RC servos are handy when you need to rotate something. You can even modify them to rotate continuously if that’s what you need. However, [Roger Rabbit] needed linear motion, but wanted the simple control afforded by an RC servo. The solution? A 3D printed housing that converts a servo’s rotation into linear motion.
The actuator uses five different parts, a few screws, and a common RC servo. The video shows the actuator pushing and pulling a 200g load with a 6V supply. There’s some room for adjustment, so different servos should work.
We were wondering about the STL files; [Roger Rabbit] offers to send them if you e-mail. We asked and they have been posted to a GitHub repo. There are also a few similar designs on Thingiverse if you want to try a different set of parts, although many of those use stepper motors.
We’ve seen some homebrew linear actuators before, but the attractive part to these is how easy it is to control the RC servo with a pulse width instead of requiring an H-bridge or stepper motor controller. Just the thing for feeding that cat while you are on holiday.
FYI: Those $5 servos are very, very unreliable. I’ve had many of them fail, often with magic smoke escaping.
I have a box of 10, none have failed so far.
well they won’t fail if they’re still in the box.
But seriously, I have used a few dozen of those $5 servos in an art project where they turn a few degrees every couple of minutes and need some holding torque on the edges, running 8h/day, for about 6 months now, not a single one has failed (yet).
It would seem to be totally random which sellers are mixing in rejects, because I once hunted down the cheapest mini servos I could find – got like 30 of them for $20 shipped… About 25% were DOA or failed instantly.
The Tower Pro SG90 (not the one pictured) and the HTX900 are favourites for the Chinese cloners. So far I have been lucky with the HTX900 on ebay.
Did you ever actually measure the loading to ascertain you were not exceeding the servo’s specifications?
great!
Pretty sweet, though i wonder if the buldge for the gear/servo isnt to big, to my knowledge most projects that use linear actuators do so due to size constraints now allowing for things like rotating arms, so then this would prolly be too big too.
But ye, still nice
The bigger the gear, the bigger the couple. If you make it smaller, it won’t be able to lift that much.
You got it the wrong way around
Wouldn’t a smaller drive gear give you more force at the output, like in a gearbox?
I think what Shakipu is saying is that decreacing the gear size would reduce the length of movement available. The way around that’d be to remove the potentiometer & limiter from the servo, and wire in a linear slide pot, attached to the output, in it’s place. That’s what they did on this one; http://makezine.com/projects/linear-actuator/
The EMS LINEAR SERVO CONVERSION ( http://www.emsjomar.com/SearchResult.aspx?CategoryID=18h ) work also very good if space is a constraint (we used it once for an retractable Pitot-tube in an experimental rocket). A flexible strip is rolled onto the shaft of the servo and pushed back. It should be possible to make something comparable with 3D printing and spring steel stripes / wires. Drawback compared to the method here is range.
you can buy linear servos on ebay for about the same price as that kit
Very cool! If I wasn’t leaving for a Christmas party soon, I’d already have OpenSCAD running to make a parametric version for Thingiverse Customizer. (Probably not. :grin:)
Not the point you can buy many things people build. Difference is you know how they r ok when you build them.think of the skills needed to make this versus buying one. 3d design ed printing mechanical design electrical design. Awesome example. Just my 2 and 3/8th cents
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Very cool. Very very cool. He really should publish the files though. I’d love to try this out.
He did. See github link above.
What kind of 3D printer is it made on? Much higher resolution than my printer :-(
It’s a good old Ultimaker I – wooden housing but great precision :-)
Clean build, I’d like to see a geared down version.
there was a geared version first – but it turned out to be to expensive and to bulky for me:
https://www.youtube.com/watch?v=29BYh9lcHWQ
then I built a smaller version with 33 mm of stroke path – that seems to be nice and handy overall
https://www.youtube.com/watch?v=3_Bq3Zj3838
Check this out :)
low geared version – much more expensive – and how can you make it smaller?
https://www.youtube.com/watch?v=29BYh9lcHWQ
smaller version – super light and cheap
https://www.youtube.com/watch?v=3_Bq3Zj3838