Was noticing that in Walt Disney World where trams that are trains, but on rubber tires and no rail, can move like a train at curves. For example when the cars go around and island in the road to make a 180 degree turn all cars follow the same route the lead motor car makes.
As we all know that defies physical laws as, for example, a semi when turning a corner that is tight requires a wide area as the trailer can't follow the path of the cab. If the cab is to close to the side of the turn, the rear wheels of the trailer will either jump the curb or hit whatever is on the side of the turn. Even on a bicycle the rear wheel doesn't follow the front wheel on any curve due to the radius of the curve differs on each end. Also watch your own car in the snow while taking a turn. Your front wheels will have wider tracks than the rear wheels due to physics as well.
How can parking lot trams actually all follow the same alignment when making turns despite the radius law?
I never thought about this so I did a quick search and found this answer from someone who did this in the past (https://forums.wdwmagic.com/threads/tram-curiosity.899898/). Perhaps someone else can explain the actual physics.
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The trailing cars do not follow the same path as the car ahead of them. There is a "whip effect" when going through turns where each car will come out of the turn a little further to the outside than the car in front of them. When taking the tight 180 degree u-turn, the operating procedure was to make the turn at half speed or else the last car could swing out and hit a tree or pole.
I was supposed to be an expert in the opposite side of this equation, but am certainly not in this specific area. Obviously, trailers with steerable axles allow the trailers to "follow the leader" in tight curves, but the steerable axles also have issues trying to maintain a straight line unless electrically or mechanically controlled from the lead vehicle. But any trailer with fixed axles can be designed to roughly "follow the leader" using a few basic features. First, the towbar needs to be long enough to prevent jack-knifing (ergo, the length of the towbar is somewhat longer than the rotated radius of the back face of the lead vehicle). Second, to accommodate such a tight radius, the suspension of the trailer axles needs to be designed to force the inner wheels to "yaw and roll" (ergo, change the rotational diameter of the contact part of the tire so that the diameter is significantly smaller than normal).
Now to the opposite side of this equation. There are a myriad of designs related to axles width, suspension, tires and run-flat arrangements. Certain failure modes change the "dynamic envelope" of the lead vehicle and its trailers. For any environment with tight vertical and horizontal clearances, the vehicle designer needs to either specify the minimum clearances or design the vehicle to stay within a set of clearances. This is an obvious issue in railroading and also rubber-tired trains, but it also applies to road-based vehicles. For instance, the specialty buses that were once used in the lower level of the Miami Airport (arrivals loop) needed to be designed to meet a short vertical clearance (9-foot-6, if I recall correctly). They weren't cheap.
Quote from: skluth on August 07, 2022, 10:40:35 AM
I never thought about this so I did a quick search and found this answer from someone who did this in the past (https://forums.wdwmagic.com/threads/tram-curiosity.899898/). Perhaps someone else can explain the actual physics.
Quote
The trailing cars do not follow the same path as the car ahead of them. There is a "whip effect" when going through turns where each car will come out of the turn a little further to the outside than the car in front of them. When taking the tight 180 degree u-turn, the operating procedure was to make the turn at half speed or else the last car could swing out and hit a tree or pole.
On page 2 of that thread someone illustrates the type of mechanical linkage (https://forums.wdwmagic.com/threads/tram-curiosity.899898/post-6717818) that allows such trams (https://en.wikipedia.org/wiki/Trackless_train) to "follow the leader" .
The LeTourneau Overland Train (https://en.wikipedia.org/wiki/Overland_train#TC-497_Overland_Train,_Mk_II) was able to do this 60 years ago:
(https://upload.wikimedia.org/wikipedia/commons/thumb/d/d7/The_Overland_Train.jpg/566px-The_Overland_Train.jpg)