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Electronics Linear Actuator RC Control

Discussion in 'Modding' started by Explicit, 16 Dec 2006.

  1. Explicit

    Explicit What's a Dremel?

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    I'd like to control a linear actuator with a surface FM radio control reciever... But I'd also like to do it proportionally...

    There are some kits available that will allow me to use a relay to turn on/off a relay, but I'm unsure as to how I would be able to reverse the polarity and control the actuator in both directions?

    Anyone have any insight?
     
  2. hydro_electric_655

    hydro_electric_655 Dremelly Dude

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    Most good RC car radios are exponential as for a linear actuator you could use an RC car speed control to control motor power.
     
  3. Explicit

    Explicit What's a Dremel?

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    Oh, good thinking...

    I was thinking of a mechanical system where a servo controls a switch, but an ESC to the motor on the linear actuator is a much better idea!

    There might be a problem though, most linear actuators I have found are 12v and most RC motors run alot less current...

    I may be able to swap the motor in the actuator for an RC variant I suppose.

    I want to use the actuator so a steering assembly though, so I'd need to be able to control the motor forward and reverse at the same speed, I think most ESCs put out less power for reverse to simulate a transmission.

    Does anyone have any alternatives? I need to control a heavy steering assembly and a servo just doesn't have enough power to do it...
     
  4. Explicit

    Explicit What's a Dremel?

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    Last edited: 17 Dec 2006
  5. Ultistealth

    Ultistealth What's a Dremel?

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  6. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    by proportionately do you mean you want the position of the linear actuator to match up with the position of the stick on the RC transmitter, or just speed?
     
  7. Explicit

    Explicit What's a Dremel?

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    I think I have it sorted out.

    It wont work proportionally like a regular rc servo but it will work.

    I'm going to use a kit that converts the PWM signal that RC uses into instructions for an H Bridge motor controller.

    Basically what this will do is allow me to push a stick on my transmitter to the left or right and that will control the motor in the actuator, either forward or reverse.

    Regular RC servos self center, and move proportionally, so if you push the stick only halfway to the left, the servo will only rotate a quater of it's range of motion. But if you push the stick all the way to the left, the servo will rotate a half of its range of motion, and then pushing the stick all the way to the right will rotate the servo in the other direction also half it's range of motion. But when you let go of the stick, the servo self centers, which is what I will be missing with my setup.

    However I can use coil springs on my steering arrangement to mechanically center the steering unless the actuator is powered.
     
  8. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    If you could find a long enough linear pot, you could hack a servo by replacing its pot with the linear pot, and hook the output from the h-bridge on the board up to larger h-bridge, powering the actuator. Using the servo board to decode the PWM and control the motor.
     
  9. Explicit

    Explicit What's a Dremel?

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    You mean use a the servos PCB to decode the PWM, then hook the output of it to another H Bridge that controls the motor in the actuator right?

    I don't know where I'd find a linear pot to match the stroke length of an actuator though... Do you?

    That's actually a really smart idea, hopefully I can find the right value pot, I could probably make any length one work.
     
    Last edited: 19 Dec 2006
  10. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    yeah sounds like you got it, I'm not sure where you would get such a long linear pot either, but if you could find one, or possibly use a toothed belt + cog and a multi-turn rotary pot it could work too.
     
  11. Explicit

    Explicit What's a Dremel?

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    Yeah, maybe a gear rack and sprocket to turn a normal pot.

    Any idea how I'd get the servo pcb to control another H Bridge, most of the kits I've found expect input from a microprocessor... I know you can make an H Bridge from 4 transistors w/ diodes on them, but I'm not sure how I'd control them from the pcb of the hacked servo?
     
  12. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    well, the output from the servo board going to the motor is most likely a H-bridge itself... so that should be a start ;)
     
  13. Explicit

    Explicit What's a Dremel?

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    Luckily I have a servo here to mess with before I buy an actuator...

    Wish me luck.

    Update:

    I've been searching high and low, seems like unless I want to order 1000 or more of these huge pots im out of luck...

    I was thinking about making my own though, using a range of resistors, one lead with a metal tab on the end and have them all equal size tabs, then run a brush/wiper along it... Should work.
     
    Last edited: 20 Dec 2006
  14. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    your using this for a steering linkage, correct? Isnt there some pivot point where you could use the angle of a pot on that pivot to determine the position of the steering rack?
     
  15. Explicit

    Explicit What's a Dremel?

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    That would probably easier... Less compact though.

    I think that's a better solution.

    I just wonder how hard it will be to match the range of motion of the pot to the steering assembly.
     
  16. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    most servos dont use the full range of motion of the pots anyway... just 90 degrees or so (the particular ones ive seen) so adding resistors (or trimmer pots, which could let you trim the steering too...) on either side of the variable resistor would increase the range of motion, (effecively making the pot 'longer') not sure how you would lessen the range of the pot...
     
  17. Explicit

    Explicit What's a Dremel?

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    I should open up the servo I have and see I guess. That's really the only way to tell.
     

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