How about very light thin shutter with a string and pulley to a weight which is free to fall vertically. Releasing the weight will always cause it to fall at the same speed regardless of the angle of the shutter. No batteries.
How about very light thin shutter with a string and pulley to a weight which is free to fall vertically. Releasing the weight will always cause it to fall at the same speed regardless of the angle of the shutter. No batteries.
Bookmarks