The weight of the dome (not
inconsiderable!) is carried by 6 sets of 2 bearings. 6 bearings
riding on the inner edge keep the dome in place.
Powering the dome was a challenge. The
system ended up like this. A 600W drill provides the power and 2
relays control the drill (1 on/off 1 direction). The drill comes
complete with an internal 12 to 1 gearbox and a shaft connector
(drill bit). This goes into a ford wiper motor gearbox (100 to
1) then through a flexible link to a modified RS 25 to 2 gearbox
with a small bicycle gear on the output shaft. All of the
previous stages are mounted in a ridged iron frame. A bike chain
is used to connect the drive to a small pneumatic tyre riding
under the base ring (5 to 1 further reduction). The base ring is
'squashed' between the tyre and a bearing riding on top of the
ring. The tryre also acts as a clutch slipping if things jam. The
torque transmitted can be varied according to the pressure in
the tyre. xxxx also uses this approach. (I have lost the url! if
you know the site I mean please tell me) Loft insulation is
packed into to drive area to dampen noise.
As I have mention this bit proved a real
challenge and I have a garage full of failed attempts to prove
it! However this system looks though it will be reliable and
robust enough to prove a long-term solution.