The Solar Wanderer is a solar powered autonomous small boat. It is very much inspired by the Microtransat Challenge and https://www.bluetrailengineering.com/fun-stuff. The design principle is that whatever can go wrong will go wrong, and I'm not great at finishing projects, so it has to be as simple as possible. This means just solar, no sails.

There is one 100W solar panel powering two thrusters when the sun is up (roughly 17h/day in UK at summer solstice). There is a battery backed Pi Zero to maintain GPS tracking and occasional GPRS communication.

• Large 100W lightish solar panel (£29.40 eBay)
• 12V Underwater Thruster Motor 3 Blades (£14.72 eBay)
• several (six?) two litre fizzy water bottles for bouyancy
• Raspberry Pi Zero 2W (£15 Cambridge shop)
• Power bank with pass-through charging, claims 10400mAh (£9 eBay)
• Boost-buck regulator to maintain power when powerback glitches (£1.74 each when ordering 4)
• SIM800L 2G GPRS module (eBay)
• GPS6MV2 GPS module (eBay)
• HMC5883L digital compass (eBay)
• USB UART for second UART (£2.39)
• 1p mobile SIM (£1)

Prices above include delivery. The aim is to be under £100 for school projects. Currently about £80 plus scrap bits.

• Make it cheap, fail fast, don't worry if it gets lost: From Microtransat Challenge boats get lost and many don't even make it further than the pond. There's also a lot of student interest, and building something under £100 puts it in a school project range (IMO). Better to get something in the water and lose it than never get it finished.
• Solar power: Solar seems much simpler, there's no boat to balance, the forces are much less, the weight is less and there's no mechanical adjustments needing servos. This puts it in the non-sailing class in Microtransat Challenge, but that's okay as just making trips from UK shores and back would be success.
• Battery back up for location communication: Originally I thought I'd power on only when the sun shines and call home with location. However, the boat could be blown onto shore overnight and I wouldn't know where it was, so now I'm planning a powerbank just to keep reporting the location. The main thrusters will only work when sunny.
• 2G data connectivity: This means it's not ocean going, but satellite is way out of budget (e.g. Iridium 9603 Short Burst Data Transceiver). 2G was chosen over 4G/5G because it has greater range (perhaps 10 miles).
• Raspberry Pi: A mobile phone is more waterproof, is easier to manage the power, includes a data connection, position/direction sensors a camera and has it's own battery. It's just harder to hack, and who doesn't want to ssh into your boat just to type top?
• Power Management: Need to keep power to electronics at all time to transmit position, need to power the thrusters when surplus power exists. Power electronics from solar if possible, else powerbank. Electronics monitor solar voltage, power thrusters only if solar has enough voltage to charge powerbank. 'Power OR' the solar and powerbank to give continuous power failover to electronics:
  • 10,000 mAh battery with pass through gives about 5.0+-0.1V, it has back current protection
  • Solar gives 3V-12V, transformed with boost-buck (and optional diode) to 5.2+-0.1V

Details:

• Self righting - maybe lower thrusters along with top buoyancy
• If no power off then DietPi else Raspberry Pi OS Lite readonly
• Real time clock to come from GPS via gpsd
• 2G antenna to be on the top of the pyramid (with top buoyancy)
• Call home with position every hour? Allow ssh in?
• Camera? Or will this be too low down?
• Some watertight box for all electronics
• Filter historic GPS to get direction, match that with the digital compass
• Pulse width modulate the power to the thruster with two FETs controlled by GPIO
• Operations:
  • If enough power then orientate on last known position (or away from land) and move
  • Every minute: Log position, direction, GPS velocity, GPRS strength.
  • Every hour: dump log summary to server, allow ssh in

• Power management:
  • Two feed to electronics:
    • 10,000 mAh battery with pass through gives about 5.0+-0.1 V
    • up to 12V solar feeds a boost