I went to Greece for 6 days last week, in cooperation with the Archaeology department of the University of Geneva in order to take photos of a site they discovered underwater of an ancient village (5000 B.C) with my OpenROV 2.6.
Here are some details, pictures and a recap of the past week (long text, pictures and links at the bottom):
Site location: A remote bay near a small village called Kilada, 3 hours from Athens. No internet, 3G or electricity available. https://www.google.ch/maps/place/37°25’40.6"N+23°08’02.7"Efirstname.lastname@example.org,23.134092,580m/data=!3m2!1e3!4b1!4m2!3m1!1s0x0:0x0
Area to be covered: 2 hectares
Distance from shore: First walls start to appear from 60meters up to 150meters
Depth: 3 to 6 meters
The archaeologists discovered a “village”, with fortified walls and 3 towers. When archaeologists talk about “walls” from several thousands years ago, underwater, they just mean a line of rocks and stones.
What is the aim of taking photos with the ROV?
Rebuild 3D models of the artifacts using the SfM techniques, (big thanks to @Scott_W and everyone who helped on this thread Structure from Motion for documenting for Citizen / Community Science and Marine Archaeology)
What went right?
Laptop battery, my biggest fear was that my laptop battery wouldn’t last for a longtime. The solution to this was to get another laptop battery, however switching batteries without turning off the computer was a problem. So I used an external power bank that allowed me to hot-swap the batteries and also gave me 40-50 extra minutes of battery charging time.
With this setup I was able to get 5-6 working hours on the laptop.
Motor’s anti-rust coat, I was worried that salt water would rust the magnets/bearings on the motors. Using an anti-rust coat, silicon spray and cleaning with fresh water BEFORE and AFTER each dive made salt water have almost no effect on the motors.
Reconstructing 3D models from 2D images. I used a software from Aegisoft, the results are surprisingly impressive!
Transport. It was not very obvious how to transport all the materials (with batteries, chemicals and a fragile robot), coordinating with the airport authorities and the airline, they gave me a list of how/where to pack each type of battery and they handled transporting the rov as a fragile item. I used 2 UTZ boxes.
Laptop shade. Using a screen outdoor in the bright sun is nearly impossible. Thankfully, I had a “laptop tent” that provided shade and protection for the screen. (http://www.icap-shop.de/)
Deatchable tether. Very useful to connect/disconnect the ROV.
What went wrong? Basically everything else.
The EasyJet flight was full and asked me to put my hand luggage in cargo. When we arrived to Athens, someone mistook my luggage for their’s and I spent the whole week with no clothes, no solar panels to recharge the powerbank and most importantly all my cash. Luckily I got it back (cash included) 5 days later. So the lessons learned are: Do not trust EasyJet, do not leave your hand luggage, the economic situation in Greece is overrated and you don’t actually need that much cash.
Cable buoyancy. I have seen several complaints on the forum here that the ROV’s cable was getting stuck underwater because it’s negatively buoyant. Someone online posted a design of 3D printable floats that you add to the cable every 5.7meters to make it neutral. I managed to print some, however when placed in water, the 5 meters area between each float was still getting stuck under the rocky bottom of the bay which sometimes completely paralyses the ROV.
To solve this, I added fishing floats to the cable, which made it completely float on surface, it added lots of drag to the ROV, but the cable was moving freely without getting stuck at the bottom. This solution only worked because the depth was not too much. In deeper water this would have never worked.
One day the ROV wouldn’t turn on. After a lot of debugging, it turned out that a cable from the main battery pack and another from the secondary batteries have been cut (cut from 2 different locations next to the endcap and next to a motor bell, I made the cables pass from different locations to avoid this kind of problem. Murphy’s laws at their best!)
I think the cables were cut due to the ROV rubbing against some rocks or someone pulling it the wrong way.
Resoldering the cables was hell, not only because the cuts were in inaccessible areas, but mainly because the soldering iron I took with me sucks. It was unable to melt the solder at the tip, which gave very bad solder and damaged other parts of the wire.
The 800kv motors used are very weak against current and the ROV design is not very stable. There was not that much current in the bay, but it was very difficult to drive the ROV in a straight line. The “auto pilot” function in the software works great outside of the water, but is really useless in water. Following a certain direction or a straight line was VERY difficult.
It was very difficult for me to recognize actual areas that needed to be scanned from normal stones on the seabed. They all just looked like rocks to me. Even the archaeologists were unable to do it through the camera, a person snorkeling had to go and point out the areas and the ROV followed him/her.
The battery of the HD camera was the bottle neck. it lasts only about 1hour. (The ROV battery lasts about 2.5-3hours). Since I only had 2 batteries for the camera, the maximum dive time was limited to only 1 hour.
On the last day, I have either badly locked the housing of the HD camera, or maybe it’s just a crappy Chinese model. At the end of the dive the camera was full of water and now no longer works. (SD card is ok though)
There is no practical way to tell if I have covered a certain area before or not, since there’s no GPS in the ROV and no other means to track locations.
There is also no way to tell where a certain photo has been taken, since many “walls” look alike, it’s very difficult to tell where exactly it belongs on the map.
I forgot to think about a way to measure the size of things in the photos/3D models
What can be improved?
For a site not too deep like this:
- A wireless ROV can be made with a floating WiFi buoy
- A floating GPS unit can be attached to record the exact location (and also maybe guide the ROV underwater)
- Better HD camera battery/housing
- Stronger motors and more stable design to combat the current
- Better cabling/wet connectors
Here are some pictures taken by the ROV’s camera:
Here are some 3D models reconstructed with pictures from the HD camera (walls are the aligned rocks)
More models here:
A screenshot and photogallery: