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How to check a motor for sync.
I have been modifying motors for sync-gap use these last days, and have
found a nice way to verify, wether it is syncėng, or not, and would like
to share it with all.
Since I had no success with the "strobe" effect of neon tubes, this is
how I did:
The motor preferably has a thread in the end of the axle, because then
you can just screw a piece of PCB board, or plywood, whatever, right at
the end of the axle. Else use the hub for the rotor.
Now drill 2 holes, about 1/2 inch from the perimeter, 180 degrees apart,
and mount an iron screw with nut in each hole.
These screws will act as moving shunts for a magnet you will fix to
something, so that when the disc spinns, the screws will pass close to
the magnet.
Hold pickup coil here |
\/
+-----+
+------------------------------------+-+-+-++
+-+---+------------------------------+-|-|-++ <- Disk
| | +-|-|-+
| | | |
| | <- Motor axle | | <- bolt and nut
| | +-+
| | +------+
| | | |
| | | |
+---+ | | <- Magnet
| |
| |
| |
+------+
Now hook one channel of the scope to the mains, and trigger on that
channel. The other channel is connected to a small pickup coil you make,
a cliplead spun into 4-5 turns is fine.
Now start the motor, and move the pickupcoil close to the spinning disc,
where the screws are flying by, and on the scope you will se a fine
little peak, for each passing screw, and if the 2 curves are aligned,
the motor is in sync.
+--------------------------------+
| |
| |
|------/\ -----------/\ ----- |
| \/ \/ |
| ** |
| * * |
| * * |
| * * |
| * * |
| * * |
| * * |
| * * |
| * * |
| * * |
| ** |
+--------------------------------+
It is nice to see, how much friction you can apply, and how little the
rotor actually is displaced in relation to the rotating field, doing
this.
I also think you need to do this only once. In the process, you will
develop a feel for the sympthoms of the motor "hunting", and know from
this behavior, that it does indeed sync.
I would imagine, that applying DC to the (closely spaced) electrodes of
a finished gap, would allow some similar ( capacitive ) pickup to
occour, for calibrating the finished gap, but I have not tried this yet.
Anyone tried this?
Hoping this is usefull,
Cheers, Finn