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Old Feb 02, 2013, 09:47 PM
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Bearings and cables

What happens when you model real bearings that have friction? Unlike the previous video where we used frictionless bearing pivots, this video will use commodity bearings which indeed do have friction. The result of which is when an outer frame or axis is rotationally disturbed, friction in the torque domain will transfer some of that rotation undesirably to the successive inner axes.


Angular with bearing friction (0 min 11 sec)


Thought exercises:
-more bearing friction means more undesired coupling
-more coupling means more unintended motion
-lower axis MOI means more unintended motion
-higher axis MOI means it is harder to command a purposeful axis slew

Bearing friction is a virtual given for the vast majority of gimbal configurations but it can be reasonably managed with proper selection and by design. Proper selection of cabling and the routing of that cabling is equally important. Cabling likely will increase the unwanted coupling between axes in a similar fashion that bearing friction does.

Lastly, attached is a zip folder with an Excel Spreadsheet that can be used to explore the relationships desribed in this post.
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Last edited by otlski; Feb 03, 2013 at 02:59 PM.
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