Servo control signal losses

[jackytwoshoes]

I have 2 simple servo controllers which use a rotary potentiometer to control the position of a servo.
They are these ones: **broken link removed**

I would like to have the contoller about 20m away form the servo. Is this possible by extending the cables or would the losses be too great?

 

[Diver300]

You would probably be OK with screened cables for the potentiometer signal.

 

[jackytwoshoes]

Aahh, would that be better than having the cable stretch between controller and servo?

 

[Diver300]

Well I was referring to the potentiometer which provides feedback for the servo. It is attached to the servo shaft.

However, looking again at the kit, I now think that it contains a standard radio controlled model servo. If that is the case, the signals for those will go 20m over standard cable with no problem.

 

[jackytwoshoes]

thanks for this. They are indeed standard R/C servos and they are working fine over long distances.

The next problem is that when I connect them both to the same power supply they interfere with each other a little and the servos tend to twitch.

Would a decoupling capacitor sort this?

 

[jackytwoshoes]

Perhaps I should have said, the circuits are currently running form batteries but will eventually be from a wall-wart style mains PSU.

 

[alec_t]

A decoupling cap may well be sufficient. If not, then powering each servo via a respective diode might provide the necessary isolation (albeit at the expense of a drop of 0.6V in the supply voltage).

 

[jpanhalt]

Most servos today are rated for up to 6V or more, but operate fine at 4.8V. I have only run leads 3M or so, but agree 20M should work. If voltage drop is a problem, you could increase your voltage. These servos can draw a surprising amount of current under load, enough so that loading one might cause the other to twitch from low voltage.

As for the twitching, how close are the leads to each other? Are you running 6 lines (i.e., 2 power for each servo plus 2 signal) or only 4 lines (i.e., share the power lines)? Please confirm that there is no twitching with only one servo. Many cheap controllers, particularly the 555-based ones, cause twitching. In models, we routinely twist the leads, but I have no data to support that practice.

John