Selecting a flight controller

What is a flight controller?

A multicopter uses several motors to spin multiple rotors, somewhat like a helicopter.

A Quadcopter.  Photo by no.

The spinning of any single rotor is going to introduce a spin to the motor too (Newton's Third Law). Helicopters deal with this by using a tail rotor to counter-act the spin. Multicopters deal with this by using an equal number of engines and having half of them spin in the opposite direction.

Flying an RC Helicopter
Photo by Deep Frozen Shutterbug

But there is a whole balancing act beyond keeping the torque of the motors (called yaw) under control. Multicopters will flip if the force of the engines is too far out of balance, but balance it just so and the aircraft's pitch tips in the direction of travel.


No human would be able to remotely balance the motor speeds of three or more engines while standing on the ground. Instead multicopters depend on a microcontroller on a circuit board to read position sensors and make minute adjustments to the motors according to a program. This bit of electronics is called a flight controller.


So, the brain of every multicopter is a flight controller. In my case I expect to upgrade the frame and motors over the course of the project, but keep the same flight controller, updating the software as needed. So I had better start there when making decisions about what to build.


There are a variety of flight controllers and software to choose from. It took me several days of reading bits and pieces off of websites to reduce my apprehension over which to select. Here are some of the websites I had to consider:


The Multicopter Table. A comparison, somewhat out of date, listing dozens of open source and commercial options for flying a multicopter. This lists the base capabilities of hardware and software. DIY-types can program more capabilities themselves, in theory.

Frank26080115's Instructables step-by-step on building a quadrotor helicopter. Here is shows how to take an Arduino microcontroller and build a flight controller board from scratch. He goes into depth about the inner workings and has code examples. Perhaps too advanced for me now, but a great reference.

Aeroquad has flight controller kits and open source software. For about $200 you can have a full flight controller, with sensors and expandable options.

Multiwiicopter actually has pre-built flight controllers, again with all of the sensors you might initially need. These are sold as "plug-and-play." These flight controllers are built around the Nintendo Wii accelerometer, which is apparently a highly sensitive, but low cost sensor.

And then there are commercial vendors, like Mikrocopter (US sales site). Certainly fully capable, often built-in with the code to add camera mounts and GPS already. But very much in the pricey range, starting at $460 and going up from there.

Decision

After looking at all of these options I have elected to go with an Aeroquad kit. It comes with the four main sensors. And it has a shield to make installation of add-ons easier. The shield also has ten PWM outputs for motors, ten servos outputs for cameras and stuff, and pinouts for GPS and video display. When compared to the best board by Multiwiicopter, it is obviously heavier, but clearly has more motor controllers and extra servo outputs.

I do find it interesting that pretty much none of the suppliers list the weight of their flight controller. I guess from their point of view, you don't really have a choice. You need one (theirs) in order to get started. But the pictures give you a general sense of the size and that is a primary indicator.

Okay, so now to order the Aeroquad v2.0 kit...

Aw crap, it's out of stock. Well, I set up an e-mail alert for when it is back in stock and will wait a week or two. Meanwhile, time to figure out what I want to do for a frame.

NEXT POST: An airframe. Do I go with a kit, hand build or something in between.