Advice for multi layer rotation project

[jelockwood]

I am completely new to Lego Technics and any associated motors. I am however considering a (to me) significant project and as a newbie coming here for advice before starting.

If/when the concept looks feasible and begins progressing I will reveal more details about it but for now conceptually it could be considered to be similar to a three layer sponge cake with each layer rotating at different speeds. (It will not actually be a cake.) The stack would rotate about a vertical axis with each layer needing to be powered at different speeds from the same vertical input. The three layers would need to hang off the vertical tower containing the drive axis which will be inside the build.

Potentially the upper two layers could rest on the bottom layer which would rest on buttresses from the central tower. Bearings between the layers could allow each layer to rotate freely whilst still allowing the upper layers to rest on the bottom layer.

The issues are to ensure that no gearing or support between the layers prevents full 360 degree rotation and also to allow the full diameter of the upper layers to be supported sufficiently so it does not fall off or through the lower layers.

If it makes any difference I would need the middle layer to rotate the fastest. Due to the anticipated diameter I am expecting that using the Lego banana gear i.e. the 11x11 circular rack would form a major part of the structure.

Apart from advice on how to ensure support without each layer crashing in to part of the other layers I am also interested in advice on choice of motors and power. Lego have and/or had a vast number of options not limited to EV3, NXT, Power Up, and so on. The drive input would come from an externally mounted motor providing a horizontal axis which would then enter the build at the bottom and be translated to the vertical central axis. This will not require high speed rotation, only smooth, steady rotation and the build will likely end up being reasonably heavy. Strength will be more important than speed.

The gap between layers should be kept as little as possible, since bearings between the likely three sets of banana gears will I feel be needed that would probably be the constraint for the minimum gap although possible overhangs outside of the banana gears may help disguise this. All three layers will rotate in the same direction. Looking down on to the build this would be considered to be a counter clockwise direction.

Thinking further it might have been easier if the drive was possible at the circumference instead of the centre but this will prevent the intended design appearance. 

[JintaiZ]

Pictures would be useful, thanks!

[1963maniac]

A turntable has been use to produce two such rotating structures and with the banana gears should allow for the three layers.

[jelockwood]

1 hour ago, 1963maniac said:

A turntable has been use to produce two such rotating structures and with the banana gears should allow for the three layers.

Thanks, this sounds promising, do you have a link? Most of the turntables I have seen have a static base with one rotating layer, in my case it will be three rotating layers. Ah, looked at one, it seems for my case it would translate to a static bottom i.e. my hidden internal pillar and then three rotating layers on that which would be very similar to each other. I also see that it looks like a planetary gear approach might be simplest and thinest but will have to check further to see if the rotation speeds for each layer are possible.

I am currently bidding for some parts to get started prototyping with.

For @JintaiZ it is not even started let alone built so I have nothing yet I can take a picture of.