reciprocating motor control

Hi, I'm building a project, the mechanics of which I've got covered. The tricky bit is the electronics side.

It's to control a small motor and gearbox to drive a cam in 180 degree steps in either direction... It's reciprocating like the old carousel slide projectors. Yes I could us stepper motors, but I want it to be simple DC operation.

I've been toying with the use of a micro switch to control its end stops, which don't have to be 100% accurate because there is some play at each 180 degree stop.

I was thinking a 12v supply could be charging a capacitor. When a pulse signal is sent, this capacitor would discharge through the motor... but then all my brains started to melt.

Any thoughts on this would be brilliant.

Dunc

If a microswitch is something you understand, then use that. You could also use an opto-interruptor or two and maybe some digital logic (a flip-flop, perhaps). Overkill would be a simple optical encoder wheel and a microcontroller...

Motor

You didn't say how you were going to make it go. Here is one with a double pole switch that should work.

Go to a car junk yard and buy a windshield wiper motor with a gear box on it.

The micro switch made sense until the motor came to its first rest position and switched power to the motor off. If the power is now off, how do I now power the motor to the next position. I'm sure there's almost a mechanical solution to this, but my head's starting to hurt.

The other thing that was running through my mind was the use of a good old 555 timer. I know you can send a pulse to give a Timed output. But I guess that's going down the flip-flop route anyway.

BTW I do have a small amount of electronics experience, but it's generally rather clumsy. I know how a microswitch works... its just the application of it. I'm sure this must be something realy simple but it hasn't come to me yet.

Does it not go in one direction, stop, and then go the other direction?

Oh I see back and forth.

ronv said:

Does it not go in one direction, stop, and then go the other direction?

Oh I see back and forth.

Click to expand...

To make it a little clearer, the cam flips the positions on a model rail turnout, or points. The cam is moved through the 180 degree movement of the motor. The motor can move in just one direction to flip between the two positions, or reverse it doesnt really matter. whichever is simplest is best.

I think the torque on a windscreen wiper motor would rip a track layout appart like tornado.

Dunc

dkvfx said:

...
I think the torque on a windscreen wiper motor would rip a track layout appart like tornado.

Click to expand...

It wasn't until your last post that you mentioned a model railroad...

I know Mike.... that's why I thought I should mention it. You had a good point to offer though. The windscreen motor is the mother of salvageable motors. And don't forget the washer pump....lots of fun to be had with that.

I was working on a TV show with RC Model characters. We had a character who was having a tantrum, so I asked the director for 60 mins time out. I removed the pump from my car, in the car park, fitted it inside the model with an RC motor controller and capillary tubes to eyes feeding water from a 35mm film canister. Back on set, ready to go and "Whah... Whah... Whah!" I throw the switch and comedy squirty tears appear. "Fantastic!!! Cut." I had to run the car for the rest of the series without a washer, just in-case we used it again!

Not relevant... just thought I'd share the fun.

Dunc

Maybe I still don't understand. In the circuit above you put the switch in one position and the motor turns until the micro switch stops it. To put it back to the original stop you put the switch in the oposite position and it reverses to the other micro switchand stops.

Hi Ronv

There's only one circuit on this post, and you posted it.

My brain is turning to jelly (or jello for the US) and thats without the technical stuff.

Cheers

Dunc