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I have a trio of the AristoCraft Streamliners and love the way they look. I've even modified one adding a drum head and rear flashing lighting that stays on when the engine comes to a stop.

But what I don't love is the way they continually derail on me on the slightest trackwork imperfections. I know that improvement may be had by changing the springs, I think that there is an inherent flaw in the truck/body interface that exacerbates the problem.

I feel that the problem lies in the fact that truck pivot point does not lies midway between the axles, but rather just behind the front axle. The result is that changes in the position of the coupler from side to side that also pull the near axle over are "amplified" to the far axle forcing it further out in a curve making it want to/more prone to jump the rail head.

The axle actually pivots around the screw on the right, not the screw at the centerline on the left as one would think. Therefore, a lateral force on the coupler creates a torque about the pivot point with the rear axle sweeping a larger arc than the front axle, potentially adding to derailments. In my mind, one would want this symmetrical about the pivot point:
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There are several other problems, and I've identified what I consider to be the five primary flaws. These include:

1) The existing bolsters allow for no side-to-side rock. If one side of the car is tilted in a curve, this motion is transmitted through the body to the other set of trucks and becomes a source of derailment. This lets the car now rock side to side, as well as forward and backward

2) The center of gravity is too high. This modification lowers the center of gravity both at the car due to a lower body, but also below the trucks from the metal bolt/nut combination and heavier materials,

3) As noted above the centerline of the axles is not the pivot point for the trucks and movement of the coupler tangs in a turn puts an uneven torque about the centerline of rotation as the rear axle is fored into a wider arc than the front axle. This addresses the issue of unbalanced torque about the centerline of rotation. This may not be an issue with body mount couplers. But on truck mounted couplers (like I use), as the cars go through a turn, the tangs are forced outwards which forces the inner axles inwards by a greater amount potentially adding to derailments.

4) The original bolsters are weak. These are much stronger than the plastic originals which are prone to crack at the mounting towers, like several of mine have done.

5) The gap between the body and trucks is too big and the cars sit too high. This improves the looks by reducing the gap at the trucks.

This modification uses 1/8" and 3/16" thick acrylic cut on a laser table. All parts were modeled in CAD and people are welcome to the .dwg files.

The lower bolster (closer to body) is 3/16" to allow the head of a 1/4-20 bolt to nestle into. A nylock nut keeps things in place and avoids the bolt from tightening/loosening on itself. The open triangles allow for the wires to pass through into the body:
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The upper bolster (away from body) is 1/8" acrylic with a 1/4" hole:

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A 1/2" OD, 1/4" ID 1/8" thick acrylic washer lets the trucks rock in all directions.

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And a 1/8" thick acrylic plate locates the bolt into the existing trucks providing the new pivot point, located almost centered between the axles.

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All of the acrylic pieces:
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Assembled bolster:
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One down, two too go:
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Resulting pics in next installment. (No more room in this one.)
 

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