# Continuous servo motor and micro Maestro controller

Hello everyone,

I’m new in the servo community. I’m using 2 continuous servo motors (GWS S35) with a mini maestro controller board.

Here is my problem:

I wanted to synchronise a rotation of the two servos. I saw that there are huge differences between the servos. Entering the exact same position for the two servos, one is rotating much more than the other (see video:

After 20 sec, the first one rotated 180° more than the second one.

Is there a way to calibrate the rotation of the servos without feedback?

The only thing I can do is trying to reduce the target position of the faster servo to reduce the rotation. But I can do it only visually and it’s not accurate enough for my application. And it seems that the offset on the rotation is not constant.

Also, what is the relation between the target position and the angle of rotation? I mean how can I calculate the angle from the target position I entered.

Sam

Hello, Sam.

Since you are new in the servo community, I recommend reading our president Jan’s series of blog posts about servos:
pololu.com/blog/

In particular, here is the article that explains continuous rotation servos, and should clear up the confusion you are having:
pololu.com/blog/24/continuou … urn-servos

There will be unit-to-unit variation in servos, so it’s not surprising that one turns faster than the other. I don’t know of any automatic way to calibrate these servos but you could try adjusting the target values (pulse widths) until you get them to turn at roughly the same speed.

It looks like you are not actually rotating the servos all the way around, so maybe a servo with feedback would be a better fit for your application. It’s hard to keep continuous rotation servos in sync, but it’s very easy to keep servos with feedback in sync, whether they are a standard servos or a multi-turn servos.

For continuous rotation servos, there is no relation. Target position corresponds to angular speed, not angle.

For normal servos with feedback, the relation depends on the manufacturer and model.

–David

Hey David,

Thanks a lot for your answer. So I read the post on continuous and multi turn servos. Interesting.

So I will tell you a little bit more about my application. I need two motors, that I can control the angle, to rotate at the same time with the same angle. I need at least a 720° maximum rotation for now. This is why I can not use a standard servo with feedback.

Now the multi-turn servo seems interesting but the precision is not great. I might try to use stepper motor instead of servo for this application. Any suggestions or advices?

Sam

It sounds like you’re on the right track. I don’t have any more advice at the moment. Good luck with your project!

–David