Servo Transmission?

I'm trying to transmit servo actuation via pull cables. Can anyone recommend a supplier of the miscellaneous hardware (horns, stranded
cable, etc) for a relatively small scale application? A local hobby store had some stuff by Du-Bro, which make parts for RC aircraft, but they didn't have a large selection.
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On Sun, 25 Jul 2004 22:28:37 -0400, "Chris S."

This place probably has everything you need, though I think they're relatively expensive:
http://smallparts.com /
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Ben Bradley wrote:

Yeah, I've known about Smallparts for some time, but they're essentially a comprehensive hardware store. RC aircraft control parts are more of what I'm looking for.
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Don't recall ever having seen stranded steel wire in a hobby shop.
The big distributor is Horizon. http://www.horizonhobby.com /
wrote:

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Blueeyedpop wrote:

Hmmmm. Should be there with the rest of the linkages. The typical package includes the cable, a plastic outer sheath, and horn connectors.
The best place to find stranded steel wire is any music store.
-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza
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I'll keep my eyes open... hmmm I have 10 servos lying around, I need 29990 more to build a robotic elephant trunk. + 1154 servo pods...

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Blueeyedpop wrote:

I have been thinking about how to build a robotic tentacle (blame it on too much bad SF in my past).
I think that it can be done with two servos for each three segments. Unfortunately that means a *lot* of servos even for a simple 12-segment tentacle.
Someday... -- D. Jay Newman http://enerd.ws/robots /
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The control rods used by RC modellers are usually piano wire (or nylon rod) in a nylon or ptfe tube, or wooden push rods with bent piano wire ends. Flexible stranded cable in an outer tube (Bowden cable) gets used for brakes and gears on bicycles.
Stranded cable may not be a good choice for robotics, as it tends to curl a bit, adding a sort of spring to the motion. Additionally the frictional losses of running in a tube can be quite high - piano wire is better from this point of view. If power is going to be a problem, then avoid push/pull rods in tubes, and work out a scheme with bell cranks and pulleys.
A better solution, particularly if you require precision movement, is to use 'tapes' - essentially a thin flat strip, which can be very flexible in one direction, but stiff and strong in the other. There are also some very good synthetic cables around. One particular advantage of very thin things is that you can bend them quite tightly if space is limited - you don't want to bend a stranded cable around anything that is tighter than ten times the diameter...
have fun ! Dave

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Dave is right about stranded cable being springy and will not curve around a small pulley. I used some fishing line with a 50 lb rating called "Spider Wire" from WalMart. Very little stretch about $9.00. imma
Dave Garnett wrote:

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Imma Roadrunner wrote:

Some spring wouldn't necessarily be bad. Wouldn't a little give make the actuator less prone to damage and over-stressing?
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You need to distinguish between several uses.
You might need 'give' in a system to prevent damage (for instance when an RC model crashes). The best answer here is a clutch or something that breaks - a shear pin for instance.
You might need 'give' to provide compliance - you might wish to provide a certain force, rather than move to a specific position - for instance with a gripper. You can do this with a spring, or using a suitable feedback loop.
You might need to isolate the servo from vibrations or similar in the load
Apart from those reasons, 'give' in a servo system is a curse, making it difficult to position precisely - servos tend to hunt and use lots of power, over heat etc
Dave

around a

"Spider Wire"

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Gordon McComb wrote:

Oh? What's it used for there? Not musical instrument strings anyway. Those are wound, either on a stranded nylon core, a gut core, or on a single wire.
I've used bike cables in a couple of places, though they're a bit heavy for hobby robotics.
Clifford Heath.
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Clifford Heath wrote:

You're right...it's not stranded. I used the term too loosely. My point was that wire for linkage cabling can be found just about everywhere, and it needn't be anything special. Some *stranded* electrical wire can also work in many applicatioons, and most people already have that.
The idea is to think outside the box.
-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza
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On Tue, 27 Jul 2004 08:23:23 -0700, Gordon McComb

I can think of a few things offhand, one is the stranded picture-hanging wire, though since it's not made for this purpose, I suspect it may have fatique problems rolling over small pulleys. There's also the dial string assembly used to move the dials in old radios. If it's strong enough, such dial string might be ideal. If you want strong stranded steel wire, get an old dot-matrix printer (while they still show up in thrift stores) and pull out the wire that wraps around the stepper motor and moves the carriage back and forth. The pulleys at the ends should give you an idea of the smallest radius it should reasonably wrap around.

----- http://mindspring.com/~benbradley
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Exactly! Lots of things might work, especially since the motor is an R/C servo, most of which don't exhibit that much torque. I've successfully used 1/16" "aircraft" cable from Home Depot. The ends were terminated with standard wire crimp terminals. It wrapped around a 1" hub for producing a similar action as what you describe for the DM printer. (I used it with a stepper motor to slide the movable part of a drawer slide mechanism.)
While it may not be strong enough, depending on the application, the dial cord you mention is available from online sites that sell replacement parts for old radios. The "no stretch" nylon braid is really cheap...maybe 25 cents a foot or so. I've used it for finger linkages, as it's very flexible and can be readily tied.
-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza
Ben Bradley wrote:

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On Mon, 26 Jul 2004 04:01:17 -0400, "Chris S."

You may want to check servocity at the below link. They seem to have some servo attachments that might be of use. You might check the hobby shop for control line model airplane wire for braided wire. Fishing supply stores may also carry what you need. For low load use, I've used a Radio Shack switch knob to attach a .25" switch shaft to a servo control horn (bottom link).
http://www.servocity.com / http://www.geocities.com/zoomkat/switch.htm
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Chris S. wrote:

www.servocity.com has a good selection of everything servo-related.
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Servo city has various servo horn adapters - note the menu selections to the left. Also, the splines on Hitec servos are apparently different from all the rest - [cannot say for sure since I don't have any Hitec servos].
http://www.servocity.com/html/hitec_pulley_wheels.html
- dan michaels www.oricomtech.com =========================
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dan michaels wrote:

The splines are indeed different. They seem to be slightly shorter and might even have a different tooth count on the outter friction surface. The spline diameter and threading are the same though.
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On Tue, 27 Jul 2004 03:34:43 GMT, Jason Tang

I've got servos that have two different numbers of splines. There seems to be one spline different between them, like one has 24 splines and the other has 25. Not official, but black control horns and servo splines seen to have one type, and the white control horns and servo splines seem to have the other number. I've also noticed that one type turns to the left on increasing pulse length, and the other type turns to the right on increasing pulse length. That caused me a little confusion when I mixed the brands of servos in a project.
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