Let's Make Robots!

What causes servo "jitter" and how can I cure it?

Edit    Sorry, should have read this first.

http://letsmakerobots.com/node/3541

Not sure I'll be able to implement fritsl's solution, though.

 

I have a humanoid robot, which has 16 original servos, plus I have added 2 standard servos in claws, and recently 2 more micro servos for the head.

These 2 micro servos occasionally get a bad case of the "jitters", not all the time, but intermittently.

As soon as I touch the head, the jittering stops.

Can someone explain to me what possibly could be the cause, and how I could maybe cure it, please?

(I should say that the servos themselves do not appear to be faulty, as they work fine off the robot.)

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I had a similiar problem on a robot i have built years ago, it was solved adding a resistor on the signal wire of the servo, i don't know why it has solved this problem but it did.

 

Sorry but i can't remember how many ohms i used, it was on a PIC microcontroller running at 5V.

Hope this helps(someone)!

 

Sorry for my bad English.

I was using a 556 servo controller schematic by Hansen Hobbies. This schematic allowed me to use a ne556n dual timer chip I had on hand to implement the schematic which is just a Pulse Width Modulator. Basically I found out that all I needed to do was replace their recommended .01 microfarad capacitor for a 47 microfarad electrolytic capacitor between pins 3 and 7 which conditioned the chips internal voltage for the first stage of the PWM. It worked and it also gave me precise control over an old cox/ sanwa 80111 servo too. I hope this helps.

   Cheers,

          Andornot

You could try adding additional capacitors on the jittery servos power connection.

For each servo try adding a 100nF monolithic ceramic to supress electrical noise and a 100uF electrolytic to help with surges.

Thanks for the suggestion, OddBot.

There isn't an awful lot of room to do that, but I'll have a look :)

I bought them from HobbyKing.com. But I guess you need pico servos, never tested servos so small, no idea what to recommend. A Hitech, Futaba or GWS servo will not have any jitter, provided the code is good, of course.

I had jitter problems on my MiniEric robot. I was using HXT900 micro servos for pan/tilt and the jitter was at the tilt servo, because the head is heavy. After I changed the servos with Turnigy TGY-S3101S servos the jitter stopped. Better quality servos... but still cheap enough. Also the new servos have a better accuracy, they turn in 1 degree steps with nice precision and a lot less noise, both mechanical and electrical. Very pleased with them and I recommend them any time I get the chance.

Thanks for the advice, Ro-Bot-X.

I have to say the ones I am using are not the best quality, they are eSky digital micro servos. The reason I chose them is because they are slightly smaller than all the other micro servos (hxt900, sg90 etc), which allowed me to fit one inside the head with enough room for a wireless camera. (Plus the fact I had a couple in my box :D).

I'll look the Turnigy ones up, thanks.