6" Diameter AUV Hull for R&D

Build DIY AUVs
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The engineers at Blue Robotics have strong motivation for marine projects and we often design some things in our free time. Sometimes they lead to new projects and sometimes they don’t. Its fun to tinker around and push capability/cost boundaries.

I like working on vehicle systems and I have done my share of ROVs and surface vehicles. Now, both types are made by a few companies. The last vehicle outside that capability/cost boundary is the Autonomous Undwerwater Vehicle (AUV).

There are a few manufacturers of micro-AUVs out there, but the cost is a bit absurd for even the base models: Bluefin Sandshark ($30,000), Riptide AUV ($15,000), NemoSens AUVs (?), and there’s more. This has kept them out of the range of hobbyists. I also could never get the only other AUV control system that I know of to work: MOOS-IvP

I am also not totally in agreement that control surfaces on these micro-AUVs are a good thing for keeping a level keel for side scan or photography work:

Years ago before there was an ArduSub, I started a thread on DiyDrones trying to figure out what would be needed. (AUV Development with the EKF) The consensus came down to needing a new firmware, a method for underwater telemetry, and a method for underwater navigation.

Fortunately, with upcoming M64 Modem, the S1 Locator, and the Ping, technology may have caught up to the point where AUVs for hobbyists may be possible in the near future. Driving around a BlueROV2 with an early version of their modem is certainly encouraging:

Pending the software and firmware work, I thought an ArduSub compatible AUV hull would be in order, so I started working on one based off a 6" WTE that would use thrusters instead of control surfaces.

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The files aren’t complete but everyone is welcome to take a look and download them. 6" AUV Hull files OnShape I’ll continue to work on them in my free time and hopefully get around to printing a hull in a few weeks.

Right now, it uses the following:
1x 6" WTE with 2x 15-hole endcaps
1x T200
4x M200s

The intent is to have a 3D printable reference frame AUV by the time either the Water Linked system works for short range ArduSub AUVs or somebody comes up with a DVL. Optical flow may also be a possibility for really clear water.

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I remember that DIY Drones thread! Awesome to see the project coming along

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Hi Kevin,

Awesome work!
That reminds me a bit MARES AUV capabilities, probably your model will be more versatile with this number of actuators, and probably easier to create a control algorithm :wink: since it’s not so sub-actuated, probably roll will be the most complicated one but it’s possible to manage it.

If someone wants to check what is possible with this kind of approach, take a look in this video:

I would recommend to read about the DART project, it has a similar structure and the paper may help you with some software or structural development.

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Hi Kevin

First off great to see you picking this up again

Please don’t take any comments out context I love that you are looking at this and just trying to throw my 2 cents in at potential issues you may have to overcome

I strongly agree with your concerns over control surfaces and think they are a likely failure point, but what they give you is control over the unit to prevent it from barrel rolling (which with a single rear thruster you are putting some rotational forces into the unit to make it want to do this) maybe 2 thrusters at the rear counter rotating to prevent this? (also would give you some skid steer, if you had this you could do away with the rear lateral motor as it is unlikely you are after true lateral movement) Or maybe a keel

I also have some concerns as to how you are “hanging it all together” if it is based on a 6” tube and about 1.5m long (just a guess couldn’t get the measuring tool to work properly) it would be around 30kg’s and getting it into and out of the water would put forces on the endcaps (yep some of the sections would be flooded but people tend to grab what’s handy) and I wouldn’t want that hanging on the end caps maybe some solid ridged backbone may assist (and may allow for expansion as I assume there would be modules that may be slotted in [battery module/SSS module/ photogrammetry module/XXX module]

Given that its most likely use (aside from being a cool toy) is some sort of medium to large area scanning tool (a standard ROV is for [what?] 50m by 50m area) I would also consider adding 2 down facing (for and aft [long base centerline]) cameras (likely 2 cut down 3” tubes with domes) to try and give it the ability for visual navigation system (I am assuming that the cut out’s on the underside of the printed structure area a ping [Nosecone] and ?? not sure what the more elliptical one is for in the AUV Mast Hull Section??) as for medium to large area scanning I suspect you are pushing beyond the water linked 100m range limitations so will need something based on the unit

Anyway take it as it was intended

Scott

PS if you are doing some 3” cut down Aluminum Tube Watertight Enclosure let me know as I’m up for most likely a couple

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@kevin,

we are with you!!! Great thread! Low cost, configurable AUV is a dream…for some of us.

Keep going,
Nikos

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@Scott_W Ha no worries! I left out a lot of my design commentary from the initial post otherwise it would have been a very long opening post!

Vehicle Rolling:
That has been on my mind a bit even during the initial concept. On vehicles this small, it is hard to get enough distance between the CB and CG. We’ll see how much rotational torque one thruster exerts. If it is too much for the hull then I’ll remake the tail with two counter-rotating propellers. Figuring out the number of thrusters I need is one of the first things I want to do when making a custom frame.

Skid Steer:
We have tried a few surface vehicles with skid steer (and ArduSub) and we found when we set it to AUTO when facing away from a waypoint, the vehicle would oscillate and never really align to the next way point. We know the AUTO functions are very developmental and we haven’t spent much time on them, but we did have some waypoint following with some tuned position controllers a few years back. With ArduSub being derived from ArduCopter (instead of ArduPlane), the thinking is that AUTO functions may not be possible with skid steer as it needs full maneuverability in the horizontal plane (forward, rotate, strafe) that skid steer just doesn’t give you. We’ll know more when we spend some time on it.

Keel:
Yep, thought about it for the rigidity and ballast weights.

Hull Rigidity and the Endcaps:
With the current WTE flange/tube design, you are completely right, everything would probably fall apart. Fortunately, BR is working on a new flange/tube retention design that would still use the current endcaps. I can’t go very far in explaining the method, but it is being worked on. If this proves insufficient, I can re-design for a “wet-hull” with the WTE mounted internally like how the Amethyst AUV is built. It would just make access a bit more difficult as I would need to remove hull sections to reach on/off switches.

Bow Section Cutout:
Yes, that is appropriately sized for a Ping. I call it a “Ping Pocket”

Mast Hull Section Cutout:
That elliptical cutout is actually so I can stick my fingers up there and reach an on/off switch and the vent plug for the WTE. I am not super happy with that section or the mast. It will be determined by the GPS and Wi-Fi antennas or modules.

Navigation:
Navigation is the hardest part for developing an AUV platform based on ArduSub as it needs constant position updates. With Water Linked being pretty range limited, I can at least work on the frame and hull and maybe get some small area transects done with the Deep Vision system that was designed for the BlueROV2. At least it will be able to be tracked in case it gets caught. Easy for an ROV to go retrieve it.

Optical flow is going to be fairly limited for the environment off Southern California. It may work in some of the shallow water on the Channel Islands where the water is clearer, but it drops off fairly quick and our visibility isn’t very good. Regardless, I was going to consider it for a developmental hull section.

An ArduSub AUV is really going to need a DVL to have some range and be useful.

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Hi Kevin

Thanks for understanding where I am coming from you know I want you to succeed so I can piggy back off what you have done

Totally understand cutting it down to be brief as there is a lot that goes into a beast like this

Another (sort of) way to dissipate the torque induced on the main body of the unit is if you can make the rear fins somewhat adjustable (see pic similar to the ROV lights and then lock them off maybe ±5 degrees?) although the induced torque would be related to the speed you could set them once (like trim tabs on outboards) for the “average speed” the AUV would tend to run at so they counter act the induced torque and lower speed perhaps too much and a higher speed too little and then you would have to rely more on the distance between the CB and CG

temp

Again maybe too little words for the skid steer (if you go with 2 motors) I would say a “turn” would be done more with the front lateral thruster but a minor course correction or “trim” with skid steer (think driving slightly into a off centerline current) for slight corrections (say a couple of degrees) given the lateral arm moment of force from the lateral thruster from the distance from the CG it would require very very little force(ie hard to control)[eg bow and stern thrusters are great for spinning a vessel on the spot but a really poor on course correction whilst underway]

PS bet you a beer there will end up being some sort of keel :wink:

Great to hear on the endcap rigidity the Fishplate joiners from the Amethyst AUV is

As an assumption I would had assumed that the AUV would fly about 3-4m off the bottom given

  • It’s a “lightweight” or “consumer grade” AUV [not sure of a good name ie not big and chunky with 24hr duration] I would assume it would be limited to say low range [swath] SSS in part due to their [SSS] power requirements and transducer size (think 900 – 1200kHz Trident Starfish or Deep Vision system running at high frequencies giving really great detailed images but poor [comparable] swath[ie not a wreck hunter but a site documenter]) and hence if running SSS you want it 10% of the SSS range off the bottom and the assumption it could most likely “see” the bottom at this height off it
  • Its other most likely payload is photogrammetry and or video transits and thus also needs to see the bottom

(I would love some other “cheap” payloads (towed mag or fixed metal detector [there is a difference]) lidar, which other than MB they would all be pretty close to the seabed)

Given this (and it’s me just discussing it) I would have thought it would be an easier navigation route than a developing a low cost DVL (and its associated low cost accuracy limitations)

Again thanks and take it as it’s intended :+1::+1:

Scott

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What a great project! We have been looking for something to replace the Iver from OceanServer (since the L3 acquisition) and would love to help as much as possible. I’m even more happy to see you guys are already designing around the issues we have with most previous AUVs.

One huge issue we have with AUVs is the ability to vertical profile. Since most designs require forward propulsion to navigate, they are useless for finding a target (nutrient or other variable) and stopping to continue sampling. For this reason, the Hydromea Vertex is an interesting concept, but still not out of production. I wonder what benefits and detriments such a design present.

On the communications side, has anyone else had any experience with optical modems? I certainly don’t mind floating a buoy (or four) in my AUVs area of operation if I can keep costs down and data collection up. And, they seem to work quite well, conditions dependent.

Finally, please don’t forget about the water quality sensors! Sonde integration has always really botched up the CG CB as originally designed.

We will be watching this thread!

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Great idea!!! The Bluefin sandshark Video you posted, is actually from me :wink: The bad vehicle position is mostly due to a firmware problem… If you look closely you can see in that video also that there is quite some roll even though the control surfaces should account for it. Main argument against only rear control faces is that any type of AUV has a hard time getting to dive if buoyancy is not perfect.

I’d be thrilled to see AUV components from BR.
On the other hand, please don’t only think your tubular thruster modules as AUV! In a 6" form factor they could be also very useful for a narrow acces ROV through tubes/boreholes etc. I was actually considering building an ROV that fits through a 10" ice hole.

As i mostly work in polar areas, the pricetag is really key. And i bet you can easily beat the current commercial competitors if it uses existing BR parts

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@Scott_W

I’m working on a major center section re-design, so expect a lot to change here. I am going to try and do a wet-hull option with a 4" WTE. I’m planning for an HDPE keel. I may also downsize the hull diameter to 5".

With a 4" WTE, I’ll need to figure out the battery situation without the AUV being too long.

Adjustable Fins:
Easy to implement, I’ll play with them. I heard from the manufacturers that the Sandshark and the Riptide were designed with 3 fins to actively counter roll. I don’t know how successful that has been, but we can certainly play with the roll trim.

Skid Steer:
Yep, understood. I don’t think ArduSub can have multiple methods of turning. Something to test.

Utility:
You have that about dead on! With some of the deeper sonar anomalies off Southern California, it makes dragging a towfish difficult. I have a pretty long tow cable and even with gentle turns and speeding up and dodging other boats, I have almost gone into the dirt a few times.

Sending down an AUV with a high frequency SS seems more appealing to get an overview of a site before an ROV goes down. SS and especially mags work best when you can get a constant altitude off the bottom :wink:

@iSENSYS

I am interested in what you liked or didn’t like about the Iver, or why you are interested in replacing it. I haven’t heard much from actual AUV operators and there is a lack of public user material.

Interesting feedback on the vertical profiling thanks! Thruster based AUVs definitely have the maneuverability you are looking for, they’re just aren’t many around.

@ckatlein

That is such a coincidence with the Sandshak video! Did you ever get it working properly? How did you like the UI?

I’ve thought about tube and borehole utility too and that would definitely be the easiest to do right now with a conventional tether. No special communications or positioning needed.

I’ve been keeping up with the Icefin AUV and it looks like they have a dropweight in the nose to get down boreholes, then they level out. I’m not sure how it gets back out of the hole,
icefin%20auv

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Hi @kklemens

If you haven’t hit the bottom you haven’t been scanning :wink:, although it has been a few years since I have, but, I have also been doing a lot more really long range swaths (hence higher off the bottom scanning)
bump close

I didn’t mention this earlier as I thought you were a little more set on a path as it depends where you are up to in the development, but I had always thought in section it may be more along a figure 8 design looking section with a 4” electronics tube on the top and a 3” Battery tube (keel) below broadly speaking you could have a pretty much a stock standard 4” electronics tube near “as is” and a second 4” tube as the pseudo “surface computer” providing mission planning image processing whatever then a number or “string” of 3” battery (as is) under them etc

Still encasing it all using a 3D plastic printed fairing / framework / hydrodynamics covering approximately 4” wide 7” tall or at least a pregnant part in the “middle”

Just a thought
Scott

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Update for today:

  1. Redesigned the mid-section to be a “wet hull” and working on cradles for a 4" WTE.
  2. Redesigned the mast. It now has space for an ESP32 Wifi module and an mRo uGPS.
  3. Added a keel and allotted enough room to standard 200g mount ballast weights

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@Scott_W That is certainly another way to do the battery/electronics sections. It would look kinda like the Blueye Pioneer. I’d like to see far far I get with the torpedo shape for now before I get too radical.

Without a Fathom-X on that side of the E-tray, I have some room, but not much. The other thing I can do is sling battery tubes to the sides kinda like the Cambridge Barracuda AUV.

barracuda

“Build now, refine later”

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Have you seen SV Seeker’s towed sonar fish?

http://www.svseeker.com/wp/sv-seeker-2/underwater-rovs/open-source-towed-sonar-rov/sonar/

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@Oddmar I was watching that build years ago, that’s definitely some heavy machining. Far beyond my capabilities and tooling, but fun to watch!

Some updates for today:

  1. Slimmed down the hull OD from 6.5" to 5.5".
  2. Lengthened the mid-section from 400mm to 500mm to accommodate a 400mm 4" WTE.
  3. Started work on the 4" WTE E-tray. Things don’t exactly fit quite yet, so I’ll have to do some re-arranging.

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Yours is a really good looking project; are the fins on the back mobile or are they just static? Are they particularly effective in controlling roll?

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We’ve sort of ended up with the same internal configuration for the electronics - I take it that’s the cell in the centre?

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We are currently investigating two-axis differential steering and propulsion. For the application we have we don’t suffer from cross currents…

…has anyone investigated this sort of arrangement before?

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@Grant, yes we have but it’s off this topic. You could pm me at geromat@hotmail.com.
@ Kevin Great job! keep us updated.
Matt

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Hi Kevin,

I’m starting on a AUV project as all the pieces are finally in play. Would I be able to use your 4” hull design as a starting point? The 6” hull on Onshape has been great to play around with.

3D printer is up and running and with ROS2, low cost sensors cheap brushless motors it’s a great time for prototyping.

Cheers
Jesse

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And I’m happy to contribute back. I’m developing a cool ROS2 tool that would be similar to 1980’s cruise missle TERCOM guidance system. Basically using the Nav2 toolset with an additional odom update that would use the seabed depth to help predict the AUV location. I’m also looking at adding in a current model so the AUV could navigate within a box on a predetermined route, and then pop up for occasional GPS fixes. I have a long term goal to cross the Straight of Georgia but will start with some there and back trips near Victoria.

Anyways, if you’re able to get me the 4" onshape files I’ll start printing and help develop an open source AUV in my spare time!

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Hi @westcoast I’ll work on a new document of the 4" hull I was working on. I need to strip some things out of it and repackage.

I did a little work on it in 2020, but its still not at the point for directly 3D printing or anything.