WARNING

This is experimental firmware, use at your own risk! This repo is intended for academic and research purposes.

There is still a significant amount of research required to validate the behavior of neuro-flight controllers. If the neural network is not trained properly, instabilities and unpredictable behaviors will occur.

Neuroflight: Next Generation Flight Control Firmware

Neuroflight is the first open source neuro-flight controller software (firmware) for remotely piloting multi-rotors and fixed wing aircraft. Neuroflight's primary focus is to provide optimal flight performance.

Neuroflight aims to address limitations in PID control used in Betaflight through the use of neural network flight control (neuro-flight control). Neuro-flight control has been actively researched for more than a decade. In contrast to traditional control algorithms, neuro-flight control has the ability to adapt, plan, and learn. To account for dynamic changes Betaflight has introduced gain scheduling to increase the I gain when certain conditions are met, for example low voltages or high throttle (anti-gravity). On the other hand, neuro-flight control learns the true underlying dynamics of the aircraft allowing for optimal control depending on the current aircraft state. For example neuro-flight control has the potential to learn the batteries discharge rates to dynamically adjust control signal outputs accordingly. The goal of this work is to provide the community with a stable platform to innovate and advance development of neuro-flight control design for drones, and to take a step towards making neuro-flight controllers mainstream. For further details refer to our preprint and please use the following BibTex entry to cite our work,

@article{koch2019neuroflight,
  title={Neuroflight: Next Generation Flight Control Firmware},
  author={Koch, William and Mancuso, Renato and Bestavros, Azer},
  journal={arXiv preprint arXiv:1901.06553},
  year={2019}
}

News

• 2019-08-09 Thesis defended, Flight Controller Synthesis via Deep Reinforcement Learning
• 2019-08-06 Neuroflight reaches new level of performance https://www.youtube.com/watch?v=MByCyEnsYP0.
• 2018-11-14 Stable flight has been achieved with Neuroflight https://youtu.be/c3aDDPasjjQ

Features

In addition to features provided by Betaflight 3.3.3,

• Neural network based flight control
• Mixing replaced by neural network

Supported Neural Network Interfaces

Interfaces are defined for the sensors available on hardware. As models become more sophisticated additional sensors will be used (e.g. ESC telemetry, voltage sensor, etc.)

Gyro-based Neuro-flight controller

Input (x) is of size 6, where x = [roll error, pitch error, yaw error, delta roll error, delta pitch error, delta yaw error]. Inputs are unbounded and in degrees/s. Output (y) of size N corresponding to motor 1 ... motor N. Each output value is in range [-1, 1].

Compiling

Pre-requites

1. Build Model Use GymFC to train and create a neural network in the form of a Tensorflow checkpoint.

Place the generated checkpoint files (four of them: checkpoint, *.data, *.meta, *.index-*) in a directory which can be independently version controlled.

Create a file called tf2xla.config.pbtxt in the directory and define the neural network configuration according to https://www.tensorflow.org/xla/tfcompile. For example if building with OpenAI baselines PPO1 with angular rate error, and delta angular rate error as input ,

feed {
    id { node_name: "pi/ob" }
	shape { 
		dim { size: 1}
		dim { size: 6}
	}
}
fetch {
	id { node_name: "pi/pol/final/BiasAdd"}
}

2. Install Tensorflow Update: A patched version of Tensorflow is now available here. If you'd like to patch your own copy of Tensorflow continue reading,

Neuroflight was developed using Tensorflow-1.8.0. There appears to be a bug/issue in Tensorflow-1.8.0-rc1 preventing the ABI type from being passed to tfcompile used to compile the neural network. A quick hack to force the correct ABIType is to modify compiler/xla/service/llvm_ir/llvm_util.cc. At the end of the function SetTargetOptions place,

target_options->FloatABIType = llvm::FloatABI::Hard;

Need to investigate whether these bugs have been fixed in newer versions or come up with a better method to handle this. Install Bazel and then build Tensorflow.

There appears to be a second bug in which tensorflow/compiler/aot/runtime.cc does not import malloc.h.

3. Install Python Dependencies

Use a virtual environment to isolate Python packages. In this directory,

python3 -m venv env
source env/bin/activate
pip3 install -r requirements.txt

Neuroflight compilation

1. In make/local.mk define TENSORFLOW_DIR to the location where you have installed Tensorflow or alternately export this as an environment variable.

2. In make/local.mk define FC_MODEL_DIR as the directory containing your neural network checkpoint.

3. Refer to Betaflight or src/main/target for list of supported FCs.

Current Tested Flight Controller Hardware

Any F7 should be fine. Flash memory is sufficient for F4's however it is unknown how the decreased processor speed will affect execution of the neural network. Flight controllers known to work,

• Matek F722-STD

To build firmware,

make TARGET=MATEKF722

Flash FC with obj/neuroflight_3.3.3_MATEKF722.hex

Configuration

Neuroflight is compatible with the Betaflight Configurator however any modifications to the PID controller and mixer will not do anything as they are not used by Neuroflight.

Development

In order to reduce maintenance, avoid merge conflicts and keep as in sync with upstream Betaflight, Neuroflight's architecture will maintain a minimal footprint and isolate its code from Betaflight as much as possible. The following table describes the files modified (M), and added (A) for Neuroflight,

Delta	File	Description
M	Makefile	Include neuroflight.mk
A	make/neuroflight.mk	Specifics for compiling the neural network
M	make/source.mk	Add new sources and Tensorflow dependencies
A	tools/graph-compiling/*	Tools for compiling the neural network graph
M	src/main/fc/fc_core.c	Replace PID with neuro-flight controller
A	src/main/graph/*	Source directory supporting interface and execution of the neuro-flight controller
M	src/main/flight/mixer.*	Inclusion of throttle mixing
A	gen/*	Auto-generated files to support neural network integration
M	src/main/platform.h	Remove poisoning of sprintf functions which is used deep in Tensorflow until we can find a better work around.

At the time of development Neuroflight was forked from Betaflight 3.3.3. Since then, newer versions of Betaflight have increased in size as more features are packed in. Further testing is needed to identify if the neural network will fit in newer versions of the firmware.