Re: Disk size for 3600 RPM sync TTY motor

Hi Gary,

> Original Poster: Gary Lau  07-Jun-1999 2057 <lau-at-hdecad.ENET.dec-dot-com>
> A machinist-friend of mine just finished making me a perfectly
>balanced 1/2" thick by 8.75" diameter lexan disk and mandrel
>to mount it on my 3600 RPM synchronous TTY motor.  I was
>planning on having two 3.5" long by 5/8" copper pipe
>electrodes going through the disk (1.5" on either side), arcing
>along their edges like a cylinder gap.  The disk is indeed
> perfectly balanced, but the motor just doesn't seem to have enough
>oomph to get it to sync, even without the copper pipes.  It appears
> I'm going to have to scale down the disk diameter, and probably
>thickness too.
> I was wondering what size disks others have been using with 3600 RPM
>TTY sync motors?  Is the problem one of rotating mass, where it just
>can't get over the startup hump, or is it air drag, where any attempt
>at such prominent rotating electrodes would be too much drag for
>this motor?

Your motor is 1/12hp, if I remember correctly. This translates into
~62W. The 1/2 x 8.75" disk might just be a little too hefty for this
(little = wattwise) motor. I suspect that your next problem might be the
air turbulence you will create, due to your constuction (i.e. hollow
copper electrodes). There will be drag created because of the
electrodes sticking out. As these pipes are hollow, you will also get
turbulences, which are 90° to this already hefty (for your motor)
drag. The effect you are seeing now (w/o the copper pipes installed)
is probably a "light-weight" version of the problems you will see,
once the Cu pipes are installed. Have you tried plugging the holes
with cork, or similar light weight material to see if your motor can
then pull the disk into sync (i.e.: effectively reducing turbulences)?

My personal thinking: go for a different motor. I suspect you will
have to reduce diameter and thickness quite a bit, before this
TTY motor will be able to "sync" it. The 3600 rpm will further
aggrevate the problem (canīt remember if its the square or ^3
law for drag vs. speed).

Coiler greets from germany,