SSC-32 Servo jitter

Lynxmotion Electronics & Software
1

Hi all,
I apologize if this topic has been covered here further down but I could not find it so I post this question. Let me emphasize I like the SSC-32 very much.

Problem: Jitter occurs after initialisation of the servo with SSC-32 microcontroller (MC).

With “jitter” I mean some random erratic small movements of the servos. There is no other movement programmed, the servos are in default 1500mS position.

There is random servo jitter occuring after this procedure:
attach power to SSC-32 MC and Servos (no jitter)
connect serial cable (no jitter)
start RIOS software or LYNXterm software (no jitter)
press TEST (1500mS) command (initializes arm and jitter begins)

either:
disable servos in RIOS (no jitter)
enable servos in RIOS (jitter begins)
unplug serial cable (jitter still present)
unplug power of MC (jitter gone)

or:
disable servos in RIOS (no jitter)
unplug serial cable (no jitter)
unplug power of CPU (no jitter)

I can exclude any power source related cause, power comes off two fully charged batteries, 9V for the CPU and 6V for the servos. VL/VS Jumper removed of course.

Attached servos are 2 servos only, type HS-422, attached to port 1 and 2

They form a shoulder and an elbow for an arm. There is no other load than gravity on the joints so that the servos run without counterforce, no springs attached, no hand/gripper attached.
All constructed with SES.

Jitter is present with all firmware versions of the SSC-32.
Jitter stays present with load on the joints by adding weights.
Jitter is also present with a replacement SSC-32 board

Does anyone know how to reduce the jitter or get rid of it?

Thanks
noDNA

2

To simplify your description the servo is jittery whenever it is powered up and receiving pulses. The pulses generated from the SSC-32 are rock solid. There is NO jitter in the pulses. Even if the SSC-32 had a 1uS jitter, the HS-422 would not be fast enough to respond to it. Jitter in the pulse stream if present, would not be random anyway. So I think it’s safe to conclude the SSC-32 is not at fault. The RIOS, SEQ, or Lynxterm only sends a command #0 P1500 for all channels when all = 1500 is clicked. So they can’t be at fault. The 422 is an inexpensive low power servo, the jitter may be normal. It would help if we could see the problem in video to be sure it’s not something else. Although I’m at a loss as to what that something else could be…

3

Thanks Jim,

I found serveral simultaneous causes for the problem and can now state this problem does not occur with good quality servos, such as the Hitec 5995, 5990, 5955 which I tested successfully.

So, reason for the jitter in my installation was a broken internal servo controller board and two low cost servos and two servos other than Hitec which do interfere using the Y-cable of the Lynx Arm.

Also the servos jitter when there is no gravity load, but this can be overcome with a rubber band or spring attached,
regards
noDNA