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[on:]

I have a mechanical/electrical problem..

I have two steel plates mounted with ca 5mm distance(0.25inch), which are rotating compared to each other.There is  a circular tube welded to the top plate which runs through a ball bearing in the lower plate. On the top plate I have a potmeter, but the rest of the electronics is mounted on the lower steel plate. I need to get the signal from the potmer at the top plate to the arduino on the lower plate. I could always mount a small solar panel, battery charging circut and a xb and transmit it wireless to the arduino. I just think there has to be some better ways to do it..

Kim

[Reply #1 on:]

You basically want a multi-contact sliding conductor system; its possible to build one if you can etch your own PCB, but it might be simpler to try something else (well, a couple of somethings). First would be a telephone handset (RJ11) cord detangler; these have 2 or 4 conductors, and spin, and keep those coiled phone handset cords from tangling up (not sure if they are still easy to find - landlines are going the way of the dodo, but they are still used - so probably). Another option would be to use a multi-conductor 1/8 inch (or 1/4 inch) headphone jack - a stereo plug has three conductors. The only issue with both of these solutions is the fact that they won't be mechanically robust; they might wear out rather quickly. The multi-contact connectors like you normally see in such applications typically use heavy metal pieces mounted on a plastic substrate (you can simulate with an etched PCB, but some of the more heavy duty ones are made using heavy copper bonded to plastic), and the brushes for the contacts are made of carbon with springs (just like a brushed DC motor). Something to keep in mind with all of these solutions is the fact that the signals may be noisy, depending on the quality and care of construction.

You might also want to look at this tether design for an homebrew underwater ROV - it used slip rings and such; maybe the design could be adapted for your project:

http://www.homebuiltrovs.com/hbrd3tether.html

Good luck!

[Reply #2 on:]

Thx,
So there is at least 5 different possibilities>
1  stereo jack
2 Phone detangler
3 PCB multi contact
4 slip rings
5 wifi

So my application normally turns 180 degree back and forth in 3 seconds running 24/7, however when the wind direction changes the zero position changes.. It is also operated outside, so it has to be more or less water resistant.

So which of the options should I choose?

[Reply #3 on:]

Thx,
So there is at least 5 different possibilities>
1  stereo jack
2 Phone detangler
3 PCB multi contact
4 slip rings
5 wifi

So my application normally turns 180 degree back and forth in 3 seconds running 24/7, however when the wind direction changes the zero position changes.. It is also operated outside, so it has to be more or less water resistant.

So which of the options should I choose?

Personally, I would go for the slip-ring system (mounted sideways, since it sounds like your shaft is vertical), or the multi-contact system (don't use a PCB if this is meant as a long-term running system - instead, have some rings of thin-gauge copper sheet made up, and bond them to ABS sheet with epoxy). Be sure to set things up to keep this contact/slip-ring system (whatever is used) out of the weather as much as possible (if you can machine a system such that you can isolate it from the outside world - perhaps with covers and lubricated o-rings and such - that would be best).

Depending on your bearing/shaft setup, the shaft could also (potentially) act as one of the conductors (depending on how well the bearings and such make contact). Something to keep in mind with the system as a whole (and especially if you use the shaft as a conductor), is the amount of noise the system may have; you'll probably want to mount some capacitors in place (like you would for a DC motor from terminal to case) to clear up as much noise as possible (you can also handle some of this or the rest in software, by doing averaging readings of the pot). There's also the possibility that the system may change the total resistance due to the contacts and conductors, so keep this in mind as you are calibrating things.

The other options probably wouldn't stand up to constant outdoor use - they just aren't designed for that...

[Reply #4 on:]

Here is my setup. The blue part is the line..

Then there is the potmeter mounted on the top arm..

The large plate are fixed. I want to measure angle of the line in 2 dimension..

Let me know if something is unclear.

[Reply #5 on:]

What about having a moving magnet and measure the strength of it?
Or measure distance to a steel plate?

Kim

[Reply #6 on:]

So I can make a mechanical mechanism to transfer a 0-90 degree angular movement into vertical movement. swash plate mounted to an arm.
I found this proximity switch: http://cgi.ebay.com/8mm-Detect-Distance-DC-NC-Inductive-Approach-Sensor-/250832377077?pt=LH_DefaultDomain_0&hash=item3a66c654f5

So if I assume I can mount 2mm away when the angle is 0 degree and that it is 8mm when its 90 degree, and that I can make my mechanism with +-0,3mm accuracy.

What kind of angle resolution can I then get into arduino? I have no experience with these sensors and have therefore no idea about noise and filtering of the output of them.

[Reply #7 on:]

potmeter

yes I mean potentiometer

The movement of the line?

Yes I am trying to measure the movement of the line in 3D: 2 angles and radius.
I have an encoder on the drum so I know the radius. Then I will be able to calculate the position of the end of the line.

[Reply #8 on:]

Yupp for the azimuth I have 2 proximity sensor and a rotating disc with holes in it. That way I can detect which way it is rotating.. and also increase the accuracy. The problem with

DCDW ("Dirt Cheap Dumb Wireless") for the angle "telemetry": 

Then I need to add lipo charger, and a solar panel or inductive charging circuit.

So I am not sure that's the way to go...

[Reply #9 on:]

Here is a rough sketch of a setup with 3 proximity sensors to read out the two angles.. Any feedback?

[Reply #10 on:]

Sorry couldnt resist. 
potmeter....