[sdiy] Telharmonium motors, perhaps?

[Tim Parkhurst]

> -----Original Message-----
> From: john mahoney [mailto:jmahoney at gate.net]
> Sent: Tuesday, November 23, 2004 3:17 PM
> To: Gene Stopp; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Telharmonium motors, perhaps?
> 
> From: "Gene Stopp" <gene at ixiacom.com>
> 
> > Random thoughts which keep popping into my head despite my attempts
> > to suppress them...
> >
> > Smaller motor = less portamento?
> 
> Maybe. The ratio of torque to rotational mass seems pretty important.
> 

What you want to do is reduce the rotational inertia. Ideally, you would
make the motor as small in diameter as possible, but longer to increase the
magnet / rotor area. There are "low inertia" servo and stepper motors which
are designed like this (remember the spinning figure skater with her arms
pulled in... =lower polar moment of inertia).

> 
> > Tone wheel idea - metal disk with "waveform" around the edge, again the
> > smaller the better for inertial reasons?
> 
> Smaller = less precision.
> 
> > Disk can be made with Dremel tool - any accidental (or intentional)
> > asymmetry would be a subharmonic?
> 
> You'll get "wow" (subharmonics), flutter, and jitter, I think.
> 

I would have to think that an optical approach would be much superior.
Printing the disks on a laser printer should be a snap, and the response
time of a good opto sensor (i.e. a phototransistor) would be much better.
Nice sharp transitions would be a breeze. 


> > Optical disk may have less weight, less momentum, sharper possible
waveform
> > edges?
> 
> I guess "yes."
>

I second that emotion...
 
> 
> I favor the polyphonic approach, in theory, especially with such small
> motors. Cherish the minor tuning imperfections!
> --
> john
>

I think this could be a really fun little project. We can all thank (or
blame) John M for finding these motors...


Tim (less momentum, sharper edges) Servo

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