"@gustavo: I can assure you, this one works: https://github.com/festlv/mavbridge (I'm the author).
I have only tested it using ESP12 modules (SMD ones, without pins), and my custom hardware board: https://www.tindie.com/products/festlv/mavbridge/"

"@Kaan: check that baud rate of your APM matches what's configured in firmware (in web control panel). Also, web control panel shows sent/received packet counts- you can verify that firmware decodes packets from serial correctly).
Another feature-…"

"Sorry, no. I've mostly done the development and actual usage indoors (e.g. it's designed as replacement for bluetooth, not 443/915 MHz telemetry links).
There are ESP modules that are pin-compatible with ESP12, so if there's enough interest,…"

"I've done a bit of prototyping with ESPs for Mavlink transmissions. I've found that UDP works best (reliable up to 921600 serial baud rate). In case anyone's interested, here is the source code of the firmware: https://github.com/festlv/mavbridge A…"

"I've done a bit of prototyping with ESPs for Mavlink transmissions. I've found that UDP works best (reliable up to 921600 serial baud rate). In case anyone's interested, here is the source code of the firmware: https://github.com/festlv/mavbridge 
A…"