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I have recently found that the turntable of the crane has been sticking when turning! Having taken apart the crane and investigated the issue, it seems to be the interplay between the turntable's teeth and those of the small black cog: they are not meshing smoothly! The cog moves nicely when turning the turntable, but is stuttering and jamming the other way round (the more useful way)!
Any help would be appreciated!
P.S. any tips on lubricating the yellow pistons?
This is a known problem with that gear combination. It's a flaw with Lego's design of the bevel gears. See this discussion on the EuroBricks forum.
Bevel gears are typically designed to fit with only one other size of bevel gear. Specifically, the cone-shaped pitch of each gear needs to intersect with each other at a single point to ensure smooth operation.
All Lego bevel gears are intentionally designed with a 45-degree pitch so that any gear can mesh with any other. This means that only bevel gears of the same size can actually mesh perfectly, although in most gear combinations, the loose tolerance means the incorrect pitch isn't really noticeable.
However, in extreme cases like the 12-tooth-bevel to 60-tooth-turntable in the Arocs, the gear pitches are so mismatched it creates an extremely "noisy" or "sticky" effect.
I don't have this kit, but when you have an issue with cogs/gears meshing poorly it usualy has to do with how the forces are causing the tolerances to slip. It sounds like the load to the cog (or gear) is such that in one direction they are being forced together.
Ideally, we want gears to mesh within some ideal tolerances, so see how you can reinforce the shaft blocks so torsion doesn't change those tolerances too much.
Also, check for too much backlash, which could show you where the gears are meshing too loosely and then digging in.
The turntable gear you are speaking of has the same connectivity options on both sides. However, only one side of the gear ring on the black piece is actually beveled. If you use the turntable incorrectly (upside down), this will result in poor connection between the gears. So it is essential to place the turntable correctly.
