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Motor control diy

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

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  1. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    That motor is rated for 6W which is 0.5 amps at 12V. I would use a 12V DC power supply rated at 1A or more. Any type will be OK. A plug-in adapter would be fine.

    Both of those switches look OK. Personally I would go for one with a "paddle" that you can push or pull with your finger, but a rocker will work fine.

    Both of those switches are non-momentary types, i.e. the switch will stay in whatever position you put it in; it's not spring-loaded to return to the centre position. I would use a limit switch at BOTH ends of the travel.

    Are you going to get some microswitches to use as limit switches?
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I'm not saying that all target transits are like this but all the indoor ranges I've used had spring loaded (center off) momentary toggle switches like these. Drilling a mounting hole is a lot easier than cutting out large square or rectangular holes that have to be close fitting.

    http://www.mpja.com/DPDT-Momentary-Off-Momentary-Full-Size-Toggle-Switch/productinfo/16090+SW/

    The spring loading has the big advantage of much easier target positioning at range markers along the target's travel, prior to tripping the limit switch at maximum range. Goosing a non spring loaded switch is a peta.

    Chris

    Edit: MPJA also stocks a variety of fractional HP DC motors too.
     
    Last edited: Aug 21, 2012
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Chris, that's a nice looking switch. And that's a good point about that style being much easier to mount.

    I guess the OP has to make the choice between a momentary (aka spring-loaded or centre-biased) switch, and a switch that stays in position. If there's no advantage to being able to walk away from the switch while the target is moving into position, and/or you want to be able to position the target at different distances, then a momentary switch is clearly better.
     
  4. masterarcher

    masterarcher

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    Jul 8, 2012
    Ordered the toggle switch as recommended, as noted easier to drill a hole rather than cut a square hole! thanks for the tip!
    Have ordered a 12V 1Amp DC adapter!
    Nearly there!
    right just Micro switches is there any sdvice how to set these up.
    Need the switches at the power end, thought one on the top when the target is retrieved and one underneath where the cable comes back (stopper in the cable that catches the microswitch) when the target is at the distance
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Here's a wiring drawing and description.

    [​IMG]

    It looks confusing at first glance but it isn't. I've marked the "away" and "back" circuits separately with arrows, which show the direction of current flow (conventional current - positive to negative). I've drawn the switch as it appears in real life, not as a schematic symbol. The limit microswitches are drawn as schematic symbols.

    Let's take the "away" circuit first. This circuit is active when the motor is moving the target away from you.

    When you push the switch to the "away" position, which would be rightwards on that diagram, the switch will internally connect pin 2 to pin 1, and pin 5 to pin 4. This seems backwards but it's a characteristic of how toggle switches are constructed. Usually. I'm going to assume that the switch you use will work this way.

    So, current will flow from the power supply positive output into switch pin 2, and out of switch pin 1. It then flows through the far limit switch, which is normally closed (not open as shown in the schematic) and back to the positive terminal of the motor. This makes the motor turn in a particular direction (which direction is not important), which will make the target move away from you, because you have put the cord around the motor in the appropriate direction to make that happen.

    The path from the negative terminal of the motor goes through switch pin 4, switch pin 5, and back to the power supply. When the target reaches the far limit, the far limit microswitch opens and the power to the motor is cut.

    Operation in the "back" mode works the same way. Current flows into switch pin 2, out pin 3, through the near limit switch, and into the negative terminal of the motor, out of the positive terminal of the motor, through switch pin 6, switch pin 5 and back to the power supply. The motor turns the other way and brings the target back. When the target reaches the near limit, the near limit microswitch opens and the motor stops.

    I'd be interested to know how you intend to set up the hardware. It should be possible to have both microswitches at the "close" end, activated by different parts of the cord. So everything can be close together.
     

    Attached Files:

  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    It can be wired like this. S1A & B is your toggle switch. The mechanics of the limit switches will need some thought from you because you don't want them to re-close because of the traveler coasting past the trip point. I have some ideas on that and will try to draw it up.

    Chris


    Edit: Oops Kris's schematic wasn't there while I was setting up to upload mine. Believe it or not they're essentially the same circuit. ;)

    Target position ********************** Motor Rotation Capability

    Home ****************************** Forward Only
    InTransit ********************************Forward Or Reverse
    EndOfLine *************************** Reverse Only
     

    Attached Files:

    Last edited: Aug 22, 2012
  7. masterarcher

    masterarcher

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    Cheers for the info appreciate your time in explaining this in detail, when I recieve the parts I shall get it wired up as per the diagram and test, the only thing I had not bought was the micro switches, these are what you have as Limit Switches?
    Is there different types open as standard or closed?
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes but it's very common to find them as Single Pole Double Throw (SPDT) micro switches that have 3 terminals. This way it can be used normally closed or normally open. ;)

    Chris
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I liked Kris's idea of having both limit switches at the Home end but I didn't think it could be done until I started drawing this. Give a look.

    Chris
     

    Attached Files:

  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Thanks for the nice physical drawing Chris. That should work nicely.

    I should have included a fuse in my schematic, as you did. 1A should be plenty since the motor is specified as 6W i.e. 0.5A. Anti-surge would be desirable I think.

    In this case I think the motor pulley will need to be quite small as the motor turns at 4500 rpm. Probably you should use plain wheels at both ends, and drive the cord part way along its length. My thought was to use the motor spindle, with the cord wrapped around it once or twice, with the spindle entering at a slight angle so the cord doesn't rub against itself at the entry and exit points. No doubt there would be better ways.

    I'm not sure how to arrange the "contact bars" that activate the microswitches. They don't have to be able to fit around the pulleys - unless the limit system fails! I guess I would build the parts I know about, then try and get hands-on creative.

    Will the bottom cord need to go over any other pulleys during its travel? For support, maybe? I don't know how heavy the target is. If it needs extra support pulleys, that might cause problems with the "contact bar" on the bottom cord.

    I'm trying to think of a better way to detect the limits. Maybe splice in a section of conductive cable and detect continuity? Maybe splice in a transparent section and use a photodetector? Those are both methods that were used with audio tapes to detect the leader (conductive, or transparent).

    Maybe put a small pulley next to the main pulley at the home end, and run a separate cord around that to operate the switches? I would like to see how it's done in a professional setup!
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Thanks for pointing that out Kris. I've modified that schematic to reflect a 1A fuse.

    This is one of those times that I wish I had paid more attention to the transit mechanics of some of the ranges I've used. For one thing, you're point of cable sag has me thinking about that. I do know that most of them are in fact steel cable but this would be too much of a load for that little motor. On the other hand I once fired at a range that had a hand crank. This thing used rope. I really hated that thing because it made you huff and puff, which is the last thing you want to be doing when target shooting, especially during a match. Kinda makes you appreciate the shooting portion of the Triathlon event though! :D

    RE, motor RPM: Wow, I didn't know it was 4500 RPM. Is he going to need gears or PWM?

    Chris
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    As long as the pulley on the motor is small enough I don't think he'll need gears or PWM. The 4500 RPM is unloaded; it'll be a bit less loaded. The shaft is around 3 mm diameter and I did calcs in an earlier post that worked out at 0.5~0.75 m/s using the motor shaft as a pulley.

    A steel cable would make things pretty difficult. He certainly couldn't wrap it around the motor shaft! He would have to use large diameter pulleys because of the large minimum bend radius of the cable, and couple the motor to a pulley using some kind of gearing system (but not necessarily cogs). I had assumed he would use sash cord or similar.

    I think sag is worth considering. If you want to keep an unsupported cable from sagging, it needs to be under a LOT of tension. I discovered this when I tried to make a clothes line with low height (for easy access) and full height, by slackening and stretching the lines. Even with a small weight hanging off the line, bringing the line anywhere near horizontal required a huge stretching force. Trigonometry at work :)

    Maybe he could use something like a metal curtain rail to provide the support, with a curtain hanging thing (don't know the proper name) that slides inside it. The rail could be braced to the roof at several places, and the cord or cable could go through the inside of it. (I'm thinking of a hollow rail with a square cross-section, with a slot from end to end along one side.) Then the cable wouldn't need to be very taut at all.
     
  13. masterarcher

    masterarcher

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    Hi thanks again for all the usefull information again, looking to get the microswitches, various ones on ebay I was going for one with a long arm then there are others with little wheels
    http://www.ebay.co.uk/itm/2x-Mini-M...al_Components_Supplies_ET&hash=item35bbe0c45a

    http://www.ebay.co.uk/itm/Microswit...al_Components_Supplies_ET&hash=item35bc165ea2

    Is there anything else I may have overlooked on this project?

    I had bought a small pully to go onto the motor - you dont think I can use that with the 4500RPM?
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Those ones look good. They've got NC and NO contacts. The decision really depends on how you plan to detect the limit positions.

    Have you visited any shooting ranges to see how they do it?
    Ten to one, yes! That's why I like to buy a few types of components to keep my options open. "Plan to throw the first one away. You will anyway." - Eric S. Raymond
    I calculated that wrapping the cord around the motor spindle would give you a movement of 3/4 metres per second with the motor running at 4500 RPM. But 4500 RPM is the UNLOADED speed so in your application it would run slower; I don't know how MUCH slower. That seemed about right to me. What do you think?
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Here's a few things to keep in mind..

    There is no way to guarantee that the cord isn't going to twist. It probably will. All target transits that I've used moved at least half the speed that yours will be. They also bobbed up and down and swung laterally as they traveled. They also twisted from the wind. In short, not a stable ride.

    Because of this, microswitches are looking less appealing to me.That said, I've included a drawing that may help stabilize the cord and the contactor when it reaches the microswitches. Note that the contactors completely envelope the cord and are beveled at both ends. The contactors have to be long enough to insure that the traveler has completely stopped before inertia causes it to over shoot the microswitch, which would re-energize the motor. This shape contactor will also be suitable to ride over anti-sag wheels.

    Note: Though I don't show one, a roller type microswitch would be preferable. To use one you would have to cut a slot, instead of a hole, in the pipe guide.
    Chris
     

    Attached Files:

  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Be careful with your microswitch selection. Many switches are rated for AC current with no DC rating listed. The DC current rating will be about 1/3 the AC rating but this is a guess. Input welcome. ;)

    Chris
     
  17. masterarcher

    masterarcher

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    Jul 8, 2012
    Microswitches ordered last thing I just thought of it would be handy to buy wire, helps it work I suppose.
    What Amp wire should I look to use?
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Excellent advice. That looks workable to me. I guess you've done this before.
    Right. Perhaps the most important characteristics for the microswitch would be the activation force (should be nice and low) and the travel distance (should match the thickness of the contactor section, I guess).

    I can see that microswitches might not be the best solution (although they are probably the easiest option to use in the circuit). Chris, do you have any suggestions for other ways to do the limit detection? Reed switches come to mind, and I've already suggeted a photointerrupter.
     
  19. masterarcher

    masterarcher

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    Jul 8, 2012
    Hi

    Any advice on the best wire to buy and where from?
     
  20. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I'd use "speaker wire". Get the "twin trurip" type. "True-rip" means two pieces of wire individually insulated and joined together, so you can rip them apart if you need single wires. Stranded (many thin pieces of wire twisted together inside the insulation, rather than a single thick wire), rated to carry a few amps. Don't go for "monster cable" or anything thicker than about 18 AWG (thicker means a lower AWG number - aim for 18, 20 or maybe 22 AWG). You should be able to get it from any electronics shop such as Radio Shack, I think, or an auto electronics shop. Anyone else have advice?
     
    Last edited: Aug 26, 2012
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