Help with a Hitec HS-785HB servo limiter

I have two HS-785HB on an aileron ch of my R/C transmitter but I need to stop each servo at its neutral point because the servos have line which run through pulleys. The objective is to have the servo only rotate out in the positive direction then back to the neutral position for each servo.

The problem is that the servo act in an opposite so as I rotate one servo to the correct positive position, the other counter rotates in the negative. Once passed negative the pulley prevents any further rotation becase of the gear attached to the line.

A Programmable digital winch servo would work but none have the torque that match the HS-785HB.

So I was wondering if there was a circuit that I could add that would allow me to adjust the starting and stopping points of the servos individually?


I do not know of a simple circuit or stock product to do what you want. If you are familiar with microcontrollers, it should not be that bad to program one to read the signal out of your RC receiver and then generate a new signal that follows whatever rules you want. Also, are you sure your transmitter can’t do it for you? A lot of these programmable radios have all kinds of mixing options built in, though I don’t know if they typically cover your situation.

- Jan

The radio is a big one. I’ve mapped the a aux ch to the right hand stick to control the right servo. So really the aileron is split left and right movements but two ch. Nothing as far as mixing goes.

This has marginally worked under strict R/C but that is very problematic now…we are integrating an autopilot and it doesn’t understand the split ch issue. It want’s to see the standard aileron setup and we can’t physically rig it up that way.

Does that clarify the issue a bit more… I don’t have much of a background in R/C so my vocabulary is a bit limited.

The radio seems irrelevant if you want your autopilot to get covered, too. If you are programming the autopilot yourselves, then it seems like you should be able to do whatever you want with the servos, so you could reduce it back to the radio problem. But, if you’re making autopilots, the microcontroller approach I mentioned should be relatively trivial.

- Jan

You give us too much credit, we’re not that smart. lol

The autopilot is a commercial unit and as such is made for fixed wing aircraft. We approached the manufacture but they are largely to busy to fiddle our project.

So we can’t really address the autopilot directly, the only way around it is servos… which is where we are at i think.