with RC PWM as usual, or rip out the electronics and supply your own
for better servo algorythms.

Peter

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2000\09\23@175937 by Mark Willis

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Lots of good ideas - Pager motors with a rack attached may be "the"
thing I need, the control electronics could be completely remotely run
(I'm going to keep looking and thinking <G>)  Cheap is good, servos
would be great (don't need exact positioning so no encoders etc. needed)
- some servos are too large for part of this, some might be just right
for part of the deal though.  I think I need to start playing with
"popsicle stick and hot glue" mockups some time and see how it goes <G>

 Mark

Peter L. Peres wrote:
> Look for RC servos designed for rocket gliders. There are 2 or 3 makers. I
> think Robbe or Hitec or someone like that will have some. These you can
> drive with RC PWM as usual, or rip out the electronics and supply your own
> for better servo algorythms.
>
> Peter

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