Automatically change the rotation of the miniature motor

if you dont need it to dip at some exact time, just use a cam.

yeah, use a reciprocating mechanical arrangement. thats far simple and easier.

As an alternate, you can use pneumatic cylinder arrangement with solenoid valve and timers.

But mechanical cam arrangement would be low cost solution.

LIMBKAR

Think of a square wave power supply. You can adjust the amplitude symetrically for negative and positive as well as the frequency. Seems to me I remember an old Wavetek oscillator we used in school. It was capable of 10 second periods with amplitudes of 10 volts at 300ma. I think the model number was 175. Surely by now some IC mfr has reduced this to a chip.

Old toy trains (Marx. Lionel, etc.) that had a three-rail track system (1950s vintage) used a mechanical toggle that switched polarity every time the train stopped. This was needed because they ran low-voltage AC motors, with the two outside rails as "ground" and center as power. The next start would always be in reverse, if you had been going forward. To go forward again, you'd back up for a second, then stop again. The arrangement was sort of like the ball-point pen action, with alternate clicks to extend and retract. In a Rube Goldberg set-up, you could wire a solenoid into the motor's power supply, and have it operate a ball-point mechanism, with the ball contacting a switch. But there are push-push switches that would do that part for you more reliably, and I think you can find relays that will accomplish the same alternating polarity output.

thanks much for the help, great forum you have here

One solution is to use a stepper motor. The circuitry is more complex since you need to step between four phases one at a time but there are advantages. Firstly the speed is controlled by the speed that you switch between phases so there is no complex current control circuitry. Secondly if you keep count of the number of forward or backwards steps you know the position of the motor which means you don't need any positional feed back circuitry. You can buy chips that have everything built in to control stepper motors off the shelf so you can actually achieve the end result with buy off the shelf electronics, all you need to do is wire it up and program the controller.

Sorry for the slow response, I have gotten a bit bogged down with a couple of other threads and am now only catching up with last weeks mail outs.