Bathymetric UAV mapping boat construction and getting my feet wet with ardupilot

Designed as a Lake Michigan coastal cruiser, this one meter cedar, bottom heavy boat is supposed to cruise at a modest sonar mapping speed for at least eight hours. I am a novice at micro electronics and am going through a steep learning curve. Having read and reread the documentation, it is time for me to start making hardware decisions.

I have tentatively set my sights on an economical path of the Beagle Blue for autopilot, Turnigy basic controller, Ublox Gps and Compass module, QgroundControl on android, chromebook, and Windows 10, Cuav Pw for telemetry, and no clue yet on servo/rudder or ESC/brushless motor drive.

I see a whole set of experienced folks doing this better but here goes the newbie questions. These hardware choices are my best attempt at following the advice in the docs, I may not have it right. The idea is to have limited telemetry with mostly scripted mapping. So what hardware choices are dead wrong, what choices allow the use of my masts for the telemetry and gps? Assuming a 800kv 12v brushless motor run at the bottom end amperage, what battery system am I looking at for eight hours service. Finally, what are the best resources (discussions or people) for me on the forum going forward. Appreciate any help, thanks.

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Now I have reconsidered the linux route as more than I can handle so I am back to looking at autopilots, excuse me as I stumble around.

For the autonomous boat as you describe you will want reliable hardware. The Mro PixRacer Matt suggests is good and pair it with one of their GPS/compass modules. A 1m mono hull boat may be on the small side for the purpose you have described (I’m in Michigan). What is this hull?

The hull is a patterned after the Bulger Box, a simple sailing design that allows for easy builds. The hull is eighth inch cedar soaked in epoxy penetrating treatment and coated with multiple coats of oil based paint, a system of wood boat construction. It has a one kilo steel keel for self righting and is designed to have a low wind profile. As soon as the last features are completed it will get an epoxy resin finish. I stubbed out antenna masts in case the gps and telemetry could be raised from the water surface and to attach a strobe in case of lost contact.

I agree one meter is small for the job. I am hoping for a tugboat arrangement where this is a heavy pulling machine that powers through a wave crest with something of a surfboard plunge through rather than a super buoyant ride over. I am also trying to imagine a fifth-wheeler style following unit which would be the sensor package, I think it important to separate the two. The sensor package, in a sense, extends the footprint and stability. Originally I had thought of a sailing unit but the small scale havoc on the lake surface would stall such a craft.

Thanks for the pointers, I am reviewing many interesting post in this forum.

Thank you , I am review products and prices.

After the barest education on servos a low cost full size unit was chosen for this prototype. The homemade arm, rudder shaft and bushing are scrap brass, 7/32" brass tube, and 3/16" brass rod.

The rudder is brass sheet soldered to the shaft. The pattern for bending is based on the naca0012 symmetric airfoil plot with a given length. Allowing just a few millimeters more than twice the width of the rudder for the brass sheet, bend evenly over a tube shaped anvil to well over 90 degrees. Mark where the shaft will align with the inside of the rudder sheet, sand and flux both the shaft and the sheet here and at the trailing edge. Continue to bend over the shaft and clamp in a vise being sure to do it in a manner that will not steal all the heat when soldering. The soldering is relatively easy with a torch and the excess solder will run down into the trailing edge making a very hydrodynamic surface. Trim and sand excess brass and solder.

The Nacelle the rudder sits on is also naca0012 based and is ready to accept the thruster.

With hull penetrations almost complete, the hull will be finished. The next step is to learn about and decide on the power source. The forward compartment is dedicated to the battery pack(s), power management, On/off switch, and charging access. From the limited reading so far I am hoping it makes sense to have two or three multiple cell packs that separately fit into the craft and are then wired in parallel and are charged as a single unit while still being balance charged.

Hardware choices are looking like; mRo - Pixracer, WiFi module, better power unit, better GPS.

I charge my LiPo’s individually balancing. Then top them off a bit more with a non balancing charger. I run 4 to 6 hooked up in parallel and have never had a problem. The batteries are always used together more or less with the same amount of cycles on them.

I at one time had a problem with the rudder shafts bending from the force of water being pushed over the them by the thrusters. My final solution, after four tries, was properly sized rudders with a hollow brass shaft and a carbon fiber rod inserted into them.

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I am getting ready to make a decision on battery pack and charger. I am looking for a 10000 milliamp hour pack to fit my compartment of standard size for this pack. The trouble is, I have no concept of who to buy from for quality and price. Any vendor recommendations or product recommendations would be appreciated. I am hoping to permanently instal the battery pack and have a waterproof charge cable extend outside the waterproof hull.


I have been happy with the orange batteries from Ready Made RC.

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Here is a pixracer mounted on fan vibration isolators on an aluminum radiation shield. The power module is in the background, shown without the shield cover.

Thruster, rudder and servo are ready to go.

I am now working on battery, charger, and rc remote. I chickened out on soldering the telemetry wire after successfully tinning the pad. I’ll buy a replacement before trying something that small. After a learning curve the rest of the soldering is going well.

I managed to convince myself the references to powering the servo rail were meant for some other situation than mine until recently. Next is trying to understand how arming is different than turning something on and how I will do both. Now that I have the pixracer, I can go to step one.


Very nice project you got going there.
I just saw that you’re using the same thrusters I’m about to buy for my bathymetric USV.

Did you have the chance yet to gather any experience with them?

Looking forward to your next updates.

What thruster is that? I mean, brand/model.
Nice project!

They don’t really have a brand name. If you search for “underwater thrusters brushless” you should find them in between all the other China stuff.
12-24V, 900kv.

this one?

Yes, exactly.
They look quite promising for the price.
And than there are also These thrusters. Pretty much the same. But only 12v, 800kv and they do have a little more thrust. The white ones are what I wanted to buy.

White Thrusters

How did you manage to attach that link so nicely? :smiley:

The white thruster you listed is the one I wanted but it took too long to come in. The 1200 kv engine is really overkill, I imagine I will be running these at very low power and conserving as much as possible. It was during the rush of Covid and I didn’t wait the weeks and weeks it took to get here. It ran past the delivery and I got money back from alliexpress one day before it came. I paid the guy directly by paypal. It did finally get here and I really like the design that went into it. I am planning on using the 1200 kv for the Version1 model here and switching to the 800kv for version2.

The smaller white one looks like it can be ducted in any way desired if you can accurately drill 1mm holes. In both cases of the white ones and the colored ones, they look well made but I have no experience yet.

I am researching the rc boat community for even smaller systems to save even more watts. There are interesting applications of dual 280kv motors reduced by 4:1. The advantage here is duplication in case of engine loss, and very low power consumption.

Design of the boat is the factor determining the power requirements for any particular application. For a working example: Assuming a cruise speed of 3 knots - the hull speed should be a little more for the best efficiency (solve for length with the bow wave/ wave height calculation) so maybe a little smaller than 2 meters waterline and a water piercing profile similar to the hydrofoil ideal of naca0012.

I am progressing on the build but life is getting in the way.

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