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8020 Based ROV With Custom Battery

Hey guys, just wanted to show off my build so far and hopefully get some feedback from an experienced community. I had been wanting to build a rov since I was a kid and decided as an adult with the funds and technical expertise now is the time. I wanted to do a frame based on 8020 extruded aluminum. The idea is that it would be easy to shift components around and be a somewhat modular platform. Drew a quick frame up in Maytech and it generated a nice bom.

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I drew up and 3d printed various brackets that help attach components such as lights/thrusters. I got these thrusters for very cheap on Amazon. I’m skeptical of their performance (I took one apart and there was a dji brand motor inside) but don’t have the budget for decent thrusters for now. Opting for a 6 motor thrust vectored layout. (Had to split this into separate posts as new users can only post one image per post for some reason?)

Currently in the process of building a 39 cell battery out of 18650s recycled from old modem batteries. Each cell was discharged and tested for internal resistance and capacity. Hoping to have around 26AH of capacity at 11 volts. I wrote a small python script to sort the pack into a 3s13p balancing the 3 parallels packs so they all have the same capacity. I then designed a housing so they all fit safely inside a 4 inch blue robotics housing.

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Still need to sort out the esc situation and am currently waiting on another housing for the battery. Getting close to the first dive!

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Welcome to the forum Josh - cool build! :smiley:

Is your intention for the profiles to be water-filled or sealed? Curious what the difference in buoyancy would be and whether it’s significant. I’d recommend choosing one and either drilling several small drainage holes or sealing off the access points so you avoid a mix of water and air sloshing around, but not sure how much effect it would have either way.

Neat idea, nice!

Interested in the battery pack, if you don’t mind sharing extra details :slight_smile:
What material have you printed the housing out of, and how are you setting up/connecting the conductors between the batteries?
Also curious about how you’re planning to charge the batteries. Have you got a charger that can balance all 13 cells at once?

Your designed housing looks solid, and the aluminium enclosure should help keep things cool :slight_smile:

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Sorry its been a minute. Just finished up the battery recently. Housing is printed out of PLA, Using a hx-3s-fl25a to charge/balance the pack. The battery is in a 3s13p configuration. Since its 3 groups of 13 cells in parallel we only need to balance the 3 “groups” of batteries to match each others voltage. Pulled some inspiration from how tesla builds their vehicle batteries for added safety. Each 18650 is connected to a bus bar with thin nichrome wire. This acts as a fuse isolating problematic cells without compromising pack integrity. Seems to work great so far but have yet to put a real load on it. One thing is for certain, I don’t think it would make it through airport security :sweat_smile: . Hoping to finish final assembly in the next few weeks and do a first dive before 2022!



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I built an 8020 main structure for exactly those reasons as well. I drilled drain holes in it to help with the concern that @EliotBR brought up

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That is awesome! Yea it is a huge oversight on my part and I’m glad @EliotBR brought it up. I just recently had the idea of filling the top railings with expanding foam then drilling holes in the bottom part for drains. Any thoughts on this? I don’t have anything in mind for making the ROV neutrally buoyant yet.

Thank you guys for the ideas.

Without looking into it, maybe check that the expanding foam doesn’t degrade too much in salt water?

For the drainage holes remember that air in water wants to go up, but water in air wants to go down, so you may need vertical holes that go all the way through (or perhaps some on top and some from beneath if there are strength concerns from too much cross-section reduction).

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