The 3rd experiment in the Almabraxas series is expected to be a solar-powered autonomous boat (hence the trailing B). The computer is based on the one from the Almabraxas 2 high altitude balloon. Of course, you can follow the development on the blog.

General description

Every robot is composed of sensors, actuators and a calculator in between, with a power source. This family of ro-boats is no exception.

  • The power source is composed of one or several photovoltaic solar panels.
  • The actuators are the two thrusters.
  • There are two families of sensors:
    • The "internal" sensors allow the calculator to measure the voltage and current provided by the solar panel, and thus the available energy given the lightning conditions.
    • The external sensors let the calculator know the position of the boat: a GPS gives the location of the boat, allowing the computation of the "ground" (or rather sea) path. The ro-boat also features a magnetometer (electronic compass) to get a first orientation when the roboat isn't moving.
    • The roboat as no proximity sensor ! So it can bump into the ground or other boats...
  • The calculator with its sensors is called the ABOC (Almabraxas Boat On-board Computer). In its memory resides the navplan, which is the list of the geographical points the roboat is supposed to go through. This is how it is programmed. So at the most general level, the role of the ABOC is to sense the position and direction of the board, evaluate the available energy, and decide how much power must be affected to each of the two thrusters,


The project is divided into two phases: Almabraxas 3-1, the prototype, and Almabraxas 3-2, the real stuff.

Common characteristics

The characteristics common to phases 1 and 2 are:

  • Mono-hull, static stability
  • differential thruster steering (no rudder)
  • Solar power without backup batteries
    • Solar MPPT management through motor power variation
    • MPPT controlled by MCU
  • Same (homebrew) software !
  • OS: mbed
  • MCU: STM32F4 (Nucleo board)
  • Electronics:
    • GPS
    • magnetometer (electronic compass)
    • No proximity sensor !
    • Voltage and current sensor (for solar power management)
    • SD card logging

Main differences

Almabraxas 3-1 Almabraxas 3-2
Expected resistance Calm lake, no significant wind or current Ocean crossing
Dimension 1.2 m length about 3 m length
Power 25 W solar panel 2 x 100 W solar panel
Thrusters 2 x DST-700 2 x T200
Hull EPS enforced by an acrylic sheet resin surf longboard
telemetry transmission 433 MHz radio (RFM 69) Iridium satellite transmission (Rockblock satellite)
Telemetry frequency 2-3Hz 1 per hour
Data collector timelapse camera
Electronic circuit building breadboard PCB

Detailed description

  • Power Management
  • On board computer: the ABOC
  • Software architecture
  • Hull

Similar projects


Not so hobbyist

Some considerations

What speed to expect ?

Here's a page with some hard numbers. In short: it's a 1-2 persons dinghy weighting ~35 kg, 8ft long. Powered with some motor it runs at 4.3 km/h drawing 100W, and 6km/h drawing 250W, so with a well design enough boat, we can expect 2,5-3 kts with 200 W solar panels (assuming an average power of 50% the panel's peak power).