James,

I would have to dig up the old firmware to see what is causing that error, and I think transposing settings from the old to the new RC6 would be your best bet. Did you define the number of servos? define the z endstop as a servo? Define the servo endstop angles?

Unfortunately firmware varies wildly from printer to printer, and I don't know if there will ever be a one size fits all guide for adjusting it. The Marlin firmware is relatively easy to manipulate, in that you will only really need to make changes in the configuration.h file, and possibly the configuration_adv.h file after you become a little more familiar with the settings and what they do. Configuration.h is essentially a list of parameters while most of the "code" that makes it work is behind the scenes. Unless you are proficient in C/C++, I wouldn't recommend mucking around with anything other than the .h files. After a couple of firmware updates, you will be intimately familiar with the settings necessary to run your printer. Printbus has several excellent guides for adjusting firmware settings in his build guide.

I posted a rough guide for major firmware changes for RUMBA using clough42's dual extruder setup a few months ago. It may be useful in pointing out the variables you will need to change (note that you can ignore some of the settings related to dual extruders). You can see it here: http://3dprintboard.com/showthread.p...-Firmware-help