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Open-Source Mini Sub Can Be Made On the Cheap
An anonymous reader writes "Eric Stackpole is a NASA engineer and avid outdoorsman. He is the chief designer of a cheap, portable underwater ROV that could change the way we explore our oceans. And he wants to make it so cheap and easy to build that anyone can do it. The device in question is the OpenROV, a small, lasercut contraption powered by several C-cells, a small, cheap computer and a webcam. Right now the price per vehicle is around $500-$600, As with all open source hardware projects, further development will likely drastically reduce the price. Or you can buy a kit for $750 and support the project, once the Kickstarter gets going."
Perhaps the sub doesn't need many non-standard precission-engineered parts.
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That could be useful in many freshwater locales as well. Providing it doesn't generate too much turbulence and disturb the inevitable silt at the bottom of many lakes, ponds, etc.
Its nice to see good technology properly applied and then tied together with the right software. Off the shelf parts, even a micro Linux computer to run the on board electronics, and inexpensive parts round it out. Its a case of "Hey if I used this technology, I could advance a science" instead of "Hey, look, my wrist watch is a web server!"
Nicely done!
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My gut tells me that it could be done cheaper (probably $300 or so), but the price estimate for parts looks reasonable. The electronics cost around $200, the propulsion system around $125, and the frame about $100.
On a side note, the design is to be neutrally buoyant. I don't necessarily agree with this. A slight negative buoyancy is beneficial to submarines because they can more easily fine tune and control their depth with their propulsion system. Maintaining a constant depth with a neutral buoyancy will result in hunting (up, down, up, down, ...). With a negative buoyancy the motor would constantly operate at slow speed giving greater control.
I wonder how much increased depth the chassis could sustain from purging all air and filling it with mineral oil. The hydrostatic properties should make it structurally stronger, but could be an issue for the webcam optics. Alternately everything could be water proof coated and skip the sealed cylinder altogether. I'm pretty sure several layers of enamel or rubberized undercoating would sufficiently work for the home builder on the circuit boards and wire contacts. Old school would just be resin back fill everywhere, and that has worked for years.
Any sort of flooded arrangement would need pretty careful camera selection as one would be best served by a fully sealed unit that could handle the pressure at depth. Too many cheap webcams have nearly exposed CCD arrays or are vented cases for mics. Cameras sourced from cell phones are probably the most solid bet.
I would ditch the C-cells entirely and use relatively cheap LiPo batteries made for remote control aircraft for increased time and power. If he is using Cat 5/6, he should be able to dump power in though there reasonably easily as well.
Also, the new camera add-on for the Raspberry-Pi sounds like a potentially more compelling combination. I'm curious what manner of motor control he is using. Arduino would work fine with a Raspberry-Pi and is vastly cheaper than RC servo and motor controls, though at that point it might be just as easy to go completely Arduino and skip the PC brains. I do have to say the price point sounds a bit high, but I am guessing most of that is the custom plastic and steel molding and mill work. Fiberglass or even carbon fiber should be cheaper because you just need molds and cutting patterns or dies. Building everything for sub 200-psi pressure should be pretty easy.
I don't know what he's using for thrusters but those are normally the killers. Communication can be as simple as 3 0-255 values. 4-6 if you want the extra DoF.
Many projects get bogged down in protecting motors from corrosion. Even scuba gear gets a bath in fresh water after use. I dip my robots in Isopropyl after I'm done. Computer case fans will run under water for some time if you simply insulate the drive electronics. Petroleum jelly would probably be enough.
The forums look like they're going in a good direction but I would modify a CoTs dive light for the camera housing and use glad-ware for the frame, put your H-Bridges in mineral oil and hot glue the wire penetrations.
KISS. If it's cheap enough it doesn't have to last more than a couple hours. I'd bet a hot glue tupperware bot could make $100 last 12 hours before failure.
Seriously, an MSP430 should be able to do this job. Don't let feature-creep turn a camera with motors on it in to a huge undertaking.
The OpenROV is a great design from what I can tell, but the barriers to entry can go so much lower.
It is a shocker that any wire that is exposed to water, even very shallow water, will eventually allow that water to creep along the copper underneath the wire insulation. Getting gear to be truly water proof is always more difficult than one would think. I believe there are some electronic watches that are filled with silicon oil to resist water intrusion.
Of course you need to waterproof the LED leads, but the LEDs themselves should be outside of the vehicle. Much better match between the high refractive index of the water and the high refractive index of the LED means more light gets out into the water. It also allows you to place the LEDs far enough from the camera that you don't get so much "red eye" from your fish, better shadow definition and and less backscatter from suspended particles in the water.
I had this idea when I was twelve! I sketched it all up on graph paper and everything!
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