Milestone 5

This past week, construction of the boat started. The CAD for the propulsion system was finalized, and we ordered many of the necessary parts. Work on the electrical system also started in the EE lab.

Hull

hull_5aFirst, we glued all of the ash pieces onto the plywood to make ribs for the boat. Here are 4/5 of them, glued and clamped to the base of the boat.

hull_5bWe encountered some problems when attaching the bottom two side pieces. They would not bend as much as we had hoped, and we had to remove the second rib so that the front would line up neatly. The back of the side pieces is not attached. We planned to soak the wood and weigh it down to encourage it to conform to our view of where it should go.

hull_5cThe wood refused to see the world our way, and we admitted that the curvature at the back was too extreme. To account for this, we will make a larger back piece once we finish attaching the upper sides. And here they are. We had to use the less visually pleasing zip ties because we ran out of copper wire.

hull_5dHere is the back. Instead of bending the sides to meet the back, we will simply make a larger back piece and attach it to the current one.hull_5eHere is the boat all stitched! We will start epoxying when our order comes in.

Propulsion

Ryan finished the CAD, and Sophie laid the pieces out on a grid in excel to determine how much sheet metal we need. We ended up ordering a 1/4″ thick piece of aluminum that is 2 feet x 3 feet.
prop_5a
Here are the propulsion parts laser cut out on a piece of thinner wood.

prop_5b

And the pieces assembled into a model!

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Milestone 4

This week, we finalized our designs, researched and ordered parts, and started using the router to cut our wood.

Hull

hull_4a hull_4b hull_4cFor the first two boards, the end mill didn’t go deep enough. We had to use the wood saw to cut the pieces out afterwards.

Drilling holes takes a long, long time.
hull_4d

Propulsion

We improved the CAD model for the propulsion system and also ordered a few necessary parts off Amazon.

prop_4a prop_4b prop_4c

Electrical

Cedric, the electrical mastermind, ordered some parts that he will need. Now we’re just waiting for them to arrive.

BATTERY TERMINAL FUSE HOLDER ESC HEAT SHRINK TUBES

Milestone 3: Models

This week, we finalized our designs for each of the components.

Hull

hull_3a

Initial sketches of hull

hullproto_3a hullproto_3b hullproto_3c hullproto_3d hullproto_3e

CAD model of boat hull from various angles – This model is that of our final hull design, without the interior of the boat seen. It follows closely to the design which our group had presented from the beginning of the project.

hullproto_3f

CAD model of boat, unrolled into individual pieces of plywood – This ‘unrolled’ model allows us to better visualize the pieces we will need to cut, and also allows us to start thinking of the construction process.

hull_3b hull_3c hull_3d hull_3e hull_3f

First prototype (Laser-cut sheets of cardboard) – To test out the overall design of the e-boat, our team decided to laser-cut the initial CAD model which we had with cardboard we coincidentally found in the lab. It pieced together really well, and seeing a physical product made us much more confident in the design!

Propulsion

prop_3a

Sketches of different possible propeller types – Initially, we were at a loss on how to design the propeller system. In fact, it was one of the more difficult tasks so far! Brainstorming allowed us to throw out our (limited) ideas and come to a consensus on what we wanted our vessel to look like.

prop_3b

Initial sketch of propeller design for our e-boat – This is a sketch of the propeller we wish to have, based on what was available online as well as our calculations (to be seen below).

prop_3c

Sketch of complete propulsion system

prop_3e prop_3d

Solidworks model of propulsion system

propcalc_3a

Propulsion calculations with various pre-determined diameters and pitch

propcalc_3b

Motor calculations given various pre-determined engine sizes (in cubic centimeters)

These are screenshots of the calculations we had done on Excel. They include further calculations on the motor from the previous Milestone, as well as calculations on propulsion to allow us to decide which system would be best (in a feasible manner) to achieve our desired speed of 8 knots. Finally, we decided on a 80cc motor as well as a 9.25”x11” propeller.

Electrical

elec_3a

Diagram of electrical system to be used to power the e-boat

 

Milestone 2: Optimization of Stability, Drag, and Propulsion

This week, we started to analyze our designs with some models and simplified calculations.

Buoyancy and Stability

Estimated weight of vessel + estimated weight of battery pack + weight of heaviest memberx2 = 3780N

Based on this value, the hull was adjusted (Rhino) such that the volume of the hull underwater was close to 3780N.

Cross-sections of the hull was taken, and tilted to a degree of 10 degrees to test stability by comparing the center of gravity with the center of buoyancy. As seen below, the latter is above the former, confirming the stability of the boat should it tilt to an angle of 10 degrees in the event of choppy waters.hull1

Drag

prop1

Desired Speed: 10-15 kts
Length: 2.4m
Estimated Weight of Vessel: 150kg
Heaviest Passenger: 80kg

Thrust

Screen Shot 2015-06-23 at 2.38.28 pm

η = (T × V) / (2π n × Q)

Assuming the ideal efficiency of 80%, we can find n x Q = 29.901 based on a speed of 10kts, and drag force of 29.22N.

Motors

http://www.hobbyking.com/hobbyking/store/__31677__Turnigy_AquaStar_4084_1050KV_Water_Cooled_Brushless_Motor.html

motor1amotor1b

http://alienpowersystem.com/shop/40mm/4070-inrunner-brushless-motor-rc-boat-2700kv-7600w/

motor2a motor2b

Propulsion

Based on our list of motor candidates, 2 battery packs of 12V will be sufficient. From the equations given in the lectures, we have deduced that nQ=30. This constant shows the trade-off between rotational speed of the propeller and its torque.

Electrical

Our battery packs will be placed right at the front of the boat to maintain neutral balance between the bow and stern, even though it will not be sufficient to keep the boat balanced.

Milestone 1: Brainstorming and Preliminary Design

Last Thursday, we learned about the factors to consider in designing a hull.

  • buoyancy: The boat needs to float! (and not sink)
  • stability: The boat should stay upright in rougher waters.
  • waterproofing: The internal components (namely the electrical system) should stay dry.

We also wanted to consider potential speed and maneuverability since the ultimate goal would be to complete the boat challenge course (preferably quickly and without unplanned incidents).

With all this in mind, we looked at various boat designs on the Internet and drew a few of our own.

ryantse1ryantse2ryantse3ryantse4ksmori1ksmori2cedricy1cedricy2ryanchee1ryanchee2

We got together and discussed what we would like to have on our boat. We quickly decided that building a wooden boat would be a good experience and a challenge in craftsmanship. We also opted for a one-hull design rather than a two-hull design because of maneuverability. Our mutually agreed upon design resembles Ryan Chee’s design 1. To reduce drag, we proposed an altered bottom that we can construct given enough time. However, this would be hard to fit to the boat due to the curvature of the sides.

proposed

Next week is incorporating electrical and propulsion systems and drafting the design in Rhino or SolidWorks. Yay!

Also, on Friday, our last team member arrived in Boston (delayed due to an unfortunate mosquito bite). Welcome, Shobs! We named the boat after you!