I was contacted by the local science museum recently. It seems their VDG
has stopped working. I thought it was just in need of a good cleaning
and adjustment, so I went by the museum today and here's the story...
Their VDG was made by a graduate student at the U of Texas out of spare
parts. The base is made of cast aluminum with a small induction motor
connedted to a plastic drum shaped spindle. The belt is a grey thick
rubber-band that looks like the one's you see on some home vacuum
cleaners. The belt runs up a piece (30-35 cm long) of 2 inch PVC pipe.
The upper end of the pipe has a metal pulley holding the other end of the
belt. The top ball is a one piece sphere that has a hole for the PVC
pipe to go into. The ball is supported by a metal inverted V that is
attached to the PVC pipe.
When I first started the VDG, the motor ran fine but there was NO
potential produced at all. Upon inspection of the base section, There
was a strand of fine copper wire acting as a brush contacting the belt
and the aluminum base. This was puzzeling in that I had only seen
induction combs in this position, never actual electrical contact between
the base and the belt. HUMMMMMM.
Upon inspection of the upper section, I discovered the same arrangement.
The fine wire brush connecting the top globe to the top of the belt.
I completely disassembled the unit, cleaned the dome, the support column,
the pulleys, adjusted the tension and reconnected the brushes.
Still Nothing!!! No spark, no attracting the hair on your arm, no
nothing!
I then fabricated an set of induction combs from some copper foil and
used them to replace the copper brushes. Same effect.... Nothing .....
So that's where I am. Anybody with more experiance with VDG's than I
needs to help me out here. I thought these things were fairly simple.
I'm beginning to wonder.
petel@tenet.edu
Pete Lohstreter "The first rule of intelligent
North Garland High School tinkering is to save all the parts."
Physics Department Aldo Leopold
2109 Buckingham
Garland, TX 75042