The Admirable Admiral

Ship’s Log 30/10/08

Today, I am meeting with my project supervisor, Dr. Lorcan Coyle.

I can use this time to serenade him with reports of progress, ideas and possibly Erasure’s A Little Respect. The meeting will take place in CASL (pronounce castle or the dungeon…), which will be a bit of a trek in my current condition.

I intend to broach the following:

• Pseudo code algorithms for simple navigation based on two 2 known vectors (Angle from magnetic north and angle from wind direction) and possible one known scalar (wind speed).
  • How to deal with the Dead Zone
  • How to deal with running and the associate lack of control
• The arguments for and against direct control of the boom with a servo as opposed to indirect control via the main sheet
• My arguments for and against possible control systems
  • Expected issues with scalabiltiy
  • My inability to solder breaks another servo shield

What I hope to gain in this meeting is final decisions on the control system, some feedback on the suitability of my proposed control methods and discuss gaining regular access to the boat. I would stress that tardiness on my part is the sole reason I have not yet inspected the boat itself. I hope to rectify this at a meeting with the other students involved in the project on Friday afternoon.

I will post anecdotal minutes shortly after the meeting. - D.N.T. (30/10/08)

Under the Bridge

I am not one for micro-management. I’ve always believed that the best results are gained when clear, concise expectations are set, and people are left to use their initiative. Unlike my love life, however, this yacht needs a microcontroller.

How to pick the brains of the operations is always a hotly contested question. Elections, civil wars, even divorces: all the results of contests for control. On this boat, one man, or component, will have control, and the yardarm is ready for mutineers. The only question is who will be at the helm; Captain Arduino, the dashing Italian; Commodore Stix, and his sons Gum and Robo; or even the ever elusive pirate, Mister Handyboard.

Each has his advantages, but each also has the potential the sink this project, Arduino by his hesitance to act, the Stix family because of their obscure mind and Handyboard, because I simply can’t find the bastard son of MIT and lego. To elaborate, a profile of each is necessary.

First off the starting block is the Gumstix family. These are tiny computers running linux, with available bluetooth, and GPS and digital I/0 daughter boards. They are powerful, with 400Mhz cpus, flash memory and SD storage, and ethernet. It’s biggest problem is the OS. Although it’s runs on linux, during a project last year, the team I was in found it very difficult to get a stable buildroot for the gumstix, and when one was found, we could never get all the services to work at once. Cillian Murphy, who had the unenviable task of dealing with the gumstix for that autonomous dirigible project, wrote about some of his woes, and successes on his blog.

Thanks to the experiences I had during the aforementioned Project Hindenburg, I would be very hesitant to use gumstix/robostix. The problems associated with simply setting them up are quite daunting, which could waste valuable time during the project.

Next is the Handyboard. The handyboard was developed by MIT, for a Lego robot contest. It is quite expandable and has an LCD screen, the only option I have investigated which offers such. It runs a 2Mhz Motorola processor, and has 32Kb of battery backed SRAM. It can control four 1A motors and has an add-on board to support servo control.

The biggest advantage of these is that UCD engineers have used them before, and (to continue with my anti-engineer bile) if they can use them…. They have low power consumption, are reliable and, as far as I can gather, the university already has some to hand.

Finally, onto Arduinos. This Italian-made microcontrollers is quite promising. It is much less powerful than the Gumstix,  as it is not a micro pc, but is a board based on the ATMEGA168 microcontroller.  It has 14 digital I/O pins, 6 of which are capable of Pulse Width Modulation, which is required for controlling servos. It has six analog inputs, a 5V linear regulator and a USB interface. There are available shields aimed towards specific applications, including servo control.

Programming for the Arduino is done in Wiring, a C-like language, and it supplies it’s own IDE in Java, which is available for Linux, Mac and Windows. Loading the program to the board is very quick, over a USB interface, as he Arduino has an inbuilt USB-to-RS232 chip. It has 14KB of available Flash memory to store code.

The fun part, now, conclusions. Years ago, I was told that the fastest way to lose money was to bet on every horse running. Usually it’s best to make a decision and put it into action, and, to paraphrase a popular Japanese children’s cartoon, I choose you, Captain Arduino.

I favour arduinos, for ease of use, lots of i/o and it has enough computational brawn to control the boat.

A close second is the handyboard, which has much of the above. The handyboards have less i/o ports, but do have a track record in the college.

Which will be picked by those in the higher echelons, like the fate of the tanks taken by the pirates of Eyl, has yet to be decided. - D.N.T. (29/10/08)

Common Sense

It has been decided by those on a higher paygrade than I that for the initial prototype, I will restrict myself to acquiring two types of environmental data only: Relative wind velocity and Vessel velocity.

First off, I need to determine wind velocity. I am tackling this first because it is considerably more difficult to discern than the velocity of the vessel. Of course, velocity is a vector and is made of two distinct pieces of information: direction and magnitude, so there is in effect two sensors required for this task.

An anemometer, of either the cup-on-stalks variety or the proppeller variety, and a weather vane, to determine the wind speed.

I have been advised to only (if possible) take into account off-the-shelf components for this build, as they would be significantly sturdier than any hardware that I, a computer science student, could put together. However, as commercial anemometers are quite expensive, it is likely that the engineers involved in this project will be respeonsible for the construction of a custom anemometer. It’s interface remains to be seen.

In order to determine the yacht’s velocity, I feel that a GPS reciever would be the ideal option, as it would allow accurate tracking of relative positions of waypoints and course logging as well as basic velocity information. By reading successive GPS co-ordinates, a bearing can ascertained. Driection by:

tan(Angle) = (currX-lastX)/(currY-lastY)

Speed by:

(((currX-lastX)^2 + (currY-lastY)^2))^(1/2)

Reading in the GPS co-ordinates from serial should not be difficult, depending on the platform chosen.

For the basic prototype, however, it is likely only a magnetometer will be available. This will mean I will be able to discern magnetic north. By knowing magnetic north, and relative wind velocity, it should be possible to set the rudder and sails so as to set the boat on a specific bearing.

Here is some very simple code to set the angle of the boom. Let alpha be the relative angle of the wind and setBoomAngle to be a function which sets the angle of the boom relative to the boat (where 0 is the boom parallel to the boat, postive is to port and negative is to starboard).

if (45 < alpha < 180)     setBoomAngle((alpha-45)*1.5);

else if (180 <= alpha <315) setBoomAngle((alpha-315)*1.5);

By using the rudder to steer onto a magnetic bearing and the above algorithm to set the sails, basic navigation should be attainable. A special case must be implemented to avoid the deadzone (which is 45 degrees either side of the wind direction) and to tack (or zig-zag upwind) towards any bearing in the deadzone.

The Points of Sail with the resultant boom angles from the pseudo-code snippet above.

The maths of the above is subject to confimation, and is based upon my trusty RYA notebook from when I was a budding sailor. The basis for the formula is that at close haul, the sail should be as close to parallel to the boat’s bearing as possible and when running the sail should be perpindicular to the bearing.

I’ll need to invest further study into this to ensure plane sailing (pun intended) - D.N.T. (14/10/08)

A Titantic Undertaking

First off, there’s going to be a lot of puns on these pages, and I won’t apologise for them, so here goes…

The project is called roboboat, and it’s essentially a robotic sailboat. Yes, sailboat. I know, cool. I thought so too. I’m the software guy, I think. I’ll be working with a postgrad computer scientist and some engineers. (I know, but I can’t hold it against them, since, like Somali pirates, they have the yacht and aren’t likely to give it to me.)

The project as I see it, is as follows:

There will be some sensors to determine variables like wind velocity and the velocity and pitch of the yacht, which is a one meter model of a large sailing yacht.

There will be some motors to keep the mainsheet taut and a servo to control the rudder. Depending on the model yacht, another may be required for the centre/dagger board. To keep the boat balanced, either a weight attached to a servo or a liquid pumped from side to side can be used as the equivelent to a sailor hanging off the side. I’ll need to speak to the engineers working with the physical boat to see what’s needed there.

The motors and servos will be controlled by an Arduino microcontroller with a fitted motor shield. It can easily handle the required number of motors and servos and has accurate timers and lots of pinouts. You programme for it in C, with lots of nice libraries available. It’s own supplied compiler then converts it to machine code. I have had the misfortune of working with gumstix and robostix before, and while they have significantly more processing power, they are not very user friendly. Sure they can do the maths fast, but trying to talk to them is painful. Arduinos are eager kids. They do what you want, when you want it, as long as it’s simple enough to be explained in crayon. In that respect, they’re similar to the copywriters of the News of the World.

For an added challenge, try to read the original:

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I’m not sure yet if there will be a need for a gumstix on the boat, or if I can unload the maths to a landlubbin’ computer. Actually, I’m not 100% sure of anything in this project yet, except that I need to obtain an eighteenth century Royal Navy Admiral’s hat, and fast. I’m not sure appropriate headdress will count when grading, but it can’t hurt to show commitment.

Now, down to the knitty-gritty that every computer scientist purports to revel in but secretly can’t stand. The maths. The environmental forces acting on a sailing vessel are quite complex. The idea for this yacht is to have it sailing around UCD’s lake autonomously, which has very flat water and no currents. That’s nice because currents and waves and bad weather requires a human sailor, that beast I’m trying to obsolete, to have a good feel for the boat. How a boat “feels” is going to be hard to ascertain with limited sensors, so sailing on flat water will is a real advantage. That’s an assumption though, and anyone who’s met assumption’s children knows how dangerous getting in bed with her is.

Even if I do hop in with her, there’s still a lot going on, though. The basic problem is:

1. Find yacht velocity.
2. Find wind velocity.
3. Adjust rudder to correct yacht velocity’s direction component.
4. Adjust sail to obtain maximum force from wind engaging the sail.
5. Goto line 1.

There’s other things to take into account, like controlling the speed of the yacht by loosing and tautening the mainsheet, the effect of the jib, the use of the centre board, actually working out the yacht’s position and how to beat, or sail upwind.

This is not to mention the physics of the sail, which is actually an airfoil, which generates lift, not dissimilarly to a wing.

I’m thinking that I will have to:

1. Write control systems for the boat (and possibly build them) (codename: Engine Room)
2. Write a control loop for the microcontroller to:
   - Read in sensor data (codename: Crow’s Nest)
   - Process data or send it to shore for processing (codename: Captain On Deck)
   - Set the pinouts (codename: Helmsman)
3. Write a shore based interface (codename: Haulbowline)
4. Work out how to wirelessly talk the yacht (codename: Semaphore)
5. Test (codename: Sea Worthy)
6. Goto line 5.

How it actually shapes up remains to be seen, I’ll sea you later (pun intentional). - D.N.T. (01/10/08)