Building a jack-in-the-box using a 12VDC lift motor - need a timed reverse circuit

Discussion in 'The Projects Forum' started by bradleyland, Dec 7, 2008.

  1. bradleyland

    Thread Starter New Member

    Dec 7, 2008
    2
    0
    For christmas, my mother has asked me to help them animate a jack-in-the-box that will pop in and out of a box in their christmas display. I acquired a screw actuated lift-motor, which has a mechanism that allows the motor to run unloaded at the end of the travel. In other words, I don't have to worry about switching the motor off when it reaches the end of its range of motion. The motor is 12VDC, so we plan to run it off of a deep-cycle marine battery or a 12VDC power supply (we have one that is 6A, but I'm not sure if that's enough).

    What I need to build is a circuit that will run the motor in one direction for 10 seconds, then reverse it and run it in the other for 10 seconds. I've done some research, and I've arrived at the fact that I need to build a circuit that involves a 555 timer, a DPDT relay of sufficient amperage to run the motor, and various other resistors and capacitors to regulate the timer and protect the 555 from the relay EMF.

    I found this thread, which does a great job of explaining most of what I need, but I don't see how to wire in the 555, and I don't need the run-out switches to prevent stall.

    I'm an IT guy, but I've never done any circuit building, so virtually everything I read is brand new to me. I'm able to read the schematics by using a symbol reference, and I used to solder on RC cars back in the day, so I think I'm OK in that regard, but I'm really in the dark when it comes to what and where to connect the components.

    Can someone help me build a parts list and a wiring schematic. I know how to drive to Radio Shack, so that's a start! :) I figure I can grab a project box and some circuit board then put something together that will do the job with the right direction. I'd really appreciate any help that I get.

    Photos and schematics of the jack-in-the-box:

    Shots of the motor:
    http://www.flickr.com/photos/97514955@N00/3091108694/sizes/m/
    http://www.flickr.com/photos/97514955@N00/3091108512/sizes/m/
    http://www.flickr.com/photos/97514955@N00/3090267437/sizes/m/

    The collet is designed to spin freely at the end of the travel, so the motor can just keep running.

    Jack-in-the-box 3D drawings (Google SketchUp amateur):

    http://www.flickr.com/photos/97514955@N00/3090266795/sizes/m/

    The lift motor is positioned under one of the arms and attached with a fixture we fabricated to fit in to the pin holes on the existing collet.

    Jack-in-the-box schematic:

    http://www.flickr.com/photos/97514955@N00/3090266829/

    This is a measurement schematic I made to determine the radius length and chord deflection we'd get through the range of motion.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You need to use a 555 connected in astable mode. When the output of the 555 will be low (relay off) the motor will spin in one direction. When the output of the 555 will be high (relay on) the motor will spin in the other direction. Look here for more information about the 555:

    http://www.uoguelph.ca/~antoon/gadgets/555/555.html
     
  3. Otaku

    Active Member

    Nov 19, 2008
    128
    2
    Have you considered using a car wiper motor for this application? I have a circuit that uses an optosensor to detect when the motor has turned 1/2 revolution, allows an adjustable pause time, and then completes the revolution. It uses a R/C master timer that controls the duration of a 555 astable circuit and requires a short 9VDC pulse to initiate. I don't know how large your JITB container is, but this may be an alternative for you.
     
  4. RiJoRI

    Well-Known Member

    Aug 15, 2007
    536
    26
    How about an eccentric gear? (Think of the shaft-and-wheel of an old steam locomotive.) That way you would not need to worry about reversing the motor.

    --Rich
     
  5. Otaku

    Active Member

    Nov 19, 2008
    128
    2
    That would work. If no pause time is needed between full extension and the start of retraction, then that's the easy solution.
    If a pause time is involved, or some kind of triggering capability, then the 555 circuit will be needed.
     
  6. RiJoRI

    Well-Known Member

    Aug 15, 2007
    536
    26
    Oh, these electronics guys! :D

    If Jack is like the standard JitB -- spring-loaded -- the arm could pull down the lid of the box, and at some point (12 o'clock?) of the upswing it would release the catch, and up pops Jack! The arm would probably need to have two parts to allow the rapid rise of the lid, and to keep the eccentric from pushing the lid up on the rise. (I wish I could sketch this out!)

    --Rich
     
  7. bradleyland

    Thread Starter New Member

    Dec 7, 2008
    2
    0
    Haha, thanks for all the suggestions guys. The christmas spirit seems to bring out the inventor in all of us ;) We've got a good build going though, so I'm reluctant to go back to the drawing board this year. Next year we're going to make the switch to a pneumatic actuator. They're just a bit spendy, and we've already blown budget on this year's efforts.

    Here are a couple of shots of the current build:

    http://www.flickr.com/photos/97514955@N00/3093160129/sizes/m/
    http://www.flickr.com/photos/97514955@N00/3093998984/sizes/m/

    I've been reading and looking at more schematics and I think I have an idea that could eliminate the requirement for a timer.

    * Two switches; one normally open, the other normally closed
    * One DPDT relay
    * One SPDT locking relay

    Position the switches so that they are engaged at the top and bottom of the lift-arm's range of motion. The switches energize the SPDT locking relay, which is used to energize the DPDT relay in the appropriate direction. The switches limit the range of motion and provide the reversing action at the right time. Because this is a worm-gear motor that drives a screw driven collet, there isn't much run-out. When you switch the power off, the arm doesn't move even 1/10th of an inch.

    Thoughts?
     
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