Design for less wobble?

[mozartk626]

Just finished my first race, and my son took 1st place in his den. We got crushed in the pack finals, though. I was confused by the results, though. I had built a really sleek, skinny in the middle car. It weighed in spot on 5 oz, a full 3 oz of which was set behind, above and around the back axel with only a very small counterweight near the front so the center of mass balanced EXACTLY 0.9 inches in front of the rear axel. What surprised me is that almost all of the really fast cars, including the pack winner, were VERY bulky looking (imagine the shape of a 1970s muscle car) that looked like way too much weight was probably distributed all over the car instead of the back. The only thing I can figure is that those cars appeared to wobble very little through the flat track, whereas our seemed to get really wobbly toward the end of the races. Our pack uses the two lane yellow plastic tracks, and the plastic strikes me as very bouncy. Does anyone have any idea as to why bulky cars were clobbering my sleek, racy looking one, and where I’m going wrong? Is wobble the issue?

[FatSebastian]

Is wobble the issue?

Perhaps. A bulky body such as your competitors will not have an aggressive CoM placement and thus won't be as susceptible to instability. I personally have no experience with a plastic track or channel-shaped lanes, but generally speaking, if the axles are leveled so that the wheels are not cambered, the clearances between the body and the wheels should be pretty close to avoid the rear-end sliding around on the axles. Also, a slight negative camber in the rear causes the car body to be "slung" and may offer a bit of added stability as well as reducing tread-to-track contact, even if you aren't rail-riding; testing of the alignment on a tuning board is then necessary to ensure that the wheels behave as desired.

Did the wobbling cause your car to impact the sides of the channel? That would take a lot of energy out of the car...

[Loud2ns]

Got a pic of the car and perhaps a pic of the weight placement? Center rail on the track in the middle or just the outer edges of the lane? Just need a bit more info to give an opinion.

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[whodathunkit]

Our pack uses the two lane yellow plastic tracks, and the plastic strikes me as very bouncy. and where I’m going wrong? Is wobble the issue?

There are 3 types of yellow extruded pvc tracks on the market that I know of.

1st: The Derby Magic Track.. it has a rail that of like a best track 1 5/8'' wide by 1/4" tall.
2nd: The Pinewood Pro Track .. it has no center rail in between the wheels.. just 2 guides that are set out side the wheels.
3rd: The Super Timer Track.. normally there are 2 yellow lanes and 2 blue lanes for there 4 lane track.. also no rail between the wheels.

For the Derby Magic track with rails.. your car could need more steer to hold it to the rail if rail riding on canted axles and 3 wheels.

Also wobbles could be from to big of wheel hub to body gaps on un-canted axles causing shifting from side to side on the axles.
Out of round or bad wheels to improper alignment of wheels and axles toe in toe out.. and an over aggressive COG weight to far back in the car all lead to wobble problems
as the car comes off the ramp and into the flat.

For the tracks with no center rails try making a straight running car with tight wheel to body gaps maybe run with a cog around 1 1/4'' to keep the front from bouncing
over the rough and bumpy/ bouncy extruded pvc tracks.. and hope for the best that the track has no tilting or twisting to it's lanes.

[FatSebastian]

For the Derby Magic track with rails.. your car could need more steer to hold it to the rail...

mozartk626's "pack's track does not have a center rail, so no rail riding is possible."