Running power through an axil

Dear Michelle Stone:

Batteries. Light and solar cell. Two all-metal bearings installed on insulated surfaces (with capacitors to smooth out the "commutation bumps"), one bearing for each polarity. Solder a wire to each race. I've seen devices advertised that will transmit 24vdc (not sure of amperage) through a 1" separation, presumably using rapdily changing magnetic fields. Split the axle lengthwise and carry one polarity on each "half".

Is it power, or signal you need to transmit?

David A. Smith

Some ideas:

if the rotation is limited to say 180 degrees or less, flying leads make a convenient power transfer.

If rotation may be continuous, a method the radar scanner designers used to favor (for low noise signals certainly) was a rotary transformer, which amounts to two coils on a common axis - which couple AC no matter the angle.

If you want to home brew: a car alternator uses two slip rings.Attaching the rotor to one plate and the stator/brushes to the other might be made to work.

Another home brew tactic. A printed circuit board with two concentric rings etched in copper, for one plate. And a pair of brushes (like those in an electrivc drill for the other plate.

A pair of alkaline 6 volt cells could power 1/2 amp for a fair while - and damned the expense!

Brian W

Search for "slip rings".

It's been quite a while, but these folks have given me good service in the past...

Ned Simmons

Hi Michelle,

Thomas register lists many entries for brushes and slip rings, but given the cost sensitive nature of most Dobsonian telescopes this is probably one you will want to engineer yourself. Purchase metal bushes and brush holders from one of these sources and integrate a couple concentric brass rings in the ground board for your other contacts. Also, given the environment that these will be operating in I would recommend a conductive grease be used to protect the electrical contacts: Jeff Lowe, Springfield Telescope Makers,

First, if it were an informal application, I'd try cheap. I'd pop into Radio Shack and get a couple of a telephone cord swivels. Half an amp sounds like a lot, but you do get 4 conductors (I think).

If it were a formal application (I was getting paid to design it and would go to jail for malpractice if it didn't work, wore out, or hurt someone), I'd google for 'slip ring.'

hth, Fred Klingener

; p/n 7631K43 or equivalent. Available with up to 8 conductors

I would try GlobalSpec

You can search for components by specifications and find suppliers quickly. Much faster and better than Thomas Register.