Rotating ring mechanism help !

Thread Starter

rory_malone

Joined Mar 31, 2020
16
Hello guys !
I have a question that I think belongs here but not 100% sure.

I am trying to recreate the device in this video
Post image
It is basically just a rotating ring with a polarizing filter mounted in the centre. I would presume that an Arduino and motors is being used here but I have no idea how it was executed, or even what kind of motor one would need to rotate the ring.
If anyone here would be able to shed some light on how they think this is made on this I would really appreciate it !
Cheers,
Rory
 

atferrari

Joined Jan 6, 2004
3,930
Hard to know if it is a simple visual effect (most probably) or the final result of a scientific process.

Not very appealing, let mi tell you.
 

KeithWalker

Joined Jul 10, 2017
822
It looks as though the disk may be resting on two rollers at the bottom and could be driven by a rubber roller pressing against the top edge. I have seen a similar clock mechanism that had two rotating transparent disks, one for hours and one for minutes.
Regards,
Keith
 

shortbus

Joined Sep 30, 2009
7,623
If you look closely at the last picture you can see a roller on each side of the disc, coming out of the frame, near the bottom of the frame. The rollers look like they might be what is used on shower doors or in inexpensive drawer slides.

The motor is probably at the top center of the frame, with another roller fixed to it's shaft. As that roller turns, it can then turn the disc, because the two bottom rollers support the disc and are free to turn.

A link to the type of roller at the bottom of the picture, to illustrate what I mean.
https://www.homedepot.com/p/Prime-Line-5-8-in-Flat-Shower-Door-Roller-M-6065/202636488

Keith types faster :)
 

djsfantasi

Joined Apr 11, 2010
6,367
At what rate is the polarized filter rotating? Does it rotate continuously or start and stop? Does it reverse at any time? And does the background rotate at all?

Depending on your answers, something like an Arduino is not necessary. A low geared motor (such as a Hankscraft) may be all that is needed. Of course, a Hankscraft may be too large.

Or maybe you can find a small geared motor, at someplace like All Electronics.

A pancake stepper motor might work and would be smaller. A circuit to rotate the motor would be needed (a clock, signal mapping and coil drivers)
 

Thread Starter

rory_malone

Joined Mar 31, 2020
16
At what rate is the polarized filter rotating? Does it rotate continuously or start and stop? Does it reverse at any time? And does the background rotate at all?

Depending on your answers, something like an Arduino is not necessary. A low geared motor (such as a Hankscraft) may be all that is needed. Of course, a Hankscraft may be too large.

Or maybe you can find a small geared motor, at someplace like All Electronics.

A pancake stepper motor might work and would be smaller. A circuit to rotate the motor would be needed (a clock, signal mapping and coil drivers)

I would like the filter to rotate between two set points. So for that I would need to program it I guess. I would also like for the mechanism to be reasonably silent. Would you know of any motors that can be hooked up to an arduino and are silent ? From using servos I have found them to be quite noisy.

Thanks !
 
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Thread Starter

rory_malone

Joined Mar 31, 2020
16
If you look closely at the last picture you can see a roller on each side of the disc, coming out of the frame, near the bottom of the frame. The rollers look like they might be what is used on shower doors or in inexpensive drawer slides.

The motor is probably at the top center of the frame, with another roller fixed to it's shaft. As that roller turns, it can then turn the disc, because the two bottom rollers support the disc and are free to turn.

A link to the type of roller at the bottom of the picture, to illustrate what I mean.
https://www.homedepot.com/p/Prime-Line-5-8-in-Flat-Shower-Door-Roller-M-6065/202636488

Keith types faster :)
Ah yes I see now ! Could you explain the top motor mechanism again please ? In my deign I would like accurate control of the front filter in terms of rotation. I was thinking that if the motor and the disk had toothing around them like a toothed gear, and then you could put a toothed belt around both of them to get accurate control. but this would be very difficult to get the exact right sized belt and to tooth the entire front ring. Would you have any other idea on how to do this ?

Thanks !
 

djsfantasi

Joined Apr 11, 2010
6,367
I don’t know if the noise level is acceptable, but for accurate control I’d use a stepper motor. The Arduino has a library to control a stepper, so you could easily accomplish what you want.
 

shortbus

Joined Sep 30, 2009
7,623
I would use a small stepper motor, like the ones used in a ink jet printer(they can usually be found for free or very cheap.) Such motors usually have a small gear paced on the shaft, by taking short piece of rubber tubing that fits tightly on the gear, you then have a rubber roller that can move the disc. The difference in diameter between the circumference of the disc to the roller will make the disc turn slowly. Depending on the speed you want or need it could possibly be done using just a DC brushed motor, still putting a rubber tube on the motor shaft. Don't know how big the disc actually is. The ratio can be found by comparing the two diameters and the use that to find the speed.

I don't quite understand why you would need it to have a forward and reverse though? Don't most polarizing filters work if you just turn them in either direction? You would still get the same effect by just rotating it continuously in one direction - Polarized - Unpolarized - Polarized - Unpolarized this would continue until it was shut off. And it would make it seem to fade in and out as it rotated. Or at least that's my take on it.

Also it may be better to get those shower door rollers that have a groove in them. That would also keep the disc from leaning in the frame. Like these -

1585750673823.png
 

Thread Starter

rory_malone

Joined Mar 31, 2020
16
I would use a small stepper motor, like the ones used in a ink jet printer(they can usually be found for free or very cheap.) Such motors usually have a small gear paced on the shaft, by taking short piece of rubber tubing that fits tightly on the gear, you then have a rubber roller that can move the disc. The difference in diameter between the circumference of the disc to the roller will make the disc turn slowly. Depending on the speed you want or need it could possibly be done using just a DC brushed motor, still putting a rubber tube on the motor shaft. Don't know how big the disc actually is. The ratio can be found by comparing the two diameters and the use that to find the speed.

I don't quite understand why you would need it to have a forward and reverse though? Don't most polarizing filters work if you just turn them in either direction? You would still get the same effect by just rotating it continuously in one direction - Polarized - Unpolarized - Polarized - Unpolarized this would continue until it was shut off. And it would make it seem to fade in and out as it rotated. Or at least that's my take on it.

Also it may be better to get those shower door rollers that have a groove in them. That would also keep the disc from leaning in the frame. Like these -

View attachment 203137
Yes it seems that a stepper motor is the right way forward. Interesting yeah that rubber method would work well, but do you think it would have enough traction on the larger disc to be able to accuratly rotate it backwards and forwards ? Would it just be a matter of having them really pushed against each other ?

And yes I have a piece of plastic that actually changes 3 times depending on the orientation of the polarizer. With the polarizer at 90° the plastic is a blue colour then when the polarizer is rotated to 160° the plastic becomes clear and then when the polarizer is at 180° the plastic turns yellow, then back to clear and blue as the polarizer rotates the full 360°. For the effect I am after I just want the plastic to change from blue to clear and not go through the yellow phase. So to achieve this I would need the motor going back and fourth.

Yes those would work well to stop the glass from wobbling !
Thank you
 

Tonyr1084

Joined Sep 24, 2015
4,394
Old record player motors consisted of a step tapered shaft and a pilot wheel. All the pilot wheel did was make a direct connection between the motor shaft and the record player platen. (the spinny part). When you wanted to play a 78 (remember those anyone?) you would select the 78 on the selector lever and it would position the pilot wheel against the largest diameter of the motor shaft. You would then select 45 and the pilot wheel would adjust its location to ride against the mid-sized portion of the motor shaft (slower than 78). For LP's (Long Playing) (records) you would set it to 33 and the record would spin at its slowest speed setting.

Using just the motor shaft with a rubber coating riding against the plate glass with the polarized filter would produce about the same speed as in the video. You can use an old motor out of a CD player or an old tape deck motor. I don't know how they polarized each and every little dot - that part you'll have to figure out for yourself. But if I were going to build this - that's the approach I'd take.

But I must concur with @atferrari - I didn't find the display all that impressive either.
 

Tonyr1084

Joined Sep 24, 2015
4,394
How fast would a 15 inch glass disk spin if using a motor shaft as a drive? Let's make some assumptions and run some numbers.

Suppose the motor shaft diameter is 0.200 inches (you can convert to metric if you like but I'm a Yankee). And suppose that motor spins at 1800 RPM. Multiply the diameter by the value of Pi (3.14). Then multiply by the RPM. You will have the linear distance of travel:

0.200 x 3.14 = 0.628"
0.628 x 1800 = 1,130.4" of linear travel. Remember that figure!

a 15 inch disk has (15 x 3.14 =) 47.1 inches in circumference.

Divide 1,130.4 by 47.1 and you get 24. That's 24 rotations in one minute, or 24 RPM. Didn't measure the rate of spin in the video but going from memory watching my LP's spin at 33 RPM, 24 is a little slower and very close to what the video showed. And these numbers were just "supposed numbers", the motor RPM the motor shaft diameter and the glass disk diameter. But using those fictitious numbers I accidentally came up with what appeared to approximate the video. Whether those numbers are close to reality or not - I'd have to start measuring things; and this has been an exercise in "Suppose You Have".
 
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Thread Starter

rory_malone

Joined Mar 31, 2020
16
How fast would a 15 inch glass disk spin if using a motor shaft as a drive? Let's make some assumptions and run some numbers.

Suppose the motor shaft diameter is 0.200 inches (you can convert to metric if you like but I'm a Yankee). And suppose that motor spins at 1800 RPM. Multiply the diameter by the value of Pi (3.14). Then multiply by the RPM. You will have the linear distance of travel:

0.200 x 3.14 = 0.628"
0.628 x 1800 = 1,130.4" of linear travel. Remember that figure!

a 15 inch disk has (15 x 3.14 =) 47.1 inches in circumference.

Divide 1,130.4 by 47.1 and you get 24. That's 24 rotations in one minute, or 24 RPM. Didn't measure the rate of spin in the video but going from memory watching my LP's spin at 33 RPM, 24 is a little slower and very close to what the video showed. And these numbers were just "supposed numbers", the motor RPM the motor shaft diameter and the glass disk diameter. But using those fictitious numbers I accidentally came up with what appeared to approximate the video. Whether those numbers are close to reality or not - I'd have to start measuring things; and this has been an exercise in "Suppose You Have".
Wow I love the calculations ! And yes the pattern the person in the video chose is very boring, I intend to have a more engaging design in mine !

And I would'nt really be looking for speed, I do not mind if the glass plate spins slowly what I am really looking for is smoothness of movement and accurate control of movement. Do you think that the motor shaft with a rubber coating method would allow me to be able to accuratly have the wheel rotating backwards and forwards to specific positions every time ?
 

Thread Starter

rory_malone

Joined Mar 31, 2020
16
After thinking more on this I 'd probaly use 4 of the grooved rollers, 90* apart. With the motor in between two of them that would greatly limit the wobble.
Ah yes on each of the "corners" of the disc.

And just a question on your previous suggestion ,do you think the rubber tubing method you mentioned would have enough traction on the larger disc to be able to accuratly rotate it backwards and forwards to specific positions ? Would it just be a matter of having them really pushed against each other ?
 

djsfantasi

Joined Apr 11, 2010
6,367
Wow I love the calculations ! And yes the pattern the person in the video chose is very boring, I intend to have a more engaging design in mine !

And I would'nt really be looking for speed, I do not mind if the glass plate spins slowly what I am really looking for is smoothness of movement and accurate control of movement. Do you think that the motor shaft with a rubber coating method would allow me to be able to accuratly have the wheel rotating backwards and forwards to specific positions every time ?
I think the problem here is “specific positions”. Due to slip and coasting, the accuracy may not meet your needs.

You can minimize the coasting effect by designing a circuit that includes a brake. Like using an H-bridge with a braking option.

Instead of going on about slip, let’s define the degree of accuracy you need. Is it within 0.1”? Or 0.001”?

Another approach is to mount a magnet on the back of the disk with two Hall effect sensors in the frame. The signals from the sensors would define both ends of travel. If you can program a MCP (Arduino), I am liking this method. I’d mount the sensors a bit before the end of travel and programmatically adjust when to stop the motors. This technique would work well with the H-bridge and braking.

But it really comes down to the actual degree of accuracy you need.
 

Tonyr1084

Joined Sep 24, 2015
4,394
Do you think that the motor shaft with a rubber coating method would allow me to be able to accuratly have the wheel rotating backwards and forwards to specific positions every time ?
The record player method works well for one direction at a constant speed. The idler wheel is positioned inside in such a way that if you stop the motor dead cold the wheel would pinch and stop the record. In the video it only showed single direction and non-stop. Designing a system for a definite stop position as well as forward and reverse would likely require a geared edge of the disk and a gear on the motor. Using a stepper motor you could advance or back up to specific locations based simply on the calculated pulses per revolution of the disk. But even there could enter some error. @djsfantasi mentioned a Hall effect transistor and a magnet. That would be useful to remind the micro controller where the disk is in its rotation so that if there's error, the sensor can reset it so you get specific stopping points accurate to the number of pulses per revolution ± any small error.

To reproduce the video I'd just go with a motor with a rubber coating on the shaft. Maybe a shrink sleeve. Use friction to drive the wheel always moving always in one direction, non-stop.
 

shortbus

Joined Sep 30, 2009
7,623
And just a question on your previous suggestion ,do you think the rubber tubing method you mentioned would have enough traction on the larger disc to be able to accuratly rotate it backwards and forwards to specific positions ? Would it just be a matter of having them really pushed against each other ?
Yes it does work. Just make sure you get rubber, not vinyl tubing. Small rubber tube can be bought at an auto parts store, they call it "vacuum tubing" and it will be black in color. The vinyl tube is usually clear, you don't want that. It will take a small amount of pressure against the disc to make it work. What is the disc made of?
 
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