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linear actuator lift a truck rack

Discussion in 'Sensors and Actuators' started by Keith Gonyea, Feb 17, 2016.

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  1. Keith Gonyea

    Keith Gonyea

    1
    0
    Feb 17, 2016
    I am planning on using 4 linear actuators to lift a rack I have build on a trailer of mine. As of right now I have 4 posts that slide loosely into 4 sleeves. The 4 posts will be lifted straight upwards using 4 225-325 lbs each actuators. The rack itself ways about 100 lbs and the tent that will be on top of it weights about 150. The load will be well below the limit. My question is, how can I wire my own switch in the mix to lift all 4 at the same time. The actuators come with a positive and a negative wire. When the polarity is reversed the direction of travel changes. I was thinking, maybe a momentary on/off/on switch may work? If i could wire it such that the polarity would change when selecting 1 side vs the other. Does this make sense? Am i thinking about this in the right light? I'm open to any and all suggestions.

    Thanks

    Keith
     
  2. hevans1944

    hevans1944 Hop - AC8NS

    4,615
    2,154
    Jun 21, 2012
    Clearly you have never tried to synchronize the motion of "linear actuators" which is what this project requires. AFAIK there are two ways: use just one actuator to operate a scissors lift, or add a linear displacement transducer to each actuator and implement a negative feedback control system to force all four actuators to move the same distance. With modern electronics, option two is less costly and fairly easy to implement.

    You didn't specify which linear actuator you are planning to use. Please provide us with the manufacturer and model number. Since your actuator apparently operates on DC with a reversible motor, it should be easy to control its extension or retraction with a variable speed, perhaps using pulse-width modulation (PWM) of the motor current. Add four linear position transducers and some analog electronics and... voila! A synchronized lift!

    You could wire up a remote control box on the end of a pendant cable to control all four actuators. Four center-off, momentary, double-pole, double-throw toggle switches, one for each motor, would allow independent control of each actuator. You would need some good eye-hand co-ordination to operate the lift without one (or more) actuators "getting ahead" of the other actuators and "jamming" the lift. The switches would also have to be rated for the operating current required for each actuator. I would not recommend this approach because it will require a skilled operator and is highly susceptible to operator error. It would probably require that you space the switches for two-handed thumb-operated actuation for good ergonomics. You should wire up four switches and try it to see how "easy" (or not) it is. Just mount the actuators vertically and place a sheet of plywood across the actuator pistons. Place a glass of water in the center of the plywood board and practice raising and lowering it without spilling the water. Might want to try this with a plastic tumbler filled with confetti until you get the hang of it.

    If the automagical lift approach has any appeal, some of us here will help you with that.
     
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