This is an object I draw in order to counterbalance the weight of my garage shutter. This is needed when you change the weight of the main door. In this case you need to counter-balance the weight used at door side.
To do this I built this object. It is a very easy container with a whole used to be fixed at the beginning of the gear with a screw.
To increment the weight you can fill it using small lead balls. I bought some lead plates used to balance wheels of the car. It works well and is more stable (see the picture). Use some glue to fix it better.
For this and other interesting projects you can visit: http://www.bvRobotics.com