I said I would help my nephew to make a training blade as a father’s day gift. I’d planned on a simple wooden trainer – but he had other ideas. After saying that “his dad deserved the best” – he talked over his options with me then spent the day in the shop making a rather awesome knife.
I was impressed, as it was a lot of time-consuming work. We started with an old piece of scrap, a half finished milling prototype for a knife I made a while back. He used files to finish shaping the blade. The blade was made out of aluminum, and he insisted on 5 sanding passes to get the blade face to look just right.
Once he was happy with what the blade looked like – we stamped in his dad’s name on one side, and “I love you dad on the other”. He even made sure we checked that “I love you dad” would be right way up, and readable, when his dad was using the knife.
We watched a bunch of YouTube videos on para-cord wrapping knife handles. Once we found a pattern he liked, we drilled the handle and he wrapped it up.
It was a tricky process, as he had to hold tension on the cord, while setting the pattern on the top and bottom of the blade. I offered to do the wrapping, but he wanted to do it.
In the end I was really impressed with what he made. It is a sweet training blade in itself, but my nephew was right – you can read “I love you dad” when you are using it, and thats just awesome.
I have started interviewing for gigs outside of Seattle – and that has me thinking about furniture and moving. Well the Seattle Bouldering Project has some awesome – but comfortable – collapsible chairs. I am thinking they would be easy to make, easy to move, and a decent way to store crash pads the 99.9% of the time when you are not climbing.
This picture shows how the pieces of the chairs slot together (and Tyler tying his shoes). I’d probably add some reinforcement to the sides of the slots, but with a high quality plywood they should be really strong.
I am thinking I could sew up a cover for when they are acting as couch cushions. That would give me something easy to wash, and help a bit as the crash pads get used I am not dragging dirt or chalk dust back into the house.
More I think about it the more I am really liking this idea.
I needed to go make a bunch of tests of different techniques for epoxy cast hull construction. Rather than just test putting hatches and portholes in a bunch of simple hollow geometric shapes, I decided to go ahead and run them on a simpler and smaller hull design. Since I really liked the Manta Ray robots – I used the shape of one of those for inspiration.
Here you can see my first pass. It may look a little funny as I am designing the wings to bolt onto the frame, and they are missing in these renderings.
I am using this design to test the casting of an epoxy hull, using the BlueRobotics portholes, and different designs for a 3D printed seat for a pressure rated hatch. I may have been guilty of over engineering on my first design, since once I started digging into it I think I may be able to accomplish most of my design goals with this smaller design.
I am testing using an external tank with this design, but down graded the tanks size since the hull will be much smaller. I don’t have the printed hatch seat shown in this design though.
Heading into the holidays. Either I’m going to make a lot of progress on this project – or none. It all depends on what we pick for the holiday hack-a-thon.
I am building my AUV to be a configurable platform on which to try out a bunch of ideas, so I am going to need some sort of hatch through which I can assemble, repair, and modify the internal components.
My first thoughts were to make a sort of beveled seat you can see here. The beveled seat in the hull mates to a complimentarily beveled plug piece. You have a rubber layer between the two pieces, and the more water pressure there is on the plug the tighter the seal.
Unfortunately after talking this design over with some friends who has a lot of experience deploying things deep in the ocean, I decided not to use the wedge hatch. Apparently at depth even slight deformations of the hull can corrupt the seat seal, and the hatch will sweat water into the pressure chamber. My maximum target depth for this is only 250 feet, but I would like the design to be able to stay submerged for very long periods – so a sweating seal is a problem.
Right now the leading contender is using the pressure rated caps Blue Robotics sells for their watertight enclosures. Here you can see a hull design where a 6-inch plug has been added towards the nose. The tank you can see is a 24 Oz CO2 tank and pressure regulator. I’m checking that I can install the tank and regulator through the hatch.
I have not found a hatch position that I like yet, but the one pictured is as close as I have come. Things get a lot easier if I switch the CO2 tank to be screwed on from outside the pressure hull, while keeping the pressure regulator contained in the hull, so that’s what I am likely to try next.
One nice part about using the Blue Robotics pressure flanges – is that they offer clear outer faces of an optical quality. So I can easily add internal cameras looking outward through the hatches. So if I can make this hatch style work, I will probably add several smaller ones for camera and sensor mount points.
I am experimenting with soft robotic actuators lately, and that has me reading papers and tracking what work people are publishing again. This has to be one of the coolest soft robotic ideas I have run across.
I highly recommend looking at their video. Ideas elegant in its simplicity. Arstechnica has a decent writeup of the tech, with a better description of how it actually works available here: Arstechnical Writeup
Whoop! I finally have a hull design. I found a STL model for the type of shark I wanted my design to mimic. The white you can see poking up behind the red shark is my hull design.
The elliptically shaped flats on the hull are for mounting fins. This approach will let me push out the problems of fin design until later. I’m hip deep in problems as it is. I also like that it will let me repair the fins, try out multiple fin designs, and remove them for transport. I’m going to shop off the tail as well, but I am debating how to add control surfaces, so I left it intact for now.
Here you see the outer surface of the hull. I am trying a cast acrylic hull design. The wall thickness will be just over an inch. So there is much less room inside the hull then it initially seems. Since things are going to be tight I modeled up the critical parts first so I could play with different layout designs and test fit.
The ballast system is driven off of a 24oz CO2 tank, which you can see got pushed out into the tail. Electronics will be housed inside a 4inch pressure chamber. The weird grey cylinder is a bilge pump being repurposed for propulsion and steering. I am still figuring out where to put another pump, ballast tanks, ballast weights, batteries, and some other goodies.
I have a lot more work to do on this – but I am happy how it is shaping up.
One of the problems the AUV project needs to solve it making electric connection through a pressurized hull. I found this interesting tutorial for making making watertight electrical connectors from pvc.
Initially I was drawn to Rays for a bio-inspired design. However, eventually I would like to use the active ballast to have the AUV be able to glide over large distances and Rays don’t really glide through the water in the right way.
So right now I am thinking I will use the general design of a small shark. After some quick measurements though I’m going to blow out its belly to be more like a grey whale. That should still give more storage and decent flow over the frame.
I am toying about adding two smaller fins – if I am right it could help with glide stability – but man it does not look weird. I will probably ditch the two fins, but keep the long thin tail. Since I am going to be printing all the hull mold pieces in chunks on my 3d printer – I also am strongly incentivized to minimize hull surface area.