In my tandeming days, we had problems tensioning the front chain which connects the front rider’s power output to the rear rider’s alleged power output. A separate chain delivers the combined power to the rear wheel.
This front chain presents similar challenges to a giraffe chain. On a giraffe, the adjustment is typically with sliders and threads with locknuts, similar to on a traditional motorcycle. On the tandem, adjustment was with an eccentric bottom bracket - an idea now adapted for use on some motorcycles.
But the chain could develop more slack than the adjuster could take up, and this is where the clever bit came in, because it was possible to slip a large-ish chain ring in half way along the chain. By careful selection of the chain ring size, the excess slack could be taken up.
So the top of the chain moves forewards, and the bottom moves backwards, and the ‘free’ chain ring spins on the spot.
Adapt this idea for a giraffe, and many cosmetic possibilities arise… little tumbling clowns bolted to the chain ring, bells threaded through the chain ring bolt holes, all sorts of stuff.
not the best,but certainly th lowest tech way to tension a chain is to put another chainring in the middle.one big enough to take up slack while tight enough to stay and float there.
when it comes time to shift,just take it out or put it in.it can be your necklace too.
johnfoss wrote:
> Don’t know why it would be so terrifying, unless it’s a big change of
> ratio or if you have to do something like freewheel to get the gear to
> change. Then I can see it!
Unfortunately I can’t remember what the reason was - or even whether they
mentioned a reason. My first thought would be something to do with the
change in pedalling cadence, but ISTR some change in pedalling style was
also required to change gear - may have been freewheeling, but I don’t think
it was.
It doesn’t sound stupid at all. I also had this idea a while back, but I thought it was a little crazy to advertise (so was the Unibike). I have accumulated most of the parts necessary to build this dual freewheel giraffe. Hopefully, this winter, (after I relocate again) I will get it built. I’m not sure if chain slack will be a problem. It’s not a problem on my Unibike, but I may have just become used to it over time. Having to pedal in both directions may present much more of a problem.
I haven’t seen Michael Grant’s idea on this. Is there a project in the works?
i’d say a 5 because its not a stupid idea,but since it wont work its a bad idea.
Unibiker,dont bother to make this because it wont work.i suppose i now have to tell you and everybody why?
pick up any bicycle so the rear wheel is off the ground,then spin the wheel backwards now watch as the cranks move backwards too.
with two free wheels and two chains on one wheel it still will have no freewheeling action.the pawls in the freewheel need to be reversed for it to even be possible and that aint likely to be an option.
What you need is called a freecoaster - used by bmx people to avoid this very problem. Two of those back to back would almost work.
The problem with freecoasters is a) good ones are really expensive and b) they have a clutch mechanism so in between the back and forward pedalling there’d be a really quite noticeable gap while the opposite direction freecoaster kicked in and also you’d be really screwed if you tried to pedal the backwards freecoaster while going forwards, you’d just get thrown right off.
What would be great fun to try would be some kind of centrifugal clutch on the attachment between the chainring and cranks, so that if you stop pedalling you coast, this would be hard though because you wouldn’t have access to the small adjustments you do all the time normally and again it would probably jerk like mad when it kicked in.
I’m not sure if any freewheeling action is necessary. I was thinking that if a cog was used on each side, while the right one is driven by the chain, the left one (as you mentioned) would be driven backward by the hub. I think this would keep the left chain spinning around the front sprocket at the same rate as the right chain (which is doing the work). Wouldn’t the left side be free spinning? (Front sprocket spun by the crank; rear sprocket spun by the hub; and the chain making the rounds with no force on it?)
Then, when pedalling is reversed, the left chain would do the driving, and the right would be free spinning.
I think this might work if the right and left sprockets are the same size and if shifting is done simultaneously. I was planning to use a front derailleur on the bottom of the left cog to allow both chains to be shifted while the hub is spinning forward.
In either case, I’m open to comment from everybody. If you can talk me out of the possibility before I waste time on it, I’m sure I can find other things to do with my time. It will likely be a couple of months before I get to it anyway.
Thanks for the photos. That is a cool looking giraffe. It looks to be all aluminum (aluminium) construction. Do you have a spot on the frame to stow your wrench (spanner)? Is it more or less difficult to ride in 26" mode and if so in what way?
I especially like the UW. I have never seen that design with the large, hollow hub and short spokes. Again, the hub (and in particular the welds) look to be aluminum. Way cool looking. More details of the giraffe shifting mechanism would be nice. I realize that for some cameras the close-ups get kind of dicey.
The UW was a college project a few years back. It has an aluminium, box section hub; custom length, stainless spokes and a 72 hole aluminium rim. The welding was all done by one of the technicians and is really good (boy, do I miss having that facility now)
I have a steel hubbed prototype in the shed somewhere but this has two right hand pedals as I couldn’t find a left hand tap at the time
The wheel is really light and very easy to carry and great for bunny hops but I prefer doing tricks, juggling etc on my solid wooden disk UW.
The giraffe was built by myself a nd a friend (Dan, former unicyclist) and is mostly square box section aluminium. It is all bolted together as I had no aluminium welding capability at the time.
To change gear you need a box spanner to loosen and tighten the axle and a screwdriver to tension the chain. There is a tonne of room inside the oversize frame but I haven’t made a space for the tools.
The high gear ratio actually feels quite nice. It has cranks that are a bit too long so the small ratio feels a bit frisky. They were the shortest cranks I could get at the time I haven’t got round to changing them yet.
Dismount;)
Slacken both axle nuts
Slacken the tensioner screws
Move the chain
Tighten the tensioner screws
Tighten the axle nuts
Remount
Try again
Try again
etc…
A while back I was talking to someone (can’t remember who) about juggling on a giraffe, and what happens if you drop a ball… on a normal uni you can pick them up again, but on a giraffe? Is it possible to climb down, pick the ball up, then climb up again, without touching the ground? That’d be very impressive…
At the UNICON Opening Ceremonies Show, Dustin Kelm climbed DOWN his 6’ giraffe to hopping with one foot on wheel and the other on crank, he then stepped gracefully off the uni. (This may belong on the “No level 1 riders” thread too regarding graceful dismounts)
I wouldn’t be surprised if he could figure out a way to picked up an object with out a complete dismount from the giraffe.
Even if I get this thing to work, I would not consider shifting (or even riding much) in reverse.
Shifting would definitely be very touchy, just as it is on the unibike. And (if my theory is correct - which I do not claim) in order to keep one side or the other from binding up, (short of simultaneous shifting, which would be less dependable) it would have to be downshifted on the right side first and upshifted on the left side first to make sure that any excess cog spin is applied to the left side (while pedalling forward). This would of course be reversed if anyone had the crazy idea of trying to shift while riding in reverse.
This would cause the reverse gearing to be slightly higher than the forward gearing during shifting, but I don’t think this would be much of a problem as long as it was shifted one gear at a time.
