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Rocker-Bogie Inline Tricycle

Replace the rear wheel with a 2 wheel bogie
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The rocker bogie is a simple mechanism that allows wheel articulation to smooth travel over obstacles. The best examples of this technology can bee seen on the Spirit, Opportunity and Curiosity Mars rovers.

To adapt this system to more Earth-bound ventures, imagine a bicycle as one side of the rover with a standard front wheel and two inline smaller rear wheels forming the rocker bogie. Power is delivered by conventional chain drive with two possible configurations. 1. Drive one wheel in the standard manner and then drive the second directly from that. 2. Drive a sprocket between the wheels and distribute power to each individually.

Unlike the Mars rovers, the bogie motion should be constrained by a spring and damper, since it would be better to prevent the front wheel of the bogie descending completely into any hollow at higher speeds. The two smaller wheels effectively simulate a much larger single, wheel while maintaining the strength, weight and aerodynamic characteristics of smaller wheels*.

While the vehicle would technically be a tricycle, you'll still fall over if you can't balance. Handily, with clever folding jiggery-pokery, the whole thing should fit into a smaller space. It's the wheels that are the space hogs. Off road, there should also be increased traction and the pivot point can be played with to stop the annoying wheelie tendency you get with climbing steep hills.

*Raleigh conducted a study back in black & white days and the 20" wheel is the fastest on the track.

bs0u0155, May 27 2019

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       It would be fairly easy to make a bolt-on accessory to a conventional bike to test this, but cornering might become interesting.
8th of 7, May 27 2019
  

       If you need to corner, you were going in the wrong direction to begin with.
MaxwellBuchanan, May 27 2019
  

       Replacing the front wheel with a similar arrangement would be necessary to enable the smallest folding.   

       How steerable would such a pair of wheels be? (A grammatically valid reading of that sentence: How would such a pair of wheels be steerable?)
notexactly, May 28 2019
  

       It will be effectively Configuration 2 anyway; even if you drive front, which drives back, the drive is initially coming in via the pivot (ie: not an axle) unless you're doing REALLY complicated things with the chain tensioner.
Cornering will be interesting as 2 wheels mounted in a line like to follow that line; perhaps the rearmost wheel could be some-what flexibly mounted on it's axle (a la semi-trailer self-steer wheels)?
neutrinos_shadow, May 28 2019
  

       Or the rocker-bogie could just have a vertical-axis bending hinge at the same place it has its horizontal-axis rocking axle, making the rear wheel a caster. That would make driving the rear of the rear wheels harder, but you can get away with driving the front one only. More importantly, it might not actually allow them to follow the same track.
notexactly, May 28 2019
  

       No, the 2 wheels at the back need to be able to turn/bend relative to one-another. Try going around a corner on a normal bike without turning the handlebars...
If the pair are still fixed in a straight line, but can rotate relative to the frame, they will keep going straight while the rest of the bike turns, which would look funny and provide endless "Fail" videos for YouTube.
Perhaps an offset, angled pivot (for just the rear wheel of the pair) that will take advantage of gyroscopic effects the same way the front wheel does (ie. you lean, it turns. You straighten up, it re-aligns).
neutrinos_shadow, May 28 2019
  

       I would think you coulld have a mechanical linkage between front handlebars pivot and rear wheels, so that the three wheels of the bicycle are always automatically arrayed along the arc of a circle. Might not work for slalom courses though.   

       Alternatively have a second handlebar which controls the alignment of the rear pair. Perhaps attach the linkage to the saddle post, so that the rider can steer the rear pair by wriggling their arse.
pocmloc, May 29 2019
  

       "Rocker-bogie" is obviously some sort of 1950s slang, as used by Teddy Boys. How is this not part of the idea?
pertinax, May 31 2019
  

       // No, the 2 wheels at the back need to be able to turn/bend relative to one-another. //   

       That's exactly what I was saying: //vertical-axis bending hinge […] making the rear wheel a caster//   

       But the contact points between the three tires and the ground must always be along a straight line, so that the bike can lean to the side when turning. Could be tricky.
notexactly, Jun 14 2019
  

       [notexactly]; sorry, I mis-interpreted your comment...
I think, because the rear pair can also move vertically relative to one-another (the whole point of the idea) the 3 wheels don't need to be in a line, as any sideways offset (when leaning/cornering) will be compensated by the vertical change at the same time. The mechanics of the steering (whether controlled or passive at the rear) will be interesting...
neutrinos_shadow, Jun 16 2019
  

       It may be useful to consider the geometry of 6 x 6 vehicled, be they 2 - 2 - 2 or 2 - 4 in configuration, altho since the wheels are differenially driven and don't intentionally tilt it's not the same geometric problem.   

       The nearest thing might be a single-track version of the Kleines Kettenkraftrad.
8th of 7, Jun 16 2019
  

       Wikipedia says "The vehicle was designed to be delivered by Junkers Ju 52 aircraft, though not by parachute. " That is one tough motherfucker of a vehicle.   

       But that is by the by. Bogied bicycles (and tricycles) were used in the 1970s and 80s by the Botswanan police, to help them negotiate rutted and/or log-strewn tracks in going about their duties. The most common versions (known as nyoka, or snake) had a normal front wheel and a bogied rear wheel. One variant had both front and rear wheels replaced by bogies, and were affectionately known as nyoka-nyoka. They were provided to all patrolling policemen (no policewomen at that time), and were universally reviled. Most were converted to "normal" bicycles by their owners. The rear bogie assemblies were often re-purposed for use in home-made air conditioners, some of which are operating to this day.
MaxwellBuchanan, Jun 16 2019
  

       //home-made air conditioners, some of which are operating to this day// I believe there is one in the houses of parliament, part of an "alternative" official gift from unafilliated members of the Botswanan counter-parliament.
pocmloc, Jun 17 2019
  

       There is, but unfortunately the Botswanan broke down after two years and they haven't replaced him.
MaxwellBuchanan, Jun 17 2019
  
      
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