A skilled mountain biker can cross some extreme terrain, but [The Q] thought there might be room for improvement, so he converted a fat bike to all-wheel drive.
The major challenge here is transferring pedal power to the front wheels, especially around the headset. [The Q] solved this by effectively building a differential from the parts of a very old hand drill. Since the front wheel needs to rotate at the same speed as the rear, one long chain loops from the rear wheel to the headset, tensioned by a pair of derailleurs. This front sprocket turns a series of spur gears and bevel gear arranged around the headset, which transfers the power down to the front wheel via another chain.
It would be interesting to feel what the bike rides like in soft sand, mud, and over rocks. We can see it has some advantages in those conditions but were unsure if it would be enough to offset the penalty in weight and complexity. The additional chains and gears certainly look like they’re asking to catch foliage, clothing, and maybe even skin. However, we suspect [The Q] was more likely doing it for the challenge of the build, which we can certainly appreciate. With the rise of e-bikes, adding a hub motor to the front wheel seems like a simpler option.
We’ve seen several interesting bicycle hacks over the years, including a strandbeest rear end, 3D printed tires and an automatic shifter.
well. the main problem will be that of friction. the ride will be a lot tougher. you already see him pushing really hard at the pedals even on almost horizontal ground.
but a nice try anyway. although metal guitars is not my choice for background music. fortunately there is a button for that. :-)
Yep, interesting build – but definitely some issues from practical (not that I have a better solution). Pedaling isn’t exactly smooth torque delivery – and you’re probably(?) going to be fighting the surging torque-steer, which will get worse the harder you’re pushing it. Front tire is probably going to want to wash out in corners – due to being under-rotated to keep pace with the rear. Maybe good for riding in sand, but other than that seems it’s going to be pretty much downsides only.
Not sure we can say that, there is definitely extra friction, but we have no force gauge, comparison shot etc, and riding on soft surfaces is more work anyway – this might actually on the soft surface be easier to ride than the bike was before modification.
I expect you are right, and its certainly not a system that makes sense on more normal riding surfaces, but on nasty soft sandy stuff it might actually work better.
You can estimate that each gear contact or chain loses 3-5% efficiency, so with two extra chains, two gear contacts, and the extra derailleurs, you might be looking at 20-30% loss, or 25-42% increase in effort to drive power through the front wheel.
This is also the criticism leveled against bicycle hub gears: the planet gear contacts inside the hub adds losses compared to throwing a chain across different sprockets – although having the chain not running straight between two aligned sprockets also adds losses because it requires a chain with looser tolerances to allow sideways motion, and it gathers dirt and rubs against itself (wears out faster).
You can estimate that, but is it realistic? As Foldi-One said we have no measurements to go by, and it might still be more efficient on the soft surface.
Indeed, I also agreed that its probably worse.
We just don’t have any way to actually tell, and because soft sand is so horrible to ride on, something I expect many of us do know, it becomes plausible it is helpful.
I probably shouldn’t have said “more efficient on the soft surface” it might better be phrased “more effective on the soft surface”. I’ve never cycled on sand (that I can recall), the closest I’ve experienced would probably be snow and ice. I suspect having a powered front wheel would make handling on ice significantly worse, just based on being near the limit of traction all the time. I can imagine that cycling on dry snow would have been much better with a powered front wheel though, a bit of a pull up the snow as well as being pushed into it, could be similar with sand.
Jeep built this a long time ago. All gear driven internally through the frame.
Why not put a brushless electric motor on it with a nice battery pack like the old racks on the back and you could may e sell a few if them? David Medway
Turn it back on at 2:47 for some sweet acid licks
Rokon has been making 2 wheel drive motorcycles. I wonder how their front wheel mechanism compared to this one. Pretty cool stuff all around. Hopefully turning with a powered front wheel doesn’t just slam you into the ground with a torque steer.
If I was them I’d use a hydraulic motor and plumb it with hoses to at pump driven off the motor. This would allow a hydraulic pressure relief valve to limit forces, particularly from unmatched tire perimeters when on pavement. It would also allow bypassing it entirely with a bypass valve to allow an amount of free-wheeling if two-wheel drive was not required.
IIRC this was tried in a concept model (20yrs ago?), but the hydraulic fluid resistive losses are huge, making it impractical. I’ve heard them called frictional losses but that seems like a weird choice of word when we’re talking about essentially oil. Shear forces, maybe? Regardless, the losses were far higher than any chain drive losses.
Some of our mechanical engineering colleagues are prob better positioned to elaborate on the exact details of the hydraulic losses.
Not a big deal for a hydraulic excavator to overcome those losses with a massive pump and diesel engine, but for something that you have to haul around under your own power…
PS: mostly talking about bicycles, but still prob applicable to a large extent to motorcycles
“Viscous shear and turbulent losses” doesn’t roll off the tongue as well….
The major challenge is that unless there is a lot of slip between the front and rear wheels any difference in tire perimeter between the two will put a lot of strain on intermediate components.
True, this is the bicycle equivalent of a 4×4 that’s stuck in 4WD all the time and has a diffless transfer case. A slipper clutch for safety on the front drive would be a decent idea.
It effectively has one – the chain that carries the power from back to front has tensioners on it, which will allow the chain to skip teeth if the force gets up.
Not what I was expecting when I read the title…I’ve been thinking a 2WD bicycle might be possible using an “electric shaft” drivetrain – these are usually used on boats, basically an electric generator and motor pair that are electro-mechanically tuned to each other are wired directly together and they transfer power at a fixed “gear ratio.” This would be a mechanically simple and not too heavy way to get power from a bicycle’s pedals to the front wheel. Of course 2WD bicycles don’t have a huge traction advantage over a regular RWD bicycle in most situations anyway…if you’re running out of traction you’re either in slippery muck with a serious risk of falling over, or climbing in which case you’re more likely wheelie-limited or gearing-limited than traction-limited anyway.
I’ve ridden a similar implementation of a 2wd bike made in the 1980’s by a guy named Jon Lebsak, who appears to have vanished off the face of the earth, but he used to run a bike store and make a line of bikes called Vertebrae Cycles. His design wisely used a straight pull (no derailleur for slack) chain on the tension side. This design with the two derailleurs handles the wheel travel offset and prevents the bike drivetrain from winding up in tension, but means the front wheel isn’t able to take a lot of power because it’ll just yank the derailleur to full extension (and probably injure it) before the wheel takes up the slip. But the interesting thing about a front wheel drive bike that’s kinda unexpected is you can roll right into a curb as high as the wheel is tall, and if you’re going slow so you don’t bounce off, it climbs right up. It’d go up a set of stairs with very little effort. I never got to try it on serious offroad conditions, but if it behaved there the way it behaved in the parking lot in front of the bike shop, it would make short work of erosion bars that usually stop bikes if you’re not good at wheelie/manual/hops. I’ve a paper plan to use a 3 speed rear hub in the front, with one of the three speeds modified so it’s open rather than geared. That way you could ride 1wd most of the time, and when you came up to a big obstacle, you’d shift into second, that would be an overdrive and take the slack out of the system, then down into first, which would be 1:1 with the rear wheel and be ready to climb. What Jon did, which I think is a better idea, is he had the tension line feeding up to a cog on a bearing where the front edge of the cog was directly in line with the head tube centerline, and he used a profile or mongoose offset stanchion fork so the chainline could go straight down the fork line to a second cog. That way the tension line never saw a change in position during a turn, just a twisting movement, and didn’t need any sort of length compensation. (Implies no front suspension.) The return line had a sprung idler to handle slack changes as it wasn’t a zero offset chainline.
I also found this link: http://www.ihpva.org/HParchive/PDF/30-v9n2-1991.pdf See pages starting at 11.
I don’t understand the need for the second take up on the tension side. The spacing from the front to rear sprocket does not change and neither does the amount of chain wrap on any gears. There should not be enough variation to notice and any excess is just transferred to the slack side anyway.
Technically they aren’t derailleurs as they do not derail the chain from one sprocket to another – just acting as tensioners.
Lots of exposed sprocket and chain to catch your pants or other parts.
Now I can catch my shirt in the chain too!
I’ve built my fair share of weedeater-powered bicycles in the past, and actually appreciate the way he routed the chain to allow for steering with only jackshafts and an extra derailer.
That said, NOPE. 30mph on a ten-speed on level road is scary enough, this monstrosity off-road? There ain’t enough beer in the world to make it look like a good idea.
What he has built is not a differential. If he had, this may be ok. The front and rear wheels will need to turn at different speeds when the bike is turning. However, this is just a fixed gear set that is using the bevel gear to transfer through the head tube. This will not let the two wheels rotate at different speeds.
But the chain that transfers that power and its tensioning system should let them move at different speeds if it comes to that, it will take up some of the difference on the tensioner then if the imbalance continues the chain will skip.
But with the tiny contact patch and low weight on the tyres I expect it will just wear them out a bit faster scrubbing them over the ridden surface in a turn.
the bike should fare well in the oncoming Ice Age
So, when a bicycle makes a turn, the two wheels *must* go different distances: At the end of a turn, the front wheel has made more revolutions than the rear wheel. Always.
So what happens here? Does it shudder and lose grip like a locked-diff 4WD?
Think I’d cheat and use an electric motor in the front. Not a v strong one, just at an assist level. A spoke sensor on the rear can drive the speed if the front and just add a pinch of overspeed. Of course it would not meet competition requirements. It could even be set to freewheel unless a throttle is turned. Regen braking would be suggested. A limited slip clutch could be added to the mechanical version and operated via a hand brake mechanism could be left engaged or again, freewheeling… or pull the lever to engage, because your hand won’t be pulling the brake lever when you are climbing. You don’t need the 2WD ALL the time. It’s a v good start… Kudos! He has the platform and now can tinker. Steering could even be achieved by a hinged frame. This might make the drive simpler. Brainstorm, guys –
thats what I was expecting to see while I waited for the image to load –
It’s been done to death, but I still like someone doing things for fun.
I’d be more interested in the effect on steering and suspension forces. The feedback from the road going motorbike world was that it created a very unnatural feel and locked up suspension forks in some circumstances, but definitely gave an improvement in road holding and cornering that outweighed the power losses.
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