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I'm thinking of building a dicycle, specifically a sociable one like the picture below but pedal powered. Has anyone seen one in real life, or better yet, tried to build one?

enter image description here

The broad design is easy enough, I can get ordinary wheels from the local racing/historical scene. It's the drive and handling that concern me. I suspect I will need an adder-subractor gearbox to balance the pedal power and allow it to be ridden solo, but I've never built one except using Lego so I'm not sure how big it'll need to be.

I'd really appreciate tips from people who've built one before.

Móż
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    I've never seen one of these, even in pictures (though I've seen sociables with the riders side-by-side and the wheels fore-and-aft). What stops it from tipping forwards/backwards about the wheel axis? – Chris H Jan 28 '16 at 16:57
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    @ChrisH good design and rider experience. Sloshing is unavoidable and you have to explicitly design around gerbilling because it will happen. – Móż Jan 28 '16 at 20:07
  • @ChrisH Center of mass below the center axis. Still going to rock and and maybe even rotate. – paparazzo Jan 28 '16 at 23:55
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    @Frisbee, it would have to be directly below for that to work alone, and with moving humans in there it won't stay in the same place. Wikipedia wasn't clear, but I'm guessing gerbilling is basically the effect of torque while sloshing is the pendulum effect that doesn't need pedaling to cause (?). – Chris H Jan 29 '16 at 06:52
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    @ChrisH gerbilling is when you stop pedalling/running and the vehicle keeps rotating. You go round and round (or round and down, depending on whether you're attached to the vehicle). Sloshing is as you describe, but is most obvious when you start pedalling (or start braking). – Móż Jan 29 '16 at 08:36
  • @ChrisH It is hanging below directly below. They work. This is not an imaginary bike. – paparazzo Jan 29 '16 at 10:29
  • @Frisbee, I know it's not imaginary, I'm trying to figure out how. The wikipedia article linked in the Q refers to electric control/damping, and we're talking about building a bike, not a segway; besides, there's no sign of electronics on the picture at the wikipedia article. – Chris H Jan 29 '16 at 10:35
  • On a seperate note, the picture doesn't show pedals (as it's from a patent for an electric version). You might get away with a simple differential (to allow 1-wheel braking to steer) and a common drive input (so riders pedal in sync, like a tandem, pedalo etc.) I doubt anyone has built one before, I assume you would have found it if there was anything online. For the single-rider version you may get some hints from the TU Delft unit via their youtube video, but presumably you've seen that. – Chris H Jan 29 '16 at 10:39

1 Answers1

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Some thoughts - but not really an answer.

Fundamentally its a RWD tricycle with no front wheel.

Drive shaft drive. I'd be exploring a driveshaft that runs horizontally under both seats, and using a tricycle-style open differential in the middle.

There is a shorter jackstaff drive axle that runs from the rear diff up/forward to the half-shafts through a closed differential. Otherwise this would not be rideable solo.

Drive chain drive. For this you'd have a chain from a front pedal axle to the rear axle. This would allow conventional bike components to be used for chainrings and rear cassette, and even deraileur gearing. However you'd want to incorporate two more freewheels out by the wheels themselves, to allow for skid steering

In this case both riders will pedal at the same cadence, and the spare cranks will rotate when riding solo.

Some excellent concepts of "chain drive to two wheels" show up in this answer https://bicycles.stackexchange.com/a/38875/19705

Final drive To get drive up from the under-seat cross axle up to the wheel hub, you're probably looking at another chain on each side. Good thing about this is the gearing could be swapped out as required.

Steering Steering would be achieved by skid-steer, braking the inside wheel on the turn so the outside wheel drives around. Ideal turning circle would be twice the horizontal wheelbase or width. Brakes would be best as disks attached to the wheel hub, outside of all the chains. That way any drive failure will not stop you from braking.

Brakes I'd contemplate a pair of motorcycle-sized disk brakes, one per side. Possibly use two bicycle calipers per disk, and connect each pair to each seating position. That will give a redundant braking solution.

Visibility Too much framework and it will be difficult to see around.

Roll-around Gerbilling will always be an issue, so put in a pair of three point racecar harnesses in case you end up inverted. Likewise, racecar seats would be appropriate rather than bike saddles.

Off road gerbilling would be awfully dangerous - even flat-land there could still be an obstruction that catches part of the frame, or part of a rider.

Safety You might want to consider drag rails at the back in case of "wheelie" when taking off, and possibly a front outrigger too (Though this would need a wheel or a skid/ski to prevent digging in)

You require wheels to be larger than the maximum "size" of any rider so that no part of the riders comes outside the "can" shape.

Other The passenger's hands will be bored. Consider adding a cupholder.

Side slope - most roads have a degree of slope to assist water running off. Even pathways and sportsball courts are generally not completely flat. So your ride will be canted in one or the other directions almost all the time. Whether its worth allowing the seats to rotate or not may be over-engineering.

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Criggie
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  • You want that no rider can get a hand or foot onto the tread of either wheel while riding, else its a crush hazard while rolling. – Criggie May 22 '16 at 06:27