Getting Telemetry Working, A Short Review of Excelvan Radio Telemetry Kit 915Mhz

I recently purchased a small Telemetry module from Newegg.com for about $25, it runs on the unlicensed 900 MHz band.  It was quite easy to hook it up to my Hobbyking Micro APM and now I can monitor the Quadcopter while in flight, just as if it was connected to my PC via USB.  No need to connect USB on the ground, as this telemetry connection handles all communications.

A new cable must be made using the supplied telemetry cable from the telemetry module and the one supplied with the APM.  Also remember to connect as follows:

Telemetry Module with black antenna

Telemetry Module	APM
5V	5V
Gnd	Gnd
TX	RX
RX	TX

The PC connection was also painless, stuck the module into a USB port and the driver loaded automatically onto my Windows 7 laptop.

The only other trick is to select 57.6Kbps in Mission Planner to get the link to work.

Note: Telemetry module is from Excelvan and is called "Radio Telemetry Kit 915Mhz Module for APM APM2.5 2.6 Pixhawk PX4 RC Multicopter Quadcopter" and is available on Newegg.com

Update-Pixhawk Test

I also purchased a unit for use with my Pixhawk-S500 quadcopter covered elsewhere on this blog.  This time, I could use the included cable to connect the telemetry unit to my Pixhawk, although I had to shave a little plastic on the Pixhawk end, as the Pixhawk uses unusual connectors.  As with the APM, I set the rate to 57600 and was connected to Mavlink on the Pixhawk.  Works like a charm.

Pixhawk Versus APM Comparison Review

This blog entry compares two flight controllers from the Ardupilot 3DR-Open-Source stream: the generic APM 2.X controller and the Pixhawk.  I am an intermediate multirotor builder and flyer, so this comparison will focus on functionality and useability, not on advanced features.  Also, this review is based on my experience with 5 different APM modules (none sourced from 3DR) in three different physical forms: standard, mini, and micro (also called mini by some) sourced from Hobbyking and generic Chinese manufacturers.  The Pixhawk is available from multiple domestic and Chinese sources and you should check the reviews to make sure you are getting one with decent build quality.  Each was used with corresponding GPS/Compass units from the same manufacturers.  I built three different quadcopters and used them with different controllers.

Feature/Characteristic	Generic APM 2.X	3DR Pixhawk	Comment
Size/Weight	Small	Larger	APM is available in 35x35x5 mm board.  Pixhawk is 81x50x16 mm
Cost	Low	Higher, about 4X	APM with GPS ~$65
Quality	Variable	Better	Inspect a generic APM after you get it for poor soldering, loose USB..
Support	Good	Good	The best support is from peers on DIYdrones and APM forums
Flight Stability	Good	Good	This is my experience with a well setup APM and Pixhawk, your experience may vary
Accuracy	Good	Better	It does depend on your GPS and its accuracy.  Pixhawk has a more powerful processor and more memory
Onboard indicators	Poor	Good	Pixhawk has multiple LEDs and tones to tell you status, APM has a few LEDs
Ease of Setup	Moderate	Moderate	More components to interconnect on Pixhawk, but well documented. Cables and connectors often an issue with APM and documentation must be found on the Internet.
Ability to fly autonomous missions	Yes	Yes
Mission Planner Ground Station Compatibility	Yes	Yes
Flight logging Capability	Good	Better	Pixhawk logs more information and has a microSD for storage. APM has limited storage of most important variables.
Upgradeability	None	Yes	APM code is now frozen to my knowledge, but Pixhawk software with improvements still being released
Debugging difficulty	Good	More difficult	APMs seem to always work, Pixhawk is more finicky about ESCs, setup, etc.

Overall, both controllers are excellent and have worked well for me.  The APM is a better fit for small quadcopters and is probably better for the beginner builder due to its simpler setup and low cost.  The Pixhawk is very good but it takes more time to set up and it is likely higher quality and performance, so it works well in larger camera quadcopters and similar expensive vehicles.

APM equipped SK450 "Dead Cat" Quadcopter

S500 Quadcopter with Pixhawk