Re: [CAD_CAM_EDM_DRO] Re: gearmotors,encoders

Brad Heuver wrote:

> That was me with the Tape-O-matic. Last winter, when I got the
> beast, the group looked at some of the hard to read schematics that
> are on the RCM file site, and indicated that the amp bandwidth was
> low. (I want to say even less than the 100Hz mentioned above, is
> 10Hz possible?

Yes, quite possible. The positioning bandwidth on my old Allen0Bradley
7320 was about 2 Hz!

> I didn't go back in the archives and search for the
> reply.) I'm glad I now asked he question!! It seems likely that
> I'll have to remount the encoders when I conduct the brain transplant
> on the P&W.
> I'm still not quite sure how the possibility of this twist is
> worse than the possible lash in the old cogged belts that connect the
> servo moto to the leadscrew.

I'd suggest you replace the toothed belts. I tried to run with the old belts
in my axis drives, but they only lasted a few hours.

> Especially if either cog is bored
> eccentric.

Well, you can't say it IS eccentric, unless you measure it.

> Won't this be a greater risk than the screw twis &
> resonance?

Not likely. I have the tach and encoder driven by the leadscrew, on the
other side of the belt from the motor. Slipping of the belt would be
a problem, but new belts show no sign of slipping.

As for resonance, the torsional resonance is not going to be the big
one, in most systems. there are other resonances involving the mass
of the table that get you first. Ever see a Bridgeport rock from side
to side due to oscillation of the X axis servo drive? I have!

Jon