[sdiy] Tonewheel relics

Tue Oct 24 19:39:46 CEST 2017

Reading Tim Burns post caused me to open Allen Douglas's 1962 "Electronic
Musical Instrument Manual" , the "Experimental Methods" chapter where he
describes ("for those with limited workshop facilities")  machining
sheet-iron or mild steel tone-wheels by drilling and filing.  55 years
later and DIY tone wheels  are still a topic.

http://gallomagnetix.com/AlanDouglasEMIM/TWheelFab.pdf

Also interesting was his "pantograph" rig "for marking out the tooth
profiles".

p

On Tue, Oct 24, 2017 at 9:53 AM, Timothy Burns <snrubmit at gmail.com> wrote:

> 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/Gea
>> rs-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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