We started out the day brainstorming ideas. I had a hard time thinking of something at first, but when the idea hit me I knew it was perfect. I wanted to create an energy storing unit. I was not really sure how to make one, so I spent quite a bit of time googling ones that already exist. I found ones that use gas, water and other materials. I decided to make one that works with a weight and a motor. When electricity is put into the motor it causes the motor to spin. Coiling up a string that lifts a weight up into the air. The string gets wrapped around the motor storing the energy as gravitational potential energy. Then, the weight is pulled back down, by gravity, causing the string to unravel and the motor to spin in the opposite direction. This process releases the energy back out.
Before I could start to build and prototype I had to do a lot of calculations. I decided to make it around two meters tall. Then I wanted to figure out how much power I could produce. I wanted to see how big the weight would have to be to for one watt hour. To do this I had to convert watts to joules. Once I found the joules I could figure out the
PE (potential energy) by using the formula PE = MGH. It ended up being 183 kg. Considering that would be around 400 lbs, I decided to uses a 10 lbs weight instead. With this figured out I could begin to build my first prototype.
The first prototype was built on top of a tripod used for cameras. It was a motor, with a gear ratio of 11:1, a string, a 10 lb weight and a hand crank to power it. This model worked great. After seeing if it would illuminate a light bulb, I did some tests to see how much energy was being stored. I used to multimeters to measure the volts and amps going in and out of the machine, and a stopwatch to see how long it took to coil up and down. It took in around 238 ws and put out around 18 ws. This made it 13 times inefficient. In hopes to make it more efficient I tried using a large gear ratio motor, and more weight. This made the device hold more energy, but it became 30 times more inefficient. In the end I decided that the efficiency of the first model was more important than the overall energy storage.
Bumps and Bruises on the way:
As with everything there were so pretty big structural problems with my system. Most of them were caused by the weight. When I started to experiment with larger weights everything started to break. First it was the string. So I tried fishing wire, but that broke too. I ended up having to use a steel cable. After I fixed the string problem the tripods platform broke. To fix this I designed many different versions of a platform for the motor rest on. The final version was made out of plywood. It has four holes in it for screws. Then a hole for the motor the rest in and a hole to guide the string through. I, also, experienced problems with the part of the motor the string wrapped around. To fix this I attached a longer thicker tube of metal. This was great, but it would get pulled on by the weight preventing the string from wrapping around properly. To fix this I created a rectangular piece of plywood with a circle in it. In the circle is a screw, that spins freely, and attaches to the metal piece. This can all be seen in the picture of the motor above. With this fixed I could move on to the final version.