"clifto" <clifot@gmail.com> wrote in message 
news:o18qm4-pub.ln1@remote.clifto.com...
> Roger Hamlett wrote:
>> If (for instance), you have a 3mm shaft, and 10mm balls, the casing has 
>> to
>> have an internal diameter of 26mm, and the ratio is 26/3 = 8.66:1.
>
> I could be missing something, but at first glance I read the radius as
> the diameter of the 10mm ball (10mm) plus half the diameter of the 3mm
> shaft (1.5mm) and get 23mm internal diameter, ratio of 23:3 or 7.66:1.
>
> Just in case this turns out to be a corecktion I've included speling
> erors to comply with tradishun.
Yes. Sorry, I just added up the internal diameter wrong....

It is fairly simple to visualise what is happening, if you realise that 
the balls are rolling round the internal diameter of the casing, driven by 
the small shaft at the centre, and for the assembly of three balls to 
complete one complete turn, their surfaces, must travel the internal 
diameter of the outer casing. Since the surfaces of the balls are driven 
by the internal shaft, you get the ratio from the ratio of these two 
diameters.

Best Wishes

Roger Hamlett wrote:
> If (for instance), you have a 3mm shaft, and 10mm balls, the casing has to 
> have an internal diameter of 26mm, and the ratio is 26/3 = 8.66:1.

I could be missing something, but at first glance I read the radius as
the diameter of the 10mm ball (10mm) plus half the diameter of the 3mm
shaft (1.5mm) and get 23mm internal diameter, ratio of 23:3 or 7.66:1.

Just in case this turns out to be a corecktion I've included speling
erors to comply with tradishun.

-- 
Postulate a group whose intent is to destroy the United States from within
via anarchy and bankruptcy. The actions of the United States Congress are
completely consistent with the actions one would predict from such a group.

> The ratio, is determined by the shaft diameter, to the internal diameter 
> of the casing in which the balls sit.
> If (for instance), you have a 3mm shaft, and 10mm balls, the casing has to 
> have an internal diameter of 26mm, and the ratio is 26/3 = 8.66:1. The 
> drive can be made remarkably good (the same system is used on some micro 
> focussers for telescopes, which carry significantly more torque than 
> needed for a pot). Units like the 'Williams optics feathertouch focusser', 
> use exactly this drive.
=================
Sorry ,but I don't understand the above .
If the shaft has a diameter of 3mm and the balls a diameter of 10mm, the 
inner diameter of the casing should be 10 + 10 + 3 equals 23 mm

When the shaft makes 1 revolution the balls will make 3/10 revolution .
When the balls make 1 revolution the casing makes 10/23 revolution .
Hence when the shaft makes 1 revolution the casing will make
3/10 * 10/23 equals 3/23 equals 0.13 revolution , hence reduction factor 
is 7.7
Please correct me if I made an error.

Frank    GM0CSZ  /  KN6WH

"Alan Nishioka" <alan@nishioka.com> wrote in message 
news:1184425080.691443.83770@z28g2000prd.googlegroups.com...
> On Jul 13, 7:12 am, msg <msg@_cybertheque.org_> wrote:
>> Please view these photos of a three-turn planetary drive
>> pot that uses a conventional "stackpot" formfactor 
>> athttp://www.cybertheque.org/homebrew/rcvr/images/antennas/pot.jpg
>> Resistance = 1K
>
> Interesting.  I've never seen a pot like this.
>
> So the turns ratio is determined by the shaft diameter to ball
> diameter ratio?
> And the wiper arm is connected to the ball carrier?
> So this assumes the metal to metal, shaft to ball won't slip, but the
> ball will turn in the carrier, causing the carrier to have 1/3 the
> rotation of the shaft?
>
> Sorry, this doesn't help you at all...
> Alan Nishioka
The ratio, is determined by the shaft diameter, to the internal diameter 
of the casing in which the balls sit.
If (for instance), you have a 3mm shaft, and 10mm balls, the casing has to 
have an internal diameter of 26mm, and the ratio is 26/3 = 8.66:1. The 
drive can be made remarkably good (the same system is used on some micro 
focussers for telescopes, which carry significantly more torque than 
needed for a pot). Units like the 'Williams optics feathertouch focusser', 
use exactly this drive.

Best Wishes

Jackson Brothers http://www.mainlinegroup.co.uk/jacksonbrothers/
Makes some excellent planetary drives. There are dealers in the USA.

Bill W0IYH

"msg" <msg@_cybertheque.org_> wrote in message 
news:139igmhfkoveg16@corp.supernews.com...
> Gary Tait wrote:
>
>> msg <msg@_cybertheque.org_> wrote in news:139f22h91ghhna7
>> @corp.supernews.com:
>>
>>
>>> I need the form factor for modifications to antenna
>>>rotator assemblies
>>
>>
>> Do you mean the rotator or the controller?
>>
>> For the rotator, you can maybe use a standard pot with gearing.
> <snip>
>
> I had considered gearing but the available space and the
> necessary additional fabrication was more involved than
> the solution I chose.
>
> Here are photos of the modified rotor:
>
> http://www.cybertheque.org/homebrew/rcvr/images/antennas/rotor/
>
> This rotor is common to a number of makes and models; the controller
> that came with it was for the Cornell-Dubilier AR22R, an interrupter
> based spring and escapement controller version.
>
> The modifications permit continuous rotation and rely on the
> controller to manage limits.
>
> Regards,
>
> Michael
> msg _at_ cybertheque _dot_ org 

msg wrote:

<snip>
> http://www.cybertheque.org/homebrew/rcvr/images/antennas/pot.jpg
> Resistance = 1K
<snip>
> Does anyone recognize this pot technology? Any suppliers
> nowadays?

Thanks to all for replies so far.

Regards,

Michael
msg _at_ cybertheque _dot_ org

Gary Tait wrote:

> msg <msg@_cybertheque.org_> wrote in news:139f22h91ghhna7
> @corp.supernews.com:
> 
> 
>> I need the form factor for modifications to antenna
>>rotator assemblies 
> 
> 
> Do you mean the rotator or the controller?
> 
> For the rotator, you can maybe use a standard pot with gearing.
<snip>

I had considered gearing but the available space and the
necessary additional fabrication was more involved than
the solution I chose.

Here are photos of the modified rotor:

http://www.cybertheque.org/homebrew/rcvr/images/antennas/rotor/

This rotor is common to a number of makes and models; the controller
that came with it was for the Cornell-Dubilier AR22R, an interrupter
based spring and escapement controller version.

The modifications permit continuous rotation and rely on the
controller to manage limits.

Regards,

Michael
msg _at_ cybertheque _dot_ org

On Jul 13, 7:12 am, msg <msg@_cybertheque.org_> wrote:
> Please view these photos of a three-turn planetary drive
> pot that uses a conventional "stackpot" formfactor athttp://www.cybertheque.org/homebrew/rcvr/images/antennas/pot.jpg
> Resistance = 1K

Interesting.  I've never seen a pot like this.

So the turns ratio is determined by the shaft diameter to ball
diameter ratio?
And the wiper arm is connected to the ball carrier?
So this assumes the metal to metal, shaft to ball won't slip, but the
ball will turn in the carrier, causing the carrier to have 1/3 the
rotation of the shaft?

Sorry, this doesn't help you at all...
Alan Nishioka

msg <msg@_cybertheque.org_> wrote in news:139f22h91ghhna7
@corp.supernews.com:

>  I need the form factor for modifications to antenna
> rotator assemblies 

Do you mean the rotator or the controller?

For the rotator, you can maybe use a standard pot with gearing. I made an 
old 3 wire rotator a 5 wire with a pot an a 4 to 3 gear. One gear was fixed 
to the output shaft, the other to the pot, so that one full rotation (360 
degrees) of the rotator shaft turned the pot its full path, or therabouts 
(270 degrees). The controller just had a typical 270 degree pot and a 3/4 
scale that rotated N-E-S-W-N.

http://cgi.ebay.com/CTS-Potentiometers-137-8418-VA45R502A-Ball-Bearing_W0QQi
temZ7595963466QQihZ017QQcategoryZ58164QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

try ebay  search  "ball potentiometer"


"msg" <msg@_cybertheque.org_> wrote in message
news:139f22h91ghhna7@corp.supernews.com...
> Greetings:
>
> Please view these photos of a three-turn planetary drive
> pot that uses a conventional "stackpot" formfactor at
> http://www.cybertheque.org/homebrew/rcvr/images/antennas/pot.jpg
> Resistance = 1K
>
> It was made in 1966 by CTS; stampings: 36129 137.6637
>
> Does anyone recognize this pot technology? Any suppliers
> nowadays? I need the form factor for modifications to antenna
> rotator assemblies in a space that does not permit using
> larger multi-turn pots and using trimmer versions is not
> sufficiently robust.
>
> Regards,
>
> Michael
> msg _at_ cybertheque _dot_ org