Re: [CAD_CAM_EDM_DRO] tach output

> Hi all,
> Can you use servo motors without the tach drive hooked up.

Yes, it is possible to build a sevo system without tach feedback.
Two things are required:

- a 'torque mode' amplifier with internal feedback so that output
current is a function of input voltage (as compared to a 'velocity
mode' which will peg its output if there is no feedback from a tach to
show it that the motor is spinning)

- a servo loop that doesn't need velocity input, most likely because
it is calculated internally as the derivative of position.

In the past servo systems without tach feedback tended not to work quite
as well, but the state of the art is advancing.

Of some of the more popular current solutions for pc-based machine
control (Gecko step servo, servo to go card, delta tau pmac) I believe
none require tachometer feedback (although the STG or pmac would if
used with velocity-mode amps).

Chris Stratton

-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html