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Cheap linear actuators

Discussion in 'Sensors and Actuators' started by Ian, Feb 28, 2018.

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  1. Ian

    Ian Administrator

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    I'm interested in integrating a hidden "drop down" compartment as part of a home automation project, i.e. using linear actuators to drop a platform of around 0.5kg by 100mm.

    It's only a gimmicky project that I don't want to spend much building, so purchasing a standard linear actuator seems like overkill.

    This got me wondering what alternatives there may be for small loads like this. Stepper/belt combos could work, but for such a small load I'm sure there is an easier way. I spotted these N20 motors with a small gearbox on AliExpress:

    https://www.aliexpress.com/item/M4-...terminals-100MM-thread-shaft/32846788887.html

    They come with a 100mm shaft, so I could buy a pair of these and build a platform using enclosed M4 nuts, perhaps also adding guide rods if required (although for this application I think it may be ok without). Add a couple of endstop microswitches and it's done :).

    Have you spotted any products that may be better suited, or have you got a better idea for something that may work? I considered using a rack and pinion style mechanism on a 9g servo, but I think that may rattle and be too noisy.
     
  2. Alec_t

    Alec_t

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    The units in that link look just the job. I would have suggested the same method.
     
    Ian likes this.
  3. kellys_eye

    kellys_eye

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    I use a reduction geared motor to lift the hen coop door (timed, automatic) that I knocked-up a few years ago.
    I have a couple of motors left over (with, IIRC, 40:1, could be 60:1 reduction gearing) that I could send you FOC if you need one?

    The motors will run from 6V to 24V (nominally 12V) and have enough torque to pull a wall down!

    Motor:

    http://www.ebay.co.uk/itm/Maxon-Mot...805997?hash=item1a0cbc22ed:g:p8sAAOSwqrtWooaw

    Gearbox: (100:1 shown, mine are 60:1)

    http://www.ebay.co.uk/itm/MAXON-MOT...234434&hash=item1ed0df92c9:g:KGEAAOSwuOxZw25d
     
    Ian likes this.
  4. Ian

    Ian Administrator

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    That's extremely kind of you @kellys_eye - however that motor and gearbox look far too nice for a little tinkering project like the one I'm dabbling with, so I'll pass on your generous offer so that you can put them to better use (like pulling walls down ;)).

    I'll pick up a couple of these little AliExpress N20 motors as they're only a few quid each :).
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    I have an ancient "drill press" adapter for use with earlier model Dremel Moto-Tools. Instead of moving the quill (the Dremel Moto-Tool) up and down, a cam underneath the table moves the table up and down when the cam is rotated manually by means of a knob, shown below and to the right of the table, in the image below. So, if you have sufficient room under your platform, you could rest it on a cam that moves it up and down 100mm, or about 4 inches, under the control of a geared PMDC motor. Easy to add micro-switches, actuated by the cam, for use as limit stops.

    [​IMG]
     
  6. Ian

    Ian Administrator

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    That's an interesting mechanism and that idea may be useful for another project I've got in mind - but unfortunately the platform is dropping from a hidden void in a cupboard, so it can't have anything underneath it. I've gone for the 100mm motors (which will no doubt take a while to arrive from China), so knock up a platform in anticipation of their arrival.
     
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  7. Alec_t

    Alec_t

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    If you're going to use two motors you might need a toothed belt or other link to synchronise their rotation, to avoid the platform tilting.
     
    Ian likes this.
  8. Ian

    Ian Administrator

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    Good point, I'll stick to one and use some guide rods to keep it simple :).
     
  9. Alec_t

    Alec_t

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    A scissor-jack movement could work with a single motor.
     
  10. hevans1944

    hevans1944 Hop - AC8NS

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    No, @Ian said in post #6 that the platform drops from a concealed location in a cabinet, so it's not possible to place a lifting mechanism underneath. A scissor-jack on top would severely limit what one could place on the platform.

    The motor-driven linear screw mechanism is Asian-cheap and will probably do just fine if the platform does not twist when it raises and lowers. The only other possibility I can think of at the moment is a string mechanism with one or more strings attached to spools that are motor-driven from a common shaft or otherwise synchronized by cogged belts or chains. Seems to be overly complicated for a concealed platform lift.

    Perhaps a simple latch could be used to secure the platform in the raised position, and then let gravity do the work of dropping it down when the latch is tripped. Of course you would have to raise it back into the concealed position by hand. No Electronics Point technology required, unless you wanted a remote release capability.
     
  11. Alec_t

    Alec_t

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    Well, we don't know what the platform size is or what is to be placed on it. The jack wouldn't have to be the size of a typical car jack :). I agree, strings and pulleys would be an option.
     
  12. hevans1944

    hevans1944 Hop - AC8NS

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    I think @Ian is building a password safe, so he can write down and hide all of his plethora of passwords, while still having ready access to the ones he forgets. Or it might hold the recipe to the McDonalds Secret Sauce, or the Colonel's Secret Mixture of 11 Herbs and Spices... something small and valuable, no doubt! :D
     
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  13. Bluejets

    Bluejets

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    Ian,
    The motors in the link in your first post are available with tiny encoders mounted on the back end which would help for position control.
    Also Hobbyking have a range of servo-less retract units, some for around Aus$12.00 which are basically a linear servo. Just thought you might be able to adapt something from there.

    https://hobbyking.com/en_us/digital-servoless-retractable-system-1pc.html
     
  14. Ian

    Ian Administrator

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    The funny thing is I'm not even sure what I want too use the concealed lift for yet... we've got a void behind a tall cupboard in the kitchen and I've recently started using home automation software and ESP8266's to automate a lot of things in there (lighting, music, power, temp, etc...). As I've got power behind that void, I thought it might be a fun project to nicely integrate with the rest of the home automation stuff. Usage suggestions are most welcome ;).

    Thanks, I did see some of the N20 motors that come with encoders, but none that came with the combo of a 100mm shaft and encoder at the same time (and I can't find where to buy it separately). I think a microswitch end-stop should be ok for this project, as it's just a novelty one - however if I re-purpose these motors I may see if I can add an encoder at a later date.

    I really like that servoless retract you linked to - I'll keep this in mind for future projects, as I can see this being really useful (especially at that price).
     
  15. Alec_t

    Alec_t

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    Hiding something you don't want your other half to know about? :).
     
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  16. Ian

    Ian Administrator

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    I suppose I could make it secret whisky storage :D.
     
  17. hevans1944

    hevans1944 Hop - AC8NS

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    Hmmm. Like a few quid for "emergencies" maybe? Or a few gold bullion coins as a contingency fund? Your BitCoin private encryption key? Nah. Save the hidey box for something that has permanent value.:D Properly aged single malt whisky sounds good... Lagavulin 37 Year Old Single Malt Scotch Whisky perhaps. Other possible candidates can be selected from a list found here.
     
    Last edited: Mar 2, 2018
    Ian likes this.
  18. Externet

    Externet

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  19. kellys_eye

    kellys_eye

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    Like your internet history perhaps?
     
    Ian likes this.
  20. kellys_eye

    kellys_eye

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    Is that where cupboards meet in a corner?

    If you need to make something with significantly greater 'pulling power' then my motor offer remains! Just found some spare gearbox parts for them too so you could have 20:1, 60:1, 200:1 or 500:1 reduction!

    Imagine a shelf that dropped down a special bottle of whisky in the midst of subtle downlighting and CO2 'smoke' with the theme from 2001 playing loudly :D
     
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