RSSMatt Mets just started a residency at the Pittsburgh Children's Museum, working on educational installations. In his first day in the shop, he built this articulated arm prototype. If you know of other systems that use this concept, post in the comments below, he's looking for leads.
Articulated arm prototype
Posted by Becky Stern |
Jun 18, 2009 10:18 AM
DIY Projects, Robotics |
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Hi Matt,
That looks great. I know OC Robotics uses a similar technique to make their very long and articulated robotic inspection snakes/arms.
http://www.ocrobotics.com
Here is a short video
http://www.ocrobotics.com/applications/files/security2.wmv
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A few years ago I used a similar mechanism in a robotic hand I built.
To get it to work smoother and easier try tying some type of elastic between each each section along one side. If the tension is the same in each section of elastic to begin with,it will create a uniform arc when the string running through the other side is pulled, rather than all curving at one end. It make this clearer I have some pictures on flicker here:
http://www.flickr.com/photos/hodgie/156705956/
Using this arrangement you only need to pull 2 wires to get the two movements.
You will also probably want to use smaller wedges (not thinner though) in between the layers, possibly even curved pieces in a crude ball socket arrangement.
For an added cool factor, you could even use Nickel Titanium wire (Flexinol brand is what I have used). When an electric current is run through it, it heats up and contracts.
Anyway, good luck with it.
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That's pretty much how the Pleo's neck and tail work, too. iFixit has a teardown:
http://www.ifixit.com/Guide/First-Look/Pleo/597/1
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i have built a unit out of brass, a spring, and carbon fibre it is about 10 " long and is driven by 2 servos it can moved in any direction
and kind of looks like a octopus leg
if you want to see it let me know
terry
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I was working on a similar mechanism a while back but the prototypes have been shelved until I get a few other projects out of the way.
http://www.youtube.com/watch?v=sjfqfSynQGI
These designs use flexinol actuators and an electric guitar string in the central column. The range of motion is limited but enough that it could probably do something practical.
and some build pics:
http://readeonly.com/wpg2
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http://coolthingsinrandomplaces.com/rolling-bridge-in-paddington-basin-london/ is a bridge in London that uses the same principle.
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I recently designed mechanisms similar to what you are building. Check out the video page on my website at www.jameshudakdesign.com to see some of them in action. I live in Pittsburgh and would have no problem giving you some help/advice building your own. Feel free to contact me via my website.
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this is how most manually adjustable wing mirrors work
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Thanks to everyone for all of the wonderful links and advice! It's really neat to see this sort of action being used in such diverse applications.
I fixed up my current prototype today by replacing the electrical cord with some metal wire, nailed down the spacer pieces and added a lever to the bottom. Next time around, I will try increasing the spacer height and making it more rounded.
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Great job, love the way you used very simple materials to prototype the mechanism. I've used a similar mechanism for a robotic tentacle which you can see at: www.isobot.org
good luck and can't wait to see what you come up with!
chris
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This is how most cable controlled puppets work in special effects for older movies. Very popular when an effects producer didn't want to go stop motion or radio/servo control (from a price and simplicity viewpoint). A simple search on "cable controlled puppets" should yeild a lot of results on movies on which they were used, but I know that some of the Audrey II puppets in Little Shop of Horros were cable controlled, as were some of the puppets in the Puppetmaster series.
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I worked for a company called GreyPilgrim that made a huge version of this. We had a demo unit that I think was about 20' long, and had multiple stages (2 or 3, I can't remember). It was driven by hydraulic rams, and used urethane couplings for the flexible segments. The company is now out of business, but I can put you in touch with some of the engineers who worked on it if you'd like.
I don't have any good pictures or video but you can see a small pic here (scroll down):
http://www.nist.gov/public_affairs/taglance/tag97fal/tag97fal.htm
We were working with NIST on using it with their cable driven work platform:
http://www.isd.mel.nist.gov/projects/robocrane/
Some ideas for your model:
* Use flexible material for your couplings. We used custom made urethane couplings (about 10"-12" dia IIRC), but for a model your size, a rubber stopper might work fine.
* Use bicycle cable and housing to make the arm multiple stages for complex bends.
Z
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The Computer History Museum in Mountain View, CA has an early robotic arm that used a similar concept, but instead of strings under tension, this arm used little air bags between each joint. The bladders were inflated or deflated to control the direction of the arm.
http://www.flickr.com/photos/wallofhair/12674324/
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