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Oak Matthias
triPod
Concept
The triPod project is a concept watercraft.
Imagine, if you will, a speedboat as a 'water sports car', and a jetski as a 'water motorbike'. The triPod is a 'water off-road buggy'.
Space frame - the main chassis contains the power unit, and enclosed cockpit, this is mounted on 3 turnable floatation pods.
Pods - The pods turning axis has a rake angle that makes the pods 'bank' as a mono hull speedboat does as it turns.
Main Parts
The front two pods would be steered together using a wheel or pair of lever controls. The rear pod would have a rudder (or keel, given placement on hull), this would be steered like an aircrafts rudder, with the feet. Not having the front and rear pods steering linked would create a dynamic handling experience. In turns you could hold the rear pod close to the steering line for speed, or allow the rear pod to break loose and let the rear of the craft swing out, like a car drifting!
Propulsion - The two front pods would contain electric jet drives. propulsion powered by an onboard hydrogen fuel cell. There would be two throttles for independant control of the thrust generated on each side of the craft. This would add to the natural turning produced by the pods turning, and make for a fun craft with nimble handling.
Design Process
I had recently started CAD modelling using ProDesktop as part of my then current role of Technology Technician. I liked it and started expanding to more current software, my choice was Autodesk Inventor. This project was my first real design project, reiterating and evelving the idea as I learned the software and changed aspects of the design. The images are of the latest of a long line of previous versions, each with their own conceptual or modelling strategies.
This was the final frame I designed for this project. It is the 'same' version as the above phot album and would fit inside the body shell.
The difference is it is made up of straight sections, rather than curves. This made it makeable for me at the time, with the tools and materials I had available.
I designed it the way I would build it, using profiles derived from 2D profiles rotated in space to known positions (or previously added profiles). I could build up this frame, using relatively simple flat jigs, piece by piece.
But First!
Before making a full sized prototype, I should really check to see if it actually works as I think it will. Enter triPod RC, what better than to embark on a whole new design process to make a scale version and remote controllable version of the craft?
See triPod RC project for design, build and a very short testing video of the RC model version.
Stress Analasis and Frame Iterations
During the iterations of design, I also imagined how it could be built and, how strong the frame needed to be. I explored the frame analasis environment withing Autodesk Inventor. Being self taught, I cannot be certain that the results were accurate, but I did carefully explore the options and set up the analasis model in a may that made sense given the forces involved, the results also responded to changes in the frame in a predictable way that was congruent with the expectations of ech design change.
The concept started out as a much smaller more basic craft with fixed pods. I was having a lot of fun exploring the frame generating capabilities of Autodesk Inventor at the time, including adding custom frame members for use in the environment. Pictured is the first version of the frame.
As I discovered new to me ways of working with workplanes and equation driven dimensions the frames became more complex as did my understanding of the software.
Note the large T-section beams are not part of the design, but an 'anchor' part for the simulation model.
Here we have my first simulation of the frame. I have considered the weight of the pilot and multiple forces acting on the outboard motor mount, including weight of the motor, thrust and a twisting moment, due to the distance from point of attachment and point of thrust.
I don't have recorded the exact figures I used, but we can see from the image, the maximum frame deformation was only 1.266mm.
I thought that was quite rigid, gave myself a pat on the back, and promplty scrapped this version for a more advanced model. "Wouldn't it be cool if the floatation pods themselves rotated?!"
Prompting another evolution, with different frame characteristics due to the axial nature of the turning pods attachment. Here we have the first (I think!) version of the turning pod frame.
Another evolution, the craft is becoming more something you sit in, rather than on.
My mind is now thinking about speed and performance, more than sedate meadres as would have been fitting for the earlier versions.
Now I had figured out the frame analasis, I always checked in with it. Starting out with an underbuilt frame, adding frame members to tame the areas of greatest deformation. This one has just under 4mm of deformation.
True to form, I scrapped it, sometimes it's easier to start from scratch rather than wrangle an old model having learned how I should have designed it during the process.
I did however design the pods for this one, as I was beginning to see in my minds eye this thing actually working.
The next iteration or two (total iterations 14!) took me to the one you saw at the top of the page and the conclusion of this part of the project.
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