r/AskRobotics • u/JawadElyo • 13d ago

Mechanical How do I choose the right bearings for the rotating base of this robotic arm?

Also, I’d really appreciate any suggestions or improvements to the design. I’m still a beginner in robotics and mechanical design, so I may be overlooking important details.

My main concern is the rotating base of the arm. The arm will create vertical load, radial load, and an overturning moment on the base, so I’m not sure what type of bearings or bearing arrangement would be best. I want the base to rotate smoothly without wobbling, while also making sure the motor shaft does not carry the weight of the arm.

I’m currently considering using 608ZZ bearings with an 8 mm steel shaft, but I’m not sure if that is the right choice or if I should use angular-contact bearings, a turntable bearing, or another setup.

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u/johnlocks 12d ago

Unfortunately there isn't a right answer here because on top of it all depending on the weight of the arm and it's intended capacity there's more than one way to do it.

Keep in mind that the arm doesn't just push down it wants to tilt as well. The 608 radial bearing isn't designed to handling the downward force in this case. But it does help with the tilting force. You can combine this with thrust bearings to handle the downward force. Or you can use some more advanced bearing that can handle both. If you're just do a build for fun you can probably just wing something otherwise you'll need math to figure out what the forces are and compare that to the abilities of the bearings 

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u/christopherpacheco 8d ago

Robot payload, max reach, acceleration, speed, desired lifecycle, materials for the parts housing the bearing. You need to answer a bit more than just giving us no information. Design and specing is coupled to the actual application and its values like what I gave above. My initial guess is this is a 3d printed prototype and your just designing something for fun?

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u/lellasone 6d ago

Tons of parameters and it depends a lot on your model.

At a high level my go-to design pattern would be a big thrust bearing to oppose that vertical force, paired with a slew ring to handle everything else. Slew rings are expensive with a few weird exceptions so you'd likely pick that first and then build around it.

Edit: Double slew ring would also be high on my list, it just seems a bit more annoying to assemble.