I have looked closely at the whole model of the locomotive and I see that many details are missing.
The axles of the right wheels are missing, also the bars and wheels are not properly positioned and rub against the armAssembly, just as the right axles do not reach the locomotive. I think they have not entertained themselves in building everything properly and that this section "Rigging the locomotive" is dedicated to explain the controls of the wheels without going into detail.
But if all the above is not well designed, it will not work and therefore can not say in "Finishing the Rig" that those who study the book continue to make the connections of the wheels on the right side, because it will not work properly.
I think your book deserves a thorough review, to correct, at least, all the mistakes I've been sending you for days. I hope to take into account the above and correct it.
A cordial greeting.
Juan Pedrosa Luna
Thank you for your errata submission. This will be presented to the editorial team for review.