Troubleshooting the wiggles out!

[ichiban]

Hi, my boys cars had severe wiggles today at their pack race. We built the cars for rail riding eventhough all four wheels have to touch the track surface. The cars steered 4 inches over a 4 feet alignment board which I assumed was aggressive enough for the 3/4" CoM(CoG) they had. However the cars were not sticking to the rail. The front wheels supported around 25 grams of the overall weight where 28 grams would have been 20%. To troubleshoot I'm assuming we should process through the areas based on effectiveness at reducing the wiggles. What is the order of effectiveness? Thanks!

[speedie4u]

1, is to look at alignment and re go over it well. Is the bend to much and causing it to push back out and away from the rail and then back in ?
2, axle gap ?


have you tried narrowing the width some more ? This can reduce wiggle, but is not competely eliminating the friction loss.

[ichiban]

1. Kickback crossed my mind but we need to test.
2. The fdw body side was narrowed by 1/16" and a maxv business card was used for the axle gap on the front wheels only. A metal axle gap tool which I don't have at this post was used for the rear wheels so their gap was at least twice as large as the front.

Note, we drilled our axle holes at the standard BSA wheel base location so the wheel base is 4.375".

[MaxV]

If by "wiggles" you mean the car zig-zagged left to right on the flat part of the track, the trouble is most likely too agressive of a balance point. When the COG is too close the rear axle for a given track, cars will tend to exhibit this behavior.

What is the distance of the balance point from the rear axle?

[ichiban]

Center of mass(gravity) is 3/4" in front of rear axle.

[MaxV]

If the car is zig-zagging on the flat section of the track, then most likely the balance point is too agressive for the track. I suggest moving some weight forward on the car until the car stabilizes.