running servo's

Hello all,

I' m busy to enhance my EMC knowledge with servo's but unfortunately my brain can't figure out what is going wrong.

I have:
Working Deckel-machine with servo's
STG-board
RedHat 5,2 with kernel 2,0,36 Rt-patch and EMC 16/9/99
Working and properly connected encoders (tried this out when working with original controller and EMC but leaving DAC cable out and so determined INPUT SCALE 1000 0 )

My problem is that when I disconnect the original DAC cable from the amp's, the servo's are drifting the moment I switch on the machine. Can this come from the fact there is to much gain on the amp's? (I don't like to turn this pot-meter as I still want to work with the original controller and this value is yet tuned for the machine.)

Then with this fault and connecting to the DAC of the STG-board, starting EMC; out of E-stop and put the machine-on, I can be impressed to see that I have a speedy machine, still it would be great when he waited for a command to move.

So I thought that this movement came from the fact that I reversed the DAC cable, so one movement could compensate the other, tried that out, the result was even worse as I had a servo flipping one side to another for just a couple of degrees (shaking is maybe a better word).

Tried also with other PID value but no improvement was seen.

So what knowledge am I missing ?

and what is BIAS? I do not find a description of this parameter.

Thanks in advance for your reply.

Jan.