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motor control question (1.5 - 3.0V motor) — Parallax Forums

motor control question (1.5 - 3.0V motor)

RPrattRPratt Posts: 19
edited 2009-02-05 18:05 in BASIC Stamp
I am working on a prototype setup for a new turnstile product idea. I put together a small desktop version (picture big enough to look normal next to a barbie doll) to work out the programming kinks with, and just used bi-color LED's to signal when the gates would be opened for traffic coming through or going out. I am to the point of moving to actual gates with motor control, and was thinking of using the small 1.5 - 3.0V hobby motor sets from Tamiya. I know with a larger motor (6V and up) I would need to look at some type of motor controller, but would that be necessary with motors this small? manufacturers specs say they are a "no load" motor at 1.5V DC, but I would rather be safe than blow out my STAMP. any advice would be greatly appreciated! thanks

Comments

  • remmi870remmi870 Posts: 79
    edited 2009-02-02 02:35
    is this a turnstile for a model train set or something?
  • RPrattRPratt Posts: 19
    edited 2009-02-02 02:57
    no, small scale for what you would see in a building entry.
  • JonathanJonathan Posts: 1,023
    edited 2009-02-02 03:02
    You can't run a motor directly from a Stamp pin. If you don't need direction control, you can just use a MOSFET. Don't forget a back EMF flyback diode. If you need directional control, you need an H-Bridge or other motor controller. These are easy to make, or there are many chips out there. You can also use a couple relays to change direction too.

    BTW, there is no such thing as a no load motor. More than likely this refers to the current draw with no load on the motor. You need to figure out the max current needed for the motor and your application and make sure you can provide it. However, for the small mototrs you mentin, basically any controller or MOSFET or relay will work.

    Jonathan

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  • JonathanJonathan Posts: 1,023
    edited 2009-02-02 03:03
    Forgot to ask, do you need speed control as well?

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  • RPrattRPratt Posts: 19
    edited 2009-02-02 03:13
    no, not speed control really. the Tamiya kits i was looking at are fairly heavy geared for torque not speed, which is what I want. the motors will only operate for a short pulse in each direction - forward to open 45 degrees, pause until the sensor resets that passage is complete, then reverse to the original position. the suggestion was made from one of my co-workers to use servos for the desktop mockup (I have several laying around from RC plane kits), but I have not been able to figure out a linkage system that works for the range of motion I need. havent scrapped the idea mind you, but a $2 motor versus a $15 servo (and getting it out of the plane lol) seemed like a good idea.
  • UghaUgha Posts: 543
    edited 2009-02-02 03:24
    I use four of the same motors in my projects and I can tell you that you absolutely need some kind of protection for your stamp.

    I'd recommend an h-bridge. Most single chip h-bridges can support two motors with direction control... or four motors/relays with no direction control.
    The SN754410 is the one I use (available at www.sparkfun.com for $2.35) and it works great with those motors, it doesn't even heat up.

    There are three problems with hooking motors to stamps... first is they draw far more current than a stamp can handle.
    Second is when they first start up they can draw as much as twice as much current as normal.
    The third is that when you stop them or cause them to reverse direction, they very briefly turn into little generators that produce power that will
    kill any microcontroller that's not properly protected.

    The SN754410 has both control and protection built-in so it's as simple as connecting the chip to your stamp and then to the motor.

    Edit: I forgot to point out that you can get speed control by simply using PWM on the enable pin of the h-bridge.
  • RPrattRPratt Posts: 19
    edited 2009-02-02 04:01
    thanks for all the input guys. always better to ask advice first than just blow things up I always say..
  • ercoerco Posts: 20,259
    edited 2009-02-02 04:37
    Or, just use a simple on/off·relay per http://forums.parallax.com/showthread.php?p=727502

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  • remmi870remmi870 Posts: 79
    edited 2009-02-02 06:49
    i can supply a pretty cheap two relay control that uses two wire that will allow you to either be off state, forward, or reverse, the cool thing is the simple two wire setup is failsafe if you get a unwanted output on both relays.
  • RPrattRPratt Posts: 19
    edited 2009-02-02 12:55
    thanks guys. I went ahead and ordered a couple of the H-bridges from spark fun to try out and see how they do. for the price, seems like a good choice. I will have to post an update as I get further with all of this
  • UghaUgha Posts: 543
    edited 2009-02-02 14:18
    If you need any help with the H-bridges either post on the forum or send me a PM.

    Have fun with your experimenting!
  • DataJDataJ Posts: 23
    edited 2009-02-05 18:05
    I would like to thank Ugha for his comments on the·"H" bridge chip.

    I have been trying to get an L298HN to come up on like for a model railroad
    switching display for our club, and have not been able to get it to turn on.

    It appears that I have missed sending a PWM pulse to the enable pin, with
    the speed set at somewhere between 0-255.

    Comments would be appreciated - - I have been digging around the web and on
    the forum trying to find an answer, or a source to research.

    Thanks
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