Monday, May 11, 2009

No Rules Pinewood Derby or "Extreme" Pinewood Derby

This is SUPER nerdy I know, but the OU LDSSA held a "No Rules Pinewood Derby" and I really got into it. Below are pics of my car and a bit about how I did it. It blew the competition away! It did the length of the track in just over a second. The only things that could have been faster are a CO2 or compressed air design, both of which I am considering for next year! Either that or a 5000-10000 RPM brushless motor that runs on a smaller, lighter LiPO battery. I'm not sure that even compressed air or CO2 could beat it. We'll see!

Obviously, this is the bottom of the car. You can see the battery connection (little red box) and the wiring to the motor and switches.

This was the first "complete" car. I replaced the crappy looking homemade wheels and stablized the motor/gear box mounting with a plate rather than brackets.

(I'm going to get a clearer picture soon.)

This is the final-final car with alkaline batteries. I jacked the back wheels off of a toy I found at Wal-mart. They were rubber and a lot better looking than my homemade ones. I bought the toy, shredded everything to get the 4 wheels, then carefully drilled new centered holes to mount on the axle. They really are just for looks. They had a smaller diameter so they reduced the speed and didn't give much more traction either, but at least they don't look like they are from hillbilly hell. The front wheels are just the standard pinewood derby car wheels mounted on a block to keep the switch off the track.
For the first two races I used the alkaline batteries I had spent a week and a half testing with. They were half dead but everyone was amazed at the speed of the car. For the higher end of the bracket (elite 8, final 4, and championship races) I switched to brand new lithium batteries (half the weight and full of juice) and blew EVERYONE away!!! It was close to twice as fast!

Adam at Home Depot helped me with getting the rear axle 90 degrees to the frame of the car with this plate. I had to pop 2 holes in the front through the wood to stablize the rear axle. After every race I had to tighten the nuts because they had vibrated loose; one of the wheel holes wasn't exactly on center so there was some vibration.
There are 2 switches, a toggle switch on the top of the car and a lever switch on the nose. I wired them in line so that the car had a double off position. This helped me place the car on the track without the car being in the "on" position until the starting pin dropped.

This was the first modified gearing. You can see the slight torque on the red gear. It ran smoothly enough and I estimated the ratio at around 25-30:1 although I didn't count all the teeth.

This is the second gear configuration I came up with. The ratio here is 6.6:1, much, much faster than the previous configuration. As with every modification I made, there was always some conflict. You can see the scrapes made on the motor casing from cutting it to clear a path for the tightening screw on the axle nut. I also had to drill a hole for the axle and glue a couple gears together to get everything to work together. The hole for the axle had to be in exactly the right place as well as perpendicular to the casing and body of the car. Try doing that with a handheld cordless drill. I should have used a drill press, but since I couldn't get access, I made due. It hit right on the money and the result was pure speed baby! :)

All-in-all the car took about 40 hours to build. This includes all the time spent at the hobby shop, Radio Shack, and Ace Hardware asking questions to be sure I got the right parts, as well as the design (didn't do as much of this as I should have), building, and testing. It was a fun little project that looks cool too. I think I'll have my artist friend paint it though.


Anonymous said...

I think your artist friend would love to paint it!!!

Anonymous said...

Awesome stuff! I just linked to this blog from my site, Very cool design...

-Diabolical Dave