Do springs and gears look a bit too much iron for you? Don't worry. Wind-up mechanics can be implemented even with wooden or plastic gears. But the spring! It should always be made of iron or steel. Or maybe it can be simplified. Rubber band powered toys are kind of...
simplified wind-up toys
where the rubber band does the work of the spring. Or almost.
The Rubber Band Kinetic Energy
The principle of operation of the rubber band is indeed very similar to the one of the steel spring. When you stretch the band you are loading potential energy into it - similar to the potential energy stored in a spring. When the band is released, the potential energy is converted into kinetic energy which powers the toy. Here is a really good and detailed explanation of the process.
Generally rubber band releases faster than a spring and it's harder to make toys with long motion times using it. Although with some cams even this may be achievable.
Winding up the rubber band is done in similar way to springs too. Then it's either released immediately or locked in a position with a stopper and then released later.
The main advantage of powering your mechanical toy with rubber band is its simplicity. It's
easy to work with rubber band
when making toy yourself, and rubber bands are cheaper and easier to find even at a local grocery store. Even when I buy a bunch of parsley from the open market it has a rubber band to keep the plants together. They don't put any springs on the parsley unfortunately!
The main disadvantage is the shorter life or the rubber. A good spring can power your wind-up toy for years. Rubber quickly wear and tear and should be replaced.
So, what rubber band powered toys exactly you can make or buy? Here are some:
Rubber Band Cars
These can be made at home from cardboard, a few pencils and some duct tape. You can make the wheels out of wood, or from cardboard. Some even use useless CDs for the wheels (are there any CDs that are not useless nowadays?). Here's an entire book giving really detailed instructions on a DIY rubber band car. Click on the cover to start reading the book. It's all made of cardboard and pencil (the car, not the book), so making it comes nearly free.
It's also easy to make such a car if you have Lego meccano on hand. Legos come with some useful gears so you'll only need to get the rubber bands and some creativity.
Rubber Band Airplanes
They are also pretty popular toys. In them the rubber often powers directly the propeller so ideally the airplane starts flying quickly after releasing. More often than not
these airplanes are gear-less.
They are also made of very lightweight material like balsa wood, foam or plastic.
They come rather cheap - kits cost often less than $5 and can be bought from Amazon or any other aircraft model store. So making one yourself makes sense only if you do it for fun.
Boats and Ships
In boats and ships the rubber band engine also often powers directly the propeller. Because the water opposition is stronger than air resistance the boats can keep motion longer than the airplanes. If the propeller is in the middle of the boat like in the picture below you can simply twist it around and it will work:
Boats like this are fairly easy to make. Another funny idea can be seen here at instructables. On the other hand if you want to make a ship that has a propeller on its back then you may need to use a gear or two to transfer the kinetic energy to a rotation.
Rubber Band Guns
There are several types of these toys but the main thing about them is this: they not only use rubber band to power the toy but also use it for their bullets. (I guess they'll reach singularity once a rubber band gun is made out of rubber too!) Oh, well, some types actually transfer energy directly from your finger to the shooter through a bunch of mechanic gears.
These toys are rather safe as the flying band isn't likely to cause any injures even to kids.
Can a rubber band power a rocket? Why not? It won't go to space but surely it can be raised quite high. Especially if the rocket is lightweight and well made. Foam is good material for example.
Here's how do these rockets work: they use a launching tool usually attached to your hand. Or for better results you can attach it to the ground. The band used to launch the rocket should be much stronger than the typical band they use to make parsley bunches. A slingshot band will work well. The rockets can be launched horizontally or vertically. We have very direct transfer of energy here (as in slingshots). The potential energy of the rubber is immediately released to the rocket and it flies until the energy gets overcome by gravity force.
Be careful as these rockets can hit someone or break a glass - especially if they are made of some heavy or hard material.