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Sidecar outfit bus
Bus with low step/floor height by use of motorcycle-sidecar-outfit layout. | |
One problem that keeps cropping up when one tries to design a low-floor city bus is the nearside front wheel. One needs to lead a boarding passenger past the bus driver and then over some form of front suspension crossmember, or else have the entry behind the wheel and employ an additional conductor/supervisor.
Why not dispense with the nearside front wheel altogether?
The result suggests a motorcycle sidecar outfit: a radically asymmetrical layout with all the mechanical components and the primary structure concentrated along the offside. It might even be possible to have only the offside rear wheel (or wheels) driven, as in most outfits, with the "sidecar" wheel (or wheels) slightly forward.
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The problem with motorcycle sidecars is that although you can take right-hand bends at breakneck speeds, left-handers make them flip (unless you have one of those racing sidecar thingies, and I doubt if your bus passengers would be inclined to hang off a plank at the back of the bus to change the centre-of-gravity - especially the ones that need a low floor to get on board easily). So you have an unstable bus that can only turn one direction. |
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In order to keep it stable, and keep it from diving onto the corner with no wheel, you rightly suggest having all the heavy stuff on one side, but then you end up with a triangular plan. If the driver is still at the front, you still have to enter behind the driver, because it's too narrow alongside him/her. |
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Besides, the buses around here have active suspension, so the whole front end dips on command to let the infirm aboard. Or to allow them to enter lowrider competitions. That way, you can keep the ride quality and roadholding (I *never* thought I'd consider those words in the context of a bus), but still have a low floor to board. The council here also raised the kerbs at all the bus stops to a uniform height (around 6 inches, say), so that even wheelchairs can just breeze aboard. |
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Most importantly, though, if it is a design inspired by motorcycles, can it wheelie? |
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//left-handers make them flip// |
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To counter this effect (whether it is left hander or right hander depends on the part of the word the outfit was maunfactured in, and hece the side the sidecar is on by the way) you need to learn to accelerate into corners turning one way and brake slightly turning the other. |
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I prefer the idea of all the passengers having to lean out of the windows to stabilise the bus when it corners. |
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I'm thinking in terms of a vehicle that moves too slowly to exhibit such dramatic dynamic behaviour. |
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The problem is that "kneeling" suspension or no, the front suspension assembly has a vertical depth greater than the thinnest practical floor-construction thickness, and therefore needs to be climbed over. The obvious solution is a flatter suspension assembly, but the sidecar-outfit approach is more appropriate to the half-baked context. |
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It would have th be very slow
then. Force effects, and in
particular gyropscopic forces
and conering forces affect
motorcycles from less that
1mph, ifi it did not they
would not stand up. Just
adding a sidecar doesen't
change this, it's stll
essentially a motorcycle with
an "extra bit". |
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You're saying this thing will fall over at 1mph? |
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The CG is likely to be much lower in relation to the wheelbase and track than with a real sidecar outfit, simply due to the larger scale in plan. Any falling-over sorts of forces will consequently be proportionally less, and the corresponding lateral acceleration at the point of falling over (hypothetically) proportionally greater. Exceeding about 0.2g in a public bus makes things uncomfortable for standee passengers, so the range of lateral acceleration to be accommodated is in any event limited. |
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