CHAPTER 20 ■ COUPLERFitting the LEGO Cross Axle into a Tube
A LEGO cross axle must fit into one side of the coupler. By inserting a LEGO axle into various tubes, the
closest match is found to be a^7 / 32 -inch diameter tube (see Figure 20-5).
Fitting the Motor Shaft into a Tube
The shaft of the selected motor must fit into the other side of the coupler. By inserting the motor shaft into
various tubes, the closest match is found to be a^3 / 16 -inch diameter tube (see Figure 20-6).
Figure 20-4. Four pieces of tubing, each inserted inside the next
Figure 20-5. LEGO cross axle inserted into^7 / 32 -inch diameter tubing
Figure 20-6. Motor shaft inserted into^3 / 16 -inch diameter tubing
Because the tube diameters differ on each end of the coupler, a single metal tube can’t connect the axle
and the shaft. Luckily, a^3 / 16 -inch diameter tube with 0.014 inch walls fits snuggly within a^7 / 32 -inch diameter
tube with 0.014 inch walls. The^3 / 16 -inch diameter tube is cut to half the total length of the coupler and inserted
into the^7 / 32 -inch diameter tube. This way, one half fits the motor shaft and the other half fits the LEGO axle.