I have recently been working on a turreted shooter and have been wondering how to do the bearing sandwich. I originally started with no space between the plates and the bearings, However, after looking through 971’s 2017 cad, I noticed that they have a 20-30 thou gap. My question is, how big of a gap if any, should I have between the bearings and is it the same axially and radially?
Any other criticism for the design is greatly appreciated.
Can’t comment much on bearing gap, but the gearbox on the bottom left looks like it could use 3/8” shaft and 7/8” OD bearings to save some space and weight. Any reason for that form factor in particular? I’m fairly certain you can also cut out a stage of reduction by using larger bull gears (this all ignores the planetary route of course).
On our turret we had a 3/16" plate as the rotating part and put 10 thou shims between the 3/16" wide, .5" diameter bearing and R4 bearing to give a total gap space of .1875" + .02".
For the diameter of the spinning plate I undersized by around 6 thou or so, but that’s highly dependent on your machine’s tolerances.
Years ago we use the Vee bearings like http://www.revrobotics.com/rev-29-1014/ for a similar designed turret. Let us cut our bearing cost down by 2/3rds and let us use the eccentrics to overcome out manufacturing tolerance errors.
As for feed back on the rest of the design with the direct drive from the motors to the wheel might need to be re-evaluated if you are shooting anything at all “heavy” or with any kind of high cyclic rate.
Bottom line it depends on your design and ability to manufacture to close tolerances. 0.020 to 0.030 seems about right for vertical. Radially I would try for something tighter if you are using a gear drive. Keep in mind that the forces from intaking and shooting a ball will deflect things causing binding if things are too tight. Too loose will cause repeatability issues.
Not a direct answer to your question… but bearings like this one, and others of varying sizes, can dramatically simplify things.
You might also consider a chain drive for the turret, saves all the machining of a big gear profile and is much more tolerant of the gaps you’re seeing that are nice for not binding up.
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