Cable Wrap Prevention

[globular]

Hi All,

Background waffle:
I have an Evolution mount that is powered by an onboard battery - so no cables to snag.  Tick.
However I also have other stuff (like dew bands) that I power separately using a single power cable to a controller mounted on the telescope, from where it's distributed to the devices.  It's all very neat and works well - but I'm left with a cable that will wind around the tripod if the mount slews round and round in the same direction.
There is a setting in the goto options that, when turned on, prevents the telescope from slewing more than 360 degrees.  But if you're at 359 and want to slew to 001 then it takes a while to go all the way round in the other direction - so I don't want to turn that on.  I could try mounting a battery up on the mount / telescope so that the battery and cable rotates with everything else - but the extra weight is problematic.  I could try tapping into the Evolution's power... but I've heard horror stories when doing this and I actually quite like the extra battery life of having a separate power source.  In all my time observing with this set-up I've just "kept an eye out" for the cable and repositioned it as needed without any incident so far - but I have had a few near misses and I'd like to try and eliminate the risk if it's doable.

Solution ?

I saw an aluminium lazy susan on amazon... https://www.amazon.co.uk/Lazy-Susan-Rotating-Aluminium-Turntable/dp/B07G4FY6VG?th=1 

It looks like this:

It's aluminium with steel balls... so maybe it will conduct power from the inner ring to the outer?

If I stack two of them... using the rubber feet to keep them apart... then I can feed both +ve and -ve through from the inner rings to the outer? So I've created a sort of power slip ring?

I then attach the inner ring(s) to the top of the tripod, just below the mount (in an insulated way so the tripod doesn't short it).

Attach the power source to the two fixed inner rings, and a cable from the outer rings to the controller mounted on the telescope.

As the mount rotates it will drag the outer rings with it - while the inner remain fixed.

So it can go round and round and round and the cable will never snag.

Some sort of insulating cover over it all to prevent any shocks or shorts when something comes into contact with it (and to make it look 'nice').

Job done?

What do you think?

 

[wulfrun]

It'll probably work moderately well (at first) from an electrical viewpoint, other than some voltage loss. However, aluminium with steel balls? What was the designer thinking? No! Any damp (a bit inevitable with astro gear) will give you pretty nasty galvanic corrosion. Add in power transfer making things worse. I predict a short life, sorry, hate to put a downer on an otherwise neat solution.

Why not knock up copper slip-rings with spring-copper contacts?

[globular]

Thanks @wulfrun, I appreciate the reply.

I did attempt to search for copper slip rings of sufficient diameter - but rather unsuccessfully. They were either too small or rather over engineered (and hence expensive) for my low power low rotation speed needs.

Anyone know of something off the shelf more suitable as a starting point?  

I can put together and adapt parts someone else has made, but I don’t think my ‘knocking up’ skills run to copper slip rings.

Edited August 21, 2022 by globular

[wulfrun]

I'm not 100% sure of this but you can probably get copper tape, maybe even adhesive-backed. As long as it's a suitable size for the current involved. You could put it on something like pvc water pipe to make the support & diameter.  Then you'd just need a spring-copper strip to make a contact brush. Just some ideas to throw at you.

Edited August 21, 2022 by wulfrun
typo

[CraigT82]

If the weight of a larger battery pack on the mount is a problem could you go for a smaller and lighter weight battery pack, and buy another one spare to swap in when the first one runs out?

[Dr_Ju_ju]

Does the mount not do meridian flips ??  if it does then it 'should' reverse the movement direction, preventing cable snagging etc.

 

[globular]

10 hours ago, wulfrun said:

I'm not 100% sure of this but you can probably get copper tape, maybe even adhesive-backed. As long as it's a suitable size for the current involved. You could put it on something like pvc water pipe to make the support & diameter.  Then you'd just need a spring-copper strip to make a contact brush. Just some ideas to throw at you.

Thanks for the suggestions.  I have the same thoughts but just can't find appropriate parts in my google searching. I can see this ending up in a 3D printer purchase.... 🙃

 

 

1 hour ago, CraigT82 said:

If the weight of a larger battery pack on the mount is a problem could you go for a smaller and lighter weight battery pack, and buy another one spare to swap in when the first one runs out?

Good suggestion - but I quite like the idea of solving the cord wrap problem.  I'd probably forget to swap out the battery and lose my session to dew.

 

37 minutes ago, Dr_Ju_ju said:

Does the mount not do meridian flips ??  if it does then it 'should' reverse the movement direction, preventing cable snagging etc.

 

It's an Alt-Azimuth mount.  The anti cord wrap setting in software will amount to something similar - but I'm exploring the possibility of preventing cord wrap rather than living with it.

[wulfrun]

18 minutes ago, globular said:

Thanks for the suggestions.  I have the same thoughts but just can't find appropriate parts in my google searching. I can see this ending up in a 3D printer purchase.... 🙃

Ask @DaveL59 where he got his copper tape for his lens repair, covered in this thread. There may be thicker/wider grades available (what he used is probably too puny for your idea):

 

[DaveL59]

8 minutes ago, wulfrun said:

Ask @DaveL59 where he got his copper tape for his lens repair, covered in this thread. There may be thicker/wider grades available (what he used is probably too puny for your idea):

 

From the source of everything we seek of course, Amazon 🙂

Available in many widths and no reason you couldn't wrap it over itself to improve wear resistance, esp if you buy the type that has conductive adhesive (usually called dual-side conductive or similar).

20 M Copper Foil Tape with Dual Conductive Strong Adhesive Copper Foil Tape for Guitar and EMI Shielding,Soldering,Electrical Repairs(30mm (W) x 20m (L)) : Amazon.co.uk: DIY & Tools

I guess you could even use it to fashion the wiper parts, using the copper tape to make the contact to the ring, tho a thin copper strip that's bent to suit would probably be better. How much current is this likely to be trying to draw across the foil/wiper as that may be an issue if there's not enough surface area/contact pressure?

 

[Synchronicity]

13 hours ago, globular said:

Solution ?

Lateral thinking - could you wrap the cable round anti-clockwise at the start of the night so that as the mount tracks it slowly unwinds?  At the end of the night you have the cable at what would normally be the start point.

Michael

[DaveL59]

8 minutes ago, Synchronicity said:

Lateral thinking - could you wrap the cable round anti-clockwise at the start of the night so that as the mount tracks it slowly unwinds?  At the end of the night you have the cable at what would normally be the start point.

Michael

Ahh the simplest and cheapest ideas are so often the best, nice one! 🙂 

I was tempted to suggest the lazy susan idea but carrying the battery rather than using it as slip rings but decided that wasn't a great idea either.

[globular]

1 hour ago, Synchronicity said:

Lateral thinking - could you wrap the cable round anti-clockwise at the start of the night so that as the mount tracks it slowly unwinds?  At the end of the night you have the cable at what would normally be the start point.

Michael

Thanks Michael.  However it's not really a tracking issue (I'm not imaging for hours on end) it's a slewing to different targets issue (visual use) so I don't know which way I might be going from one moment to the next.  I usually think "where is the cable" before I do a big movement... but I'm bound to forget eventually.

But in any case, I'm trying, in this thread, to explore the possibility of a solution to the cord wrap problem - not work around or live with it.

Edited August 22, 2022 by globular
typo

[globular]

30 minutes ago, DaveL59 said:

From the source of everything we seek of course, Amazon 🙂

Available in many widths and no reason you couldn't wrap it over itself to improve wear resistance, esp if you buy the type that has conductive adhesive (usually called dual-side conductive or similar).

20 M Copper Foil Tape with Dual Conductive Strong Adhesive Copper Foil Tape for Guitar and EMI Shielding,Soldering,Electrical Repairs(30mm (W) x 20m (L)) : Amazon.co.uk: DIY & Tools

I guess you could even use it to fashion the wiper parts, using the copper tape to make the contact to the ring, tho a thin copper strip that's bent to suit would probably be better. How much current is this likely to be trying to draw across the foil/wiper as that may be an issue if there's not enough surface area/contact pressure?

 

I'm feeding power to one of these...
https://www.firstlightoptics.com/dew-prevention/lynx-astro-4-port-dew-controller.html
... so up to 10 Amps max @ 12v.  (In reality I'm nowhere near the max but would like to match the max rating if achievable).

The diameter of the circle needed is about 9" so a run of around 750mm is needed.

How do I calculate what width and thickness I'll need?

And my main issue is how to fashion a brush connector (that works in both directions) and how to hold it to maintain sufficient contact.

And how much drop off in voltage is there likely to be?

I'm all questions and no answers, unfortunately.

Edited August 22, 2022 by globular

[globular]

19 minutes ago, DaveL59 said:

Ahh the simplest and cheapest ideas are so often the best, nice one! 🙂 

I was tempted to suggest the lazy susan idea but carrying the battery rather than using it as slip rings but decided that wasn't a great idea either.

Yeah I considered that too... but a large battery circling around the top of my tripod doesn't feel very convienient.  And I'd actually like to solve the cord wrap problem.... I could then feed power from a mains source too.

[DaveL59]

hmmm not sure I'd want to pull 10A (120W) across a sliding contact tho it'll be a lot less most of the time I guess. Thing is as dew forms you may also find you get contact resistance issues tho a smear on each ring of dielectric grease (or vasoline) would help as well as preventing oxidation. You'd want to make the sliding contact a similar width to the ring to maximise the contact area. You might either make or buy something like:

S7171-45R Harwin, SMT SPRING CONTACT, 4MM | Farnell

 

[kbrown]

Solar power? No hang on a minute... I'll get my coat

[DaveL59]

2 hours ago, kbrown said:

Solar power? No hang on a minute... I'll get my coat

hmm got me thinking tho, microwave... but then again that could get a bit "warm" if you stand in the wrong place 😉 

[kbrown]

Tesla did some wireless power transmission tests, didn't he? Maybe a tesla coil?

Edited August 22, 2022 by kbrown

[DaveL59]

24 minutes ago, kbrown said:

Tesla did some wireless power transmission tests, didn't he? Maybe a tesla coil?

there goes your dark adapted vision tho, neighbours might enjoy the light show tho 😄 I'd throw in a laden jar capacitor to tide over the bumps in demand too

[kbrown]

Speaking of coils... This might get convoluted quickly but if you used low voltage (i.e. safe) AC power instead of DC, you could then transfer it from coil to coil without having to have a physical connection. You'd then have to convert it to DC and regulate it to correct voltage etc. How this could be achieved in your application, I'm not sure. Maybe with some custom wound toroidal coils...

Edited August 22, 2022 by kbrown

[wookie1965]

I use a power bank strapped to the centre of the scope so not to effect balance and two usb dew strips wrapped around the scope I can slew anywhere with no snagged cables. 

[globular]

Maybe I'll stick a battery on the back of one of these...
https://smile.amazon.co.uk/Adeept-Compatible-Tracking-Ultrasonic-Processing/dp/B086HLJRDT 
... and tell it to keep to the front of the scope while avoiding the tripod legs and me.

[DaveL59]

13 minutes ago, globular said:

Maybe I'll stick a battery on the back of one of these...
https://smile.amazon.co.uk/Adeept-Compatible-Tracking-Ultrasonic-Processing/dp/B086HLJRDT 
... and tell it to keep to the front of the scope while avoiding the tripod legs and me.

just don't doze off, you'll wake up finding it's hog-tied you 😄