Hi all,
further to the progress detailed in
this thread,
here are details of a simple magnetic coupling that isolates
motor shaft vibration from the mount.
Magnetic couplings are not a new idea.
Used on steppers in particular, they can remove a lot of micro and half-stepping
vibration being passed on through the reduction gearbox or drivetrain
downstream of the motor.
They can also offer a form of protective clutch.
I wanted to try and minimise or even eliminate more vibration
from my system.
There are two contributors.
One is the way the motor is actually mounted to the GEM.
Second is vibration actually transferred via the shaft itself.
The first one is almost completely removed now by the way the
stepper is mounted with a quite complicated rubber/ nylon mounting.
The second one is done with this magnetic coupler. (sometimes a simple
bit of surgical tube or flywheel weight (or a combination) can do the job,
but all steppers are different).
I obtained the quite powerful magnets from my children's toy 'Magnetix' set.
I made two matching flanges on the lathe from aluminium.
One is mounted on the motor shaft, the other on the reduction gearbox
that feeds the homemade worm gear.
Inset into these flanges are 8 of these neodymium magnets.
They are a press fit, and locktited in.
They are arranged so that the coupler searches for the right combination
of North-South match then 'locks on to it'.
They repel and won't align at any other position than '12 o'clock'.
This is a good thing because you wouldn't want it to align at 3,6,9 o'clock.
Because of this there is no pointing accuracy lost in the Bartels system.
It stays locked.
Video here.
It is quite effective, even when separated by about 5mm between faces.
The torque is transferred over this air gap and vibration seems to be
mostly left behind. With magnets sometimes there is a sort of hysteresis effect ,
where it would tend to 'hunt' or overshoot and possibly add vibration.
This doesn't seem to be the case here, in fact it behaves like a 'big rubbery'
flywheel.
Attached are a few pics and a quick result from this a.m. NGCs 6769-6771
in Pavo.
Steve
