For those of you who have not been following the latest news from the FAA this concise article should clear the mind about the impact of new regulations and the industry's opinion.

Keep in mind: The rules won't become law until mid-to-late 2016 at the earliest, though 2017 is a safer bet.

http://www.popsci.com/what-does-drone-industry-think-faas-new-rules

This post is intended to illustrate the steps into making a less-than-a-buck battery voltage measurer to monitor the life of your UAV battery. It has been used successfully on a generic autopilot board (running MegaPirateNG), but it should also work on original ArduPilot or other boards.
On the hardware side you need a simple voltage divider and optionally a capacitance-type filter (100nF):


"Wait! What's going on?"  You wouldn't want to send your raw battery power directly to the board, unless of course you wanted to see it flaming up. This voltage divider sends a ~2.2V (when battery is fully charged at ~12.6V) voltage to your controller board. This value is then multiplied by a scaling factor to get the original battery voltage level to be displayed on your GCS.

Connect GND to a ground pin on your board and insert the the socket into the AD0-Ax slot.
Measure your battery voltage with a multimeter (you'll need this value in a second). Now cable the battery to the newly made circuit and the latter to the system.
Connect your board to your computer via USB and start MissionPlanner.

You can follow these visual steplines on the wiki while reading the following.
Click on the Initial Setup tab and under the Optional Hardware slot on the left select Battery Monitor.
Select the following:
-Battery Monitor: 3 Battery Voltage
-Sensor: 1
-APM Version: <your version here>
Type the battery's voltage value in the Measured Battery Voltage entry and press enter. The following entry (named Battery Voltage (Calced)) will monitor your battery voltage. This info is also visible on the bottom left corner of the HUD in the Flight Data screen, and you can also set battery failsafe..how cool is that!

I switched from a Multiwii based board to Arducopter and ESCs were working fine.  After months of tweeking and upgrades to my quad, motors seemed to go crazy.

I applied the methods (automatic and manual) documented by the Arducopter manual but neither worked.

The solution was found by applying the calibration documented here for ESC like Hobby King 20A ESC 3A UBEC and similars. To avoid a huge waste of time and patience all (4 in my case) ESCs were calibrated manually by cabling together their signal and sending it to the rc receiver (3rd column of pins top pin, i.e. throttle). From one ESC Vcc and GND cables also went to the rc receiver (following pins on 3rd column).

Make sure throttle stick on your radio transmitter is at its maximum (this ensures you enter in ESC calibration mode) and give power to your system.

Each ESC (more or less synchronized) will start emetting a sequence of bips and blurps according to the menu you can find on the link above. This (partial) picture gives you an idea:

You may select on option (and thus set it) by bringing your throttle stick down while the sound sequence corresponding to what you need to set is playing. For a start, bring all ESCs to factory default (option/music 8) and afterwards select the options you want.

This may get very annoying if you need to set lots of options but you have the great advantage of calibrating the ESCs the exact way you want to. Also, by cabling the ESCs as mentioned above you need to do it once and for all.

I hope this will help someone out there. Rob