Shaftencoder and DC controller question

[chrugel]

Hi
I'm currently undertaking a little CNC project of my own and got a couple of questions:

Is there any reason why I should not connect the shaft encoder to the screw instead of the motorshaft?
There is a 3 - 1 reduction from the motor to the Screw.

Is is possible to connect two identical DC servos to one controller if they both are connected to the same screw, same gearing and the shaftencoder is connected to the screw?

regards
Chris

[Al_The_Man]

The encoder is often placed on the end of the ballscrew, but there should be no backlash present.
Two DC motors should not be supplied by the same drive, too many variables.
The only way it can be done is on a CNC controller that supports electronic gearing, each have an encoder and one motor is geared off the other encoder. If both on the same shaft it would be 1:1 gearing but other ratio's are possible with other scenarios.
Each would still have it's own drive however.
Al.

[chrugel]

Hi

Thank you Al_The_Man,Guess it is on to a bigger servo then!
Am I right if backlash between the servo and the ballscrew can cause oscillations? I'm going for a timingbelt setup and dont think this will give any backlash.

regards
Chris

[Al_The_Man]

Timing belt and non-backlash coupler should be OK.
Al.