These slip rings from MOFLON should mean that I never have to suffer the problems that the completely under-specced ones that I used back in the first display caused. Rated for 1500rpm with 4 power and 14 data lines these will allow the transfer of 5V up to 20A, HDMI and USB data and a tachometer pulse.
Depending on how long these last and how the campaign fares I am going to have a look into some gallium alloy/wireless slip rings.
As I have been getting quotes in for the various components I will be using for the commercial versions of Globe I hit a little snag. Finding slip rings rated for the sort of lifespan I am looking for has been virtually impossible. The rings in this blog post are rated for 80,000,000 spins, which sounds like a lot, but if you do the math turns out to not be as long as one might hope. If we say that someone is going to have Globe running for 8 hours a day (being used in store for advertising or on display as an art piece) then we can work out the amount of days it would last. Assuming 900RPM then the maths goes like…
(((80,000,000/900)/60)/8) = 185.18 days
So little over half a year of life out of them, which is simply nowhere near good enough. Finding reasonably priced longer life ones has been virtually impossible however. A similar version (minus all the data channels) by moflon would have run up to about $700 PER UNIT and that’s when buying at least 100 units. Considering that most of the slip ring suppliers seem to basically be making the same models, I didn’t have much luck elsewhere.
I then had a look into to liquid metal slip rings mercury/gallium alloy. An American company called Mercotac do a range of mercury slip rings with a life span up to a billion revolutions…unfortunately because they use mercury that makes them a massive RoHS no-no. Many of the Chinese slip ring manufacturers offer similar liquid metal slip rings, but they actually have an even shorter lifespan that the originals, only about 50,000,000 revolutions.
And so then I came to look into wireless slip rings. These use induction to transfer power over short air gaps, similar to how electric toothbrushes charge. Because they are completely contact-less there is no wear and therefore they have a very long life. The difficulty with them is that they are a fair amount more complex than conventional slip rings and depending on what your input and output power requirements are can involve some slightly complicated electronics.
Very few companies seem to be in the business of wireless slip rings at the moment. A company based in New Zealand, powerbyproxi, have some interesting products including a 150w version, but they are more designed for industrial applications (IP68 rated) and priced as such. While waiting for a quote back from these guys I was having a look at some of the off the shelf components necessary to create my own wireless power transfer system and found them to actually not be too expensive or complicated at all. A fair amount of development and testing would go into creating my own but it actually seems like the most viable option at this point, and may even result in a spin off product (though I imagine there aren’t more non-industrial slip rings on the market due to there being very little demand).