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So I want to make a Lazy Susan that is rotating constantly in one direction. I also want to have some other things on top such as neon signs, moving things, and etc. Problem is I want this to all run off of one DC source. Problem is I cannot figure out how I wire it so that things don't get tangled since the entire thing is constantly in motion.

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    \$\begingroup\$ Google for "Slip ring" \$\endgroup\$ – Eugene Sh. Jul 18 '17 at 20:44
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    \$\begingroup\$ @HotLicks a small PV cell and a very big laser? That would look good too. \$\endgroup\$ – Chris H Jul 19 '17 at 8:20
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    \$\begingroup\$ Maybe get a few worn out or cheap electric toothbrushes, and commandeer the wireless charging parts? \$\endgroup\$ – rackandboneman Jul 19 '17 at 8:58
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    \$\begingroup\$ You could also ignore electronics on the rotating part. You can shine a bright light (laser maybe) across the air gap into a fiber optic in the center of the lazy susan and create "neon" effects if the fiber leaks a little. The mechanical "moving things" can be powered by the mechanical rotation of the lazy susan with gears. Not everything needs to be electronic. \$\endgroup\$ – Mark Lakata Jul 19 '17 at 22:56
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    \$\begingroup\$ Seen one of these? \$\endgroup\$ – Boris the Spider Jul 20 '17 at 12:01

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You are looking for a slip ring. This is a device designed to do exactly what you describe - transmit power and/or signals to a rotating object. Generally, they work by having a rotating circular contact on one side and a spring-loaded pin which pushes against it on the other.

They are not super reliable long term or in harsh conditions, but should be fine for your project. More expensive ones are generally better and last longer. The other alternative is inductive power transfer/signalling, but this will be harder to get right first time, so might not be ideal for a hobby project.

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  • \$\begingroup\$ They're used on CCTV cameras and stand up pretty well to long-term outdoor conditions, years of constant movement etc. with power & video (analogue & IP) going through them. I can't vouch for the cheap eBay ones but good ones do last. I'd avoid loading them too near their maximum rating, but you can get one with more contacts than you need & double-up for reliability. \$\endgroup\$ – John U Jul 20 '17 at 10:23
  • \$\begingroup\$ I've worked on a project that has a slip ring transmitting ~30A at 12VDC along with communications signals to a board that is rotating at 3000RPM. The reliability wasn't great but it was acceptable. For something that only rotates slowly, I'd imagine you'd have a life time of 5 years or more. \$\endgroup\$ – Jules Jul 20 '17 at 15:44
  • \$\begingroup\$ Slip rings can be reliable. You can even get slip rings for ethernet. They just become ridiculously expensive. Even more on high speed. \$\endgroup\$ – Jeroen3 Jul 21 '17 at 5:46
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An alternative to slip rings is the rotary transformer. This consists of two cup-shaped cores that face each other, with the windings inside the cups. If you drive the primary at a high frequency (we used 25 kHz), the cups can be ferrite and the whole thing can be quite compact (we did about 100W in a unit that was about 1" thick overall and about 3" in diameter).

cross-section

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    \$\begingroup\$ In case anyone wonders about reliability and data transfer quality and all that stuff for these: your average VHS rotating head worked that way. \$\endgroup\$ – PlasmaHH Jul 19 '17 at 8:26
  • \$\begingroup\$ One other mechanical issue that complicates this a bit: how small must you make the airgap in order to make this relatively efficient? \$\endgroup\$ – Jason R Jul 19 '17 at 11:47
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    \$\begingroup\$ @JasonR: The smaller, the better, of course. We didn't have a lot of precision in our prototype assembly, and were getting good results with a gap on the order of 1 mm. That's one reason we used a relatively flat core design -- it maximizes the surface area of the ferrite facing the gap. \$\endgroup\$ – Dave Tweed Jul 19 '17 at 12:01
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    \$\begingroup\$ Yet another possibility would be to have a moving coil within a fixed magnetic field--otherwise known as a generator. \$\endgroup\$ – supercat Jul 20 '17 at 15:15
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    \$\begingroup\$ @supercat: Not really effective in a "lazy susan" application, where the rotation can be expected to be slow and/or intermittent. \$\endgroup\$ – Dave Tweed Jul 20 '17 at 17:01
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How about using two rings of ball bearings and use each ring as the contact. No need to add pins and contacts...

Just to add, after taking note of the comments, that I was thinking of a low voltage supply here 5v or 12v just for leds or somesuch - I was not intending to suggest a 110VAC or 230VAC solution.

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    \$\begingroup\$ The arcing on the bearings should add that extra bit of excitement that the neon signs on top are lacking! +1 for concept. \$\endgroup\$ – Transistor Jul 18 '17 at 21:13
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    \$\begingroup\$ Passing electricity through ball bearings pits the balls resulting in premature failure of the bearings \$\endgroup\$ – Tinkerer Jul 18 '17 at 22:02
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    \$\begingroup\$ ... or early onset of arcing. Whee! \$\endgroup\$ – Transistor Jul 18 '17 at 22:28
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    \$\begingroup\$ This page by SKF (I gather they're supposed to know a thing or two about bearings) lists some nice examples of why this would be an... interesting idea: skf.com/cn/en/products/bearings-units-housings/roller-bearings/… \$\endgroup\$ – Mels Jul 19 '17 at 14:46
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    \$\begingroup\$ As a practical matter, it will be difficult to get multiple bearings aligned precisely enough that they are carrying equal loads (i.e., equal contact pressure on both sets of balls) at all times. It's very likely that at least some of the time, one bearing or the other will be handling most of the load, with very intermittent contact on the other. \$\endgroup\$ – Dave Tweed Jul 19 '17 at 23:39
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The other option that you may not have considered is to put all of your power consuming items, including the motor, and the batteries or other power source onto the lazy Susan. No electrical connectors to the outside world required then.

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    \$\begingroup\$ This did occur to me as well, it depends on how long the system must operate unatended. Use Bluetooth lowpower to communicate with the stationary inertial space with minimal power waste. \$\endgroup\$ – KalleMP Jul 20 '17 at 17:32
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    \$\begingroup\$ @KalleMP or if the rotational rate is reasonably low simple IR comms, if higher omnidirectional IR transducers. \$\endgroup\$ – Steve Barnes Jul 21 '17 at 3:44
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It has occurred to me that if you are driving the lazy Susan at a reasonable rate you are also in a situation where you can generate power on it.

If either on the central spindle or round the edges you could mount fixed magnets you could use appropriately placed coils to generate power on the moving platform.

If you were looking for really low tech you could even use an old push bike dynamo on the rotating platform running against a stationary surround of some sort.

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Slot cars get their power from braid running on conductive tracks. You might be able to glue flattened coax cable shield (braid) in two concentric circles on your base board and then use braid "brushes" to pick up the voltage.
Or use one circle and brush and pick up the other side of the voltage via the central pivot.
Or use the central pivot as one contact, run the braid around the outside of the platter and use a horizontal brush.
Or think about the good old Dodgem cars where the floor was one contact and the wire mesh ceiling the other. Cover the whole of the base board with heavy duty domestic aluminium foil (leave a hole in the centre). Attach a brush to anywhere on the platter as one contact and use the central pivot as the other contact.

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I looked into this recently building a zoetrope with LCDs and a microcontroller on the spinning top. I ended up making a DIY slip ring assembly from copper sheet and some carbon brushes designed for drill motors. It worked out surprisingly well (still good after 100,000 or so revolutions).

Before I went down that road though, I investigated wireless power transfer and that looked really hopeful using a cheap tx/rx pair of modules like this: wireless power modules

Passing the drive shaft through the transmitter and attaching the receiver to the underside of the lazy Susan worked pretty well if you can keep them close together. It didn't provide enough current for my application (I needed about an amp and these give about 500mA comfortably).

For my application I also needed to pass very low-rate uni-directional data from the base to the top, rather than add to my slip ring assy, I used IR LEDs and receivers, that worked really well.

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  • \$\begingroup\$ What you have looks pretty good. You can increase the coupling by increasing the diameter of the coils. \$\endgroup\$ – richard1941 Jul 27 '17 at 12:51
  • \$\begingroup\$ The above comment assumes you do not have a metal table surface below, of course. \$\endgroup\$ – richard1941 Jul 27 '17 at 13:06
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Nicola Tesla said you could have a toothed ferromagnetic wheel on the rotor and stator each with windings. A combination transformer and synchronous clock motor. That avoids the legal expenses that you will have with liquid mercury, ozone poisoning, or electrocution.

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    \$\begingroup\$ (1) This answer is rather vague and unlikely to be of much use to the OP. (2) Can you give a reference for what Tesla said? How many RPM do you think a lazy susan would require to generate enough power to light the OP's neon signs? (3) Your sentence "A combination transformer and synchronous clock motor." is missing a verb and a subject. What did you intend to communicate? (4) What is a combination transformer? (5) How would a synchronous clock motor help? \$\endgroup\$ – Transistor Jul 26 '17 at 11:43
  • \$\begingroup\$ My reference to Tesla was just a reminder that he is the progenitor of most of our AC motor, generator, and transformer technology. The speed of the rotor is inversely proportional to the number of teeth that engage the flux. Now imagine a small winding around each rotor tooth.... that would have an induced voltage because of the changing flux. Of course, if you do the power budget, the result of this would be equivalent to increased drag and a greater phase lag in the input current. Hope this comment helps. I will have to dig for my electric machines text if you need a reference. \$\endgroup\$ – richard1941 Jul 27 '17 at 12:47
  • \$\begingroup\$ It would have to be rotating too fast so for this application, but might work for others that find this thread via google. \$\endgroup\$ – C.M. Apr 13 at 21:21
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Tweed's rotary transformer is probably the best solution when it is possible to wrap a coil around the axis and have a ferromagnetic core for the axel. But you could have a set of several smaller coils around the edge with similar coils coupling to them on the rotating platform. The power from each would be intermittent, but if they were properly spaced, you might meet your needs. Do expect nasty 60 Hz vibrations as the coils pass each other... unless you drive them at 100 kHz and use lightweight ferrite cores... If you want to go to high frequency, you might do some kind of capacitive coupling, as suggested by that great Scottish poet, R.F.Burns.

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Use two rings, as with the ball bearings, but eliminate all wear and arcing with rings of liquid mercury or other conductive fluid. Don't drink it! Of course air is a conductive fluid at high voltage, and the display would earn respect of your guests and discourage nibbling of the marzipan and aboutargo on the rotating platform.

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    \$\begingroup\$ Liquid mercury baths like that were used for lighthouse rotating beacons. \$\endgroup\$ – Solar Mike Jul 24 '17 at 14:35

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