# Objects going in opposite direction on a motor's shaft

Hi folks, I'm working a replica of a kinetic sculpture by Jeff Libereman. For the most part I'm doing okay, but I wanted to modify the design a bit: rather than making the mechanism spin with the use of pulleys, with everything exposed, I wanted to hide the mechanism behind the two plates such that they're the only thing visible to an observer. In my head, it might look like this:

But this presents a problem: the plates need to sit on a single shaft, but they need to go in opposite directions (and at the same speed) for the effect to occur. Placing them on a motor's shaft is easy, but how do I get one of them to spin in the opposite direction?

I'm fairly new to this whole thing so visuals will be appreciated if the explanation isn't trivial, thanks.

I suspect that's why they used pulleys and a line in the first place: the twist is what makes them counter-rotate.

You would need to fashion some kind of gearbox, and attach one disk to the input shaft and the other on the output. But then they won't be lined up.

That sort of thing can be fashioned with Meccano.

Concentric contra-rotation is not unusual - especially for both airplane and boat propellers.

The boat propellers use a rather simple system. Think of the drive coming down the shaft of an outboard motor. The propeller shafts are at right angles to the drive shaft. The drive shaft has a bevel gear and that drives a bevel gear on each of the shafts. Because the output shafts are driven from the opposite sides of the power shaft they rotate in opposite directions.

A system with all the shafts in line is likely to be considerably more complex.

...R

The two plates do not need to counter-rotate in order to see the effect. Only one has to move.

jremington:
The two plates do not need to counter-rotate in order to see the effect. Only one has to move.

Every demonstration of this piece has them spinning in opposite directions.

Robin2:
Concentric contra-rotation is not unusual - especially for both airplane and boat propellers.

The boat propellers use a rather simple system. Think of the drive coming down the shaft of an outboard motor. The propeller shafts are at right angles to the drive shaft. The drive shaft has a bevel gear and that drives a bevel gear on each of the shafts. Because the output shafts are driven from the opposite sides of the power shaft they rotate in opposite directions.

A system with all the shafts in line is likely to be considerably more complex.

...R

Can you find an image illustrating the concept? I'm not sure I get it.

I found this video of a similar sculpture that uses a spring rather than a motor, but look at how minimal the mechanism is. How is this fundamentally different from what I'm after?

idank:
Can you find an image illustrating the concept? I'm not sure I get it.

This is the second link when I searched for "contra rotating gearbox" with Duck Duck Go

No doubt Google is just as good.

...R

Every demonstration of this piece has them spinning in opposite directions.

As you can easily demonstrate for yourself, counterrotation is not required to produce the Moire' effect. But feel free to make the project as challenging as you wish.

Robin2:
This is the second link when I searched for "contra rotating gearbox" with Duck Duck Go

No doubt Google is just as good.

...R

I tried altavista, nothing turned up. Thanks for the link though!

Suppose the disks turn free on the shaft and are powered by air blown over vanes on the back?

Or possibly put magnets on the back of one disk (the back one) turning freely on the shaft and drive it with electromagnets, build your own motor. Turn the other disk with the shaft.

idank:
Every demonstration of this piece has them spinning in opposite directions.

It's all relative, innit?

If the front one moves and the back one is either stationary or moves the opposite way, the front one still moves relative to the back one.

In fact, you don't even need a back plate: you could paint that one on the wall

Look at how a clock or watch works: the seconds shaft is inside the hollow minutes shaft which is inside the hollow hours shaft.

I would start working on this by buying a cheap clock mechanism and pulling it apart.

You could of course use any convenient piece of pipe for the hollow shaft. In the USA, Ace Hardware has a great selection of small brass tubes and you also see the same selection in hobby shops.

The clock's a good idea. Although they all go in the same direction, h/m/s at different speeds would still give the same relative motion and perhaps a 3-way interaction would make an interesting effect.

Yes, you would have to remove or modify the clock gears.