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Motor control diy

Discussion in 'Sensors and Actuators' started by masterarcher, Jul 8, 2012.

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  1. masterarcher

    masterarcher

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    Jul 8, 2012
    hi

    Wanted to make a target retriever for my shooting range indoors, save me walking backwards and forwards swaping targets,
    what I need to workout get help with is what type of motor would be best and how to control the speed, direction and distance.
    I am going to use a pully system and thin wire cable and a metal frame for the target to fit on, I need to get the motor working ata good rate not to fast! and backwards and forwards, the distance I need to set is 7 Metres so a switch of some sort to stop exactly 7 Metres, I have a local Maplins or I can use any online store if anyone can recommend parts required to get project underway.

    Regards

    Mark
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    A quick search on maplin.co.uk found this geared motor kit, which could be just what you want:
    http://www.maplin.co.uk/geared-motor-kit-24813

    In general you'll want a DC motor, so you can reverse it by reversing the polarity of the voltage supplied to it. You can do this with a "DPDT centre-off" switch. Maplin have DPDT rocker switches but not the centre-off type, so you'd need a separate pushbutton to turn the motor on and off after you select the direction with the DPDT switch. Digikey have some DPDT centre-off momentary switches that would be perfect:
    http://www.digikey.com/product-detail/en/M2028TYW01-JA/360-2275-ND/1056647 (rocker style)
    http://www.digikey.com/product-detail/en/M2028TJW01-GA-1A/360-2274-ND/1056422 (paddle style)
    You wire these with criss-crossed wires (google "dpdt reversing switch").

    As for regulating the speed, I would run the motor at its rated voltage and choose the size of the wheel on the motor shaft to give you the desired linear speed on the wire.

    You might be able to deal with the exact distance requirement by putting a mechanical stop at the desired position and allowing the wire to slip, so when the target reaches the 7m distance it will stop and the wire will slip until you stop the motor. Alternatively you could put a limit switch to detect when the target reaches the 7m distance, which would kill the power to the motor if it's running in that direction. (Obviously you can't kill the power completely because you need to be able to run the motor the other way to retrieve the target.) A low-force switch like a microswitch, with a normally closed contact, would be suitable for the limit switch.
     
    Last edited: Jul 8, 2012
  3. masterarcher

    masterarcher

    18
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    Jul 8, 2012
    Thanks for the usefull ideas and links, thats a start in the right direction.
     
  4. masterarcher

    masterarcher

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    Jul 8, 2012
    Hi

    Will be looking to pick up few bits to start this project over the weekend
    Antone else got any thoughts or advice?
     
  5. duke37

    duke37

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    Jan 9, 2011
    The exercise would do me good!

    If you want a drive with limit switches, you could investigate how a car window winder works. As fitted to a car, it would perhaps be too slow but it may be possible to gear it up.

    Visit you local scrap yard but take someone with you to stop you getting addicted.
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    You will want limit switches or sensors. Having the belt slip is a bad idea,
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Best solution is a combination of both.

    Limit switches to stop the motor (note, limit switches at each end only inhibit movement in one direction -- toward the limit switch)

    And

    The target should not be too tightly coupled to the cable. If the limit switch fails, it is preferable that the target and whatever do not get tangled up in the pulleys and tear things off the wall.

    A good solution might also employ a slow blow fuse in series with the motor so that if something still managed to jam and stall the motor that the fuse would blow.

    Really, the only complex parts are the limit switches, and they're just complex because you've got to get the wiring right. A "not too tight" connection to the cable and the fuse are cheap and simple.

    typically you might use 2 relays to reverse the motor (assuming it's DC) the limit switches can be easily incorporated into this arrangement.

    Also, it is preferable that you have something like an on-off-on toggle switch which do not latch in either on position. This means you need to hold the switch in one direction to keep the target moving.

    The limit switches are still absolutely required as relays do fail, as it is not totally unexpected that something might fall against the switch leaving it powered.

    Anyway, that's how I'd do it.

    You need a DC motor, preferably one that is already geared to an appropriate speed.

    One source for these might be a garage door opener. The common fault is that the relays inside them fail (remember what I said above). The rest of them are typically in great condition.

    If you go this route you may find that you can simply replace the relays and convert it (they often have internal limit switches which you can either wire up to your limit switches, or use the internal mechanism)

    I actually have a garage door opener mechanism inside my garage that I picked up off the side of the road when mine started playing up. Fortunately I had a person visit me who knows garage door openers and he told me what the problem was. He didn't realise that the boards could be repaired(!) and was convinced that sticking repays would eventually necessitate replacement of the whole unit!
     
  8. masterarcher

    masterarcher

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    Jul 8, 2012
    Hi

    Thanks for the advice, I went to order the switch KrisBlueNZ above recommended but read that it was - the voltage rating states 125V AC, i was going to use mains motor from an old small fan which would be 240V, other options or would that be ok?
     
  9. duke37

    duke37

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    Jan 9, 2011
    Running components above their specfication is not good.

    How are you going to reverse an AC fan motor?
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yes, as duke37 says, you can't reverse an AC motor by reversing its power connections. It has to be a DC motor.
     
  11. masterarcher

    masterarcher

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    Jul 8, 2012
    I shall get a dc motor from Maplins and try and get a pully the right size.
    thanks for the info
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Other than ceiling fan motors, fan motors are usually high speed. They're typically low torque too, especially stall torque!.
     
  13. masterarcher

    masterarcher

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    Jul 8, 2012
    There are quite a few different 12V DC motors on ebay, I wondered if anyone had a couple of minutes to see if any are suitable for my use.
    I shall get the switch that was recommended to me, need to find a suitable mains adapter to 12V DC, they have various ones on the Maplins web site.

    Thanks for the advice you have offered, I will get there in the end.
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    We do a lot of leg work here but if you've already done it for us post the links.
     
  15. duke37

    duke37

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    Jan 9, 2011
    Small very high speed motors will take a lot of work to fit up. They will need a gearbox.

    I suggested in #5 that a car window winder would be suitable. It is quite powerful, about the right speed, has distance limits and runs on 12V for safety.
    An alternative motor can be obtained from a car radiator fan.
     
  16. masterarcher

    masterarcher

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    Jul 8, 2012
    I looked at the car window winder motors on ebay, not sure what I would have to do with it as it does not look like a normal motor,
     
  17. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Shaft diameter is 3.7 mm which is circumference 10 mm (1 cm).
    Speed is 4500 RPM unloaded which is 75 revolutions per second.
    This equals 75 cm (3/4 metre) per second, assuming you don't use a pulley.
    Under load it will be somewhat slower; say 50 cm per second.
    That sounds reasonable to me. What do you think?
    You could mount the motor so it's not exactly perpendicular to the cord, so the cord enters and exits the shaft at slightly different places so it doesn't rub against itself.
    You could vary the torque by adjusting the number of times you wrap the cord around the shaft.
    The shaft is long enough that you probably won't need to stop the cord sliding off.

    That one has gearing built in and runs at 60 rpm which is 1 revolution per second. You'll need to use a pulley with it. I think it looks a bit small for your application.
    Work out how far you want the target to travel in one second, and get a pulley with a circumference equal to that amount.

    That one is 2 RPM. It must be very highly geared internally. Not suitable.
     
  18. masterarcher

    masterarcher

    18
    0
    Jul 8, 2012
    I ordered one of the top listed motors - http://www.ebay.co.uk/itm/12v-DC-ele...item19c89d633e
    found some small diameter pulleys that fit the shaft, need to get the switch back forward and stop an a power supply.

    Any recommendations on what to use as a power supply ?
    I thought of a mains to 12V DC adapter from Maplins - any better methods?
     
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