what are the sensors you are planning to use to aquire the 3d map?
microcontrollers will work if your algorithm is not that complicated or big, cause in such algorithms you need speeed
,,memories can be handeled by interfacing into external ones but cpu freq is the issue here.
i did implement the A star algorithm on my computer but the algorithm now is more than just A* , its bigger, for a map of 6 meters by 6 meters
it will take 4 seconds for the matlab to find the path
my computer has a dual core processor which runs at 3.2 Ghz and 2 GegaRAM, now imagine running such algorithms on a microcontroller
that operates at 16 Mhz ,,,,,,, !!!!! with ram not over 16kbyte !!!