Hi,

Relatively new to UAV's and planning on getting the new APM2 and a Telemetry kit.  I was also contemplating the sonar modules for collision avoidance and auto landing/takeoff and have 2 questions:

1.  How many sonar units do you need?  Is it 1 for auto takeoff/landing and 4 for collision avoidance (5 total) or am I thinking of something else?

2.  What's the difference between the different sonar modules?  Even in the LV-MaxSonar range on DIYD store there's 4 different models that are the same price.  What's the difference in those?  How do they compare to the MB1260 XL-MaxSonar-EZL0 at nearly double the price?