I’ve had a small linear actuator on my trade-show table of tricks for years — some of you may have seen it at USITT Stage Expo, or the ABTT Show in London. It’s a little extendable “arm” that runs in and out using 2 channels of wireless D
They change direction when you reverse the polarity of the power driving them: swap the red and black wires (the + and – leads) and they run the other way.
You need 2 channels of DC dimming, a small DPDT (double-pole, double-throw) relay, and — of course — the motor or actuator. One dimmer provides motor power, the other dimmer drives the coil of the relay. Connect the motor power through the contacts of the relay to provide one polarity when the relay is NO (normally open) and the opposite polarity when NC (normally closed).
Use a linear dimming curve for motor power. This lets you control motor speed. Use a non-dim curve for the relay, to ensure it is either open or closed. If you send dimmed power to a relay, it will chatter and not switch reliably.
Here’s a diagram of how to connect the relay to an RC4Magic DMX2dim dimmer. You’ll want to use a relay with a coil voltage that is the same as the motor, and run the whole thing at that voltage. A good choice would be 12V, but it can be anything from 6V to 24V when using our R3 dimmers; or 6V to 18V with our older dimmers.
There you have it: now you can make that drawbridge go up and down… or whatever else you want to do with a reversible DC motor.