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Continuous linear actuation - switching current direction — Parallax Forums

Continuous linear actuation - switching current direction

engineerdadengineerdad Posts: 2
edited 2012-02-29 19:08 in BASIC Stamp
I plan on programming my basic stamp to control my linear track actuator to continuously run (extend and retract) when a start button is pressed and run until a stop button is pressed. I can make the actuator switch directions by manually switching the positive and negative leads from the actuator to the battery, but I would like to use the basic stamp to do this automatically. It seems to be a very simple program. Any ideas on how to program this onto the basic stamp?

thanks and best regards,
Jacob

Comments

  • ercoerco Posts: 20,257
    edited 2012-01-03 23:46
    Basic Stamp 2? Your actuator has built-in limit switches at both ends, so you just need to occasionally reverse the 12V polarity applied to the two power wires? Two relays and you're home free. Or one relay and an SCR, or...

    So many ways. How do you want to do it?
  • idbruceidbruce Posts: 6,197
    edited 2012-01-04 02:52
    Use a four transistor h-bridge.

    Switch high and low on two, four, or six outputs.

    Here is a link to a Nuts & Volts article that uses four mosfets for that purpose, but transistors can be used to make a similar bridge.

    http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol2/col/nv52.pdf

    Here is a link to another article that use six transistors but only two pins, plus it shows the use of a half-bridge for motor direction control.

    http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv23.pdf

    Bruce
  • engineerdadengineerdad Posts: 2
    edited 2012-02-28 22:19
    Yes, I need to reverse the 12V polarity applied to the power wires. Let's use the relay method. One question: Why do I need 2 relays? Won't it work with one SPDT Relay?
  • CatspawCatspaw Posts: 49
    edited 2012-02-29 03:47
    Seems to me like an SPDT would work fine except for one thing. What if you want to stop the actuator? I know you said you want it continuous.....but....wouldn't there be an occasion such as an emergency stop or a don't move until everything is initialized or just general servicability, where you would want to stop it?

    Two relays would be better in the long run I would think.
  • ercoerco Posts: 20,257
    edited 2012-02-29 19:08
    If you just use one DPDT relay, you can reverse direction. Your actuator will stop when it hits the limit switches at the end of travel. If you want to stop somewhere in the middle, you'll need a second relay. You could add an SPST relay to your DPDT reversing relay, or use two identical SPDT relays.
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