Hi! I’ve been thinking that I might like to build an rov with ardusub, and i have quite a few questions. I plan to CAD model 3d print the whole thing (with the electronics in a PVC pipe) and run it with an fpv camera. At some point, I plan to bring it out to the ocean and down to depths of around 100 to maybe (but probably not) 150 feet. Im having trouble figuring out and understanding what to really do, even with help from the ardusub documentation and some of my own research. Anyways, here are my main questions:
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Is a laptop necessary? Is there a way just to run ardusub with a plain old radiomaster boxer, walksnail goggles, and a raspberry pi companion computer? Could I even run it without the raspberry pi, and just somehow adapt an Ethernet cable to plug in to my boxer and goggles (goggles have mini hdmi-in port)? I dont have a laptop, so I dont know if I would have to buy one for this project or not.
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What parts are reccomended? I would love it if someone could give me a cheap-ish parts list that would work well. I have no idea what to use so reccomended things such as what esc, motors (I would like to use use 5 of them but can use 4 if that’s significantly simpler), or camera to use. It would be nice if the equipment could fit into one of bluerov’s smaller acrylic tubes. Im fine with spending a bit if I need to, but I dont really feel like spending ~800 dollars on my first ROV, unless absolutely necessary. Part of the reason I am making this myself is so that it is cheaper. …
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The tether… I figured that I could just use an Ethernet cable for this, but I need a solution to keep water out of the ROV itself, because I dont want water to run down the cable and into the ROV. Im not sure if it would be okay for water to enter the cable itself, so it would be great if somebody could clarify. I heard that you can cut the cable, solder it, and then put epoxy around the solder point, and that will prevent water from entering the vehicle. The issue with this is that the end caps bluerobotic’s WTE (which I was planning to use) seem to be too thin to do this. I dont know if there is something to do to make this work, or if i need to buy a different WTE. I figure that I will just use a 100 meter long cable as a tether, since that is the max range and I dont know if I can find a cheap range extender for these cables.
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Is the 2 inch WTE okay for electronics including a camera? I dont know if I would need to use a bigger one, but they seem to go up almost exponentially in price the larger they get. Bluerobotics seems to be the only WTE supplier on the market that will sell a complete set with O-Rings and everything.
Thanks for any help!
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Hi @Elmerthecat -
Happy to give some feedback! It sounds like you have somewhat of a background in radio-controller drones and FPV, but working in the underwater space has some big differences - at least in our ecosystem! It’s worth noting that most 3D printers do not create water-tight parts, and some sort of post-processing would be necessary. The tolerance variation in PVC pipes can also make sealing them a challenge - rubber caps work in some situations but would not withstand anywhere near the pressures at 100’ depth. In answer to your questions -
- Because radio-waves don’t penetrate water, ArduSub was developed to only be controlled via USB game controller. This means that using an RC transmitter is not an option - you will need a computer with connected game-controller to use the system. QGround Control is the recommended application to run for vehicle control, but we’ve made much progress with Cockpit, a browser-based alternative. An autopilot is necessary because like a quadcopter, coordinated control of the motors is required to move the vehicle while keeping it stable.
- I’d recommend our T200s for your motors - other, cheaper options may work but will simply not hold up in the long run. If you intend to only use your ROV a couple of times in saltwater, standard brushless motors or thrusters from more questionable vendors are an option. With excessive care these may even last a dozen dives or about a year! Whatever type of ESC you use, it needs to support bidirectional operation, with 1500us pwm corresponding to 0 throttle. Another advantage of our thrusters is that they (can) come ready with WetLink penetrator to install on an enclosure in a reliable waterproof way!
- Ethernet cable does work for tether, but as you say if the tether gets a slight cut, water will quickly travel along it and into your vehicle - even through an appropriately sized WetLink penetrator gland. Potting the tether can sometimes help reduce the rate of this leak, but this approach in general is vastly less reliable. Our Fathom tether may not be as cheap, but the integrated kevlar for tension strength and the water-block material that swells up internally when wet can ensure that your vehicle is not damaged in a similar situation. This Fathom tether is not standard Cat5 cable, so a 100m ethernet connection with it is only possible with our Fathom-X tether adapters - these work with just two wires in that tether up to 300m!
- Fitting your electronics in a 2 inch enclosure would be incredibly challenging! The Raspberry Pi 4 itself will not fit inside this size enclosure. You may be able to use a 3 inch, and either our Navigator or an older Pixhawk for your autopilot solution.
This diagram may help clarify things as well:
We’ve not explored or evaluated it, but this group does offer a (paid) class that details a lower-cost, more DIY / hobbyist grade approach - that still uses ArduSub. I think this size / style ROV is best suited to pool or protected water use. I recently tried using the discontinued Trident ROV from Spotter and was shocked how useless it was in the real world - unable to descend and maneuver to depths beyond 15m and impossible to control!
Keep in mind the old adage, you get what you pay for!
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Thanks for the help. How would i go about finding an esc that uses 1500 us ppm as zero throttle? This does not seem to be a commonly listed feature. Can this be programmed in the esc? Would these work?
Hi @Elmerthecat -
Those should work - the keyword to look for is bidirectional, they are typically used with RC cars and not planes/quadcopters. Some ESC firmwares do allow you to enable bidirectional operation, but the method to do so varies with the type of ESC/firmware used.
Thanks. This is going to be purely a hobby rov, so I will probably be using lower end electronics. I plan to use 6 motors, 3 vertical, 2 forward, and one lateral, so it should also be more maneuverable than the trident rov you mentioned.
Hi @Elmerthecat -
Support for other ArduSub by other autopilots is somewhat limited. The cheapest option is likely going to be an older pixhawk, but they can be hard to find. You can find supported boards listed here.
