# Correct axle rotation of partially built LEGO Cat D11 Bulldozer (42131)?

Page 173, Step 205, of LEGO Cat D11 Bulldozer (42131) instructions has a step to attach two sub-assemblies. What is the correct rotation of these two axles? Is it correct if they rotate in opposite directions?

## 1 Answer

I don't have this set, so my answer is based on online instructions for this particular set.

TLDR: Brown axles are supposed to spin in opposite directions. Long answer below.

Step 105 has two sub-assemblies attached - the ones with back axles seen on bottom left. Each of these axles drives the brown axles - one is clearly seen on bottom right and another is barely seen on top left.

Now moving forward to Step 116 we can still see both black axles present here, now with few more parts attached in between steps. Each axle has a grey T16 gear which sits rigidly on each axle (each gear will rotate together with its axle). In between both grey gears there are three more T16 in red. Now these are different - they move independently from the axle they are placed on, where none of yellow axle rotation impact any of red gears (until one of them is engaged via gearbox, but this is irrelevant now). In such setup these three gears connect both grey gears, meaning if we turn one of two black axles both would rotate. Since there are 5 gears in this gear train such combination would result in both axles spinning in the same direction. This would then transfer the rotation to tan T12 gears which, based on the way they are placed (same direction towards front of the model), would result in both brown axles to spin in opposite directions.

If you follow further down the instructions (steps 529 and 627) you can find that few more gears are attached to each axle further down the line. This would result in two connection points, used by next function, to spin in the same direction.