Re: Sync motor mod clarification

• To: tesla-at-pupman-dot-com
• Subject: Re: Sync motor mod clarification
• From: "Ed Phillips" <evp-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sat, 25 Mar 2000 21:02:05 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Tesla List wrote:
> 
> Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk>
> 
> Sorry, I didn't explain this very well.
> 
> The 1/8hp 1425RPM motor turns a 7" disk at 1500RPM with plenty of torque
> spare,  (despite having only two flats machined into the rotor.)
> 
> However,  the 1/2hp 2850RPM motor has trouble holding a 7" disk at
> 3000RPM.  (This motor has 2 flats,  which is the correct number.)
> 
> My point was supposed to be that in going from 1500RPM to 3000RPM more
> than 4 times as much power is needed to maintain sync at the higher speed.
> I guess I'll have to look for a 1 horse motor,  and mod that :-(
> 
>                                                         Cheers,
> 
>     
	To a pretty good approximation, the power required to turn a disk
varies as the cube of the angular speed. Going from 1500 to 3000 RPM
should thus change the power required by a factor of 8.  However, that
seems like a lot of windage for such a small disk.  Once upon a time
(about 1950/51) I was involved in a project where we wanted to spin a
36" diameter aluminum wheel at 3600 RPM.  Got a 5 HP, single-phase sync
motor which didn't have enough pull-in torque to bring the disk up to
sync speed.  Finally got around the problem by using a mercury clutch
arrangement.  When that wheel was spinning at 3600 RPM it pumped a LOT
of air!  Real blast coming off the edge.  Point is that if 5 HP could
spin  a wheel of that size at 3600, 1/2 horsepower should be way more
than enough to spin the 7" disk at 3000.  Your actual power must be a
lot less than 1/2 HP!

Ed
Second,

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