I will be building a propeller clock soon. I need to figure out how to power the pic while the board is spinning.

Easy solutions are an on board battery or super cap. The probably with these solutions is eventually they run out of power.

I want something that can keep on running pretty much forever. Some way to get power to the board from a remote location or generate it locally.

I saw one idea when they somehow threaded wires of the center of the shaft of the motor. First not sure how you would get a hollow shaft in a motor without drilling it yourself. And one end is still stationary and the other end moving.

Another though use a super cap but charge it though brushes and contacts on each spin. Seem making something like that to work reliably could be difficult.

I tried an old floppy motor once as a generator. Didn't generate much in the way of power.

Would a peizoelectric crystal work, perhaps charging a subercap?

 

Maybe something like this?

 

There are industrial devices out there for this sort of application. The one that comes to mind is a mercury-filled rotary contactor. Perhaps you could draw inspiration from it?

http://www.mercotac.com/html/products.html

 

Given that slip rings are used on motors for long periods of time, I would thing that would work pretty well for your application.

Another thought would be to mount a little motor/generator on the propeller shaft. After all, does it really matter if the shaft of the generator turns in fixed generator housing or a generator housing turns around a fixed shaft?

 

You can easily build a rotary transformer from pot-core halves face to face with a small air gap.
This is the true last-forever solution.

The Mercotac slip rings work well, but don't last forever, and are rather expensive.

 

I know an engineer who made a magnetic coupler for this purpose -as I recall it involved two halvs of a pot core. The primary was in one half and the secondary was in the other half.


There was a substantial air gap between them so there was no friction between the two. That's all I remember about it.

 

You could use the same technique used for wireless charging of cell phones, as described here.

Two wire coils a couple of inches in diameter mounted concentric with the shaft, the transmitting coil mounted to the baseplate and the receiving coil mounted on your propellor disc, the two coils separated by about 1/4".

Forget anything piezoelectric; not powerful enough.

 

+1 for the rotary transformer.

 

My best guess is slip rings. I have seen some tiny sets used on brushless synchro transmitters, like a miniature version of what you would find on an automotive alternator. They could be made from some copper tubing with an insulating material. The brushes could be just some light gauge spring loaded wire.

Ron

 

This is with home made slip rings
Worked really well.

 

It sounds like you want to put the PIC and LED drivers out on the propeller. Why? Also, what about the set mechanism (buttons, etc.)? Consider putting the bare minimum out on the blade. Parallel drive to 5x7 dot characters would need 8 contacts, but serial drive to shift registers would need only three.

ak

 

It sounds like you want to put the PIC and LED drivers out on the propeller. Why? Also, what about the set mechanism (buttons, etc.)? Consider putting the bare minimum out on the blade. Parallel drive to 5x7 dot characters would need 8 contacts, but serial drive to shift registers would need only three.

ak

It's a propeller clock, he only needs a 5 x 1 display.

 

It sounds like you want to put the PIC and LED drivers out on the propeller. Why? Also, what about the set mechanism (buttons, etc.)? Consider putting the bare minimum out on the blade. Parallel drive to 5x7 dot characters would need 8 contacts, but serial drive to shift registers would need only three.

ak

You will find almost ALL well designed spinning displays put ALL the electronics in the spun section.
Imagine the contact bounce issues you would have sending a digital clock signal through a rotating contact!

The rotating joint is the weak link.

 

I want something that can keep on running pretty much forever.

I thought perpetual motion/over unity was an disallowed subject here?

 

It's a propeller clock, he only needs a 5 x 1 display.

I know. I used the term 5x7 to reference a well known raster character set. But I think a 5-high display is pretty coarse, kinda the bare minimum for legibility. I have an old wand clock, one of the first, and it has a 7-high display. Fine for numbers, passable for text. 9-high would be better.

ak

 

You will find almost ALL well designed spinning displays put ALL the electronics in the spun section..

How do you get the setting buttons through? Modulating the rotary transformer primary?

ak

 

How do you get the setting buttons through? Modulating the rotary transformer primary?

ak

IR is a nice solution.

The receiver can be located at the center.

 

I think a third option used is a coil in the spinning thing and a magnet on the base, making a sort of a generator, probably quite inefficient.

 

I thought perpetual motion/over unity was an disallowed subject here?

How do you get the setting buttons through? Modulating the rotary transformer primary?

ak

A 4-bit dip switch an a set button. Just cycle through 10h, 01h, 10m, 01m. The 1x5 LED array can be used in setting mode to insure the correct digit is getting set.

 

I thought perpetual motion/over unity was an disallowed subject here?

The key word "pretty much".