Science Forums 2

[CraigD]

Since a weight-powered car like you describe, Bbandgek, differs from the rubber band-power cars previously discussed in this forum, only in that it gets its driving force from a suspended weight rather than a stretched rubber band, you can get plenty of hints by searching it – click “Science Projects and Homework” just beneath the header, then click “search this forum” and enter “rubber*band”, and browse away.

The basics of what you need to build are pretty much summed up in your assignment: build something that can roll on wheels, with at least one axle connected rigidly to at least one wheel

As the hardest part to build in something like this are the wheels and axle assemblies, construction is much eased if you’re allowed to borrow them from a large-size child’s toy car or truck – practically any sort of u-shaped staple, cable fastener, or bent nail can be used to attach a metal axle to the chassis (Wood, balsa, bass, or similar is a good, easy to work material for the chassis, though a hard foam or soft plastic would work, too). If you’re not, try your best to make something like that with the materials and skills you have.

The next trick is attaching a string to the axle, and increasing the diameter of the “spool” where the string attaches to it enough that the force delivered to the wheels is enough to overcome standing still (static) friction and get the whole thing moving – though wood, plastic, or metal spools will perform better, the easiest way to accomplish both attaching the string and building up the spool is the hobbyists best friend, plastic tape (duct tape is easiest to handle and resists coming unstuck).

As the instructions suggest, you need something that will hold the weight 10 cm above the chassis – best to build a bit higher, and not use all the available height at test time. A small pulley is nice, though a smooth, thick wire, such as a bent coat hanger, will word fairly well. A kg is pretty heavy, so if you use something as flimsy as coat hanger, you’ll likely want to attach it to the chassis in 4 places. Staples, screws, and other fasteners are good for that, or, again, duct tape, or another nifty modelers friend, epoxy putty.

Finally, attach the string to the 1 kg weight – if you’re given something with a hook or hole in it, just tie it thought that, otherwise, making some attachment – and wind the string around the axle spool until the weight is suspended the correct distance – 10 cm – from the chassis. Let it go, and it should ... well ... go.

The “coast after the mass is dropped” part is easy – just wrap extra string around the axle, which will unwind floppily as the axle/spool continues to turn.

Click on the attached thumbnail for my hurried mouse-sketch of the whole thing.

I’ve described the easiest build I could imagine, which leaves lots of room for improvement. Sturdy is better than flimsy and fragile. As with any classwork, more effort is better, both in construction and basic design.