In SX Microcontrollers, SX/B Compiler and SX-Key Tool, George Herzog wrote:

I think the first question would be this: Do you intend to use Jen's PCB design as it exists or do you want to redesign his hardware?

It is a bit awkward to write software if the hardware is first resolved.

I really like the thermopiles as they seem to  be a very stable system for recognizing horizon.  Jens mentions adding more to both provide better calibration and control on all axis.

You could use the Memsic too, but you would have to filter a lot of vibration from the data.  A hybird of theropiles on the roll axis and the Memsic providing data on the other two [pitch and yaw] might be interesting.

The biggest questions I currently have is how to easily intialize the thermopiles settings in the field [I guess it means 4 thermopiles] and the how to easily turn on the roll control on a landing approach.

The roll control needs to be triggered by an altimeter or by a 4th channel R/C signal.  I have the 4th channel so it would be cheaper, but require a different board.

There is some discussion of LED indicators. It would not hurt to have an LED indicate intialization status.  Another LED might verifya motor off condition. I suppose that it could be on the output side of the MOSfet and not waste an I/O pin

Migrating the code to SX/B or SASM might make it a lot easier to impliment.
I did so preliminary math and it seems that a 32 or 33Mhz oscillator would be more optimal for providing the various serial clocks that are required.   The slower osillator will use a bit less power too.  The oscillator selection relates to how much data you need to build a smooth PWM control - 4 bits, 8bits or 16bits. 

People who program in C seem to ignore or misunderstand that the environment of the SX-28 really doesn't efficently support a lot of divide and multiply.  Using data lookups tables and an appropriate oscillator  frequency may eliminate alot of waste in the EEPROM and program's execution.

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