Rocket Carts of all Kinds

Most recent answer: 10/22/2007

Q:
I am currently working on a design for a science theater. One of the elements we are working on is a rocket cart to explore a number of phenomena. Our science consultant referred me to your website as an example. We have a limited amount of space to work within so I am working out the power we need and a braking system. At this time we are thinking of using compressed air (a small scuba tank). I would like to know from you what kind of speed and distance you attain with a single burst from the fire extinguisher and also how the pressure from your propellant might compare to the same burst from a scuba tank. Thank you for all your help.
- Robert Creighton (age 26)
Thinc Design, New York, NY, US
A:
Robert -

The speed and distance that we get from our fire extinguisher cart depend on too many things to give you any sort of exact numbers. In general, a long burst will give you more distance than a short one. It also depends on the weight of the person riding the cart, the surface that the cart is rolling on and the amount of friction between the wheels and axels. (Rollerblade wheels work wonderfully for this!) We generally hold the handle of the fire extinguisher down for about 1/3 to 1/2 of the distance that we want to go and are stopped by a person standing on the ground. On a dirt floor (such as outside), it takes a /very/ long burst to get anywhere, and even then it doesn’t go very fast at all. On something smoother like a nice gym floor, we can get some very good distance. I think you can get a pretty good idea of how fast this actually is by looking at some of our "movies". Here’s a couple from our show at Sullivan Elementary in 1999 that should help:




As for how this will compare to what you could get from a scuba tank, it’s hard to predict without actually trying it, but the pressure of the gas in each tank is roughly comparable. However, I think that the problem will not be the pressure, but the release rate of the gas. Fire extinguishers are designed with valves that allow an entire tank of gas to be released in something less than a minute. Scuba tanks, on the other hand, are designed to release a full tank over more like 30-60 minutes. In order to use a scuba tank, you will have to find a way to adjust or replace the valve for a higher release rate. As for how realistic this is, I think you’re just going to have to try it to find out.

Hopefully this will be useful for you. You may also want to check out our page on . Good luck!

-Tamara

(published on 10/22/2007)

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