Tobe's sticks...

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Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Tobe's sticks...

Post by Pchristy »

I'm sure I recall Tobe uploading the files for his 3D printed stick units, but I can't find the post again!

I have a couple of transmitters with Dunham stick units. These use cermet (or plastic film) pot tracks - like old servos used, once upon a time. These seem to be no longer available, and some of mine are showing signs of age. I have a basic 3D printer, and was wondering about printing an adapter to use Tobe's stick pots with Dunham sticks. IIRC, Tobe used pots with less than the standard 270 degree throw, which should improve resolution and linearity.

It ought to be relatively straightforward, but I'm new to 3D printing and need a sample to study!

Can someone point me to the files? I know they are here somewhere...

--
Pete
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Shaun
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Location: West Yorkshire

Re: Tobe's sticks...

Post by Shaun »

Pete,

I may have some new/old stock cermet pot tracks. If I can find them how many would you need?
Tobe's stick's are excellent however if you go that route.

Cheers,

Shaun.
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Wayne_H
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Re: Tobe's sticks...

Post by Wayne_H »

Pete,

Single axis stick details & files here
viewtopic.php?f=42&t=957&start=10
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Tobe's sticks...

Post by Pchristy »

Hi Shaun,

Thanks for the offer! I do have a few cermets, but I suspect they are Log, not Lin - at least, they ain't very linear! There are probably better - more modern - options if I can make them fit.

Wayne: Yes, that's what I was looking for! Searched high and low for it and couldn't find it - many thanks!

The last versions of the Dunham sticks did have options for using proper pots, instead of just cermet tracks, but I never got hold of any of those. It should be possible to print something up that will do the job, but I need to see how Tobe has done it, and then try and adapt that to my existing units!

Might take a while, but worth doing, I think! :)

Thanks, all!

--
Pete
Tobe
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Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

Re: Tobe's sticks...

Post by Tobe »

Pete, hope to find you and all your beloved well.
Let me know if I can be of any assistance, if, I can resize the shaft of my knob to fit most diameters. Just PM me
If, also, I would be happy to supply you with a full "Single stick", the knob is on the large side but not larger than the old Kraft knob.
The pot I'm using are close to the "cermets" size
Attachments
20210508_173939.jpg
20210508_173538.jpg
20210508_173442.jpg
20210508_173244.jpg
Cheers,

Tobe
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Tobe's sticks...

Post by Pchristy »

Thanks for the offer, Tobe! I'll try and get some pix of the Dunhams stick units (I have a couple of unused ones) so you can see what I'm trying to achieve.

I believe a factory fire resulted in the non-availability of cermet pots, but for a while, I did have a source of plastic film equivalents. Can't even find those now, and as my originals are over 40 years old, wear and tear is starting to show!

Those pots you have are just what I'm looking for! Are they 270 degrees or less? Around 100-120 degrees is ideal for stick units, but not easy to find! Also, although 4.7K is the usual value, 47K is better, if using 5044 or Arduino encoders. Since all the pots are drawing current all the time - not switched, as in the old "half-shot" encoders - 4.7K increases the current draw for no good reason. Only a small amount, compared to the RF stages, but can become significant with low power 5V regulators used in many encoders!

Yes, we all seem to have survived (so far!) the dreaded bug! My wife, daughter and I have all had both our "shots" now. My son and his wife should be getting theirs soon. I hope you and yours - and, indeed, all "retrobates" - are keeping well!

Regards,

--
Pete
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Tobe's sticks...

Post by Pchristy »

OK, here's some pix of a (rather grubby!) Dunham stick unit from my spares box!

Here it is with the cermet pot in place:

ImageDSC00538 by Peter Christy, on Flickr

The two screws tighten a clamping ring, which sandwiches the pot track carrier against the trim adjuster. The "centre" of the pot is adjusted by the lever on the carrier - just about visible at about 7 o'clock.

Here is the other axis, with the pot track removed, showing the wiper:

ImageDSC00541 by Peter Christy, on Flickr

(Sorry, its a bit blurry!)

The wiper is attached to a nylon "carrier", which pushes into the stick yoke:

ImageDSC00542 by Peter Christy, on Flickr

The bit that sticks into the yoke seems to be 0.1" diameter (2.45mm). Ideally, I need a pot with a similar diameter shaft - I might be able to open it up to 3mm. I could probably drill the yoke all the way through, allowing adjustment to be made while the unit is being assembled, rather than the lever affair as at present. Either should be achievable though. (Analogue encoders, like the ubiquitous 5044 need the pot to be accurately set to 50% of the total travel at neutral, for reversing purposes. Arduino - and similar - encoders can be calibrated electro-magically! :D )

The innards of the stick unit look like this:

ImageDSC00544 by Peter Christy, on Flickr

For something so simple and small, they work extremely well! Remember, Bob Dunham was the man behind "Orbit" radio gear. Back in the 50s and 60s it was the "Rolls-Royce" of model RC equipment!

I know he did produce some units which were modified to take more conventional pots when the supply of cermets dried up, but I haven't got any! It ought to be possible to 3D print a suitable carrier for a small servo type pot, such as the ones Tobe has used.

Do you have the dimensions for those pots, Tobe?

--
Pete
Tobe
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Location: Varberg or Stockholm, Sweden

Re: Tobe's sticks...

Post by Tobe »

....I might have a few cermets pots or at least "ceramic" parts in my spare Kraft box and probably some wiper also! If, how many would you need?
The pots i use in my sticks have a shaft of 3.5 mm.
Attachments
20210509_125024.jpg
20210509_124736.jpg
20210509_124727.jpg
Cheers,

Tobe
Pchristy
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Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Tobe's sticks...

Post by Pchristy »

PM sent!

Cheers, Tobe!

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Pete
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Wayne_H
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Re: Tobe's sticks...

Post by Wayne_H »

There was also a later version of the wiper with bi-furcated "fingers" so that there were in fact 4 wiper "fingers" in contact with the pot's resistive surface - I don't recall if they were sold under Cermet, D&R or Dunham brand, but I purchased all of mine through ACE R/C. Regardless, they fitted the standard wiper carrier and worked well on cermet pots :)
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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