[sdiy] Tonewheel relics

[Timothy Burns]

Hi Rutger,

Have you looked into laser cutting either out of plastic or aluminum?  This
might reduce the chance of things warping or changing over time, since it's
a reductive process instead of additive.  Tolerances can vary depending on
the 3D printer but resin printers usually are the best bet for accuracy and
strength; unfortunately it's also the most expensive.

tim

On Tue, Oct 24, 2017 at 11:37 AM, Chromatest J. Pantsmaker <
chromatest at azburners.org> 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> 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>:
>>
>>> 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> 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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