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sliptonic

C02 Powered Pinewood Derby Motor.

by sliptonic Mar 14, 2011
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I ran this car for the first time in 2016. Our Pack had an Outlaw class that was mostly to keep the parents occupied while the kids built theirs. Almost none of the kids were paying attention at first, but the moment they heard the CO2 release, it got them looking. Unfortunately for the ones not watching missed the first run that actually triggered the timing missed a 0.7 sec run on a 30 foot track. I would really recommend the eye loop and fishing line to just keep it on the track.

I keep getting other parents trying to beat this car. They have tried using a 20lb lead car, a ducted fan, and tiny electric motors. The only one that came close was the electric motor.

Only issue I had was we had to bring out the old track we had last year where the end is only about 18in long. I needed to reprint everything due to impact damage to all parts.

I had all my pieces printed and got the rest from Home Depot. After assembling and fine-tuning, it worked brilliantly! I will be running it Sunday in a challenge match against a ducted fan car.

Race Day and I loved it. Found a flaw but otherwise, great!

On a 35’ track, the car covered the distance in 1.515 seconds for a conversion of 504.064 MPH

Do you have a Thing file for those CO2 cartridge?

I made a rough version of your design on my car with slight mods based on available supplies/tools. Our first time was 1.022 and our third got down to .921.

What length track was it?

Comments deleted.

For springs, Menards SKU 2027066...$1.89 each....5/16" x 2-13/16" x .036 WG Extension Springs

My husband and I are having trouble getting ours to work. It constantly wants to go off. My first thought is the spring is too tight but my husband believes otherwise. Any thoughts?

Have you considered selling these as a kit or completed car?

I have tinkered with the idea of a 3 cartridge car. I am just not a cad designer. My idea is to open the bottom two with larger holes for a quicker gas release and the third cartridge on top with a smaller hole for a slower gas release to sustain and possible continue to accelerate the rest of the way down the track. I have built two cars, but haven't had the chance to run them yet. I have also done some of the gravity powered car tricks to reduce friction on the hubs and wheels. I am trying to break a 1 second mark. I also made the bottom a little wavy to attempt to equalize air pressures between the top of the car and the bottom. Can't wait until I get to try it and see what happens.

I used 2 13/16inch springs from Menards Home improvement. Track time was 1.714. Advice, make the screws that puncture the co2 long and file them to a point.

Has anyone figured out what size springs to use for this?

"Bad Idea," LOL. This is awesome. I'd love to see an "Outlaw" class at our competition this year. If I recall correctly, Estes (of model rocket fame) used to sell rocket-car kits that were powered by an aluminum rocket engine that you filled with some sort of cryogenic propellant delivered from an aerosol can.

Edit to add: The cryogenic propellant was FREON! Amazing. No wonder they don't sell these anymore. Here's a link to a catalog page: http://ninfinger.org/rockets/catalogs/estes75/75est42.html

Can you provide the specs for the springs? Or a source?

Did you ever find our what springs to use?

Thank you for sharing plans. I'll post pictures after I try it.

Thanks for the design. I was able to get the car down the track in 1.089 sec.

What size springs did you use?

Thanks for the design. I was able to get the car down the track in 1.089 sec.

Hi Sliptonic, Great design. What OD brass rod did you use? Is the rod that goes through the hammer, trigger block, and pawl the same diameter as the two 60mm pieces?

The piece that goes through all the trigger parts is 1/8" (as is the push rod). The other two pieces are 5/32 and threaded on both ends. If I remember correctly, I chose that size because it's just slightly smaller than a #8 screw (.156" vs .164") but still threadable.

Thank you! I plan to try it this weekend.

Hello Sliptonic,

After watching your trial run of this CO2 car, you mentioned making modifications to make it release faster. What did you end up having to do to make it release the CO2 faster? Thanks! Dan

I use two drywall screws through the hammer as piercing pins. They're just screwed in through small holes printed in the plastic. This way, each screw can be turned in and out independently to tune how it pierces the cylinder.

The goal is to get both screws to pierce at the same time and to the same depth before the spring releases.

The effect was that it was releasing gas all the way down the track, and accelerating all the way. I think to release more gas faster, especially without a nozzle, would really decrease
stability and that's already a problem.

Sliptonic - do you have a recommendation where to get the 3D printing done?

What a great design! Thank you for sharing!

I did my own printing so I really haven't tried any of the services and can't recommend one. If you get it printed, please add a 'thing' with pictures. I'd love to see how it looks professionally printed.

Cars powered by a single cartridge were a favorite hobby back in the late 1940s, but the puncher was held by the builder of the car, not a part of the car. It was a straight tube that fit over the small end of the cartridge and contained a spring that, when released, drove a small steel point into it. As I recall, the guide we used was a piece of the steel wire also used for flying control-line model planes, available from the same hobby shop that sold the carbon dioxide cartridges, and we put the screw-eyes under the center of the car. The community-center building that provided a meeting place for the model-builders club had a long hall that allowed an impressive long run for the cars.

Fast and potentially dangerous.. I like it!

Sweet - if it is worth doing - it is worth overdoing.. pretty sure that is a quote from mythbusters.!

Very neat design. What program did you use to do the CAD work?

I used HeeksCAD for the 3d work and LibreCAD for 2D. LibreCAD is a fork of qcad. Both apps are open source.