One of the contributors of the thread mentioned the idea of an 3 point suspension as one of the options to improve the running of 4 wheeled cars (the other idea is to keep the wheelbase short; the shorter the wheelbase the better it runs).
The idea of a 3 point suspension is based on the comparison between a 4 legged chair that wobbles on an uneven floor and a 3 legged chair that will stand stable on the same spot on the uneven floor.
For a 3 point suspension the holder (or axle truck is the right word for it I believe) of one wheelset is rather fixed in position while the other can move up and down with a solid object at the center of the axle to act as a fulcrum.
As some of my 4 wheel cars do suffer from derailments (even the LGB standard stock) I was interested to adapt this suspension idea in my plans of building my own rolling stock (once). The thread did however not mention how this suspension could be build (only how it not should be build).
But I remembered this same solution was given for H0 scale modeltrains in a modelrailway book I had in the past and I vaguely remembered how it was made.
So, time for an experiment!
I took a piece of plywood as floor. I drew lines at the desired position of the trucks. Than I drew a line along the longitudinal axis of the plywood. The place where the lines cross is the exact center of the axle truck. Next I took 2 Playmobil trucks and removed the couplers as I wanted the car to be coupled with chains instead of the big plastic couplers. I later realized that I better had left the coupler on for testing the car...
To let the trucks have some slack, I placed a small brass rod (about 1,5 mm in diameter) along the longitudinal axle, like this:
Because of the hole in the middle of the axle truck I could glue the little bras rod in place using hot glue without the glue interfering the wobbling of the truck.
To keep the wheelbase in place I bend a piece of somewhat thicker brass rod in a sort of long U shape. The ends are pressed in drilled holes in the floor. The rod falls in slots in the truck which I made with a little file. The rod is also glued in place in a way the glue do not interfere the free wobbling.
This construction gives the truck a slack of several millimeters on both sides which must be enough to tackle the uneven tracks.
At the other side I glued a piece of balsa with the same thickness as the diameter of the brass rod in place so both trucks have the same height.
I than glued the second truck in place using hot glue though the next time I will only use one drip of hot glue to fixate it and than drill holes for screw through the truck. That way the truck can be replaced more easily when desired.
At this point the results are promising. The car runs through a curve on my layout that is notorious for derailments without derailing ... each time. So, yes, it still does derail now and than on this spot...
However I think this is now caused by lack of weight. Some extra weight could be added underneath (low center of gravity).
Also I have tested it only by pushing the car by hand through the curve. It is better to test it while being pulled or pushed by a locomotive... and that was the exact moment I realized I'd better left the couplers on the truck ;-)
UPDATE 25-08-2019
After some advise from the G-ScaleCentral thread mentioned above It seems the problems were caused by the fixed truck. The 12,5 cm wheelbase is too much for a fixed truck in the LGB R1 curves. LGB stock truck can rotate a bit to handle the tight curves so I changed the fixed truck into a rotating one, using a washer and an softdrink bottle cap to hold the truck in place:
PROBLEM SOLVED!
The car runs perfectly through all the layout without derailing. Experiment succeeded! As you can see I also altered the floor of the car a bit. It is the same floor but lowered in the middle and some balsa strips applied. More about that later ;-)
-o-
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