If you don't know what a steadycam / steadicam is good for, I'll try to explain it in a few words. When shooting video one of the most important factors is the stabilization of your camera. If you don't do it right, your footage will look shaky - and this is what we really want to avoid (in most cases).
You'll find yourself in situations when it's absolutely not possible to use a tripod. Even if some lenses do have build in image stabilization, they can't compensate the shaking that you'll get while walking or running around with your camera. So when you are filming while walking around and it's not possible to use a slider or track dolly you'll need another kind of mechanical stabilazation.
There are different steadycam models on the market. I think that most of them are really good, the only problem is their price. So if you have some time and the right tools you can try to build your own model.
This is my DIY steadycam:
My main goal was to built a steadycam for DSLRs that is as small as possible, fully adjustible, lightweight but still very strong. As you can see in the image above it is adjustible just like all the other models. But there are some more facts that I would like to point out. I used a high quality universal joint which is very agile and therefore the movement is compensated very effective. The handle is very soft and big which makes it possible to carry this thing around a while. The steadycam is made out of aluminum and therefore it's very lightweight. The weights are made out of brass. It is possible to loosen and tighten all the screws without any additional tools. This makes it possible to make quick adjustments when changing lenses or adding other equipment. It can carry my 550D wit a LED video light or other DSLRs with medium sized lenses easily. The first test runs went pretty well - I will upload a video as soon as the sun comes out.
The parts have just been painted black and are still drying - I think this thing will have a really professional look.
Hope you like it. Feel free to ask anything you want if you have some questions.