12-17-2020, 10:05 AM
(12-17-2020, 08:10 AM)jamincan Wrote: Canardiain went into depth on this quite awhile ago. If I recall correctly, most of them can't roll between sections, but I think one of the joints can, so that it's effectively a truck/trailer situation. There was a reason they can't have full degrees of freedom between sections, but I can't remember exactly why anymore.
This is my recollection of what he said: as everybody knows, all the joints allow left-right turning (yaw). This can be easily seen whenever a vehicle goes around a corner.
What is less obvious is up-down turning (pitch). This is available only at one joint, so effectively the 5 sections behave as two in the up-down direction, split up as 3+2. Additionally, each set of wheels can rotate up-down slightly with respect to the unit under which it is mounted. If you look carefully you can perceive this when a vehicle enters or leaves a sloped section of the track: you can see that 3 segments are straight in line, then a bend, then 2 more segments (or 2 then 3, depending on which way it is moving).
This design means that the position of every segment is fully determined by the shape of the track on which the vehicle sits. If, for example, there were 2 up-down joints, say 2+1+2, then the middle section could exist in various orientations on the same piece of track and would therefore wobble unpredictably.
As far as I know there is no explicit twisting (roll) joint, although presumably a tiny amount would be taken up by the real-world nature of the structure.