alphabot_swarm

Code to deploy on AlphaBots to test the STTR swarm control algorithms.
Initial work performed by RI for STTR Phase 2E.

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Requirements

Hardware

• 4 × AlphaBot2-Pi
• 8 × Decawave MDEK1001 (UWB sensor)
• 4 × SparkFun ICM-20948 (IMU)
• 4 × CP2112 (I2C–USB Converter)

3D Printed Parts

• 4 x Mount for UWB, IMU, and I2C-USB converter

• 8 x Spacer for ball casters

Note: Spacers may need to be adjusted by +-1mm due to AlphaBot2-Pi tolerance

Robot Preview

Setup

Ultra-Wideband Sensors

1. Download the Decawave Software Package.
2. Flash the UWB sensors using J-Flash Lite.
3. Use the Decawave Android app to configure sensors as anchors or tags. The maximum anchors allowed in the software is 4.

📖 Full guide: Precise Real-Time Indoor Localization with Raspberry Pi and UWB

Run Instructions

0. Login to the GUI for the RPI OS and configure the AlphaBots to the same Wi-Fi. Note their ip addresses.
1. Compile: make swarm_child.cpp and swarm_controller
2. Run ./swarm_child '{"nodename":"child_XX"} on all robots, where XX is from 01-03.
3. Run sudo python3 position_udp_main.py on all robots (requires restarting once on first run after reboot)
4. Run ./swarm_controller on a computer on the same network as the AlphaBots.
5. Run the control_demo.sh script.

Note: For more ideal initial trajectories, all robots should be setup starting at 0 degrees (facing +x-direction)

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Programs:

1. ssh_keyboard_drive.py: Control robot with WASD
2. imu.py: Reads orientation data using IMU
3. uwb.py: Reads x,y position data using UWB sensors
4. position_udp_main.py: Main driver code

Known Limitations and Issues:

1. On running position_upd_main.py for the first time on RPI boot, you'll notice it starts spinning after receiving a position command. After stopping the script and restarting, this problem with the IMU will not appear again until another reboot.
2. UWB sensors may occasionally go down and require a restart (unplug/replug)
3. Velocity is fixed during movement.
4. Optimal performance degrades rapidly due to short battery life.

Future work:

1. Re-incorporate Madgwick filter and EKF back into positioning code.
2. Consider increasing robot velocity.
3. Implement fine-grained convergence to target position.

Configure & Build

First install the dependency packages:

sudo apt update
sudo apt install -y libopenblas-dev

This repo uses CMakePresets for its build configurations.

See the available presets by running the following in the root folder of the project:

cmake --list-presets
cmake --build --list-presets

Example configuration and build for the linux-debug preset:

cmake --preset linux-debug
cmake --build --preset linux-debug -j4 --target swarm_child swarm_controller copy_agent

Example configuration and build for the rpi-debug preset: See the section below for installing the RPI cross-compiler first before building for RPI.

cmake --preset rpi-debug
cmake --build --preset rpi-debug -j4 --target swarm_child swarm_controller copy_agent

The compiled binaries will be in the build/<rpi/linux>-<debug/release> folder.

Installing the RPI Cross-compiler

The Raspberry PI on the AlphaBot uses version 2.36 of GLIBC, so the latest version of the toolchain we can use is version 12.

localuser@raspberrypi:~ $ ldd --version
ldd (Debian GLIBC 2.36-9+rpt2+deb12u7) 2.36
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.

The toolchain can be found here: https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads

Arm GNU Toolchain Version 12.2.Rel1 x86_64 Linux hosted cross toolchains AArch32 GNU/Linux target with hard float (arm-none-linux-gnueabihf)

Change folders to the /opt folder to use as the root install directory for toolchains:

cd /opt

Download the toolchain:

sudo wget https://developer.arm.com/-/media/Files/downloads/gnu/12.2.rel1/binrel/arm-gnu-toolchain-12.2.rel1-x86_64-arm-none-linux-gnueabihf.tar.xz

Extract:

sudo tar xvf arm-gnu-toolchain-12.2.rel1-x86_64-arm-none-linux-gnueabihf.tar.xz

Remove the compressed file, which we no longer need:

sudo rm arm-gnu-toolchain-12.2.rel1-x86_64-arm-none-linux-gnueabihf.tar.xz