Electrical contact between moving parts

[HevansccParticipant @hevanscc]

I'm after some advice about the best way to make electrical contact between two concentric steel tubes. Specifically, between the steerer tube of a bicycle fork and the head tube of the frame.

There is an established way of doing this, using a button spring inside the steerer (the inner tube) which protrudes through a hole and acts as a bush against a brass slip ring on the inside of the head tube (the outer tube). the idea is that the front light is wired to the slip ring, and the dynamo on the front wheel is wired up through the fork to the button spring, so supplying continuous power while the fork is turned to steer; and allowing removal of the fork by eliminating the hard wiring. Also, both contacts must also be insulated from the steel parts to which they are attached.

I can replicate this but wondered if there are more suitable components which have been used in a similar application.

 

Many thanks

 

Hywel

[HevansccParticipant @hevanscc]

[Michael GilliganParticipant @michaelgilligan61133]

Hywel,

I think I would start by looking at the brushes and holders from electric motors … these might easily adapt.

MichaelG.

.

Footnote: The 'theoretically perfect' [ish] method would be to have a moving contact that dips into a circular 'moat' of Mercury … but there are a number of practical difficulties, and safety issues involved, so best forget that one.

Edited By Michael Gilligan on 15/02/2017 14:03:22

[martin perman 1Participant @martinperman1]

My concern would be ingress of dirt and moisture causing corrosion.

Martin P

[mark costello 1Participant @markcostello1]

Rotary electrical unions, swivel joints and slip rings will all Google up to give You an idea of what is available.

[not done it yetParticipant @notdoneityet]

Make it such that the headstock can not be rotated full circle? Many 'homebrew' wind turbines have no moving connections – they rely on the wind not winding up the output leads very much, thus allowing the operator to occasionally unwind any twist in the cables through the bottom of the tower before the twist becomes excessive. You would only then need some multistrand flexible wires.

Sliprings are also used on turbines, but tend to be rather larger than a bicycle tube! Automotive alternators use a smallish slipring arrangement for exciting current for the rotor. Spark ignition engines use carbon contact with brass for the distributor rotor connection for the high tension spark energy.

You might think about the horn button within the steering wheel of some cars, although they are a rather intermittent piece of kit. Morris Minor comes to mind as an example.

There have been many bicycles made with front wheel dynamos, over the years. Surely there must be some around that you could investigate. Enquiring on a bicycle type forum may yield some precise explanations of the usual methods.

Hope that helps.

[Jon GibbsParticipant @jongibbs59756]

It's certainly not pretty but the most reliable IMHO would be an external braided strap given that the front forks of a bike have such limited travel and therefore have limited wiping/cleaning action.

Something like this attached to forks and frame…

Easily inspected for wear.

Jon

[duncan webster 1Participant @duncanwebster1]

If the dynamo is on the front wheel, and the light turns with the handlebars as usual, then you'd need 2 sets of slip rings. All getting a bit iffy. Can you mount a bit of small bore tube from the top of the forks to the handlebar stem, parallel to the steering head but turns with forks, and run the wire up that

[Jeff DaymanParticipant @jeffdayman43397]

Two joined wires looped loosely around the head tube will be simpler cheaper and far more reliable for low voltage DC than any sort of brush/ slip ring gizmo you might build. You do need to limit rotation to a little less than 360 degrees.

If you want an overcomplicated expensive multiconductor slip ring assy these folks have them: http://www.princetel.com/slipring_srg12.asp

(You can put a fibre optic rotary joint up the middle of these as well just FYI)

Or just mount the generator on the back wheel and route wires inside the frame tubes.

The KISS rule is usually best. Just my $0.02 worth, your mileage may vary. JD

[Ian S CParticipant @iansc]

My bike has a dynamo on the rear wheel, the light mounted on the handle bar, one wire, and frame return, so the return is through the bearings for the steering, works ok for me.

Ian S C

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