I had a task to inspect a culvert under a train track yesterday, and I just thought I would share some lessons learned.
On arrival our entry point was a reed bed with just a small area of apparently clear water. A Secchi disk test showed reeds 250mm below the surface, so we set about clearing them. Mistake, the water was not stagnant but had a slight flow and we were upstream, everything we disturbed went into the culvert cutting visibility to maybe 150mm or less. Plus we could never successfully clear the water sufficiently so that the thrusters would not jam.
We tried a test dive. The ROV would not arm due to compass errors. Strange, it all worked the day before on pre-task check. It took a while to figure out that the culvert was a steel tube, surrounded by reinforced concrete. Unchecking the pre-arm compass check in QGC had not effect. Compass swing needed away from the culvert, arm before getting near (not best practice) and then we were good to go.
Lastly; 1m tunnel - with an ROV in the centre - a large mass of water is trying to get around it (even with a slow flow) with little room to get past. Far more thruster power is needed than was anticipated, hence more batteries were used, by I always take plenty.
Interested to hear if others have had similar experiences. Every day is a school day!
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Sounds like “good fun” Terry
cheers
Ian
Just a much longer day than anticipated!
Just a little more learning for anyone in similar circumstances;.
Try powering upstream into the culvert. You get clearer images and any failures mean the ROV is “flushed out”. Having to retrieve by pulling the tether against the flow is risking a lot.
This won’t suit every situation, but where the option exists it’s worth considering.
Thanks Martin, there is so much knowledge out there that just sharing a little makes all our lives easier 