A survey of unicycle gearing systems

Hi all,
Apologies in advance for the rambling, I just wanted to walk you through my project ideas, and end with some questions about 2/3-wheeled unicycles.

I built this a few months back and would like to add gearing to it: I made an Electric-Assist Unicycle
In the meantime, as some machining practice, I’m building a home-made high-speed only planetary hub which should be done pretty soon.

If you saw Justin’s build, which mine was based off of, he used a planetary gear inside the motor which was brilliant. This is somewhat difficult to do if you’re an amateur machinist, as gearing alignment is extremely important, plus I’m interested in doing something novel.

After some thinking, I organized all the gearing systems I’d seen to essentially 4 types and evaluated their strengths/weaknesses:

  1. Schlumpf/planetary gears
    Pros Cleanly contained, easy to electrify
    Cons Hard to machine, limited to 2:1, difficult to add multiple gears
  2. Giraffes (pretty self explanatory)
    Pros Lightweight, uses traditional bike parts, easy to add multiple gears (derailleur)
    Cons Unreasonable if the goal is to go fast: nobody wants to ride 20-25mph on a giraffe
  3. Fake Giraffes, like the huni Rex
    Pros Pretty cleanly contained
    Cons Hard to add multiple gears, leads either to pedal scrapes or a feeling of riding a mini-giraffe, depending on how it’s built
  4. Jackshafts
    Pros Easy to add multiple gears, uses lots of traditional bike parts
    Cons Difficult to make, complex chainworks, can be ugly

As I’m focusing on an electrified unicycle, I also thought about how ebikes are typically powered, and if any of those solutions might give me an idea. Briefly, there are:
A) hub motors (shown to work on unicycles)
B) mid-drive motors (freewheel and unreasonable solution)
C) friction drive motors (e.g. Rubbee).

Friction drive motors have fallen mostly out of favor in the ebike community, generally only used on cheap kits. They have the fatal flaw of not working well in the rain, as well as wearing through tires quickly. Given that this is just a fun project, neither of those issues bothered me too much. Of course, I then realized that a friction drive is essentially equivalent to 2/3-wheeled giraffes, without the issue of being so high in the air. So the idea isn’t as novel as I had hoped, but still interesting.

So here’s the idea, and I’m hoping I can get some feedback from the community on how feasible people think this is: Use a Rubbee-style friction drive motor on a unicycle. On top of the Rubbee’s roller, add a second roller which is attached to a cog. A chain runs between that cog and a cog attached to the cranks.
Questions I’d like answers to before attempting this build:
A) How strong are these friction forces? I’ve never ridden a 2/3 wheel giraffe, does anybody know how much slippage to expect?
B) Expanding on the first question, what is the backlash like on those wheels?
C) Other thoughts on this build idea?


If you haven’t seen it before you may want to check out Kervelo which I believe fits into your category 1. They’re doing preorders now and I’m hoping to make a unicycle out of Kernel-Hub once I figure out how to get a compatible fork.

I saw this, but I assumed it freewheeled. Do you have any information on whether it does or not?

It definitely freewheels but at higher gearing it’s not as big an issue.

I own a modded Huni-rex and last month I was thinking about offering you money to buy your ewheel and fit it in my huni-rex. I already checked all ideas you are suggesting and except for a freewheel hub, adding your ewheel to a huni-rex seems the best cheap and ready ut of the box solution.

If you are willing to sell please PM me. If you are willing to experiment, than go with a huni-rex, it solves a lot of problems and is quite easy to add your wheel. And there’s no pedal stroke issue if you add a fat tire

Also I asked for infos about pedal direct drive like bikee bike but it’s not feasible due to motor dimensions (too large, it touches the spokes).
There’s still the chance to add Bimoz to a huni-rex, but they already told me that I need to completely mod the cranks (too long) and I’m not sure it will ever be produced.

I would LOVE a Huni-Rex but where do I buy one?! I don’t think my hub motor solution is the right fit for your Huni-Rex because you would need to replace the axle with a Huni-Rex axle: You’d need to unbolt the current axle I have now, cut off one cog on the huni-rex axle, stick it through the hub motor, and weld back on the cog you cut off. At that point, you’re an accomplished enough machinist you could do the rest of what I’ve done, but I am certainly down to help out and/or sell any specially machined parts you’d need. I might even be willing to sell the whole hub but I don’t think it’d do the job for you.

If I could get my hands on a Huni-Rex, I think that would be the easiest solution. I would buy a regular non-thru-axle rear hub motor like this one (http://www.ebikes.ca/shop/electric-bicycle-parts/motors/m2705rd.html#) and modify the side with the disc brake adapter to have a second casette for the left side chain (both casettes would be fixie of course).

How narrow is the huni-rex?

I added a Vee tire speedster 3.5 x 26". I cutted the rim brakes mounts and found I could go fatter but not bigger
(You need to cut the frame and add other aluminum if you want a bigger radius wheel). I had problems with the bikee bike motor because it has a 100mm thight motor where the huni-rex has the inner pedal cog.

The idea you linked for me implies a freewheel hub axle, you build a motor which could be spin backward is it true?

Also I added yesterday the disc brake to a 29" freewheel: I built it mainly to learn freewheeling for a future motorised freewheel hub. That’s the way I’m riding right now to avoid messing with an ewheel hub axle as you did

Yes my motor spins backwards, but so do all direct drive hub motors. As long as you’re not buying a GEARED hub motor, it won’t freewheel. So what you should do (and what I might do now actually) is to buy a hub motor like the one I linked above. On the right it has a threaded adapter for a cassette with a builtin freewheel, but I wouldn’t use that, I’d instead use a fixie cog like this one: (Amazon.com)

Then, on the left side, there is a disc brake mount. Instead of putting a disc brake there, I’d add a second cog; this would require some very basic machining to add bolt holes to a cog. If you don’t have any machining experience, you can actually buy a 16T cog here (16 Tooth Cog) because Grin uses it for a completely different type of ebike.

After that, the only thing left to do is mount it in the frame. I’ve never seen a hunirex so I don’t know how this will work. It could be as simple as popping it in, or you may have to create your own little dropouts that fit in the slot where the current axle is.

I’m seriously interested in a HuniRex now. I may just try to build my own but I know I’d never be able to match the build quality.