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Re: [SeattleRobotics] Re: Motion controls

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  • Peter Balch
    Like David, I m not a fan of solenoids. For the sort of force that will be needed, the current will be huge - maybe 5 or 10 Amps. Maybe more - the force you re
    Message 1 of 32 , Jun 12, 2011
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      Like David, I'm not a fan of solenoids. For the sort of force that will be needed, the current will be huge - maybe 5 or 10 Amps. Maybe more - the force you're requiring could be quite large.
       
      So, at best, that's 5A at 12V. Which is 60W. Imagine how hot a 60W light bulb gets. The solenoid will be enclosed to protect it from rain and mud so it will get very hot indeed. If it needs more current, it will get even hotter.
       
      I think you need to calculate or measure the forces involved. I've got a spring balance (as used by fishermen) which I use for those sort of jobs. If it were me, I'd build a simple mockup and lean out of the window of a speeding car while pulling on the spring. Also work out the distance the solenoid (or whatever) will have to pull. (The distance and force will be interdependent of course). Whatever numbers you get for pull distance and pull force, double the force and choose a solenoid (or whatever) that does the job.
       
      Once you've chosen a solenoid, check that it works with 12V and look at how many amps it takes. If it takes more than 3A then it may overheat. If it takes 10A, it certainly will. Then look at the price and check your bank balance!
       
      There's always a tradeoff between speed and power requirements. Solenoids are fast and require lots of power. A window-winder is slower and needs less power.
       
      The point that David and I are making is that it will be much cheaper and easier to get a window-winder that can provide the pull distance and force than to get a solenoid.
       
      I can imagine that more space is required by a window-winder - is that a problem. You could put the window winder somewhere else (in the trunk?) and connect it to the panels by bowden cables. Don't some windscreen-wiper motors work that way - if so, use one of those? A windscreen-wiper motor even has one of the end-stop switches built in.
       
      Peter
       
    • Charlie H
      Hmmm. IIRC, the interocitor comes as a kit in a BIG box.
      Message 32 of 32 , Jun 16, 2011
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        Hmmm.  IIRC, the interocitor comes as a kit in a BIG box.

        On 6/16/2011 11:24 AM, David Buckley wrote:
         

        That is where the variable Interocitor comes in.
         
        ----- Original Message -----
        From: Charlie H
        Sent: Thursday, June 16, 2011 1:10 PM
        Subject: Re: [SeattleRobotics] Re: Motion controls

         

        Cavorite. Sure. But how do you control the shutters cheaply?

        Charlie

        On 6/16/2011 7:48 AM, David Buckley wrote:

         
        Peter
        I am surprised nobody has come up with using Cavorite. That would be so simple, IF....
        DAvid
         
        ----- Original Message -----
        Sent: Thursday, June 16, 2011 10:20 AM
        Subject: Re: [SeattleRobotics] Re: Motion controls

         

        From: Tony Brenke
        > I would use a dc motor and a limit switch.
        > spring loaded close.

        Spring loaded close? Can you point to a motor that can be back driven and is
        suitable in terms of torque and current?

        Peter


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