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19Apr/1011

Steampunk Blowfish

Here's my entry for the "open class" at my son's pinewood derby.  It turns out you only have to get your nose across the finish line to win.

I did the design in HeeksCAD.  It's basically just an elongated cube with a sphere subtracted and the corners filleted.

The spherical pocket is to hold the "pressure vessel".  I'm using a bottle Coke put out for Christmas last year.  PET bottles are rated to hold 200 psi but I never pressurize above 120psi.

After cutting it on the CNC router and sanding:

There's also a couple routed pockets on the bottom for the battery, switch, and wires.

The magic is done with this solenoid valve. Model 35A-AAA-DGGA-1BA

The valve can be connected in different ways.  I've got it set up so that when current is present, the valve is open.  The switch in the front cuts off the power and closes the valve.

So when the car is on the starting line, the switch is pushed closed by the gate, holding the pressure.  When the gate drops, the valve opens.

Comments (11) Trackbacks (0)
  1. nice use for an ep.first time i’ve seen one that wasn’t on an exhaust damper or a vav.

  2. Nice.

    I think you would have got some added performance from a properly designed nozzle though http://en.wikipedia.org/wiki/Nozzle .

  3. I agree. It was a compromise decision because the schrader valve is also used to fill the bottle. I couldn’t figure out an easy way to fill it otherwise that didn’t get too bulky, heavy, or complicated.

  4. Any chance you can help me with some simple schematics (or descriptions) for the compressed air mechanism? Solenoid valve, 9V battery, trigger, etc… Looking to try with a height-friendly 20oz bottle.

  5. Most of what you need, you should be able to glean from the pictures. The solenoid valve does all the hard work. The model number link above takes you to the datasheet. Just messing around with it and a 9v batter you can figure out how it works. Then just wire a switch into the circuit. The hardest part has been getting the connection between the bottle and the solenoid to hold pressure. Make sure you use a bottle that formerly held a carbonated drink. The ones that hold non-carbonated beverages or water will not hold the pressure and are dangerous. Send me a link and pictures if you get it to go.

  6. Could you please let me know where you get the 9V solenoid? I google for hours but couldn’t find it. Thanks

  7. I never found a place to order it online. The linked part number in the post will take you to the MAC distributor that sold me mine. I ended up talking to an engineer who recommended that part. You should be able to just give them the part number and order that exact solenoid. Perhaps by now one of the other MAC distributors has a web portal. If you find one, please post a comment here.

  8. Thanks for the tip. I’ll give them a call.

  9. How much does the 9v solenoid cost? I couldn’t find pricing information online.

  10. It’s been a couple years since I built this but if memory serves it was about $20.00

  11. I had problems finding the solenoid. Zorro Tools has Part# G1419713 $25.
    It is a 12V 1/8″ solenoid. You should be able to use an A23/23A Battery. Amazon sells batter holder for <$5.
    http://www.zorotools.com/g/00060270/k-G1419713/
    I look at a sprinkler valve for $10, but I think they only go up to 80psi – bulky too.


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