Adding PWM speed control to Linear Actuators for TV control

Discussion in 'General Electronics Chat' started by Josh Kaufman, Aug 24, 2016.

  1. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    The project I'm working on is to open and close a set of TVs mounted on a hinge.

    They are installed in a church stage, they fold against the wall when not in use and the actuators push them to face the audience when needed. (then pull back to the wall)

    I didn't realize that I needed speed control, so I simply installed them controlled by a double pole relay with a reversing circuit. A single pole switch loop controls the actuators remotely.

    The relays work fine, however the TVs, moving at full speed come to an abrupt stop, so I'd like to add a PWM circuit to slow them at the end of their extension.


    Here is what my plan is:

    I want to place a mosfet or some other driving circuit between the power supply and the relay.

    I can program the speed control based on simply timing, or I can use a Potentiometer connected to the moving parts as a feedback.


    I know that I could also replace the relays with H-bridge motor drivers, however if I can source the parts to augment the current setup it would seem simpler.


    Specs and distances:

    The actuator runs at 5 amps but peeks @ 8amps at startup.

    https://www.amazon.com/gp/product/B017S3H05E/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1


    I have 12 guage -2 conductor wire between the tv locations to send the switch positions simultaneously from the switch which is connected to the first TV location relay.


    Can anyone recommend either discreet components for the motor driver, or else a board I can purchase to handle the load from the actuators?

    I'm feel I should have something rated for 8-10 Amps.


    Please let me know if I forgot to add any important details.


    Thank You!
     
  2. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    P.S. I plan on using a Pic/ Arduino micro controller to run the speed control program.
     
  3. jpanhalt

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    I would use an H-bridge and mosfet driver. The latter might not be necessary, as the micro might be able to control the mosfets itself, but for a one-off the added robustness is not very costly. The H-bridge allows you to reverse the motor. Handling 8 A with a mosfet is not particularly challenging. You will find mosfets rated at ten times that easily.

    If the only purpose of the micro is to generate the PWM, that can be done very simply. You can also avoid the micro (if you are unfamiliar with them) by using a purpose-designed chip, such as the TI TPIC2101.

    John
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Have you attempted to run them at much lower voltage? if the torque required is not that much you could experiment at what level works and is acceptable.
    Particularly if they are not presently running at the Rated torque.
    I would not think running full tilt is necessary in this application?
    Max.
     
  5. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    Thank you for listing the driver chip John.
    I was hoping to find a logic level component to run directly from the micro-controller.
    I have had some experience with Picaxe controllers and I'm comfortable with programming them. (I have several on hand to use).
    Additionally, I would much prefer 'tuning' the speed profile with software rather than hardware, so I'm hoping to use one of my PicAxe 08 M2 that I have on hand.

    I should note that I'm using a 14awg - 2 conductor cable with ground to control the actuators with the relay. The reason I chose this setup was because of the distance between the switch and the actuators would cause significant voltage drop.
    That is why I was hoping to keep the current setup, but add the speed control to it.
    (distance is ~60' from the switch to the first actuator and 40' to the second unit)

    Thank you for your suggestion MaxHeadRoom.
    The actuator that I'm using is geared for speed and not power, also it will labor briefly at the start of its opening up.
    I'm looking to gradually reduce the speed at the latter half of the opening cycle.
    Since the actuator opens fast I will have to select precise values for the deceleration. This will require some real-world trial and error as I have no idea how my program will behave without testing it and tweaking it.

    If anyone knows of specific hardware or circuitry to use, please suggest it. I need to order the hardware before I can start working on this project.

    Thank You for all of your help!
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Not sure I understand that statement? How is it geared for speed and not power, unless geared up instead of down?
    What kind of actuators are they, do you have a link to them?
    Max.
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You know what they say.. If you like your relays, you can keep your relays.:D
    You could easily PWM the ground to the actuator with a logic level FET. I'm guessing from your description the power supply and relays for the actuators are back at the switch?
    http://media.digikey.com/pdf/Data Sheets/Infineon PDFs/IP(f,U)039N03L_G.pdf
     
  8. Tonyr1084

    Active Member

    Sep 24, 2015
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    Normally we're supposed to answer the question the OP asked. Sorry, I'm not going to add 2¢ to the kitty. Rather, I'm going to ask why not just mount the TV's in the wall and actuate doors or a curtain? Much less work. And what happens if the TV falls off the hinge? Wouldn't that be a legitimate safety concern? And flat panel TV's wouldn't take up much space on the wall. Just have a curtain that drops down over the screen when the TV is not in use, and rolls up when commanded to.
     
  9. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    TV Project.jpg
    Lol Thanks Ron.
    I included a diagram to show the distance and orientation. Thats the main reasons I used the relays.
    Thank you for the part suggestion, that seems plenty beefy. Unfortunately there is no example diagram in the data sheet. If you have experience with this type of application is there any discreet components I should add to the FET? Sample diagram?


    Thanks Tony, yeah, I'd rather not distract the thread with the factors that led me to this solution, but I will indulge your questions.
    The retracting TVs are not for distraction, they serve 2 purposes.
    1) they would block view of part of the stage that is sometimes needed
    2) this solution allows them to be much closer to the audience and is less of a compromise to the projector that was previously used.
    As for the safety of the mounts . . these are custom made 3/8 X7" steal frames and a 450lb rated hinge holding a 70lb TV.
    Way way overkill, but no risk of falling off.
    The reason I wish to slow them is because I don't like the shaking motion the TVs do at the end. They are already installed and working fine, the speed control is an accessory to the main project that has already been completed.

    Thanks for your input.
    Circuit details or diagrams of how to drive the FET would be great.
    Or, is it really just a matter of connecting the gate to the PIC input?
     
  10. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    They actually have no gearing, the motor is directly driving the acme screw internally.
    See the original post for the link I provided.
     
  11. AnalogKid

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    Aug 1, 2013
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  12. ronv

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    I still have a couple of questions, but we can move forward anyway. First the questions, then I'll draw up the circuit.
    1- There doesn't seem to be any way to shut them off - only forward and reverse??
    That's okay we can shut them off with the FET.
    2- I don't see any limit switches so I'm guessing it kind of crashes at the end?? Thus why you would like to slow it down at the end??
    3- Nothing prevents some kid from flipping the switch back and forth without stopping in between???
    This "might" make the power supply rise, so we either need to design for it or prevent it. To prevent it the micro would need to control the direction so it could stop between reversals.
    I'm off to make a little schematic.
     
  13. ronv

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  14. MaxHeadRoom

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    Sound like you did not have the right actuator for the application?
    Max.
     
  15. JWHassler

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    Sep 25, 2013
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  16. MaxHeadRoom

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    Actually if reducing rpm by PWM using a constant rate it is virtually identical to just lowering the applied voltage.
    Max.
     
  17. ronv

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  18. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    Thanks AK!
    It's a little late for that now, but do they make anything in a 75" TV size?
    I'm curious as to how the motor works with these, maybe with gearing it will be strong enough. I used a massive amount of attachment to the wall I don't know if I'd trust that small base, but then maybe that's just for smaller TVs.

    Something I learned when I got into linear actuators is that they come installed in side the unit.
    Actuator limit switches will come 1 of ways: adjustable or fixed.
    The adjustable type will allow you to set the stroke length by moving the limit switches, the fixed cannot be adjusted.
    The actuator I am using has fixed limit switches internally.
    How Internal Limit Switches in Our Linear Actuators Work - Progressive Automations - YouTube



    Thank you for the link JWHassler.
    However this will only allow a set speed control, I need to slow the motor as they near the full open point, and I do not wish to control this manually.
     
  19. Josh Kaufman

    Thread Starter New Member

    Aug 24, 2016
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    Thank you for the Link and diagram RonV!

    I am not familiar with this type of circuitry, so forgive the noob quesions.
    The micro-controller output goes to V+?
    What are the specs of the diodes you show in your drawing?
    As for the "kid flipping the switch back a forth" I don't think that is a problem, but did you have in mind circuitry to counter this behavior?

    Thanks!
     
  20. ronv

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    Yes, that represents the pwm from the micro.
    They are at the very bottom of the schematic post.
    I think you can do it in code. But in any case the micro needs to be able to "see" the switch. does it do that now?
     
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