"As a seasoned lego builder I have an understanding how to build these Technic sets. This set is really impressive but I doesn't function as it should. The forward/reverse driving is jerky. The rotary bucket assembly jams where the 1/4 ring gears join because the ring isn't rigid enough to maintain a tight circle. The pinion gears that the bucket assembly rides on don't sit parallel to each other causing uneven load on the ring gear. I sent pictures to lego and they are sending new ring gear parts but I doubt this will fix the problem.
During the assembly I made sure that all the gears were turning freely with no resistance as required for this type of set. I verified that everything was assembled correctly 3 times and still couldn't get this to work.
In the pictures you can see the gear tooth spacing at the connection points of the ring gear are too wide for smooth operation."
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Tooth spacing at connection is wider causing the jam.