Wheels and axles
Design & Technology · Key Stage 1 · The School
Wheel and axle
A wheel needs an AXLE — a rod through its middle for it to turn on. Without an axle a wheel is just a disc. The axle either turns with the wheels or stays still while the wheels turn on it, and either works as long as something can rotate.
Turning freely
A wheel must turn FREELY. If it is stuck against the body of the model, or the axle is bent, or the hole is too tight, it will drag or stop. Making the hole slightly bigger than the axle, and keeping the wheel clear of the body, is what makes a model actually roll.
Fixing it
If a model does not roll, check three things in order: is the axle bent, is a wheel rubbing on the body, and is the hole too tight? Checking in order finds the fault faster than taking everything apart. Nearly every non-rolling model is one of those three.
A card car has wheels glued to a dowel, and the dowel glued to the body. Nothing turns. Fix A: unglue the dowel from the body and thread it through two card tubes, so the axle spins inside them — works. Fix B: keep the axle fixed and unglue the wheels so they spin on it — also works. Either the wheel turns on the axle, or the axle turns in the chassis. Both glued means neither.