Electrical connections to a rotating part?

I want to place a sensor or two on a rotating wheel, but I want the electronics to process the sensors off of the wheel.

Can someone tell me how people wire up multiple electrical contacts through a bearing or to a rotating sensor? Obviously, I can't use normal wire or it would get all twisted up.

Maybe something similar to the type of jacks used in headphones and speakers? THose could give a few connections along with the ability to rotate.

Well it depends on how many connections you want, what voltage, current and how fast it'll be spinning.

I recently tried to get some mercotac rotating electrical connector samples (for mains voltage) and I was told I would have to purchase them but they could tell me the price for one. ~£120 each!.

People have made their own, occasionally using audio jacks or by thick washers etc.

It's not easy though.

Normally easier to mount a battery and the whole unit in the rotating thing!

Mowcius

...how people wire up multiple electrical contacts through a bearing or to a rotating sensor?

I would think the general answer is they don't. If you think along those lines and explain a bit more what you want to do - perhaps you can get ideas on avoiding the wires too.

E.g. if all you want to do is sense or synchronize rotation - you can put a small magnet on the rotating part and sense it passing with a stationary hall effect sensor (similar to how a car's anti-lock brakes work).

Look up wireless projects with microchips. You can always use a wireless transceiver using manchester encoding or you can just buy an Xbee.

Once saw someone build a pc board slip ring to do this, the device was really low rpm. Getting it mounted, I'll leave up to you, but the conductors were two concentric circles with stationary brush pickup. Your next problem is dealing with contact wear, contact noise and slip ring runout.

What kind of sensors are you mounting on the wheels, maybe there's an easier method of doing this.

I used some home made slip rings for a POV project I did about ten years ago.

Essentially the same as Grumpy_Mike's (for a bigger scale): http://www.homebuiltrovs.com/slipringreel.html

Essentially the same as Grumpy_Mike's (for a bigger scale): http://www.homebuiltrovs.com/slipringreel.html

That's brilliant!

I may have to steal that idea :)

Anything to so with you or justy linked?

Mowcius

I once saw something similar to Grumpy_Mike's design, but for transferring signals to/from an ROV; the tether was on a winch device, and thus the slip-rings were needed. The guy wrote (this was on a web site that I can't find anymore) that it worked well, with no noise in the video circuit.

I think if I were going to be processing signals, though, from a sensor, I would do it with wireless, and only feed power through the slip-rings; you would probably need to have a capacitor in there somewhere to store a charge for transients and noise reduction on the power-rail, and use some kind of carbon or graphite brush (like is used in certain electric motors).

I am just thinking this because of potential noise issues creeping into the signal from the sensors that may or may not be easy to filter out.

You might be able to find something at an automotive junk yard. I would expect the steering columns to have a a pretty nice slip-ring assembly in them. Especially for cars with audio or cruise controls in the steering wheel.

I would expect the steering columns to have a a pretty nice slip-ring assembly in them.

Actually, I doubt that any do; the steering wheel doesn't rotate far enough, and it is far cheaper for them to just put a wiring harness in place with enough slack...

Actually, I doubt that any do

Have you ever taken one apart? All the (older) ones I've taken apart DID have a slip ring assembly for the horn switch.

Cars use a clockspring mechanism: http://en.wikipedia.org/wiki/Clockspring

They're a major cause of cars having the airbag light stuck on and the airbag being non functional. That and other connectors.

How about a Hall Effect sensor and a magnet? http://www.sparkfun.com/commerce/product_info.php?products_id=9312 I know, not exactly an electrical connection, but my bike computer seems to get a lot of info out of one.

@crosh: Have a look into the link I provided earlier, perhaps it's the site you mean?

@mowcius: Unfortnuately I got nothing to do with that. I really liked the design and just remembered it the right moment and even found it amidst my myriads of (mostly unsorted) bookmarks.

@crosh: Have a look into the link I provided earlier, perhaps it's the site you mean?

Yeah - that's it - I'm full of stupid in this thread, so I will just lurk...

:P

Unfortnuately I got nothing to do with that. I really liked the design and just remembered it the right moment and even found it amidst my myriads of (mostly unsorted) bookmarks.

Well it’s a very cool design and has given me some ideas for one of my own. Thanks for the link :slight_smile:

Mowcius