Overview
Last year we (somewhat miraculously) won the SMUD California Solar Regatta, and are technically state champions. The powertrain was however, simply a repurposed weed-wacker shaft with accompanying bevel gearbox. Not super classy, and not as streamlined as we could do. We had no testing data or models on propeller efficiency at different RPMs, and had no system for MPP tracking of the solar panels.
I spun it off as a bit of a personal project/obsession, and started to work on this, as an excuse to push my limits, and as a vehicle to learn new skills.
I researched, read, and looked around at the state of the art and what other solar and human power (similar power range) boats were doing.
I came up with a plan that had 4 phases.
1. Optimize motor/propeller system.
Test propellers at various speeds, finding greatest efficiency. Build new propellers if possible/needed.
Build a pod/nacelle that is more streamlined.
Build a strut that is more streamlined.
Test motors to find peak efficiency voltage/current/rpm.
Build gearbox that matches efficiency in motor to efficiency in propellers.
2. MPPT
Solar panels only want to be loaded up a certain amount. Beyond that, the point at which they are most efficient changes with panel temperature, and light intensity. Every system that my research revealed was oriented toward charging batteries, which isn't really what we want. We aren't allowed to use batteries with our solar panels during races.
I roughed out a simple Arduino based MPPT hill climbing algorithm that incorporates the throttle control. Hopefully this will allow direct connection from the panels to the motor using the motor as a variable load to keep the panels efficient.
3. Hull optimization
The hulls used last year were pretty heavy, though quite a good low-drag shape.
One idea was to use the current hulls as a master pattern and lay-up new glass or carbon fiber over the top of it to reduce the weight. Careful stress analysis should allow us to drop a fair bit of weight.
However. As a privateer, i don't have storage (or transport) for a pair of rigid 18ft long hulls. As a way of minimizing weight, i'm considering building my own inflatable hulls made from TPU coated nylon fabric. This will drastically decrease weigh, easy transport and storage, but also very likely increase drag. This lead me to phase 4, a "stretch goal" for the project.
4. Hydrofoil system
Once every other part is largely sorted out and roughly optimized, it's possible to design a hydrofoil system (fully submerged inline, Shutt Strutt style). The variables that define wing size, angle of attack, and loads are defined by the previous 3 stages however, so they do need to be close, and tested before i can start work on the hydrofoil system. The increase in hull-born drag from the inflatable hulls won't matter if they're out of the water.
Some of that was achieved in the time available. We ended up winning the competition for a second year, though the drivetrain and solar mppt system i devised didn’t work to their fullest potential. Bearing material choice of MDS nylon was not a good one, both for temperature resistance and expansion in water. Lesson learned. The mppt system was overridden on race day because we didn’t have enough comparative testing to prove it was working as it should. I build a simple manual over-ride into the system with this in mind.
The club’s page about the project is here
