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How does one wire a motor so that it reverses automatically?

I'm looking for a relatively simple, mechanical way (by that I mean not using a micro-controller) to wire a motor so that it will reverse direction without being switched manually. The interval is unimportant, and the purpose is to have two spools connected by a loop of string (think reel-to-reel), one of which is controlled by the motor. A low-tech solution would be awesome.

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brandegor (author) 7 years ago
So after reading these great answers and thinking about this a lot, now I'm wondering about something more complex: If each spool had it's own motor, how could I employ a 555 timer to start one motor forward, stop it, then start the other motor in the opposite direction? I have no idea how to design a circuit like this - I expect it might be similar to the Mousebot in some ways without the light sensing set-up. What I have available are the DC motors, an assortment of capacitors and resisters, the 555 and a 12-volt relay. I also have a bunch of things I can scavenge parts from. The project is intended to simulate the media's interpretation of the first supercomputers, which often show two tape reels alternating direction. I really appreciate the input and advice, and thanks in advance.
My circuit will drive two motors simultaneously in forward and reverse, but it won't pause - add another pair of contacts, switched by the 555 on the motor connections, like this version. If this isn't designed to run real reel to reel, I'd just belt drive the two reels from the back with a single motor.
seandogue7 years ago
fwiw, the actual trick often used in industry when no controller is employed is to use spring loaded limit switches to trip a dpdt latching relay...shh...
Err. Isn't that how I did it ?
Could be..I can't make anything out cause the ible-bot makes the images so hard to see. Is that a latching relay? If it is, then yeah.. i retract my clue :)
Happy with a relay and a couple of limit switches ?
agreed
brandegor (author)  seandogue7 years ago
These are all awesome suggestions - thanks.
frollard7 years ago
Limit switches would reverse them at a given distance travelled - as steve describes. (limit by distance) A dpdt switch (or relay) can be wired as an h-bridge, then any oscilator (such as a 555 timer, super simple to set up) or a 2 transistor oscilator can be used to switch the relay on and off. (limit by time)
dpdt.PNG
Try this. Its not perfect, but its the simplest way I can see at the moment. Arrange the motor so that when the power is switched on, it drives to activate LS1. When LS1 trips, relay AA/2 is set, AA1 changes over and the relay is latched on by a path through LS2 and AA1. When LS2 is hit, the relay deenergises, AA1 changes back again, and the motor sets off back again. Hopefully the cycle repeats.
Doh