[sdiy] Tonewheel relics

[Chromatest J. Pantsmaker]

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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