With five sheets of plywood. Dan is beginning work on the strongback for the new hull while he’s down at bucknell. In early May he’ll return to Tiverton where we’ll complete the female mold construction.
While it may seem like this is a step in the wrong direction, this is a great move and we’ve made more progress in the last four weeks than we did in the last six months. We’re excited with the change, and have set a launch date.
Why the change?
After moving Scout to WPI in February, we studied the motor that we had planned on using for Scout’s propulsion and found that we had settled on it in error. It would consume too much power and rotate too rapidly for our purposes. Since we built the rest of the propeller shaft/ stuffing box/ prop assembly for that motor specifically, we figured that we’d switch the small brushless motor with a larger,more suitable brushed DC motor. However, the assembly that we had wouldn’t support that. We’d need a new assembly.
As this was happening, we were also working on the hull itself. Last summer, we were under constant pressure to get the thing done tomorrow. While raw ambition and positive thinking is usually enough to get us through a project, in this case it was not enough. We didn’t realize all of the problems that we would face in every step of the process, and I wouldn’t have expected us to do so. In a conference call four weeks ago, Max, Dan, Brendan and I decided that the number of problems with this current hull outweigh the benefits of keeping it.
What we’ve decided to do is construct a new hull. Different techniques, different construction methods and composites. Building the first hull took so long because we didn’t know every detail of what the hull would need to be constructed to do. However, it let us iron out a number of issues that would have been issues anyways.
Of course, we’ve distributed the construction of the new hull. At WPI, I’ll be working with our team of electrical engineering and computer science students to finish building our electronics and coding our software. Max is back on the project at URI, once he finished the design for the hull, he sent it to Dan. Dan (at Bucknell) is starting to build the strongback which is the foundation of the construction of the new hull. You can get a basic idea of how we’re building the hull by taking a look at this link.
Is it going to be launched?
We set our launch date for June 6.
What else has changed?
While we were previously using a brushless DC motor, we’ve switched to a commercially available trolling motor.
This motor is much more simple to integrate into the hull, as instead of worrying about how to keep water from coming through the hole where the shaft emerges from the hull, the entire motor is submersible. Because we’re working on the hull and electronics separately, this motor reduces the need to have the boat in the same physical location as the electronics.
This also eliminates the need to cool the motor as it will be in direct contact with the water.
Because we switched to a new motor, we needed a new motor controller to go along with it.
A motor controller allows the onboard Arduino to regulate the speed of the motor, which is of critical importance to the strategy that we plan to use to optimize our energy budget.
This component is noted as “MOSFET” in the block diagram below. It’ll be changed in the next revision.
The electronics for the project are built around two Arduino microprocessors.
We’re using an Iridium 9602 SBD modem to send information from the boat to shore.
There are 50AH of rechargable LiFePO4 batteries aboard Scout. There are also backup batteries for the communications equipment. We have a large assortment of sensors that allow us to see exactly what Scout is experiencing. There’s one barometric pressure sensor, a humidity sensor, five temperature sensors, and a number of current and voltage sensors that let Scout tell us the state of its batteries and other systems.
Scout’s software is designed for the boat to have full control over its systems. It makes use of our redundant electronics hardware to check each decision it makes. Since the boat’s going to be unattended for months, it’s critical that the software keeps running. Examples of this are how we prioritize power to the electronics via rerouting with relays, and our backup lithium battery pack that can keep the main electronics alive for days. Our redundant communications system has a backup battery pack that can keep it online for between 4 and 6 months, depending on the rate of transmission and weather conditions.
The hull is going to be constructed from carbon fiber.
It’s optimized to be the most efficient between 3.5 and 4 knots. Its primary design concepts are to have enough surface area to house the five solar panels that generate Scout’s power, but also have low wetted surface area to reduce drag. It’s 12.8 feet long, and weighs slightly under 140 pounds including our batteries, solar panels, and the other systems aboard Scout.
It’s optimized the most efficient between 3.5 and 4 knots. Its primary design concepts are to have enough surface area to house the five solar panels that generate Scout’s power, but also have low wetted surface area to reduce friction. It’s 12.8 feet long, and weighs slightly under 140 pounds including our batteries, solar panels, and the other systems aboard Scout.