# 12VDC Motor: Forward & Reverse Polarity Diagram



## TommaHawk (Sep 18, 2007)

Got the recommendation to post this as its own thread - I originally submitted it as a reply deep inside another thread. This is a simple project to get a 12VDC motor - like any of the automotive motors we use - to turn in one direction until your prop hits a stopping point, then reverse direction until it hits the other stopping point. This is done manually: it works like a CD drive on a computer - push the button and the mechanism runs until it hits one microswitch (instantly killing power to the motor). Push the button again and it reverses direction until it hits the other microswitch.

You'll need the following:
- 12VDC motor (wiper motor, etc.)
- 12VDC power supply (I use a computer ATX supply)
- Two 12VDC SPDT relays (sockets optional) - automotive relays are cheap and reliable: http://www.surpluscenter.com/item.asp?UID=2008072410492122&item=11-3222&catname=electric (or eBay or...)
- Two 1N4001 diodes (from RS or wherever)
- Two limit switches like this: http://www.surpluscenter.com/sort.asp?catname=electric&byKeyword=yes&search=micro%20switch (or other design)
- Common fuse: get one amp-rated for your power supply
- One normally-open, momentary switch (from RS or anywhere)
- A bit of extra wire

Wire the thing up as shown in my diagram - the wires color-correspond to the relay sockets. Note: the "green" wire is actually a "white" wire in the socket. I used green here for clarity (white didn't show up too well). There's quite a bit of wire to keep track of, it looks worse than it actually is. Be sure to match the diode polarities correctly (shown with the white stripes).

I use this to drive a wiper motor to move a "mad scientist sinister mechanism" and another to raise/lower a remote control/LCD from inside a console by the couch (crowd pleaser). Both of which require me to operate it manually. You could replace the manual push button with an electronic trigger like from a Prop Controller - just decide how long you'd want between triggerings.

If you use this method for a prop, post what you did with it! Would love to see...


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## Koumajutsu (Aug 9, 2006)

Can you also draw a schematic for this wire diagram also please?
also, the "wires" drawn in white are a little tough to see in your pic


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## bourno (Jan 21, 2006)

I think it is a great little circuit too, but replacing the relays with their respective C, NO, NC points would be easier to follow than the specific brand numbers shown.


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## hedg12 (Jul 6, 2008)

The numbers actually aren't specific to the brand of relay - they're standard on automotive type relays. 85 & 86 are the coil, 30 is common, 87 is normally open and 87a is normally closed.

I agree, great circuit.


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## jabberwocky (Apr 30, 2008)

Great little piece of info there!
THANKS!


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## bourno (Jan 21, 2006)

Thanks for the translation Hedg12 as I don't ever use car relays much.


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## TommaHawk (Sep 18, 2007)

Yeah - this was designed with automotive relays because they can be had for cheap from a huge range of sources, they're easy to use, can attach to those very handy sockets, and are very reliable. The diagram was intended to be accessible for anyone who doesn't know how to read a schematic (like lots and lots of Halloween fanatics) - just plug and play.

Sorry (I always figure everyone in the world already knows what I know) - those numbers correspond to the pins on the relay - they're stamped right on the case itself (for anyone not knowing diddly about electronics). Thanks hegd12 for that guidance!

I'll change the "white" wires to "gray", or something else, and include a note that they correspond to the white wire on the socket. Just sec...

Really glad you like this - I hoped it would be helpful for everyone.


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## Phil (Sep 2, 2007)

Great control circuit - versatile and cheap. Add a sensor and delay timer and the sky is the limit! Thanks for posting it.


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## hauntcrazy (Jul 28, 2009)

*Tomahawk*

Have you ever tried this circuit on something like a fast acting riser prop? Do you think a wiper motor could run fast enough to raise an arm up quickly and then back down?
I was thinking of building my own version of the Spirit Halloween spider jumper. That thing is so cheap and I am sure it will never hold up for several nights of our haunted house.
I could use pneumatics but I am at my limit on the number of air props with my compressor capacity.
If I could build some pop up props using this circiut and a wiper motor, I am sure many people would be interested.


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## TommaHawk (Sep 18, 2007)

Good idea... I don't think a wiper motor by itself would be fast enough for a pop-up (even on the "high speed" connection), but you could certainly rig the shaft to something like this (a cam or quick return):

http://www.robives.com/mechs

Doing that, instead of the motor winding away (like a worm gear), there's a more-direct translation of motion.

You'd then need to install the trigger to activate it, which would take the place of the momentary switch I have here. Rig it to a mat switch, IR, whatever.

This isn't _real _strong - it's just a 12v motor - so pneumatics are the better way to launch anything, but it could certainly be done with a little care and finesse.

If you build this into a pop-up, we'd love to see!


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## hauntcrazy (Jul 28, 2009)

I have one of the Rocking Chair Grannies that uses a wiper motor. It seems to be very strong. Actually, it is hard to hold it back when it is in motion. The speed of the granny is probably fast enough for a simple pop up. It might not be as fast as a slam up prop but will probably suffice.


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## Shock (Apr 14, 2012)

Great circuit layout and idea.....I may use this to automate the swing of a razor pendulum. A PIR sensor activities the circuit and lights, the arm of the pendulum swings until it hits the second limit switch witch reverses the direction of the 12v DC motor thus sending the arm in the opposite direction, the process repeats.


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## Otaku (Dec 3, 2004)

I think you don't need anything that complex to swing a pendulum. Just mount the wiper motor above (or below) the pivot and attach a crank arm of the desired swing length.


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