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.

Within 0.1" there are bascially two spots on the rotation that I would want it hitting each time.And if there is an inacuraccy I would imaging that it would just get larger and larger over time.

 

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?

amazing, I am unsure of the material now, I am basically asking these questions to inform what materials I will need to purchase for this build. I would imagine either perspex or glass. Probably lazer cut perspex

 

If laser cut is an option, make the big circle a gear, the two idler rollers with gear teeth, and gear drive from the top. Laser cutting gear teeth should be no big problem.

 

Within 0.1" there are bascially two spots on the rotation that I would want it hitting each time.And if there is an inacuraccy I would imaging that it would just get larger and larger over time.

If you add the Hall Effect sensor, it would self-correct. Basically, the sensors are a target for each end of the rotation. It might be the simplest approach.

Or, for extreme accuracy, since you may laser cut the disk, maybe you can cut gear teeth around the edge. Then with a matching gear on a stepper motor, you will have accuracy at most to the distance between neighboring teeth. I and others have mentioned this before.

With a low RPM drive, I’d be concerned about the wear and aging of the rubber and dust collection.

 

If laser cut is an option, make the big circle a gear, the two idler rollers with gear teeth, and gear drive from the top. Laser cutting gear teeth should be no big problem.

I’d omit the gears on some of the idlers. With no geared idlers, the disk would bump up and down as individual teeth pass the idler. With all idlers geared, alignment is critical; Mis-aligned idlers will bind the disk. I’d used a geared stepper motor at the top or bottom, a geared idler gear 180° opposite and two plain idlers on either side.

 

Motor: one of these http://www.hurst-motors.com/lyg35geared.html

AC Synchonous always run at the same speed.

 

If you add the Hall Effect sensor, it would self-correct. Basically, the sensors are a target for each end of the rotation. It might be the simplest approach.

Or, for extreme accuracy, since you may laser cut the disk, maybe you can cut gear teeth around the edge. Then with a matching gear on a stepper motor, you will have accuracy at most to the distance between neighboring teeth. I and others have mentioned this before.

With a low RPM drive, I’d be concerned about the wear and aging of the rubber and dust collection.

Ahh so with the Hall sensor the Audino would be waiting for that signal to stop the rotation each way. So it would'nt be turning to a coordinate it would be turning until it reached the Hall sensor ?

 

Ahh so with the Hall sensor the Audino would be waiting for that signal to stop the rotation each way. So it would'nt be turning to a coordinate it would be turning until it reached the Hall sensor ?

Exactly!

 

Exactly!

Sorry I had to give Hall sensor a google there to fully understand what they are. yes That would work really well! thank you , With this method a rubber motor on a rubber edge of the disk should work very well !

 

You could also use a small piece of reflective tape on the edge of the disk, at each extreme of the disk travel and detect it with a photo or IR sensor.

 

Just to follow up on my mathematical example: I have a motor from an old CD player. It's shaft is 0.079". So at 1800 RPM a disk would turn at 9.48 RPM. IF you add a rubber barrel to the motor shaft equaling 0.2" then you'd get the 24 RPM mentioned earlier. Again, assuming the CD motor spins at 1800 RPM. They're small and not very powerful, so that may also slow down the precession of the disk.

You could also use a small piece of reflective tape on the edge of the disk, at each extreme of the disk travel and detect it with a photo or IR sensor.

That too would work. But the hall effect sensor would be easier to incorporate. They have three leads, power, ground and signal. An Arduino can easily read that signal whereas a photo sensor would need a light source. And the sensor would (like the hall) need a power source. But with the hall, you don't get interference from ambient light.

 

Motor: one of these http://www.hurst-motors.com/lyg35geared.html

AC Synchonous always run at the same speed.

But are they reversible? Never saw one that was, but they may have them.

 

But are they reversible? Never saw one that was, but they may have them.

Yes. There's 2 coils and 4 wires on a typical motor. A common is formed with 2 coil ends and a capacitor wired to the ends of the coils. Power is applied to common and one end of the capacitor. Which end determines direction.

Many things don;t like going backwards, so it's probably safer for consumers.

 

It's easy to do a variable frequency drive for these motors. I designed one for a telescope.

 

It's easy to do a variable frequency drive for these motors. I designed one for a telescope.

Hola KISS; could you elaborate briefly?
Thanks

 

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

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

Why would an arduino be needed or used to control a motor? There is no need and no benefit to that application. A vertical polarized filter resting on two rollers, one driven. Given that no details of the size are provided the whole thing could be vary small, or larger. And the drive can be a very simple small DC motor since the drive roller diameter can be small while the driven disc is much larger. Internet videos seldom are just what they seem. But this device may be very simple and cheap, and not at all complex.

 

Hola KISS; could you elaborate briefly?

back in the 1980's I had a tube Blaupunkt radio in my car and the vibrator died. So, I put two 2n3055 transistors on a heat sink and a couple of small transistors that also inverted the output of a 555 timer. So, a 50% duty cycle transistors to ground at 200 Hz. Big, but worked. You can now buy solid state vibrators.

Some researcher at work wanted to automagically move his telescope an he may have wanted it battery powered too. I gave him new component values and my schematic for 60 Hz +- (some number) and picked a Center-tapped transformer with the center tap at ground and the output devices on the ends so that you got 120 VAC on the other side. The transformer was used backwards.

It's basically a variable frequency low-power 12V to 120 V square wave inverter.

I never saw the device, I think, because he left but came back to visit periodically because of a partnership of sorts.

 

Why would an arduino be needed or used to control a motor? There is no need and no benefit to that application. A vertical polarized filter resting on two rollers, one driven. Given that no details of the size are provided the whole thing could be vary small, or larger. And the drive can be a very simple small DC motor since the drive roller diameter can be small while the driven disc is much larger. Internet videos seldom are just what they seem. But this device may be very simple and cheap, and not at all complex.

Except that the TS is not building that device. His application may or may not require a microprocessor.

That device continuously rotates in one direction. His device is bidirectional. And he requires the end stops to be accurate within 0.1” and not drift over time.

Several solutions have been presented. And others may be possible. But the requirements are more complex than the video.

 

That device continuously rotates in one direction. His device is bidirectional. And he requires the end stops to be accurate within 0.1” and not drift over time.

The synchonous motor should do that. I built two "similar" systems using synchonous motors. One was a filter wheel with 4 positions. The other was an "open loop" film advancer. the later is harder to describe, but it calculated the amount of turns it needed based on a calculated take up diameter.

The filter wheel had notches along the edge for 4-stops. A roller microswitch dropped into the notch to stop the motor. It was 2" square filters and about 8" in diameter. No reverse.

The computer knew if the wheel was moving or stopped.

Two hall effect switches with Honeywell stud magnets could sense the position. 00 01 10 11.

Both were low RPM devices.

With a PM DC motor you can utilize dynamic braking where the motor gets shorted when it's time to stop.

The other stuff could be steppers with "S-curve" acceleration and de-acceleration. I started to write a LabView driver for a stepper controller to control a monochmeter, but the project got pulled. Industry caught up with our requirements and neither MacOS or Windows was real time. The object was to replace a PDP-11. I was going to drive the steppers directly.

 

The synchonous motor should do that. I built two "similar" systems using synchonous motors. One was a filter wheel with 4 positions. The other was an "open loop" film advancer. the later is harder to describe, but it calculated the amount of turns it needed based on a calculated take up diameter.

The filter wheel had notches along the edge for 4-stops. A roller microswitch dropped into the notch to stop the motor. It was 2" square filters and about 8" in diameter. No reverse.

The computer knew if the wheel was moving or stopped.

Two hall effect switches with Honeywell stud magnets could sense the position. 00 01 10 11.

Both were low RPM devices.

With a PM DC motor you can utilize dynamic braking where the motor gets shorted when it's time to stop.

The other stuff could be steppers with "S-curve" acceleration and de-acceleration. I started to write a LabView driver for a stepper controller to control a monochmeter, but the project got pulled. Industry caught up with our requirements and neither MacOS or Windows was real time. The object was to replace a PDP-11. I was going to drive the steppers directly.

Dynamic braking works very well with PM synchronous motors. And it works somewhat on induction motors as well.