waaalrus linked this site as an aside on another thread.
Look at the drawing of the “front wheel drive hub”.
Seven to twelve hub gears. 100 mm wide. 2 kg. Too good to be true?
Not real yet I’m sure, especially as they have drawn it with radial spokes. 
I’ ve already asked them to write here to get our help developing a fixed wheel one hub
Aren’t most (all?) the multi-gear IGH systems like Rohloff based on each gear overdriving the others? How can that work in both directions such as for a unicycle?
You’d end up with multiple forward speeds and only one fixed ratio (or a freewheel) for reverse torque.
The gearing itself does not care which way it is turned, the only thing that does is the freewheel integrated into most Geared bicycle hubs. If you eliminate the freewheel, any conventional gears don’t care which direction you turn the input shaft, the output will always spin with the (rotational) speed of the input shaft divided by the gear ration.
Agree with you about input and output for one set of fixed planetary gears.
But freewheeling is integral to how these hubs can have changeable ratios, with some gears overdriving others.
The freewheel is not totally its own entity; the clutches that allow such a large variety of engagement of individual ratios also act as freewheels therefore don’t engage in reverse.
At least in my understanding of how for example a Rohloff works.
12:45 mentions the freewheel as a specific part. Even if you deliberately seized this in place, because of how the other clutches work you still wouldn’t be able to drive it in reverse in most (any?) of the ratios.
I suppose this is to avoid complexity, if the clutches were made to be more complex than engagement pawls and a spring then it could perhaps be made to work.
The old Sturmey Archer 3 speed works in a slightly different way, you can hear the clicking when pedalling in the the higher ratio as the other ratios are overdriven and are effectively freewheeling. It still doesn’t work in reverse without modification (I believe these can be converted to 2 speed fixed?)
Don’t get me wrong, I’d love to see it! Build me a three speed fixed hub and I’ve got thousands of pounds you can have!
Motor windings and strain gauges on the input side would be essential though, there is not much point gearing these things down!
Edit: Justin LE’s solution is probably the best one. The Fastest Uni Hub on the Planet. Can I finish for Unicon 18?
One ratio with variable assist. If you’ve ever ridden a half decent electric bike with a strain-gauge based proportional assist you quickly realise it doesn’t matter which gear you are in as long as it’s tall enough so you don’t spin out!
Also ISIS. We’ve been discussing this for a few weeks on the Freewheel Unicycle Chat Facebook group and it was Robin Whitfield who made the discovery. I posted it on Unicycle Chat but there was not much discussion. I’m planning to order a front end if can be equipped with disc brakes. That’s the one downside to Justin’s design and is almost essential to riding freewheel unicycles.
I’m also inquiring Bimoz http://www.bimoz.ch/ to power a Huni-rex http://unicycle-c-1/roadtourbasket-c-1_8/hunirex-26-unicycle-with-speed-black-p-650.html
I know (just a little bit) this system and this French guy. We have been in contact for the last 8 monthes but never received any details because of officially some patent reasons
I 'm going to contact him again to try to get more information and will let you know
Thank you. Everyone is excited about that. I’ll try freewheeling too if that’ll be the only way
Join us!
Personally I’m interested in the mc2 wheelset as it exists right now.
I emailed them in January and was told 2-3 months before we could buy one as they’re still fulfilling orders for bikes right now.
Only two gears (1:1.3), but two gears with a shifter (it also freewheels)
(Robin Whitfield here 
)
Completely forgot about this, but both the MC2 wheelset and Kervelo hub are in production:
https://www.kervelo.com/transmissions/gearhub-kernel-hub/
Anyone want to take the plunge? I don’t have the spare cash to throw at either right now but would be very interested to give them a try.
I’ve emailed regarding the Kervelo hub to try and get an idea of pricing and bearing spacing.
Wow, looks really interesting!
So two questions:
For the Kervelo, no it’s not possible. For the MC2 I suspect the same but I’m not totally sure.
The MC2 is square taper so I presume standard 17x40x12 bearings - not sure on the spacing but I’m sure you could bend a steel frame to fit without too many issues.
The Kervelo is provided with two 15mm diameter spigots to attach your frame/forks to (as per this image) as the bearing situation is a little complicated (the shifter goes through one of them).
<duplicate>
I’ve only just realised how the gearing works on the MC2.
The prototype version used a second disk brake for gear changes. The new version omits this so perhaps a drum brake type arrangement to do the same thing?
(https://www.youtube.com/watch?v=CLXnsXQJsX8&feature=youtu.be&t=57)
Think of the disk brake as the reaction arm on a standard hub. If you’re in low gear and the reaction arm isn’t attached to anything, everything turns at 1:1 (including the reaction arm). As soon as you lock the reaction arm, the planetary gears are engaged and you’re in high gear.
What I can’t quite wrap my head around is what happens if you drag the gear shifting (reaction arm) disk brake rather than locking it on? Do you get a really crude CVT?
Also, if you removed the freewheel and quickly changed direction while in low gear (spinning reaction “arm”), would it just change direction, or would something weird happen?
