On Fri, 14 Apr 2017 06:34:20 -0500, Pete Keillor
wrote:

On Thu, 13 Apr 2017 18:15:09 -0700, wrote:

On 13 Apr 2017 22:07:57 GMT, "DoN. Nichols"
wrote:

On 2017-04-13, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...

How well do you think an electric motor would work as a rotary
transformer? They are already balanced and built to withstand the
RPMs.

Well ... most of our electric motors are induction motors, where
the rotor is just iron and copper (or aluminum) -- no connections to it
other than magnetic coupling.

However -- a universal motor (wound rotor and commutator) could
perhaps act as a transformer -- with say AC fed into the field, and
power picked up from the commutator. But the commutator would be fixed
with relation to the field coil, so you still have the problem of
getting the power to the solenoid valve. Break out the commutator, and
pick one of the rotor windings and you have your AC (modulated by the
rotation of the rotor poles relative to the field poles), but running
those wires out to the solenoid valve would still be tricky. The wires
would interfere with mounting of the bearing at that end -- unless you
milled a couple of slots in the rotor shaft where the wires could be
passed under the bearing.

I really think that moving the solenoid valve to the outside of
the rotary coupling would make more sense as I suggested at the start of
my followup -- in spite of my having posted the design for machining
magnetic cups and coils for getting the power in through the rotating
shaft.

Enjoy,
DoN.
Of course the valve mounted outside would be better. But that won't
work because the closer is basically a double acting cylinder. This
means that it needs air pressure to clamp and remain clamped, and air
pressure to unclamp. So the rotary union would need two passages.The
way I use the closer now is with a solenoid operated valve the has one
air inlet, two outlets, and two exhausts.So when one side of the
piston is pressurized the other side is exhausted to the atmosphere.
Since air needs to be sent to both sides of a piston there needs to be
two passages in a rotary union if the valve is outside.
Eric

I've used a dual rotary union similar to this on a heated roller. Kind
of spendy. Deublin also makes slip rings.
http://www.deublin.com/2117-001-109/

Pete Keillor
The max speed for that rotary union is only 250 RPM. I need 4000 RPM.
The single passage ones go that fast while still being affordable. The
dual passage ones that can spin that fast and have air going through
them are about 10 times more expensive.
Eric