Servo potentiometers wearing out.  - Page 1
Forum section: electronics / projects

author: Azmarith
author_rank: Newbie
timestamp: January 07, 2015, 12:57:18 am
content: Hey guys, I'm new to the forum. I've come because I have a problem that I'm having trouble with. Basically I'm trying to make a servo, pretty much from scratch for a bigger project I'm working on. Overall it works well. However, after a few hours the potentiometer starts to wear out, and the signal gets really messy. At first I put the potentiometer at the end of the rotor shaft. Here's a video:http://youtu.be/YXVJW6c1R-II replaced the potentiometer a few times, but in the end I came to the conclusion that where I had it was putting too much preasure on the potentiometer. So, my next idea was to connect the potentiometer to the shaft via a gear so that the potentiometer wasn't exposed to any unnecessary force.However, I get the same problem. I left it to run for a few hours to test it, but the potentiometer wears out. Admittedly, I don't have any experience with pre-made servos, but surely they don't wear out after a few hours of use? Is there a special type of potentiometer that I need to be using? What am I missing?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2015, 01:31:57 am
content: Are you putting high current (like motor current) THROUGH the potentiometer?You should need only a small shaft (with the appropriate shape) going through the pot rotor.There should be ZERO pressure of any kind in any direction on the potentiometer.You should be able to accomplish this directly from the output shaft without resorting to extra gears.Sorry, but your "video" was so fuzzy we couldn't really tell what we are looking at.It doesn't seem to be a "conventional" servo design, so we need some explicit details here.And a schematic diagram would help us understand HOW you are doing this.

author: w2aew
author_rank: Super Contributor
timestamp: January 07, 2015, 01:39:25 am
content: Is that the potentiometer in the picture (the little blue guy just above the green twisted pair)? Looks to me that it is a trimmer style pot. Trimmers are NOT intended for high rotational life. Some are rated for as few as a few hundred wipes, since their intended for trimming or calibration applications, where they are adjusted infrequently. Potentiometers that are designed for longer rotational life are often called "controls", and will have rotational life that is substantially longer than trimmers.

author: KM4FER
author_rank: Regular Contributor
timestamp: January 07, 2015, 02:12:34 am
content: Many many years ago I worked on some flight simulators where most of the calculations were performed with analog computers. To accomplish all the calculations there were a lot of discrete component op amps and servos. Each servo had a wire wound pot on it. For each hour of running time we planned on an hour of maintenance time, most of which was spent taking the pots apart and cleaning them with alcohol and cotton swabs.Servos are very hard on pots. When in a "stationary" position they are actually jittering back and forth a little and if operated in a manner such as I believe your video shows where the pot is in one location for extended periods of time the pot will receive quite a bit of wear at that spot and not last long.Depending on your needed service life you might want to research pots designed specifically for server operation.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 07, 2015, 02:42:15 am
content: Hi and welcome.It is my job to tell newbies to go buy the proper servo on eBay. Dirt cheap, and it works. And if it doesn't, "take it apart".And if you need more, go to Hobby King.There are servos out there that'll tear your arm right off. There are servos so small you can build RC airplanes out of paper. There's no value in building your own.I think I agree with W2, wrong style of pot.