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Homework Help: Self-Contained Spring Powered Car - What Design?

  1. Sep 18, 2014 #1
    Hi There,

    I'm in the preliminary stages of building a spring powered car to race over a distance of 10 metres. It is a yearly event held in my local area and so far we've only seen one spring powered car. I think this is because it may be difficult to design a way to harness the energy efficiently.

    The previous years design was very simple: A tube with a spring inside attached to one end. The other end was attached to string which was wound around the axle thus stretching the spring ... you get the idea.

    My question is what design could harness the power of a spring most efficiently?

    Here are a few ideas I've come up with:

    ** please excuse my lack of paint skill **

    Here is where you'll find the (non)technical drawings of the two below designs.

    Design 1: A lever. From the picture you can see that there are two blocks which are attached on a pivot. On the other ends the spring is attached. The two blocks are then pulled away from each other. Then when the block is released the spring pulls tight which pulls the string around the axle , which in turn moves the car forward.

    Design 2: This design uses a linear gear to drive the back axle. A rack and pin system pulls the rod with the teeth (not sure what the technical name is) back which makes the spring taught. It is then released, this drives the back axle. ** the problem with this is that once the propulsion stops so will the back axle as the gear will still be engaged.

    This next idea unfortunately (or fortunately considering my paint skills!) doesn't have a picture to accompany it. For this my idea is to use a piston, like in a spring air rifle. However, the problem is that I've got no idea how to harness the power of the piston to create forward motion. Using a turbine doesn't seem like it would be the most effective way.

    Another important question: What sort of materials would be best to use with high power springs? And on that note, what sort of springs are best to use? At the moment I am thinking a trampoline spring may be powerful enough.

    I am also very interested in the maths behind what's going on. I'm taking A-level further maths and physics and would like to have an understanding of what forces are going on. How would I be able to calculate the the amount of force generated by a given design (provided I knew the spring constant of my spring)? And then from that how would I be able to calculate the kinetic energy transferred from the elastic potential?

    Any and all feedback and support is much appreciated!


  2. jcsd
  3. Sep 18, 2014 #2


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    Perhaps work out how much energy you might need to store. The more energy you can store and release the better. The problem is that short springs imply higher forces than long ones for the same energy. So I would think about how long/short the spring must be and if you can build a car/mechanism strong enough to handle the forces involved.
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