One servo makes the other servos jittery

DaMaster Architect

Hello everyone,

I am constructing a robot arm with a friend, for a schoolproject. For this purpose, we ordered a parallax servo controller USB, some hitec servo's (2x HS475, 1x HS422), and a GWS S06 Contiuous rotation servo. So far, everything went well. It was really a pleasure to notice how fast we managed to get the hitec servo's to work with the controller!

However, we came across one problem when connecting the GWS servo to the servo controller. Let's imagine the following situation:
Servos connected to port:
Ch0 - Hitec 475
Ch2 - Hitec 475
Ch1 - GWS S06 CR
We noticed, that in this situation, once we connect the GWS S06 servo to the servo controller, all the servo's start shaking a little. We tried tweaking the pulseout a bit, but so far we have had no success. We do not understand how the GWS servo affects the other servo's on contact, eventhough we don't send any pulses to it.

Does someone know a workaround to stop the shaking?
Thanks in advance!

PAR

DaMaster Architect said...
Hello everyone,

I am constructing a robot arm with a friend, for a schoolproject. For this purpose, we ordered a parallax servo controller USB, some hitec servo's (2x HS475, 1x HS422), and a GWS S06 Contiuous rotation servo. So far, everything went well. It was really a pleasure to notice how fast we managed to get the hitec servo's to work with the controller!

However, we came across one problem when connecting the GWS servo to the servo controller. Let's imagine the following situation:
Servos connected to port:
Ch0 - Hitec 475
Ch2 - Hitec 475
Ch1 - GWS S06 CR
We noticed, that in this situation, once we connect the GWS S06 servo to the servo controller, all the servo's start shaking a little. We tried tweaking the pulseout a bit, but so far we have had no success. We do not understand how the GWS servo affects the other servo's on contact, eventhough we don't send any pulses to it.

Does someone know a workaround to stop the shaking?
Thanks in advance!

How about these other situations:

No shaking with only the three HiTec servos connected?

No shaking with only one HiTec and the GWS servos connected?

No shaking with only the GWS servo connected?

The two HiTec servos shake (while not otherwise commanded to move) even when the GWS servo is rotating?

PAR

DaMaster Architect

Thanks for your reply.
There is no shaking with only three hitec servos connected, and no shaking with only the GWS connected. However, I didn't test whether there is shaking when one hitec and one gws are connected to the controller. Unfortunately, the servos are at school, so I do not have access to them to test them at the moment.
And yes, the two hitec servos do shake indeed when they are not commanded to move, in case the GWS servo is rotating. Same applies when the GWS servo is not rotating. The hitec servos start shaking from the immediate moment I connect the GWS servo.
I wondered whether there could be wrong anything with the power supply. Could the juttery be caused by a lack of current?

Mike Green

Yes, the problem is probably related to the power supply. If your supply can't provide enough peak current, the servos (which have a simple controller in them) start to come on, may have a transient power drain, overwhelm the power supply, the voltage drops which causes the servo to reset, and the cycle starts over again. Sometimes you can stop this by putting a large (1000uF) electrolytic capacitor across the power supply. The GWS servo may have a relatively high idle current drain. You might try measuring it if you have a multimeter than can measure current.