“Growing” robotic tubes!

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.

Information about this groups research is available here:
Robotic eversion actuators (growing tubes)

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

Hull of a day…

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.

Modor_BigBelly_V8_picture1

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.

Modor_BigBelly_V8

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.

Component_Layout_Assem

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.

Settling in on a hull design

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.

Bigbelly

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.

Bigbelly 2

Bio-Inspired Manta Ray Robots

Sketching up designs for the AUV frame I keep getting drawn towards doing a bio-inspired design. As part of that design arc I have started looking at what other people have done with bio-inspired underwater drones. Two of the inspirations I keep getting drawn back to are the whale shark and the manta ray. So I was really excited to find this. Researchers created a tiny manta-ray inspired swimming robot.

Posting it here so everyone on the project can see it, but even if you don’t look at any of the other AUV stuff this work is awesome and I highly recommend looking at it.

On a larger scale, back in 2012 the Bio-Inspired Engineering Research Laboratory (BIER Lab) (http://www.bartsmithlabs.com/index.html) put together an interesting ROV ray based robot.

This video is worth watching. It does have that TV show puffery, but it makes up for it. The video shows how they used x-rays of cartilage of the rays as inspiration. It also shows their mechanical actuator for driving the fins in more details.

This is probably my favorite stingray inspired robot. Not really bio-inspired, but its still kind of awesome.

Update: Dec 17, 2017 – Just ran across this german company Festo, which also put out a ray inspired robot. Link to it Here.

Thoughts on Ballast Control

I have wanted projects to play with some of the newer machine learning algorithms for a while, so this year’s holiday hacking project is going to be an autonomous underwater drone (AUV). The plan is to start by designing the ballast system first, as it can be independently tested and as a module.

From what I understand Navy Subs use compressed air, charged during surface stops, to run their ballast systems. Water is driven out of the ballast chamber by opening valves on the bottom of the ballast tank while leaking high-pressure air into the chamber. Similarly water is let into the ballast chamber by opening the valves on both the bottom and the top of the ballast tank, letting air escape out the top while water enters through the valves at the bottom of the tank.

I am thinking of using a similar approach for the first version of the AUV. The main difference is that rather than compressed air, I am going to try using CO2. So something like this – where there are two solenoid valves for air and water venting to a ballast tank, and a third valve and regulator system for letting CO2 into the ballast tank.

ballast_tank

So to empty the ballast tank with this system you open the valve to the water, at the bottom of the tank, and then blast in CO2.

ballast_control

For the CO2 side of things version one will use a pressure regulator intended for hooking CO2 tanks to compressed air tools. They are relatively cheap 80-160PSI regulators. For plumbing I am going to use 1/4 inch NPT push to connect fittings and pressure line meant for breaks. The design adds an on off valve to the tank as a safety for when the AUV is being transported. Best guess is $140 for ballast control.