I can't find any diagrams explaining the mechanics of the restaurant (or even exactly what rotates); which upsets me. -Can someone provide more information/pictures? Even with amazing balance I don't understand how there isn't massive friction caused by whatever it's running on...

Nearly everything says it's a single 1.5hp engine (upgraded from 1hp), however there's a case study by Graybar who did a retrofit in 2013 [0] which makes it very clear that there is (and was) actually _two_ motors, both in play. -once again, if anyone has more information? I'm massively intrigued.

"The major problem was that the two existing drives were fighting to share the load – one was lagging and the other leading. The two gear boxes were constantly adjusting according to inputs from the motors, which caused both the noise and roughness during the rotation. The team determined that the best solution was to upsize the motors, drop motor revolutions per minute (RPM) and reduce the reduction ratio with the new gearboxes. So they recommended Schneider Electric drives as well as various automation and control products to the Space Needle engineering staff. The new motors were equipped with encoders feeding the drives in a master/slave configuration. Along with this, all new controls were installed, including a wireless control system. Schneider Electric also provided engineering and software support, both at the integrator and jobsite facilities."

>>> edit: I'm wondering what wattage this/these 1.5hp motors are; the Falkirk Wheel is a rotating canal lock up in scotland. It manages to simultaneously lift/lower two canal boats + water 35 meters for only 1.5kWh of energy (and has a pleasing gear system) [1] [2]

[0] http://www.graybar.com/documents/graybar-keeps-tables-turnin...

[1] https://en.wikipedia.org/wiki/Falkirk_Wheel

[2] https://www.youtube.com/watch?v=n61KUGDWz2A

The restaurant floor, a ring around the core, rotates. The observation deck, exterior and center do not.

The point of this gearbox is the small size. The space needle gets to use a gear that is the size of the top level, and drive it with a gear that is a few inches in diameter. That has always been easy to do and is the sort of thing this compact gearbox avoids.

[edited for mistake: motor -> gearbox]

I seriously doubt they use a gear the size of the base. I doubt the facilities to manufacturer a gear that big exist anywhere. Gear machining is a very specialized operation.+

More likely it's a train of gears of much more moderate ratio...a series of 5:1 or 10:1 reductions, say.

http://www.heraldnet.com/article/20111118/NEWS01/711189872 makes it look like they do.

As kevhito says (but (s)he forgot to include the URL), it is more like a train running on a cog railway, with the train fixed and the rail moving.

Based on this photo [1], I'm guessing they use a system much like a cog railway. There would be a continuous ring of teeth along the tracks and a small motor on the platform with a few inch gear to engage the cog. Or vice versa. The cog ring would probably be made up of several smaller segments.

At that size and speed, I don't think you need the gear to be particularly precisely machined.

You do if you're going to be meshing a much smaller gear to it. For the two to fit together, the teeth on the larger gear need to be the same size as the teeth on the smaller one.

I stayed at the Westin Bonaventure in LA recently. An employee told us rotating bar at the top takes something like two hours to make a complete rotation. It was disorienting to have everything around you be constantly changing, yet so subtly.

Using the contraption in the article hooked up to a motor at 600rpm (typical for a diesel engine), it'd take about 12 and a half days to rotate something.