Making an IoT robot…

Philippe Coval <purl.org/rzr> #FOSDEM 2020

Who are we ?

Philippe Coval: @RzrFreeFr
- SW Engineer for OSS (Intel, Samsung)
  - Available for cooperation
Alin Jerpelea: @devjerpelea
- SW Architect for Sony
  - Maintainer of Sony Open Devices
OSS Advocates
Contributors to NuttX community

Disclaimer

This talk is not about:
- State of the art in Robotics
- Hard real time on critical systems
It's about experimenting:
- Prototyping a "Web of Twins"
- Validated chain from actuator to UI/UX

Do NOT reproduce in a critical context

Robots

DiY from scratch:
- Design mechanical (with FreeCAD)
- Produce (CNC laser cutter)
- Assemble with motors modules
Faster: Buy a kit (pref. OSHW / OpenDesign)
- MeArm (DXF under CC SA 3.0)
- Many lower quality clones
- More advanced: Niryo (RPi3+Arduino)
How to connect and control ?

Servo Motors

Angle is controlled by a PWM signal
SG90: 9g Micro Servo
- Angle: [-90°, +90°]
- I/O: Power: 4.8V, GND, PWM

Robotic arm's controller

Software Architecture

JS Application is a Web server:
- to expose Motors angles using HTTP/REST
- to generate control signals (PWM)
JavaScript Runtime: IoT.js
"Unix like" RTOS: NuttX

Sourcing hardware

Requirements:
- IO: 4+ PWM signals (Hardware)
- Connectivity (Ethernet)
- Memory: ~200K For JS runtime and app
Nucleo F767ZI board from ST
- STM32F7 is a good candidate
  - Cortex-M7 (Compat. M4 / STM32F4)
  - RAM: 320 KB, Flash: 2 MB
- IO: Nucleo-144 Pins
- Support: cube, mbed, STM32duino, RIOT…

NuttX

Released by Gregory Nutt in 2007
Community and code grew (2.6M LoC)
- Base of derived projects:
  - TizenRT, PX4, Sony Spresense
Incubation at Apache F. in 2019
- http://nuttx.apache.org
NuttX conference in May 2020 (Tokyo)
- Registration is open

NuttX's features

A real-time operating system (RTOS)
Committed to comply standards
- POSIX, ANSI C
- File based IO (/dev)
- BSD sockets/ uIP
Modular (kconfig)
Scalable (8/32 bits MCU)
- Support 9 archs / ~400+ boards

NuttX contribution

Only CPU STM32F7 was supported
Added patches for new Nucleo-F767ZI board
Mapping inspired by STM32F103:
- GPIO, ADC, PWM, ROMFS…
Released in nuttx-7.31

IoT.js contribution

Added native module for stm32f7nucleo
- inspired by ref board SMT32F4 discovery
webthing-iotjs module to expose resources
- REST API (uses iotjs-express module)
- Mozilla IoT schema (in JSON)

WebThings REST API

$ curl http://192.168.0.42:8888
{ (...) "properties":{"arm":{
   "type":"number",
   "minimum":-90,"maximum":90,
   "description":"Rotary actuator on /dev/pwm2" (...)
   "links":[{"rel":"property","href":"/properties/arm" (...)

$ curl http://192.168.0.42:8888/properties
{"torso":0,"shoulder":0,"arm":0,"hand":0}

$ curl -H "Content-Type: application/json" \
  -X PUT --data '{"arm": 42}' \
  http://192.168.0.42:8888/properties
{"arm":42}