My son used to spin the wheels LIGHTLY against a medium grit beltsander, to even out the "treads. Graphite, lightly applied, is a great axel treatment. Weights,...usually just behind front axel, as welll as a very slight "up" angle, from the front axel, forward. 4TTRUK
Take a piece of thin plastic, I used a piece cut from a quart of oil, and make a "hubcap". Polish the nail good, even the head. Put the car on it's side and put some graphite on the wheel, then glue the hubcap on over that. Repeat for the other side. Now the tire won't touch the car because the hubcap will hit the end of the nail, PLUS a little shakey-shakey on each side and you relube the wheels!
weights recessed into the body (I melted down fishing weights) just behind the front axles. if you front load it it will be slow out of the shoot and super fast at the end. never turned the axles as such, but I spend hours hand sanding on them as a kid. they never beleived it but I did amost of the work. dad cut the rough form and sent me away with sandpaper. he melted and poured the weights (it didn't hurt that he sold professinoal scales and supplied the ones we used on race day so I was always spot on) no paint until the car met the semi-pro painters approval. we used off the shelf metalic rattle can from the paint shop (when that stuff was hard to find). HOURS sanding those cars and axles. won pack championship 2 of the 3 years I competed.
i should add I got to test some of this last year by buidling cars for an exhibit we did here at my museum. built 5 cars for public use on a track--people at it up. had a hard time keep up with the maintenance though.
Ive built several for my daughter to race at church. Polish the axles, grooved axles work well. True the wheels with fine sandpaper. Weight in the back of the car like Top Noth said. Raise one front wheel slightly higher than the other three. That means less friction by 1 wheel. After it is totally assembled break in every wheel with a soft pad on a dremel. Make sure they roll for extended time. The car will usually speed up from race to race. Making sure the wheels are broke in makes you faster in the first heats. Out of 5 cars I have done all this and never finished outside the top 3. Theres lots of info on the internet also.
Your physics teacher must have missed something. If the center of mass is toward the rear of the car, it starts out higher up on the ramp so it falls farther. Taking the same mass and dropping it from even a slightly higher elevation results in a higher velocity. When you reach the transition to a flat track, the mass in the front has to change direction which applies a torque to the front of the vehicle. In effect, the front has to be lifted. The more mass, the more force it requires to transition that mass to the horizontal plane. The closer you can get the center of mass to the rear wheels, the less force it takes to transition to the horizontal. It also cuts down on friction on the front wheels and force required to keep the car in line if it hits the rails on the track.
we live in the same city as a nasa facility. my kids never stood a chance. the running joke was "i wonder if that one spent anytime in the wind tunnel?" plus with all their abilities to machine parts and fancy lubes who could beat them? fred
With my son having gone thru Cub Scouts and 3 daughters having gone thru Girl Scouts (the Girl Scouts call it Powder Puff racing) Ive lost count of the number of cars built at our house over the years. Ive usually built one myself as we also have Dads races. As has been stated please let your kids do as much as is safely possible themselves - my kids now all know how to use a drill press and can handle a can of spray paint with the best of them.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o> One tip Ive not yet seen is to use clear nail polish on the car where the wheels might rub. The goal is to have a car that runs true so the wheels do NOT rub but in the real world there will be some rubbing. The nail polish makes a HUGE difference. Other than the first year with my oldest daughter the kids cars have always placed in the top 3 and Ive placed either 1<SUP>st</SUP> or 2<SUP>nd</SUP>. In our area the race officials (I was one for several years) are very strict in the rules area. All wheels must touch the ground at all times for example. The other tips posted here are very accurate.<o></o> <o> </o> 1) Polish the axles in a drill press. Metal fingernail files work good on removing the molding ridge followed by emery paper and then aluminum polishing rouge. The girls always looked cute with black residue smeared on their faces.<o></o> 2) Lightly smooth the molding marks off the wheels if they have them. <o></o> 3) Use a pipe cleaner saturated in graphite to polish the inside of the wheels just slip them on and start spinning. If the wheels and axles are properly polished and graphited you can get the wheels spinning by hand and they should free spin for at least 40 seconds. If not then more polishing and graphite until you get there.<o></o> 4) We found that the cars run best with the center of gravity low and just in front of the rear axles. Hobby shops sell derby weights shaped like fat pencils. Watch your kids closely with a drill press and teach them about safety goggles. Drill out the sides of the car, slide in the weights cut to length and let your kids wood putty the holes up. Lets them develop their sandpaper skills also.<o></o> Good luck and have fun! I know the Dads like bragging rights but the kids really need to take pride in their work also so let them do as much as possible. <o></o>
EXACTLY!!! And then the kids that actually build their own cars get smoked when they are the ones that deserve to win...
My 1932...found it hard to get the proportions correct. Turned out okay. Pipes and window frame are defluxed welding rod. I also did a cop car complete with flashing lights as a tribute to the locals (some were in our Pack at the time). Wasn't fast, but was coool. Looked like we were pulling the faster cars over for speeding! Hit the bottom of the ramp and the lights came on. Too bad they didn't yield to the emergency vehicle. Can see the car build here (youtube) for those who needed ideas... http://www.youtube.com/watch?v=2l18ueOoMeg&feature=results_main&playnext=1&list=PLD54B1414B1CB7FC7
My trick was to use one of those WD 40 "ink pens" and put a couple drops into each wheel hub before the race. (It's invisible )
I had three boys go through Cub Scouts. Most of our cars were never the fastest, but we always were competing at the end. We concentrated more on looks than speed. We have made several trucks, yes the body was always made with wheel wells. It just looks more realistic that way. I think my favorite was the belly tank racer that we made, with extended exhaust pipes (aluminum tubing). I would melt down old tire weights just forward of the rear axle. Cover the weight with epoxy, then drill out the weight to get down to official weight. The axles were epoxied in at the same time as the weight, and we never lost an axle. A very good way to polish the axles is to use a micro mesh kit. This goes to 12000 grit wet/dry sand paper. I'm nor sure where tou can buy a kit. Mine is a used kit from work (airline work). Just let your child design the car. I would let other kids come over to the house and cut out the car on the scroll saw. They would trace out the block on paper the draw the design on the side of the car, complete ownership of the design. Then either their dad or I would help them cut it out. They always enjoyed that part. The sanding was up to them. If they didn't have a dad around, I would give them sandpaper. The scroll saw work still continues to this day, when a neighbor used the saw for his sons car. Have fun and enjoy the bonding. Mark
As you can see there is really no sure way to build a fast car. After more than 5 years of working with cub scouts{ GO PACK 804}. Just work with your son and don't get so caught up in winning that you take the fun out of it for him. Can't count the times that I have seen that happen. And NO it's not just for him to build it is a good time for some father and son time that he will always remember. Have fun and good luck.
Man I was looking foward to building a car with my stepson. Then he or his dad decided they didn't want to go any more right when they were getting ready to build the car. I tried to get him to work on some ideas and designs and all he wanted to do was play video games. A few years later he came up to me wondering if we could build a car. I said yes but heard no more. If you haven't looked on youtube yet you're missing alot of info. There's tons of info on there. Really worth your time. I say start there also. I think it is time for me to build a car.......
I drilled a hole in the back and put an old mercury tube out of a house thermostat in mine and plugged the hole with wood bondo ,car shot out good and always won but i suppose it may have been cheating and dangerous but it was a long time ago so i can confess now .they used to use a metal gate before i was in scouts,a magnet on the front of the car would be the ticket for those days.
Best place for weight is in the rear of the car as high as posible.. has as a greater distance to fall, more PUSH at the start. We made ours like FED. Debur & polish the axles, sand the tires, polish tires with grafite, & run on 3 wheels. 2 sons & 6 years... undedfeated!!
Hahaha... I built one a few years ago for a kid I know.... The car came in second place.... Not bad for building my first pinewood car... I was happy..
My Son who is now in his 40s, still has the car that we built when he was a Cub Scout. I cut the block in half longways and hollowed out the inside. We glued it back together and shaped it with a wood rasp into a Indy car shape. I cut the axle grooves on the bottom so they weredeeper on one side than the other, this allows it to rest with only two wheels touching at a time. The axle pins were put in a lathe and the flashing cleaned off where the ends are stamped and micro polished where the wheels ride. The wheels were also chucked up and a slight taper cut across the surface where anly a very narrow patch actually touches the track. After it was assembled and painted we weighed it on a postal scale and cut small pieces of solder until it weighed exactly 5 ounces then melted the solder into a ball and glued it into the nose inside the hollow body. The car won was won all of the local Scout and Church contests and was retired undefeated.
Finding ways to measure rolling resistance can be very helpful in learning more about what works and what does not work. Some times simply pushing with no driver involved and then measuring the distance is a learning experience. One of the things I always showed young drivers was what it felt like to put a driver in the seat and then have someone try and push him or her from behind and then just move the steering wheel a hair and you can feel the resistance and that robs power. Anything you can do to cut down roll resistance is a plus. And I agree keeping the weight as low as possible and as far forward also helps. Jimbo
We would sand the wheels as mentioned and after three years and three cars we would actually time all the wheels and piece the best four wheels. Got second twice I believe. Got beat by my son's friend who we helped straighten his car out and graphite the wheels since his dad wasn't around. We felt like winners after that. Third was another friend we helped out whose dad didn't know a drill from a pen.
I did the pine car clinic at my house for a couple of years for the dads and some single moms as well as the kids. It really helped some of them be able to compete. It was a lot of fun for everyone. Bob
Jeez, speaking as an Eagle Scout here, aren't you guys perverting the spirit of the competition? Just let the Scouts compete on their own.
LOL-- I never raced mine a council events but rembmer watching the council races at scout show one year. the big winner a kids who's dad was an aeronautics engineer. basically he built a wing and it was fast!
And for the single moms or lazy kids with big allowances... http://www.derbydad4hire.com For just $125 you can have one shipped right to your door. At what point may a fellow say "I have now seen it all"?
The Jalopy Journal
