Sturdy Screw Test
The real point of the marble machines was to test lifting mechanisms for the revamp of donkey kong. Now that I've tucked some other projects out of the way I can start looking at this again. DK uses 20mm steel ball bearings so the lifting mechanism for that needs to be rather stronger than the small lifts. I like the Archimedes screw design because, with a few tweaks, it could be scaled up to something suitable. This sturdier screw was made using a much larger central shaft (6mm x 6mm square section). The steps of the spiral overlap each other providing more surfaces to glue for each step. The whole thing is designed to be operated at 45 degrees so that the weight of the ball is on the trough rather than the moving part.
Perhaps the biggest change is the way spiral is supported. The larger ball allows me to skip a step in the spiral and I can add a bracket into the gap. This means I don't have to make a 450mm long unsupported spiral and worry about it flexing. The ball passes under the supports and barely notices the missing step and I imagine this will improve when I sand the edges of the steps down.