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The image [from yesterday] shows one of the bottom, shutter bogies. Which has been temporarily propped in place in the [overlong] upper channel. Which I have rested on blocks to level it at the correct height.
The bogie is too long at 49cm to fit under the right hand side
of the shutter cover. The red lines indicate how much shorter an upper bogie needs to be.
Ideally, the bogies want to be as long as possible. While
still fitting under the
outer, shutter overhangs. [Arrowed] This will help to ensure maximum stability against sideways tipping. By
spacing the skate wheels as far apart as possible.
The
bogie's deep, aluminium channels will protect the skate wheels from the worst of
the weather. Only the outboard sections of the track channel will be
exposed to snow and leaves while the shutters are closed. Scrapers will help to clear such debris from the
channel bed each time the shutters are opened.
I
am now wondering if I really need four skate wheels per bogie. The maximum, weight capacity of inline skates is a rider of 100kg, 16 stones or
220lbs! [All 8 wheels.]
Though I haven't weighed my shutters I would wildly guess they weigh less than 100kg each. Assuming a skater repeatedly puts all their weight on a single skate then that is a 100kg load on only four wheels. A skater also puts very serious, dynamic loads on their skates. Far more than the only occasional openings and closing of otherwise static, dome shutters.
It follows that a top and bottom bogie, with two wheels each, should safely carry 100kg. One slight worry is the bearings and the PU tires. The bearings are sealed against the weather. Skaters do skate in the rain or on wet surfaces.
However, the tires may end up with flats if they remain static while under a constant load. The firm tire treads are circular in cross section. So they have only a very narrow contact patch. They are expected to roll sideways in use. As the skater corners and maneuvers. Trials of opening and closing the shutters should allow me to judge if the wheels are being overloaded.
Or, I could spend the extra £35 for another set of 8 skate wheels
and not take any chances. Order duly placed. Fitting extra wheels with the dome raised high on the observatory building would be an extremely dangerous nightmare! Why take the risk?
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