Analog abstracts Z plane rotation?

[glorocks]

Thanks, Steve. Most helpful. Now I gotta remember where I put the pots- I have two laying around here somewhere.
How 'Ya been?
Jay

[mixedgas]

Jay

You really want the expensive to implement:

x' = (x * cos theta) + (-y *sin theta)
y' = (y * cos theta) + (x *sin theta)


On the Sin/Cos tie 0 and 180 to plus and minus five, ground 90 and 270. That will give you a unit rotation vector for the array on the wipers.
Setting the unused input offsets to avoid nonlinearity is a witch. Four Muls, two sums and an invert, minimum. Plus unity buffers on all the Gozintas and Gozoutas.

If you tie 0 to a sine wave, and tie 180 to an inverted version of the same sine wave, then ground 90 and 270, it gives you a spinning flat scan on the wipers.

Watch for glitches on the rotation where it crosses the gap in the windings.

I'm OK.
Steve

[laserist]

I was replacing a joystick. The single gang sine cosine pot put out a sine cosine signal that could be used as an offset that could be move an a circle or the rotation input to the image rotation circuits.

So I guess my next question is: Did you use the sine/cosine pot as a voltage source for a multiplier array (or something along those lines) or was the image signal passed through the pot?
Are you willing to provide a little more information?

[Photonbeam]

I have a few of these Bourns potentiometers in my parts stash. I believe they are sin/cos pots but can find no info on the internet or on the Bourns site showing obsolete parts. I had experimented with analog rotators planning to use these pots for manual rotation but ended up using a design that had sin/cos table on eprom. Can anyone ID this part? It has two wipers, four taps and no stops (continuous rotation). Also, it appears that multiple sections could be ganged together.

[glorocks]

You may have hit the jackpot on these pots. I'll check the numbers.
Meanwhile, I have for your viewing pleasure, the 'analog of the analog' that was originally incorporated in the Lasermedia "Imagen". This circuit was given to me by Gary T, who was the designer of the LM DAC 16.
As Steve has said previously, the inputs need variable gain inputs to keep the gain structure in the stage consistent with whatever voltage standard you are using ( I keep the voltage at +- 10 volts throughout), and it would be prudent to use voltage followers at the outputs. Better to blow a 59 cent opamp as opposed to a 6 dollar multiplier.

/Users/jamespainter/Desktop/Z rotation.pdf

I will be posting another option in the next day or two.
Cheers

[luxilid]

The link to the circuit does not work.

[glorocks]

Sorry about that- I'll try again.

[LaserCo]

I might have found a circuit using that there pot that photonbeam has posted.
I have been on and on-and-off venture towards finding info on this 3d rotation subject and my most recent google image search using 'Z rotation circuit' is giving me some new pages to explore. I found this an hour ago and want to share it



I doubt that photonbeam has enough of these to sell to all interested, yet, what do you think of what is said about making an equivalent component on the bottom of the image?

the guy (and I?) that kindly shares this image from a 1962 book has this to say about that:

"I do understand that I am technically in violation of copyright by providing these 4 pages in total for viewing and distribution, but the text is a rather old one (1962) and has been out print for several decades as it concerns a wholly obsolete technology. I'm quite sure nobody will mind. "

he has a bit of similar stuff at
http://www.glensstuff.com/3dpu/3dpu.htm

[glorocks]

You may have hit the mother load! I haven't had a chance to look yet, but it looks really good.
Now about that Z axis schematic I posted- There were a few problems. The math was correct, and has been double checked.
1- The multipliers need a stage with gain of 10 at the outputs. X x Y over 10.
2- The unused Z inputs (2) need to be grounded.
3- It would be advisable to put amp stages with adjustable gain at all four inputs. Remember the gain structure of your project. Building one of these consoles is no different than building an audio board.
J
I will be posting a corrected circuit in a day or two.

[glorocks]

Laserco's links are extremely interesting. I need to spend more time on the original article- Thanks, Mitch.
The only 3-D true analog processor I am aware of was developed by ECC in San Diego back in the '80's. It used 16 4 quadrant multipliers. A few boards were built, one of which is floating around, but the guy who has it staunchly refuses to share.
I have been in touch with the former owner of the company, and he has agreed to give me a schematic, but it is not high on his priority list, as it and the remaining boards are buried in a storage container. Let's all keep our fingers crossed.
In his words, "we knew it was special, but we couldn't really figure out what the f**k to do with it!" To be used effectively, it would have required some sort of digital controller. "You only have two hands" was his last comment.