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Measuring T100 RPM and estimating speed


(Avi D) #1

Hi everyone,

I’m Avi and our search for our AUV marine surfboard ideas has led us here.
I’ve scoured the forum and some on DIYdrones arduboats and some posts by Kevin and Scadden here had me start to read about underwater VLF communication, good times.
This is a long post and my only experience with RC is driving small cars so please bear with me with no Arduino/soldering experience either but I can write unix shell scripts.

This is a tiny section of south western coastline, 2 beaches, which in the past few years have seen a massive increase in tourist numbers. Photo is oriented to the West.


The Olive Ridley sea turtles lay eggs in this area and FPV to monitor them would be an awesome integration.
The lines indicate the general area they wish to monitor and the small white circle is an ideal remote controller location.
It’s in the middle of both beaches sits a convenient hill which provides ~100 feet of elevation overlooking both beaches and the ocean in front.

Some students and concerned citizens wish to collect sea water quality data just a few Km off these beaches running about 4-6 sensors.
Tourist season lasts 4-6 months of the year, and they wanted to sample a few hundred times a day but the whole year around.
We feel an AUV with a tethered surfboard on top for power/satcomms/3G/GPS could do this well. And it puts my new RPi3 to good use.

We have a few surfboards for testing, a 13 feet 3-man kayak and occasional access to a small outboard.
Our first test will attempt to harness wave/wind energy for primary propulsion (something like the LR wave glider or a single mast and sail) with one T100 + motor controlled rudder on the tethered sub below for speed and course correction.
Compared to the Solar Surfer we’re replacing a fixed keel with a tether and will be making rudder adjustments way more often than running motors for propulsion and steering.

Currently the tether seems like it will be a complicated thing to engineer, so we might get an Al or steel frame made of the board to make it somewhat easier but that’s way off.
We hope to mount only the solar panel/film on the top, moving everything else below deck maintaining a very low waterline, this will probably take some custom fiberglass work.

Wave height here averages 0.1m - 1m in fair weather and a lot more in the rains.
We hope the navigation should anchor it to station within a 100m radius in choppy waters and cloudy weather on battery alone.

  1. Why did you guys opt for skid steering and no rudder? Was it to reuse Ardurover skid steering code and test performance of the T100s?
  2. I see you made a Surfboard API, I thought using APM we could harness the current GCS available for geo fencing right away?
  3. What type of motor would you guys use to control the rudder which will won't swing more than 20-35 degrees?
  4. How can I measure RPM and current draw of the T100 and view it via telemetry? I saw some RC motor plane parts that do it, can I use those?
  5. Is there any way to estimate the flow of water current underwater, around the ROV and how fast I'm moving through it?