my son and i built our third pwd car to race with his pack. wheels and axles are treated with derby worx tools. car is appx 5/8 thick and is hollowed out the front 3/4 of the car. off the line, car is fast but last 1/4 of track there is severe wobble. the car was more stable running backwards but still had same results. this is an annual thing so do not have much background other than cutting wood and slapping wheels on with my dad as a kid. any insight would be greatly appreciated
car stability at end of track
- Thread starter pancak2k
- Start date
you can try a few things to stabalize the wiggle.
First - increase the steer
second - you can move some weight forward to adjust the cog
First - increase the steer
second - you can move some weight forward to adjust the cog
i will try those. what does increasing the steer do? is there any way to determine these issues before race day? is there a balance point to set by. a ratio of weight in front of axle vs at back of car? I'm trying to work on ideas for next years car not to salvage this years. our wheelbase is set but wheel location can be anywhere on car. should they be as far back as possible? right now they are in stock location with the back wheels closest to the end of the block. thanks again for your input
pancak2k said:
Most likely, your COM/COG is not too aggressive. Did you measure it? If not, it's easy to do by setting your car on a blank block and sliding it forward so that the front end hangs over the end. Keep pushing it forward until you hit the balance point. Measure the balance point's distance from the rear axle. this should be about 3/4" to 1". If not, it's OK (as you're not trying to change this year's car much), but it's a point of reference.
If you have a 3 wheel rail runner, you need to take the dominant front wheel (DFW) that is "steering" the car, and make sure that it stays on the rail. The only way to do this is to increase the amount of steer the car has towards the center. How much? That depends on the COM, the track type, and other factors, and each car can be slightly unique. Generally, as is stated elsewhere, you will need the car to steer 10-12" over 8". This makes sure that the car stays on the rail throughout the flat part of the track. Most times, when there isn't enough steer, the car will wiggle during the last two track sections.
Another thing to keep in mind is that wheel/axle prep will be a big key to greater speed.
Good Luck.
O.R.
Does your forward dominate wheel have a bent axle to adjust steer? The FDW is the frt wheel that is touching the track. Also is the FDW on a positive cant or camber if the axle is bent?
Good BSA tips can be found in this thread
http://forums.derbydad4hire.com/post/BSA-building-tips-5598193
http://forums.derbydad4hire.com/post/BSA-building-tips-5598193
- Nov 24, 2011
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it will migrate to the body. If you cant use Teflon washer, paint the area around the axle hole with some clear acrylic nail polish. Do 3-5 coats to build it up and after it drys hit it with a polish. Then set steer to at least 8inch over a 8ft roll. So FDW on out side of tread, rears on inside.
- Nov 24, 2011
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