Slip Rings

[Stef]

I've posted a query about slip rings before didn't get much response. I need HELPPPPPPP!!!!!! :D I need to power a receiver through a rotating connection. No signal just DC. Used 2 carbon brushes spring urged against 2 copper tracks etched into a pc board. I'm getting DC through ok but also a lot of spurious servo movement, but only when powered through the rings. I know this is commonly done can someone please help?

[omega blood]

You might try puting in capicitors like in a motor to supress the noise. Also try wraping your Rx in aluminum foil. But basicly what you have is a niose maker. What is it that you are building or making BTW?

[Discharger]

Try an electrolytic capacitor, maybe 2200mfd or 4700mfd 16v after the slip ring and near the Rx input. Your local electronics (Radio Shack?) will stock these. Be careful of polarity.

[Stef]

I have already tried supressing the the rings no joy :( . I replaced the carbon brushes with simple brass strips and no problem! :D I think I was getting intermittent cotact an it acted like inputs, like when you first plug in your battery even with TX on servos will move a little multiply that by 10 or20 :eek: Thanks for the inputs :)

[Radiofly]

Just noticed this post, sorry for the delayed response.

I would have suggested you try one of those telephone cord untangler devices. Look around at Staples or radio Shack. They come in various configurations, but they are basically a 4 circuit slip ring that is communications (small signal) grade.

[Stef]

Thanks for the suggestions, I had thought of the telephone device I was doubtful as to current carrying ability, also it needs a shaft to run through it.
I think I found my problems and have made a working prototype with improvements in mind if the project shows promise. :)

[Cas123]

A further modification to the brass strips that should improve reliability, ifyou have'nt already done so. Cut the ends of each strip into multiple fingers so as to ensure good contact at all times.
Ron...

[Stef]

Good idea :) I have the strips bent into a curve so that a smooth surface touches the rings which are etched into a pc board. Also have a pressure adjustment to keep even light contact pressure. I'm planning to change to small metal balls for the contacts.

[Cas123]

Dont know if metal balls will improve things. High resistence, prone to arcing and corrosion. Brass is good because it has high conductivity and as it wears is self cleaning. If you want to really get fancy dismantle a 5- 10A relay and use the contact arms and contacts soldered to your strips. They are usually a fancy alloy.

Ron...

[Stef]

I was going to try metal balls spring loaded to make the unit smaller and to reduce sliding force. Brass if I can find them but probably copper plated steel BBs. Thanks for heads up on the relays. I work with relays on my job all the time and didn't think of them. :cool:

[PROACE]

You could maybe do like the manufacturers of synchro's for aircraft and use stainless steel wipers on the slip rings. The only thing is the wipers have to be crimped since stainless won't take lead solder.

[Gary Warner]

Though it was said that capacitors just after the rings didn't help, I'd add that for this to work better, you would add coils before the caps to reduce fast transit spikes. From the rings, add (aprox) 10-100uh coils (depends on loads - higher for less loads, smaller for higher loads) before the capacitors.

B+---->brushes---->rings------>coil-----.------receiver B+
.................................................. ......^....................^
.................................................. ......|.....................|
.................................................. ....cap(s)..........small cap
.................................................. ......|.....................|
.................................................. ......v.....................v
GND-->brushes-_--->rings---->coil------GND---receiver GND

For good rf suppresion, use several caps in paralell - one about 1000-3300uf and one about .1uf. Also, a .1uf as physicaly close to the receiver input as possible can help.

[PROACE]

Caps work good with rf suppression by "absorbing" any voltage skikes on the line but if the spikes are consistent over time the caps will cause an increase in voltage on the line close to the average spkike voltages. I would agree with the coils but instead place inductor beads in line prior to the caps to obtain a higher inductance in less space.

[Stef]

Thanks for all the good ideas. I have produced a set of rings that seem to do the job. :) I used etched rings on a pc board for one side and BBs set in holes held in place with pieces of berrillum copper for spring tension on the other. So far have not needed suppression of any kind. If I do need rf suppression I'll try the coils (hadn't thought of that) and small caps don't have room for size or weight of 3300UFs. :D