I thought I'd share another command conversion I did, this time on the modern remake of the Tie-Jector. The stock one requires you put the track trips along the track to start and stop the process, but that seemed like a bore, so I set out to make this command controlled. One problem is the trips are actually a mechanical process, so a simple electronic control or relay won't do the trick. I settled on a model airplane servo for the motion control, and found one of the smaller ones available, the only thing that would fit in the spot I had. A cable control runs from the servo to the actuating arm for the ejection mechanism. Of course, I removed the existing lever that was used with the track trips. A small bonus was that I was able to sell the track trips for half the price I paid for the entire Tie-Jector!
Next, I had to figure out how to drive the servo, it requires a PWM signal for positioning information. Since the ERR MiniCommander didn't offer such a capability, I build a small board that housed the PWM signal generation. That board connects to the servo to provide the positioning. The circuit also required isolation, so a relay is triggered by the smoke output of the ERR board and that actually changes the PWM signal to start/stop the ejection operation.
I added directional headlights and tail lights, a backup light, and a strobe when the ejection is running to complete the picture. It's fun to get the reaction when it starts dropping the ties along the track.
Here's the completed project.
Here are a few shots of the inside of the unit illustrating how things were mounted and connected.