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I've been thinking along these lines lately:-
Take a 20" wheeled donor with rear suspension like this one: where the rear top stays are pivoted at the wheel end and the suspension linkage passes around the seat post rather than being attached to it.
Then build this:-
3x20" wheels. The rear triangle has a head tube at the top so the tube passing through it is free to rotate. The steering is by brake cable (2 each side for safety) with USS pulling on one side or the other of the cable to pull on one side or the other of an actuator bar welded to the main tube. The rear suspension of the donor is used at the front hence the desire for that particular type of suspension arrangement.
As with any tilt steer system it's a compromise and will usually be a bit too much or little lean for any given corner but rarely worse in that respect than having no tilt. It needs to be wide as the pilot is not ideally placed between the rear wheels but needs to be forward from the ideal. At rest when parked it'll probably flop as there's more weight above the axis of rotation than below but with the lard onboard the pilots weight should act below the pivot axis to bring it to rest in the straight-ahead position as a Python does.
If excessive swing is used it's going to tip with the forces being outside of the rear wheels let alone outside the three contact points area. At slow speeds this will not tip as the centrifugal force will not be sufficient to pull it over. However at faster speeds it becomes more of an issue as with any delta.
Helping in this respect is the front wheel contact point moves outwards as you turn due to the head tube angle being ahead of the front wheel though it's only a little help and the wide rear track of 37". The only way to make matters better is to widen it more or lower the head tube. The latter is not desirable because of extra wheel flop. The general idea has been blatantly ripped off from here and the stability was questioned, measured and deemed acceptable by the builder/user.
The rear suspension on the front could also be of interest to Pythoneers as it's perfectly adaptable to such a design and the main tube over the front also acts as a crud catcher / gonad saver.
Take a 20" wheeled donor with rear suspension like this one: where the rear top stays are pivoted at the wheel end and the suspension linkage passes around the seat post rather than being attached to it.
Then build this:-
3x20" wheels. The rear triangle has a head tube at the top so the tube passing through it is free to rotate. The steering is by brake cable (2 each side for safety) with USS pulling on one side or the other of the cable to pull on one side or the other of an actuator bar welded to the main tube. The rear suspension of the donor is used at the front hence the desire for that particular type of suspension arrangement.
As with any tilt steer system it's a compromise and will usually be a bit too much or little lean for any given corner but rarely worse in that respect than having no tilt. It needs to be wide as the pilot is not ideally placed between the rear wheels but needs to be forward from the ideal. At rest when parked it'll probably flop as there's more weight above the axis of rotation than below but with the lard onboard the pilots weight should act below the pivot axis to bring it to rest in the straight-ahead position as a Python does.
If excessive swing is used it's going to tip with the forces being outside of the rear wheels let alone outside the three contact points area. At slow speeds this will not tip as the centrifugal force will not be sufficient to pull it over. However at faster speeds it becomes more of an issue as with any delta.
Helping in this respect is the front wheel contact point moves outwards as you turn due to the head tube angle being ahead of the front wheel though it's only a little help and the wide rear track of 37". The only way to make matters better is to widen it more or lower the head tube. The latter is not desirable because of extra wheel flop. The general idea has been blatantly ripped off from here and the stability was questioned, measured and deemed acceptable by the builder/user.
The rear suspension on the front could also be of interest to Pythoneers as it's perfectly adaptable to such a design and the main tube over the front also acts as a crud catcher / gonad saver.