This is a simple system to close your doors automaticly. It could be used indoors, in the garden or on a fence - feel free.
Also it is fully mechanical and needs no electronics.

Parts you need in addition:

• 1 bearing 606ZZ (maybe I will add a impeller without a bearing - it should work too)
• Some weights (Sand, leadscrew, or something thats fit in the cylinder)
• some glue to close the weight-cylinder
• some screws for mounting
• a strong cord