clarify left/right and elevon assignments

ROMFS/px4fmu_common/mixers/caipirinha_vtol.main.mix

@@ -3,17 +3,21 @@ Caipirinha tailsitter mixer
 
 This file defines a mixer for the TBS Caipirinha tailsitter edition. This vehicle
 has two motors in total, one attached to each wing. It also has two elevons which
-are located in the slipstream of the propellers.
+are located in the slipstream of the propellers. This mixer generates 4 PWM outputs
+on the main PWM ouput port, two at 400Hz for the motors, and two at 50Hz for the
+elevon servos. Channels 1-4 are configured to run at 400Hz, while channels 5-8 run
+at the default rate of 50Hz. Note that channels 3 and 4 are assigned but not used. 
 
 Motor mixer
 ------------
-When standing in front of the vehicle the first motor should be on the left side
-while the second motor should be on the right side.
+Channel 1 connects to the right (starboard) motor.
+Channel 2 connects to the left (port) motor.
 
 R: 2- 10000 10000 10000 0
 
 Zero mixer (2x)
 ---------------
+Channels 3,4 are unused.
 
 Z:
 
@@ -21,11 +25,13 @@ Z:
 
 Elevons mixer
 --------------
+Channel 5 connects to the right (starboard) elevon.
+Channel 6 connects to the left (port) elevon.
 
 M: 2
-O:       10000  10000     0 -10000  10000
-S: 1 0  -10000 -10000     0 -10000  10000
-S: 1 1   10000  10000     0 -10000  10000
+O:       10000   10000    0 -10000  10000
+S: 1 0  -10000  -10000    0 -10000  10000
+S: 1 1   10000   10000    0 -10000  10000
 
 M: 2
 O:       10000   10000    0 -10000  10000