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Small Autonomous Survey Vessel

An autonomous little boat that scans and maps lakes and rivers.

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Based on an existing polyester catamaran I want to create an autonomous vehicle that can sail predefined tracks. When equipped with an Echo-sounder and maybe an underwater camera, it must be able to create bathymetric maps of rivers and lakes.

Qliner
The Qliner system with a Windows Mobile device to control it

Around 2005 the company I work for (Nortek BV) introduced a system for measuring discharge on rivers: The Qliner. It is a little catamaran, equipped with a Doppler based current meter that could measure the flow in a river over the full depth. You had to keep it in position using ropes or a long stick.

Qliner Measurement
Qliner Measurement from a bridge

After a few years we sold the design to the German company OTT GmbH, who still manufacture it today. Meanwhile, we still have some of these catamarans that are no longer in use, and I always thought it would be nice to make one of these into a remote controlled boat. Then, a few weeks ago, I came across these low-cost thruster design: https://www.instructables.com/id/ROV-Thruster-105-Lbs-From-DT700-Brushless-Motor/ and decided that these were ideal for this project. So now I finally get started. The idea is to convert this boat to an a fully autonomous vehicle that can create a bathymetric map of a lake or river.

Think something like this: the Autonomous Surface Vessel (ASV), by Seafoor :

https://www.seafloorsystems.com/uau-usv

Or this one, by CHCNAV:

http://www.chcnav.com/index.php/product/pros?cid=1&ctype=5

The boat will be driven by the two thrusters. An Arduino or Raspberry Pi will be used to control it, assisted by an electronic compass and GPS.

Though I first considered creating my own control software, it's probably not worth it since the ArduPilot project already has done a great job on this. And there is even a special 'Boat Configuration' section, so that makes it super simple to implement.

And, as always when you start looking into these things, it has been done before:

Ah, well, never mind. I'm going to do it anyway...

  • 2 × DT700 Brushless Outrunner Motors
  • 2 × ROV thruster 3D ABS printed nozzle for DT700 motor
  • 1 × Q-LINER Boat Small catamaran , made from polyester.
  • 2 × HobbyKing® ™ Brushless Car ESC 30A w/ Reverse Electronic Speed Controller with Reverse for Brushless motors

  • Thruster Assembly

    Cees Meijer09/08/2019 at 17:31 0 comments

    Finally a nice day, and some spare time so I could mount the thrusters to the boat. I used some stainless steel M6 threaded rod and some DIN rail. DIN Rails is great. It's cheap, has mounting holes and it is very stiff due to the shape.

    I kept plenty of length on the M6 rods so I can  adjust the depth of the thrusters later, if required.

    Once all nuts are tightened the whole construction became quite rigid so it seems like this is going to work. The only thing that worries me is that the metal is sticking out quite a bit to the side and that it will definitely collect weed and algae.

  • Struggling with the jargon: RC, ESC, BEC, 3S...

    Cees Meijer08/10/2019 at 20:28 0 comments

    A remote controlled is nothing new, and a lot of the required electronics and controllers is widely available. But if you are not an Remote Controlled Vehicle (RC-)enthusiast, a lot of the words and abbreviations used on the HobbyKing RC pages are not immediately obvious.

    First, I will need something to control the speed and direction of the thrusters. The motors are so-called 'brushless motors', which need special drive electronics. This is called an ESC or 'Electronic Speed Controller'. Then I found out after ordering my first pair of ESC's, not all ESC support changing the direction. Which makes sense if you use it to power a plane or helicopter. So I ordered a second (more expensive) pair 'with reverse'.

    HobbyKing® ™ Brushless Car ESC 30A w/ Reverse

    Specification:
    Input voltage: 2-3S Lithium batteries / 4~9 Ni-xx
    Cont. Current: 30A
    BEC output: 2A /5V (Linear)

    Now, as I said, I'm a newbie in RC, so first I did not know what 2-3S means. This appears to be the number of standard 3.7V Lithium cells as connected in Series. So '3S' is 11.1V. Next is the 'BEC Output'. BEC stands for Battery Eliminator Circuit. Which is not a device to actively destroy your batteries, but simply an on-board regulator that provides a regulated 5V DC for powering your external electronics so you do not need an additional power supply or battery for that. Great. Unfortunately the user manual is very extensive on the programming of this unit, but not very detailed on the connections.

      The contacts used for controlling the ESC are simply labelled 'RECEIVER'. Probably very obvious to anyone, except me. Now I think that the Red and Black wire are the BEC (5V) output, and the white wire probably carries the servo signal.

    Test setup with one motor and a potentiometer as a speed regulator
    Using an old PC power supply that can supply 12V at 8A and a Arduino Micro I just hook up a quick test setup. The 'Servo' library is used to generate servo compatible signals. A potmeter is attached to the analog input so I can change the servo signal.
    This is the test sketch:
    int YaxisInput = A2;    // select the input pin for the potentiometer
    int XaxisInput = A3; 
    int XValue,YValue;
    int Motor1 = 9;
    int Motor2 =10;
    
    #include <Servo.h>
    Servo ESC;     // create servo object to control the ESC
    
    void setup() {
     pinMode(YaxisInput,INPUT);
     pinMode(XaxisInput,INPUT);
     ESC.attach(Motor1, 1000, 2000); // (pin, min pulse width, max pulse width in microseconds) 
    }
    
    void loop() {
     XValue = analogRead(XaxisInput);
     YValue = analogRead(YaxisInput);
     XValue = map(XValue,0,1023,0,180);
     ESC.write(XValue);
     
    Serial.print(XValue); Serial.print(",");  Serial.println(YValue);
    delay(10);
    }

    And that works. After applying power, and switching the ESC on, it generates some 'beeps' using the motot itself which scared me at first.. But the beeps are  an indication that the ESC detected the neutral throttle signal (the servo output from the arduino) and the power. After that, moving the potmeter controls the motor speed and direction just fine. Only when moving the controller too fast from one side to another so the reversal of the motor is very fast, the powersupply switches off. Probably the reverse current is too much for the powersupply protection. 

  • Thrusters

    Cees Meijer08/08/2019 at 19:36 0 comments

    So the thruster parts arrived way faster than I expected from Russia.

    Thruster parts

    And they look great. Not sure how they did it, but they are very nicely printed and have a real smooth finish. Included in the box is a bundle of printed instructions for assembly. All of which are also available online, but it's nice to have them in print too. What is remarkable though is that though every aspect is of the mounting and modifying of the motors is described and illustrated using photos, there is no assembly drawing of the completed thruster. So up-to the moment I was actually assembling it I still did not really have a good idea of how it would work.

    2 Component epoxy moulding material
    2 Component epoxy moulding material

    The first step is preparing the motors for underwater. the instructions mention using a slow-curing epoxy glue, but I actually used some 2 component epoxy moulding kit that is specifically designed for moulding sub-sea cables and connectors. It comes in a convenient package where the two components are separated by a removable  seal.

    So I created the moulding form around the motor using Kapton-tape as shown in the instructions, mixed the epoxy and poured it in. After mixing the epoxy a little bit too long it was already getting warm and started curing while I was pouring it in. Which made it look like it was not filling all the gaps. But after the mix has cured and removing the tape, it turned out to have worked really well. Just a few bubbles got trapped, leaving some of the copper exposed, but these were quickly filled using some epoxy glue.


    It was only after I started assembling it that I noticed that the epoxy layer was actually a bit too high. Some filing was required to round off the edges, so the motor would fit the thruster housing.

    Epoxy in the gap between the motor and the plastic

    After that it was just following the detailed assembly instructions on Instructables, and everything worked out great.

    So now I have two thrusters. In the mean time my Electronic Speed Controllers with reverse option arrived from HobbyKing. So it's time to start putting it all together.

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