servo twitching

jawnlooi

hi all, my servos twitch when they're being controlled by a basic stamp, i was wondering is this was RF/magnetic interference.
i am using a BS2PX24, PWMPAL (for servo output) and 4 futaba servos.

the stuff work fine until i mount the servos. unfortunately, the servos are
mounted on an aluminum holder (acts as a receiver and interferes with the
servos maybe?) and the servos are also located near a kontronic motor,
which is relatively big (28mm diameter by 40mm length), so it may also
be susceptible to electro magnetic interference.

i have shielded the motor from the servos as much as i can (mu metal) to
reduce the magnetic interference, but nothing about the RF noise, is there
a way to reduce the RF noise? i noticed someone grounded his aluminum
servo mount to reduce the twitch, does this help and how?

thanks for all help.

randyaz

you didnt state how your powering your servos...one common cause of twitch is insufficient current.

Tom Walker

Another cause can be lack of a common ground.

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Chris Savage

Yet another possibility is over driving the servos…That is, refreshing them too often (less then 20mS intervals).

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Chris Savage
Parallax Tech Support

jawnlooi

the servos are powered by a receiver, they work fine away from the whole robot assembly,
but once i attach it to the rest of the robot, it twitches. common ground is present, and the
power is fine, and the pause is 20mS, although the servos actually work with just 10mS of
pause.

i deduce that its most probably some sort of interference, maybe RF, since my robot has a
large portion of it as aluminum, acting as a big antenna. is there a way to prevent interference
besides putting it inside a faraday cage? (because i still need my rc receiver to communicate)

AIman

I have the same problem and am running straight off my Board of Education Rev C. The servo's aren't underpowered because there is only one in use and the power source is a wall adapter. For me the servos twitch at the start of each move. My pause time is over 20 and the only other things running are IR and Sonar.

I am having almost the identical problem. Everything runs fine until its all put together. I can run the IR and sonar with no problem, the IR and the servo, the sonar and the servo but not all three at once.

Chris Savage

AIman,

Using a wall supply does not necessarily mean you have sufficient power. A 9V 300mA wall supply may be too weak for a servo system, especially during stall or startup conditions. Take care.

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Chris Savage
Parallax Tech Support