Circuit for timed switching of polarity?

Discussion in 'The Projects Forum' started by dbarak, Sep 15, 2018 at 2:14 AM.

  1. dbarak

    Thread Starter New Member

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    Hello,

    I'm new here, so if I violate any rules let me know and I'll do what I can to fix it.

    I have a car lock actuator (operates from 6 to 16 volts, current draw 1 amp at 12 volts: http://www.goldmine-elec-products.com/prodinfo.asp?number=G21146 ) that I'd like to push and pull somewhere in the neighborhood of two to five times a second - I'm not too picky so if it's a bit slower or faster, that's okay. It would operate when a normally-open momentary button is pushed. I believe the actuator is really just a DC motor with a rack and pinion. Any voltage from 6 to 12 volts will work for me.

    I did a search here and found several related posts, but they either seemed to not exactly address what I'm trying to do or what they describe is above my head. I did find one circuit I sort of understand, but I'm not sure if it'll work for what I need. ( http://solarbotics.net/library/circuits/driver_4varHbridge.html )

    EDIT: A regular semi-conductor circuit is fine, or it can be something based on relays - any method is fine.

    Can anyone help, or possibly point me to resource I might have missed here or somewhere else?

    Thanks,

    Dave
     
  2. Picbuster

    Active Member

    Dec 2, 2013
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    Welcome!
    I am not sure what you want.
    Please draw a simple flowchart starting with system off and all steps to end up to system off again.

    Picbuster
     
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    That's awfully fast for a motor/rack/pinion device. Did you mean per minute?

    Also, check with the vendor to see if the actuator has limit switches built in to prevent overtravel and gear stripping.

    ak
     
  4. Alec_t

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    Sep 17, 2013
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    I think even once per second would be pushing it.
    A similar-looking OEM actuator I took apart had no limit switches. I assume it's energised either for a given time or until stall current is sensed.
     
  5. Raymond Genovese

    Active Member

    Mar 5, 2016
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    As has already been pointed out, the operation frequency may be your biggest obstacle. While an embedded controller solution like an arduino with a motor shield, might be overkill for your eventual circuit, it would be helpful to evaluate the capabilities of the lock/motor because it looks like the door lock actuators are meant to be operated with a pulse and not too frequently.

    [​IMG]
    from r.hswstatic.com

    On the other hand, take a look at what this guy built using a bunch of these which look similar to what you have. If you look into his code, you can see that he is using some strict timing and it does at least look like one or two complete operations a second could be feasible. On the other hand, also take note of a couple of comments about heat buildup and worries about burning the L298 motor controller.

    BTW: What exactly are you trying to build?
     
  6. dbarak

    Thread Starter New Member

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    Hi AnalogKid,

    Ah, those are exactly what I have, so you just solved my problem! In fact, the listing on Amazon ends up being about half the cost, per unit, of what I paid and it includes hardware I didn't get. So much for the "surplus" vendor I got this from.

    I've messed around with Arduinos before so adapting what's in the Instructable should be fairly easy. This will be for a prop sci-fi rifle - no particular end use, just something fun. By using an Arduino I can add in some sound and lights to fancy it up a bit.

    EDIT: I haven't read through the full Instructable yet, but if heat and stress are problematic dropping down to one cycle every second or two is fine, and the button-push would only be for a few seconds. Can't waste imaginary pulse beam doodad ammo.

    Thanks!

    Dave


     
    Last edited: Sep 15, 2018 at 11:43 AM
  7. dbarak

    Thread Starter New Member

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    Hi PicBuster, Alec_T and Raymond,

    Thanks for replying! The response was greater and faster than I expected. As you can see, AnalogKid found an application that uses the same actuators, so it sounds like a workable solution for me. Again, thank you!

    Dave
     
  8. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Have you timed how long it takes for the actuator to complete one movement? Also, note that a car door actuator is cycled only a few times per day, not dozens of times per minute. As shown in the photo, these are not rugged devices designed for continuous use.

    1. Separate from that, is it your intent that actuator runs continuously as long as the button is pushed, and stops mid-stroke when the button is released?

    2. If the actuator is allowed to stop mid-stroke (as opposed to completing a stroke after the button is released), is it a requirement that the actuator restart in the same direction it was going when it stopped?

    ak
     
  9. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
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    Kind of a reminder, these things are basically motors without any protection operating a rack and pinion.

    These have brushes and permanent magnet DC motors act as generators, The reversing direction will be hard on the motor/brushes.

    Some H-bridge designs have the ability to do fwd, rev, brake and coast. Regenerative braking, I haven't any experience. That's when you would pump power back into the battery when braking.
     
  10. dbarak

    Thread Starter New Member

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    I'd say the travel time is about a half second, maybe one third. I'm starting to wonder now if a spring-loaded solenoid might be a better choice. To be honest, I have no real idea of what the final thing will look (just a spur of the moment thing), so the operation - travel distance, rate, even where it starts and stops - are all flexible. The only real concrete thing is continuous operation while the button is pushed, although it could even operate for a maximum duration per button push.

    I checked online and it turns out the motor shield used in the example project has been discontinued and I don't know of a replacement, so maybe a non-Arduino option is best, although I imagine a motor shield that can handle 12 volts would be too popular to eliminate altogether.




     
  11. Raymond Genovese

    Active Member

    Mar 5, 2016
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    I think that I was the one reporting the linked project...but, if it ends by going up in smoke, let's leave the attribution as is. If it turns out to be a really cool project...your welcome :):):)

    Seriously though, do pay attention to the code operating the motor shield because the terms definitely suggest braking is going on as part of the operation as @KeepItSimpleStupid mentions.

    Also, if you do finish it, please let us seem some pics or a vid because it sounds pretty cool.
     
  12. AnalogKid

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    Since we still don't know what the overall project is, it's kinda hard to say. BUT, note that a solenoid's actuation time is milliseconds, with a fast start and a really fast stop.

    ak
     
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    A direct replacement for that is the SN754410 that is more modern and doesn't drop as much current. http://www.ti.com/product/SN754410

    But if doing this from a fresh slate, this would be even better though you would need more of them if running more than one. But it also has some built in over current protection. http://www.ti.com/product/drv8870/description
     
  14. DNA Robotics

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    Jun 13, 2014
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  15. dbarak

    Thread Starter New Member

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    I think I may have found a solution. My project is very nebulous, so the requirements are inexact - I'll build the project around whatever works rather than the other way around.

    I found a video on YouTube that showed how to wire up a SPDT relay (or DPDT like what I have sitting around) to oscillate. The video also described how a capacitor bridging the coil contacts can adjust the oscillation frequency. I tried three different caps that provide rates in the range I"m interested in and it works well. As I understand it, the load - an LED, a bulb, a motor, etc. - will also factor in to how fast it oscillates. So I"m thinking that my relay setup can be used to control a solenoid.
     
  16. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If your relay switches a solenoid you will need a snubber across the relay contacts ..... unless the arcing is intended as part of the light show :).
     
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  17. dbarak

    Thread Starter New Member

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    When you mentioned snubber, I thought you were referring to my old dating life until I checked on Wikipedia. ; ) So now that I now what a snubber is in this context, it looks like I have some options - resistor, diode, combination, etc. Is a resistor or diode enough for this use? And is there any calculation I should use to determine what resistor to use if that's the way to go?

     
  18. AnalogKid

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    Please post a link to the viceo so we can review it. I know this eill come as a SHOCK, but not everything posted on youtube is correct.
    Not if it is done correctly. The oscillation frequency should be completely independent of the load voltage/current.

    ak
     
  19. Alec_t

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    A reverse-biased diode should suffice.
     
  20. dbarak

    Thread Starter New Member

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    Hi AnalogKid,

    I've got the link included here. I tried the circuit show in the video only as far as trying out various capacitors and it seemed to work, setting up various rates. I didn't add a load such as an LED or solenoid though.



     
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