Complete noob needs help on linear actuator circuitry!

Discussion in 'General Electronics Chat' started by Nipels, Sep 9, 2014.

  1. Nipels

    Thread Starter New Member

    Sep 9, 2014
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    Let me start by saying my knowledge of circuitry is lacking. I enjoy tinkering with models and radio controlled helicopters and the like. I am currently building my own Cnc router to help me with my projects. That being said, let me explain the application.

    I designed my own linear actuator. I want it to act like a hydraulic piston in a piece of heavy equipment. It also needs to be radio controlled.

    Basically, when I move the stick on the radio up, I want the actuator to extend. The speed at which it extends needs to be proportional to how far up the sticky on the radio is held. When the actuator reaches the end, I would like a limit switch to shut off movement in that direction, essentially bottoming it out. When the stick is in neutral, nothing happens. When you move the stick down, the actuator will retract.

    Is this possible? I can post images of the CAD actuator I plan on building. I can't pull the trigger on the parts until I know that I can make it do what I need to. Thank you!
     
  2. MrChips

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    Of course it is possible. The standard mode of operation with any RC servo mechanism is linear displacement controlled by a joystick.
    This can be converted to speed control
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the device is hydraulically actuated then you need some kind of feedback to indicate the position and speed, there are hydraulic servo valves, but very expensive, you will also need some kind of limit switches at either end of the stroke, unless going servo valve.
    The servo's used in CNC and industrial machinery are quite different than the simple RC type of control.
    I am curious as to why you need radio control unless an extremely large table, also what is the system controller you are using?
    Max.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Would a stepper do what you want and be easier, giving you simple control of speed and position?

    John
     
  5. Nipels

    Thread Starter New Member

    Sep 9, 2014
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    I originally thought to just hook up an rc speed controller and run everything through a receiver. That doesn't solve my problem though, which is bottoming out the lead nut on the lead screw. You get what I am saying? The DC géar motor will spin a lead screw while a lead nut us held from turning, thus moving up and down the screw. my problem is how to disable only one direction of travel when the nut runs out of screw in that direction.

    I am sure store bought actuators have this built in, but I'll be making my own. I thought to have limit switch in place to disable the motor when the max travel is reached, but I don't know how to disable it in only one direction. This is my problem.
    The cnc is a different project. The actuators I am building are for a mini radio controlled escavator. I apologize for the confusion.

    The actuator that I plan to build uses a lead screw and lead nut for the conversion from circular to linear motion. Read my OP again, I hope it makes sense. I only mentioned the CNC to qualify my knowledge with electronics, which is severely lacking.
     
    Last edited: Sep 10, 2014
  6. MrChips

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    What is the total travel distance and the elevator weight and payload?
    Give us some idea of the dimensions and weight.
     
  7. Nipels

    Thread Starter New Member

    Sep 9, 2014
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    I am not too familiar with steper motors outside CNC and the electronics I will be getting for mine are pretty much plug and play.

    Could a stepper motor more easily accomplish what I'm asking?
    total travel distance is about 5". Looking at a 12V 300RPM DC Gear Motor to drive a 1/2" lead screw/nut. I am flexible on payload as I just want the escavator to functíon like the real thing. I can always scale up when I know the concept works. I didn't get a chance to work on the model of my actuator.l concept last night but I will tonight and post it so you can get an idea of what I'm trying to do.

    I just have to say that this community has already impressed me, the speed of replies is crazy. thank you for all your help already. I cam tell I'll be coming here to pick your brains a lot in the future
     
    Last edited: Sep 10, 2014
  8. jpanhalt

    AAC Fanatic!

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    You have not shown your linear actuator design nor described what you mean by acting like a hydraulic piston. Whether a stepper will work based on what you have described can't be determined. Steppers can be used to control hydraulic pistons and pumps. Steppers inherently give control of speed and position, as you are aware of from their use in CNC. Model servos typically give position only, unless they are modified or driven by an mcu to control speed.

    John
     
  9. Nipels

    Thread Starter New Member

    Sep 9, 2014
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    I'll post it tonight, I'm at work. I could try and describe it. The 12V DC motor is coupled to the 1/2" lead screw. theThe motor had two rods that extend alongside the lead screw and pass through the nut either by two holes drilled in it or two small pipes that are welded to it. These only serve to stop the nut from rotating. The nut pushes a piece of small pipe that is welded to the front of it opposite the motor. Forget what I said about hydraulic pistons. So the motor drives the 1/2" lead screw, the nut isn't allowed to turn, so it rides up and down the lead screw. the pipe welded to the lead screw pushes whatever. All I wanted to know was a way to stop the night from bottoming out on the coupler or running straight off the end of the screw. I thought limit switches might work but I don't know how to configure it so that when the nut, say, is stopped from bottoming out on the coupler, that it would still be allowed to rotate in the other direction.

    I'll refrain from posting until updating with my design, I didn't mean to frustrate anyone. I know I have trouble clearly explaining what I mean. The design will be a 3d model with labels for everything and hopefully a better articulated request for what I need.
     
  10. Nipels

    Thread Starter New Member

    Sep 9, 2014
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    in that post night=nut. I am passed the 10 minute edit.
     
  11. jpanhalt

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    I would call that a typical lead screw or jack screw actuator. That is a really common application for stepper motors. There are some open-source CNC designs that you could access for examples of the firmware.

    John
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    From your description I gather you have a motor operated lead screw with parallel guides to prevent the nut from rotating with a pipe/pusher attached to the nut, and you need to avoid the nut either coming off the end of the screw or butting up to the coupler on the motor end.
    It is fairly easy to rig up L.S.'s to detect either end of travel, but the type of motor and controller is needed and what kind of logic is intended to operate the system, simple hard wired components or logic controller of some kind, if so, what are the details.
    Max.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    I have a habit of wanting to reuse discarded equipment and components. For this application I tend to salved disk drive head positioning mechanisms though 5-inch travel goes a bit beyond that. I would look into salvaging components from discarded printers, plotters or scanners.
     
  14. Nipels

    Thread Starter New Member

    Sep 9, 2014
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    Bingo. I would like to be able to use some RC equipment i have, like a 6 channel radio and receiver, and a DC speed controller.

    Would something like this be able to support limit switches...

    ESC
    http://www.hobbyking.com/hobbyking/store/__9090__Turnigy_20A_BRUSHED_ESC.html

    Motor
    http://m.ebay.com/itm/301065442181?nav=SEARCH

    The motor would hook up to the ESC, t hắn Go to the reciever. I don't know how to add the logic or limit switches to the equation. Am I going about this all wrong?
     
  15. MaxHeadRoom

    Expert

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    The voltage will be somewhat low for that motor, it may not be a good mach for an RC ESC .
    It would be a matter of experimenting to see if the rpm was sufficient, but with a lipo battery they supply a high current for a short period, so you may find that an inconveniance unless another battery source was used.
    Your normally closed limits switches would have to be rated for the motor current if you place one each end in series with the motor loop from the ESC and use a high current rectifier diode across each one, biased in the right direction, when a L.S. opens the rectifier only allows motor current for the opposite direction.
    Max.
     
    Last edited: Sep 10, 2014
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I needed a 12Vdc reversible linear actuator with a position feed-back pot for a swing-gate operator so I used one similar to this using an Arduino as a pwm controller. The Arduino swing-gate controller features soft stop-start, obstacle detection, RF remote control, time-outs, auto limit finding, battery back-up, solar charging, etc.
     
  17. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Building your own linear actuator is a task filled with pitfalls for the unwary.
    Limit switches are simple in concept, but the stored mechanical energy in the motor armature can cause significant and unpredictable position overshoot, leading to broken switches and jammed mechanics.

    The safest solution would be to use a motor and control solution that includes closed loop position control, so stopping at end positions can be done under precise control. This is of course not cheap.
     
  18. MaxHeadRoom

    Expert

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    Although in this case with a 30:1 gear box reduction and a final rpm of 300 I suspect this and the inertia of the G.B. there will not be much in the way of over -run?
    Max.
     
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