designing an Automatic pop-up target using a geared DC motor

Discussion in 'The Projects Forum' started by MLD, Dec 7, 2012.

  1. MLD

    Thread Starter Member

    Dec 7, 2012
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    I'm trying to build a circuit to make a pop up target stand up automatically once shot down. I preferably would like to use a geared dc motor, stepper motor or rc servo. Im using a $8 dollar large hinge from home depot as the target. Id like for the target to be reset randomly within a 10 second period after it has been shot down. Id like to make several of these self contained with its own battery supply and enclose in a metal box to keep it from getting damaged from the rain and from the .22 cal. pellets. I know how to build a circuit, i just need the design diagram schematic to build it.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I think a solenoid would be more mechanically reliable than a motor.

    When you say random, you mean that you would like the thing to pop back up after, say, 1 to 10 seconds and at a different interval on each cycle?

    You could get some randomness using a dual timer, where the first one controls the control pin of the second. I think a range of maybe 3-10 seconds would be doable with this approach.
     
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  3. John P

    AAC Fanatic!

    Oct 14, 2008
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    It's intriguing little problems like this that make this board fun to read.

    First off, you need to find some sort of latch that will hold the target in the up position, but which will let it break loose when hit with the amount of energy carried by your pellets. Maybe a small piece from one of those thin flexible refrigerator magnets that advertise pizza shops etc would do it. You'd need to do some experiments.

    Then you need to sense when the target is in the down position, or not in the up position.

    Then you need electronics to implement the delay, and a mechanical drive to push the target back up.

    Solenoids are simple, but they need a great big pulse of current, which means you have to use a big battery. I'd suggest a type of motorized drive that's used to operate the switches on model railroads:
    http://www.circuitron.com/index_files/Tortoise.htm

    This uses very low current, so you don't have to sense the end of its travel. You can just run it for a couple of seconds, and know that it's reached the end of travel and stalled, which doesn't harm it. One way to control it would be every 10 seconds, activate the sensor, and if found in "target down" state, run the motor up and back. That gets its randomness from the fact that the target could drop any time in the 10-second interval, but it means that the motor can run at 10, 20, 30 seconds etc from when you switch the system on, and not any other time.

    If that isn't good enough, I can imagine running the timer much faster (say 10/sec) and then when the target is hit, switch to a slow time constant but stay at the same percentage of the cycle as when the hit occurred. So you'd have a 100msec cycle. If the target goes down at 40msec, the timer shifts to a 10 second rate, and will trip after 6 seconds. I think that's workable. Or (dull suggestion) use a microcontroller.
     
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  4. gerty

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    Aug 30, 2007
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  5. thatoneguy

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    Feb 19, 2009
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    I made a set for an indoor range, but they were turning targets, all at once, which used a cable to each of them and a geared motor with brake.

    The best pop ups I've seen used air cylinders, they are very fast and can handle heavier steel for bigger targets. The downside is the cost of air cylinders and valves.

    Either solution will require a microcontroller for random timing in the easiest way, take a look at PICAXE controllers if you aren't familiar with them, they are programmed directly with BASIC.

    Solenoids with enough throw to push the target back upright are extremely expensive. Linear actuators, which is a sort of rack and pinon setup with a motor would work better, though a tad slower, but at lower cost.

    What size are your targets, what gauge steel are they made from, or what is their weight. What is the distance from the hinge to the attachment point for the actuator (shorter distance = faster operation, but more power needed).

    Don't forget to put some heavy angle iron front of the hinges. A piezo transducer attached to the back of the target will detect a hit to have the actuator lower it.
     
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Probably not needed

    To knock them over with pellets the targets will have to be pretty light.
     
  7. shortbus

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    Sep 30, 2009
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    No need for a magnet to keep them in an upright position until hit. Just make them so they are a few degrees past upright when in the upright position. And they will lean against a stop on their own.
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Would a windshield wiper motor work?
     
  9. MLD

    Thread Starter Member

    Dec 7, 2012
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    Hello all and thanks for responding to my post on the "Target Project"

    I need the target to pop back up randomly 3 to 10 seconds on different intervals on each cycle. I'm planning to make about 8 of these independent targets and place them on the field for target shooting. I need them to be compact, light weight, robust and self contained with its own battery source preferably a 7.2 V RC rechargeable battery since I have lots of those in hand. I need the circuit to be as simple as possible without having to use a micro-controller. The battery and circuit board will go enclosed in a metal box to protect it from weather and pellet impact.

    For the switches I am planning to use magnetic switches SPDT (view images) this way my switches will last me longer. I like also that idea of the (Piezo) for detection, but would rather go with the magnetic switches since I have a box of those in hand already.

    For the drive id like to use a geared 4.5 V dc motor / 140 RPM since I also have a lot of those in hand. (view image) motor weight is 5.4 OZ dimensions 2" x 1" inch.


    For relays id like to use SPDT 12V dc relays since i have lots of these in hand.

    The hinges im using weight 27 OZ, overall dimensions of hinge 19" in. Stand up vertical hinge 10" inches, thickness 3.75 mm. The hinge can stand upright vertically by itself with nothing holding it which has a stop (view images)



    I have the mechanics figured out, I just need to build a circuit for the electronics to drive that gear motor. On the shaft of the geared motor i will attach and Allen wrench which will serve the purpose of standing up the target upright vertical when it falls down. Since I have a lot Allen wrenches in hand I will use that. I would use a simple bracket to hold down the geared motor to the base or frame.

    If anyone knows of a circuit diagram out there that can do this, id like to build it on a breadboard and try it out.
     
  10. shortbus

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  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Take a look at the 555 timer and 4017 decade counter based electronic dice circuits. The same strategy could be used here with the manual input replaced by the knock down switch and the outputs of the 4017 used to vary the control voltage on a second (delay) 555. Of course you can use a 556 instead of two 555s.
     
  12. MLD

    Thread Starter Member

    Dec 7, 2012
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    Since im trying to keep the circuit simple and small (low consumption) would it be simpler to make a circuit where I can eliminate the 2 magnetic switches (forget about using the magnetic limit switches) I want to use and make an over current circuit so when the hinge reaches its upright position stop and down position stop will cause the driver motor circuit to stop. Sort of like a high current protection shut off that will shut off the motor when it reaches its limit?

    Or will the circuit be more complex going this route?


    Again I will use an long Allen wrench tied to the geared motor shaft to use as a lever to stand up the hinge in the upright position then the Allen key attached to the geared motor to go back down ready for the next cycle.
     
  13. MLD

    Thread Starter Member

    Dec 7, 2012
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    I will try those circuits THANKS shortus and the others. Any other suggestion circuits are welcome.
     
  14. MLD

    Thread Starter Member

    Dec 7, 2012
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    Can you email me a link to this circuit?
     
  15. MLD

    Thread Starter Member

    Dec 7, 2012
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    Im trying to build on a breadboard a one-shot monostable multivibrator to be on for about 2 seconds but when i press the push button trigger switch to be random delay between 3 to 10 seconds before it actually trigger the one-shot. How can I make a one shot circuit to behave this way randomly?
     
  16. John P

    AAC Fanatic!

    Oct 14, 2008
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    I think this might be done with a 555 oscillator. In this diagram
    http://en.wikipedia.org/wiki/File:555_Astable_Diagram.svg

    you could have 2 resistors in the place of R1, where one would be switched into the circuit in parallel with the other. With both in place, you'd want to generate a "fast" oscillation, say 10Hz. With only one, you'd want it to be "slow", at 0.1Hz (i.e. 10 seconds). You'd switch over from "fast" to "slow" when the target dropped, and the key to the operation would be that when the change happens, the capacitor stays at the same voltage it had, and the cycle you were in would continue, but at the slow rate. You'd never be able to predict where you were in the 1/10 second cycle, so the remaining time once it cuts over to the slow cycle would also be unpredictable.

    I'm not sure how to get the minimum 3 second time. You might need to have a 7 second random time generator, which then starts a 3 second timer, so the overall time would be 3 seconds plus a random amount from 0 to 7. But it should be possible somehow.
     
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  17. MLD

    Thread Starter Member

    Dec 7, 2012
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    Hi JohnP. I though of something different. Is there a single IC that can produce random outputs. Lets say for instance 12 outputs that will turn on and off the outputs logically randomly? I might just build a single roll of metal targets to pop up randomly that are driven by pneumatic cylinders instead. The geared DC motor I was using for the project I stripped and broke the gears on it. I have some pneumatic air cylinders that are even waterproof and weather resistant. I also have a set of solenoid air valves in hand that I can use for my project.


    I bought a RF remote transmitter along with 12 RF receivers which I can use remotely to control and bring back up the targets but I rather do my target range automatically just using a Random IC chip to bring them up Automatically and randomly.


    Let me know if there is a single IC chip out there that can do this randomly logically. I know how to wire up a driver transistor and some relays at the outputs thats easy to do. I just need the multi-channel random chip.


    Any suggestions I appreciated.


    Thanks

    RJ
     
  18. John P

    AAC Fanatic!

    Oct 14, 2008
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    Get the basic electrical and mechanical systems working, and come back and ask about the random time generator. It's actually the easiest part. By "basic systems" I mean something that just detects that the target is down and pushes it back up immediately.
     
  19. MLD

    Thread Starter Member

    Dec 7, 2012
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    Im going to try another DC geared motor but this time rated at 12V at 7 RPM which is slower and more powerful. Ive got a one-shot monostable built using resistance of 21K with a capacitor of 100 uF this moves the shaft of the motor about 90 degrees, enough to stand up the target upright. Im wondering how can I reverse the polarity of the motor to acquire the same timing but in the other direction without having to use 2 one-shot circuits.

    Attached is an image of the geared DC motor with an allen wrench tied to the shaft of the motor. The allen wrench is used to stand up the target which is the large hinge that I will be using. I chose the circuitry to operate at 12 VDC.

    My question is how can I get the One-Shot monostable 555 timer I built to reverse the polarity once it has completed its cycle. Im using a TIP122 transistor as the driver instead of using a relay. Attach is an image of the circuit on a breadboard. Also attached is an image of the motor with the allen wrench which will be used to stand upright the (target - large hinge)


    RJ
     
  20. John P

    AAC Fanatic!

    Oct 14, 2008
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    I have an alternative suggestion. Instead of the tried & true Allen wrench attached to the motor shaft, how about building a crank-rocker mechanism, where a full turn of the motor shaft would rock an arm through 90 degrees and back again? There would obviously be more mechanical complexity, but what you'd gain would be not needing to reverse the motor, and no need to time its motion, or to have switches to detect when it was at the ends of its travel. You'd only need one switch, which would stop the motor at a particular point in its cycle, like windshield wipers. All you'd need would be a pulse to get the motor away from the switch, and then a lifting cycle would be automatic.
     
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