BB NSK
Beam Bots board support for the Nerves Starter Kit and its Balance Bot add-on — a two-wheeled self-balancing robot with an e-paper panel, four NeoPixels and a web interface you drive it from.
Two halves. The drivers and control loops that are the same on every one of these boards ship as modules; everything a particular robot gets to choose is written into your project by an Igniter task.
Installation
mix igniter.new my_bot --with nerves.new --with-args="--target trellis" \
--install bb_nsk
cd my_bot
Then add subsystems one at a time, each leaving a robot that does something it couldn't before:
mix bb_nsk.add_wheels # its wheels turn
mix bb_nsk.add_imu # it knows which way up it is
mix bb_nsk.add_balance # it stands up
Or skip to the end:
mix bb_nsk.cheat
Build and burn:
MIX_TARGET=trellis mix firmware
MIX_TARGET=trellis mix burn
Tasks
| Task | What it adds | What the robot can then do |
|---|---|---|
bb_nsk.install | Nerves system, device tree provisioning, robot module, persistent parameters | boot on the right device tree |
bb_nsk.add_wheels | two DRV8837 wheel actuators and the motor deadband parameter | drive its wheels |
bb_nsk.add_imu | BMI323, a Mahony filter, and the lean and heading sensors | say which way up it is |
bb_nsk.add_balance | the balance loop, its states, its commands and its gains | stand up |
bb_nsk.add_leds | the NeoPixel state indicator | show its state across the room |
bb_nsk.add_display | the e-paper panel and the status screen | draw its own status |
bb_nsk.add_environment_sensor | the base board's HTS221 | report the air around it |
bb_nsk.add_wifi | an access point it brings up when it has no network to join | be reached with nothing configured |
bb_nsk.add_web | Phoenix, a dashboard, a drive pad and a wifi setup page | be driven from a phone |
bb_nsk.cheat | all of the above, in order | — |
bb_nsk.doctor | nothing; run it on the board | tell you which of five things is missing |
Every add_* task takes --robot, and every one is safe to run twice.
Hardware
| SoC | Allwinner T113-S4 (dual Cortex-A7, armv7) |
| Nerves system | nerves_system_trellis ~> 0.5 |
| Device tree | nsk-balance-bot, selected by the provisioning this installs |
| Motors | two N20 gearmotors through a DRV8837, on pwmchip0 channels 2–5 |
| IMU | BMI323 at 0x68 on i2c-0 |
| LEDs | four NeoPixels on ledc |
| Display | 4.2" 400x300 e-paper, UC8276 controller, one bit per pixel |
| Environment | HTS221 at 0x5F on i2c-0 |
Requirements
- Elixir 1.19 or later
- A Nerves project targeting
:trellis nerves_system_trellis ~> 0.5— 0.4 and earlier have no balance bot device tree at all, and crossing to 0.5 needs a FEL reflash rather thanmix upload
bb_nsk.add_display and bb_nsk.add_environment_sensor add git dependencies —
eink, emerge and hts221 are prototype drivers not yet on Hex.
Known limitations
- Simulation is bare.
SIMULATE=1 iex -S mixboots on a laptop and the robot arms and holds parameters, but every peripheral declines — there is no simulated IMU, so it has nothing to balance against. - No odometry, and no position hold. There are no encoders, so two of the four states an inverted pendulum has are unobservable. It balances while drifting.
- No buttons or battery telemetry yet. Both are behind the board's STM32,
which speaks an ASCII protocol over
/dev/ttyS2and comes pre-flashed. This is deliberately left undone — it is the obvious thing to build once the robot is standing up, and a generator for it will follow.
Related packages
bb— the robotics frameworkbb_sensor_bmi323— the IMU driverbb_estimator_ahrs— the orientation filtersbb_parameter_store_cubdb— parameter persistencebb_liveview— the dashboard the web interface mounts
Acknowledgements
- Gus Workman and Protolux Electronics
for the Nerves Starter Kit, and for the
einkdriver the panel is drawn through - Frederic Cambus for the Spleen font the panel is set in
- The Emerge project, which rasterises the panel's screens
Licence
Apache-2.0. See LICENSE.txt.