[sdiy] Tonewheel relics

[Mike HEQX]

I second toothed belts. This company is a great source for that type of 
thing, or at least they will give you all the ideas you could ever need.

http://www.sdp-si.com/


On 10/24/2017 11:37 AM, Chromatest J. Pantsmaker wrote:
>
> What about cog gear pulleys? You could maybe use toothed belts and 
> pulleys so you wouldn't have to worry about slippage and what not.
>
> Like this stuff: 
> http://www.mpja.com/mobile/Gears-and-Pulleys/products/528/
>
> On Oct 24, 2017 2:23 AM, "Rutger Vlek" <rutgervlek at gmail.com 
> <mailto:rutgervlek at gmail.com>> wrote:
>
>     I thought about that. The gear ratio's are crucial to the tuning
>     of the tonewheel generator, and I feel that varying belt diameter
>     (tension related, temperature dependant) could become an issue.
>     Though, I have no way to quantify this instinct.
>
>     As for 3D printing, this is really a nice case where it's not
>     perfect yet, as far as I can tell. I've asked some experienced
>     people, and what I heard was basically that the composite nature
>     of 3D printed objects results in a not-so-homogene material, that
>     has unpredictable wear properties during applications with
>     friction. Polishing changes the surface a bit, but lack of
>     internal homogenity is supposedly a problem for gears, especially
>     when running at higher RPMs (more friction). From memory I recall
>     the drive shaft of the central AC motor in the Pari runs at around
>     1200 RPM. It connects with a belt drive to the first tonewheel
>     drum shaft, which then connects with gears towards the last (12th)
>     tonewheel shaft, progressively slowing down each drum such that
>     identical drums given a semi-tone tuning difference. The last drum
>     connects with a belt to the vibrato scanner.
>
>     As for PLL loop: I've never designed one, but it has my interest.
>     What amount of complexity am I looking at? Can someone refer me to
>     an example circuit schematic? Each tonewheel drum contains several
>     octaves, the highest octave as (I believe) 16 dents on a single
>     revolution. So that would be the preferred source for PLL
>     feedback, I guess. The other octaves automatically align. The
>     drums are spring-coupled to the gear shafts by the way, so the PLL
>     loop may be affected by that (bouncing at startup?).
>
>     I do imagine this would be a HUGE step forward for the Pari in
>     becoming tunable and way more silent than it is.
>
>     Best,
>
>     Rutger
>
>
>
>
>
>     2017-10-24 0:48 GMT+02:00 Sarah Thompson <plodger at gmail.com
>     <mailto:plodger at gmail.com>>:
>
>         Would belt drives work? They have huge advantages over gears
>         if you need smooth transfer with no cogging or backlash.
>
>         On Mon, Oct 23, 2017 at 4:34 AM, <rburnett at richieburnett.co.uk
>         <mailto:rburnett at richieburnett.co.uk>> wrote:
>
>                 @roman and Richie: thanks! From my limited experience
>                 with bldc's I
>                 feel they would be costly, especially a 12-way driver
>                 system for them.
>                 Would they need hall sensor feedback to get the tuning
>                 accurate
>                 enough?
>
>
>             Yes, probably not cheap.  I don't think you'd need hall
>             sensors to detect the field, but you would need to ramp
>             the frequency up at a controlled rate to allow the
>             mechanical bits time to accelerate up to operating speed.
>
>                 The pll sounds nice and classic. I'll look into that.
>                 At present I'm
>                 not sure if the pick-up  coils of the generator could
>                 handle more
>                 loading, e.g. As required for closing the loop. But a
>                 high impedance
>                 buffer would probably be ok.
>
>
>             Take the feedback for the PLL from the highest frequency
>             that you can.  The loop filter in the PLL has to filter
>             out the ripple in the compared reference and positional
>             feedback signals.  The higher you can make the reference
>             and feedback signal frequencies, the larger the bandwidth
>             of the loop filter can be, and the quicker the PLL speed
>             controller will settle.  i.e.  Don't use a reference
>             signal that is just one pulse per revolution, as this can
>             mean you end up with a very sluggish control loop!
>
>             -Richie,
>
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>
>         -- 
>         [s]
>
>
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