Dome drive crank 2.

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After flirting with the idea of a [geared] electric motor drive I have opted for a safer and simpler hand operated crank. 

I am going to use a sealed bicycle bottom bracket bearing and crank. I have several sealed bearing bottom bracket [BB] "cartridges" with square axles. The bearing housing could be housed in a simple tube. Or clamped into reinforced 3/4" plywood uprights or box sections. The donor parts are shown in the image [Right.]

I need stiffness in the bearing supports to avoid too much flexure while cranking. This requirement may be at odds with a hinged and sprung base to ensure the friction roller remains in continuous contact with the underside of the dome's base ring.

The crank, BB bearing and pedal axle are the easy bit. Fixing the 4" friction roller to the other end of the axle is more difficult.

Removing the needle  bearing components left me with a 27mm bore in the cast iron roller. A more generous size in which to fit the turned down, crank stub.

This is what I did with another spare left side crank. [Image right of the cut down, crank/wheel adapter in the lathe.] Not much left of the poor old crank!

So far so good. Now I need to support the friction roller in the correct place while avoiding the crank striking the framework. It also has to be spring loaded to ensure continuous contact of the roller. The cheap, plastic pedal will be pared down to its axle casing to provide a smooth handle.

The image left shows the crank and wheel posed in the correct place. The wooden block is just a temporary support. If I removed the white wheel the friction roller would become the support and rotation device. No spring required but much greater demand on the support and roller to take its share of the dome's weight. Probably not a good idea.

Click on any image for an enlargement.

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