Advice needed - ballbearing solution for rotating table 1

[makerjack]

Hi all,

Brand new to the forum, lovely to meet you all.

I am currently undertaking a project to build a large round table composed of a series of concentric rings that all spin independently.

The basic idea is, there is a single stepper motor attached the small circle in the center of the table. The center can be spun, which locks into the other rings around them and forces them all to spin either clockwise or anti-clockwise.

Each of the rings of the table will be mounted with progressively larger arms down to a central metal 'trunk', which will allow them to all spin independently. Like those mechanical models of the solar system.

The thing I am struggling with currently is the cylindrical ballbearing solution that will allow the 'arms' to attach down the central trunk, be supported, and also spin freely. I have attached a quick exploded 3D example of the design (except the tabletop is interlocking rings, not circles). The solution I am struggling with is for the 'red' pieces in this drawing.

Any advice much appreciated!!

Cheers,

Jack Colley

 

[3DDave]

Mike H., I was thinking that putting races on the bottoms of the rings and having rollers at the tops of the arms would work out nicely as well, but they all produce a different visual appearance and offer differing resistance to wobble and moment related deflection. The original version seems wobbly though aesthetically pleasing.

 

[gruntguru]

"Is there some reason you couldn't just put ball supports upside down on the bottom of all the concentric rings and let them all skate around on the same surface plate, separated by simple radial bearings all in the same plane?"

Or simply use a "lazy susan" bearing under each ring. Link

Seven different sizes here Link

je suis charlie

 

[makerjack]

Yeah I did look at the option of using a lazy Susan bearing, I just hadn't been able to find easily available sizes at the diameter of the outer ring (around 1400mm).

The ball supports idea is a good one too, I had considered putting the rings on a surface plate but for some reason got to a point where it didn't seem a viable option.. can't remember why though! Maybe worth going back to the drawing board...

I went to some mechanics here in Berlin yesterday and asked if they had any old wheel hub bearing assemblies ('radlager radnabers', if you're interested) and found a few. They seem like they could work quite well... is there any reason instead of welding I can't just bolt brackets into the existing holes in the frame? Where you would normally attach the assembly to the wheel. If I am locking the inner shaft onto my 'trunk', therefore allowing the outer part of the assembly to spin, I figure I can just avoid welding entirely and bolt straight onto it. Am I missing something?

Jack

 

[tbuelna]

Don't forget that your bearings will likely require some form of lubrication, and some arrangement of sealing to keep the lubricant in place.

 

[SwinnyGG]

Automotive hub bearings are permanently lubricated and sealed.

No, there's no reason you can't bolt to the existing flanges, so long as your desired final assembly size is tolerant of that arrangements.

 

[makerjack]

You guys have been so helpful, thank you. Managed to find 3 working wheel hub assemblies at various mechanics here in Berlin (after much searching) and here is the super first round prototype of the assembly.

Seems to be heading in the right direction!!

https://vimeo.com/173743292

The board on top is just representative of the finished flush round table, I will be splitting into multiple pieces (you can maybe see the pencil marks) for the second prototype, before actually CNC cutting the rings and mounting the motor.

 

[BUGGAR]

Nice! I never considered leaving on the disks for adding brakes. Modern hub unit bearings come with ABS sensors that can be hooked up to measure the speed if you need to.

 

[makerjack]

Yeah that's awesome. Might need to do so if I am struggling to tune up the stepper. You're a legend BUGGAR, the wheel hub suggestion was a life saver!!!!!

Only thing I am struggling with now is how to run the wiring through the center of this structure to connect the microprocessor/power supply (bottom) and the stepper motor (top). But it's getting there!!!

Would there be a better way of mounting these rather than bolts and spacers on a threaded rod? I like that because it is easy to assemble and adjust, but it makes the cable run rather annoying..

J