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Check Pete comment for explanation below :) thank you Pete!

I need help understanding a concept im struggling with for quite a while now.

Im looking at different type of robotic arm designs, and some of them are fixed to the robot arm/body only in one side, such as that there is some offset and the load on the axis is not even (I hope Im explaining it correctly, I dont have any engineering background...)

*I hope the diagram help to understand what I mean...

anyways, I was wondering, first of all - should any specific bearing be used for such joint to deal with the uneven load? (or even double bearings in opposite direction such as tapered bearings?)

and secondly, (which I know the answer, since its commercially used... but I really wonder why) how come robots repeatability and precision is not affected by this? is it because it is neglectable or because it was well planned and accounted for?

Thank you, I hope I managed to explain myself correctly

Robotic arm moment load

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  • $\begingroup$ Bearings are chosen for the type of joint and the amount of loading - specify those and then you can select a suitable bearing. $\endgroup$
    – Solar Mike
    Commented Mar 19 at 10:02
  • $\begingroup$ Im not looking for a specific answer, im looking for explanation... what do you mean by the type of joint? as for specfying anything... again - i want a generic explanation, Im not planning to build a robot arm anytime soon.. is there a bearing type that should be avoided (prone to issue when loaded with moment) or is there a suggested bearing? $\endgroup$
    – iSoda
    Commented Mar 19 at 10:20
  • $\begingroup$ EXTRA: just to clerfiy, Im not planning on building anything, I just want to clarify some misunderstanding on my behalf if you do insist on parameters to try help a purely theoretical problem... then the robot arm consist of 2 sections (2 joins) each section is 20cm, and the second section is mounted at a 4cm offset to the first one, the end effector of the robot holds a soda can (around 450-500 grams) $\endgroup$
    – iSoda
    Commented Mar 19 at 10:29
  • $\begingroup$ In the picture, the member between blue lines is offset vs the line of {base, hand}. But the rest of the mechanism is pretty close to being in line with it. For the bearings, they'll be designed to take dynamic loads in all direction anyway, since industrial robots tend to get programmed to go as fast as can be done reliably. Would guess that a pair of angular contact bearings (installed in opposite directions) would be used. The bearings would see moderate radial load (robot flexing/extending), moderate thrust (largely from the preload) and potentially very high moment load (base turning). $\endgroup$
    – Pete W
    Commented Mar 19 at 15:57
  • $\begingroup$ The bearing that allows twisting of the "wrist" being the exception, with thrust load being comparatively larger (and with a smaller diameter bearing too). Though it too must expect all-direction dynamic loads $\endgroup$
    – Pete W
    Commented Mar 19 at 16:00

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