Component help - electrically-controlled expandable rod

Discussion in 'The Projects Forum' started by icydash, Sep 28, 2014.

  1. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Hey all,

    I'm working on a project and could use some advice for a component part. The project is a small robot that's about two inches long. The robot needs to have some kind of microcontroller-controllable retractable/expandable rod or arm that fits within about an inch space, but can expand out to about 3 inches. That arm will have a sensor on the end and reach out and "touch" things. I'm not sure what to do for the expandable arm component. I've been thinking of some kind of electronic antenna (telescopic antenna) thing, or a solenoid (but these don't seem to run on 5v - 12v and have that length of stroke), but I could really use some help!

    Of course the cheaper and sturdier the better (because if the robot runs into a wall, I don't want the arm to bend).

    Thanks in advance.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    You need a small DC motor that can rotate a threaded nut. The arm will be a threaded bolt that moves linearly through the nut when the nut is rotated.
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    It's called a "linear Actuator" and they're available from a variety of sources...quite cheaply, too
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    For that small a foot print, you could look to the RC community for adapting a servo for e.g.
    Max.
     
  5. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Thanks everyone!

    I tried looking up linear actuators, but all the ones I can find seem to be extremely expensive ($50+) and heavy duty (for like 100+ lbs). For example, see: http://www.robotgeek.com/linear-actuators ... I found some cheaper linear servos that are in the right price range, but they have a stroke on the order of millimeters instead of inches. Any specific links to cheaper alternatives that meet the stroke requirement would be greatly appreciated. It only needs to have a 2-3 inch stroke and support like 1 lb.

    I also tried to find some sort of cheap, integrated DC motor and threaded screw/jack screw component, but couldn't find one.

    I also thought about using a scissor arm of some kind, but I'm not sure how to actuate it. But it seems like that may take up the least footprint when retracted and still meet the stroke length when expanded.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    You can make your own miniature nut & screw drive.
    Couple a long threaded bolt to the shaft of your toy motor. Now you can mount a threaded nut or hollow standoff on to the bolt.
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
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  8. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Thanks for the suggestion, but I'm not quite sure I understand how this works. I attach a threaded bolt to the shaft of my motor, and put a threaded nut around the bolt...but then what do I do with the nut? Do I couple the nut to the housing? So that, as the motor spins the threaded bolt, it moves the threaded bolt through the nut? But wouldn't the motor also have to be coupled to the housing to get the threaded bolt to spin (so that the motor itself doesn't just spin around)? But if the motor is coupled to the housing, then the motor wouldn't be able to move/translate, and the threaded bolt would not be able to progress forward through the nut because the motor wouldn't be able to move... *scratches head*

    Thanks for the suggestion. I actually looked into this component, but it's far too expensive. These actuators start at $40 and go way, way up. Do you know of anythign similar but cheaper? I'm looking for a less than $10 solution.
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Part of the problem is that you want it to extend further than the device is long, so it will take multiple sections like an antenna. Unless your a machinist finding something that size is not likely. You might be able to make it out of tubing I suppose.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Perhaps you could make a miniature version of a roll-up spring-steel tape measure, using a length of fine piano-wire wound on to a motorised drum?
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    there are lots of solutions, but wanting one that costs less than $10 rules most, if not all, of them out.
     
  12. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Thanks everyone for the suggestions. That roll up tape measure solution is interesting, maybe i'll give something like that a try.

    Totally random and separate question: I want to 3D print some of my components that have weird shapes. We have a local place that can 3D print, but I need to provide the design file. Do you guys know of any good, free software for 3D modelling? There's a bunch of stuff that came up when I googled, just figured I'd see if you pros have any recommendations =)
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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  14. icydash

    Thread Starter Active Member

    Jan 14, 2009
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    Awesome thanks!
     
  15. ISB123

    Well-Known Member

    May 21, 2014
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    Blender but very hard for beginners.
     
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