Roborugby Lab1

The aim of this lab is to build a simple robot and to learn how to program the Handyboard computer. As your robot will have no sensors at first, it will be driving "blind", so the first tasks will be fairly simple. When you have mastered the basics, you can add some sensors to your robot - you will learn to write programs to use the information from these sensors next week.

To get you started quickly, we have provided two simple robot chassis designs - simple frames for holding motors, wheels and sensors. These are useful for learning how to program a robot, and experimenting with the various sensors. You can design a better robot chassis later, when you have seen what works well and what does not.

When you have built your robot, you will write some programs to make your robot do basic tasks like driving forward and backward, and turning. Then you will be ready to attempt the first challenge...

Build a Robot

Choose one of the two example robot chassis designs below, and follow the instructions to build it. To find the parts, refer to the kit pages. Be careful to use two motors with the same part number - most kits have one motor which is different from the others!

Handyboard

The Handy-Board is a small computer. You will use it to control your Robot. The picture below identifies the parts of the Handyboard which you need to get started:

The white cable with telephone-type plugs connects the Handyboard to the interface unit.

If you are using a laptop computer, you should connect the computer cable to a serial port on the laptop. If there is no serial port, ask for a USB adaptor.

If you are using a desktop computer, the interface unit should be connected to it already.

The charge switch on the interface board should be in the "NORMAL" position (at the side towards the computer cable).

The interface units has three coloured lights to show its status. When everything is connected correctly, all three lights should be on.

Warning:

The charge switch on the interface board should always be set to "NORMAL". This will charge the battery in the Handyboard at a reasonable current. The "ZAP!" charge mode is for emergency use ONLY - it allows a much larger current to flow, and will destroy the battery very quickly! Do not use it!

Connecting Motors

Connect a short motor cable to the black part on the top of each motor on your robot - it does not matter which way around. Mount the Handyboard on top of your robot.

Identify the motor sockets on the Handyboard and connect one motor cable in the socket for MOTOR-1, as shown in the picture.

Note that each socket has three holes, but the central one is not used. The motor numbers are marked near the edge of the circuit board.

Now connect the other motor cable to the socket for MOTOR-2.

Take note of which motor is on the left side of your robot, and which is on the right.

Interactive C

If you are using your own laptop computer, you will have to install the Interactive C software. Follow these instructions. We will use Interactive C version 7.0.7 - some of the RoboRugby programs will not work with later versions.

When Interactive C starts, you will be asked to select the controller type. Select Handyboard.

If the system cannot connect to the Handyboard, check that the Handyboard is switched on, and that all the connections are in place, then press Retry. If this does not work, ask for help.

Interaction

To explore the interactive mode of Interactive C, type some commands in the lower part of the window.
Try printf("Hello C \n"); Can you see the result in the Handy-Board display?

The display has two lines of 16 characters, but Interactive C treats them as one line of 32 characters. Your programs can use it to display results and let you know what is going on. You may have noticed a small heart-shaped symbol pulsing in the lower right corner - this indicates that the Handy-Board is alive and working properly.

Interactive C has some special functions for the Handy-Board. One example is the beep() function. Try it now.

Another useful function is motor(number, speed). The number refers to the number of the socket where the motor is connected, in the range 0 to 3. The speed value sets the speed of the motor. It can range from 100 for full forward speed to -100 for full reverse, with 0 indicating stop. However, the motor hardware only allows 7 different speeds in each direction, so numbers close together will give the same speed.

The meaning of forward and reverse depends on which way around you connect the motor cables to the Handyboard and to the motors. It also depends on which face you regard as the front of your robot. Try running each motor forwards to see which way it turns. If it is not the way you want, reverse the motor plug in the Handyboard socket.

Writing a Program

The interactive mode is convenient for checking values from sensors, or turning on a motor to see which way it turns. However, to do anything more complicated, you will have to write a program. Open a new program file now using the button near the top left corner, or the File menu.

Type the following program. Try to figure out how it works as you type it. You don't need to type all the comments, but do read them.

void main()
{
  printf("Press START\n");   // print a message for the human
start_press();    // wait for the START button to be pressed
  motor(1,50);   // run motor 1 at half speed forwards
  motor(2,50);   // run motor 2 at half speed forwards
  sleep(1.5);    // do nothing for 1.5 seconds - motors stay running
  alloff();   // turn off all motors
  printf("Stopped\n");   // print another message for the human
}

Save your program, using the button on the toolbar, or using the File menu, or by typing Ctrl-s on the keyboard, as you prefer. If you are using one of the desktop computers, save it in My Documents\RoboRugby. Give it some sensible name.

Now, press Check at the top of the IC window. Are there any errors? If so, fix them. Ask for help if necessary.

When all is well, press Download. If everything is connected correctly, your program will be transferred to the memory on the Handyboard.

Press Run Main to run the program. Does it behave as you expected? If not, why not? Ask for help if you cannot sort this out quickly!

When all is well, you can disconnect the white cable from the Handyboard, and run the program independently. Just switch off the Handyboard, then switch it on again - it will automatically run the last program downloaded.

Task 1

Write a program (or modify the one above) to make your robot drive forwards some convenient distance, and then reverse the same distance. You can test this on the laboratory bench or on the floor. Does your robot arrive back where it started?

Task 2

Write a program to make your robot drive forwards as above, then turn around and drive back to where it started.

Challenge 1

We will place two balls on each of the RoboRugby tables, in the places circled in the picture. Your robot should start in the small scoring area at one end of the table, facing any direction you like. It must drive to the small scoring area at the other end of the table, touching both balls on the way. It does not matter what path your robot follows, as long as it touches both balls and stops in the right place.

You have to write a program to make your robot do this. Remember the basic principles - first decide what you want your robot to do (the algorithm), then translate this into a computer program. You will have to submit this program for assessment, so write it properly, using the techniques which you have been shown. Use plenty of comments to explain what is going on.

This challenge is quite hard - your robot is relying on "dead reckoning", as it has no sensors to guide it. There will always be some slip between the tyres or tracks and the table, and this may be partly random. This means that your robot may not follow exactly the same path every time you try it.

Do not spend too much time trying to perfect this - the point of the exercise is to learn how to write a program, and to learn that dead reckoning is not very reliable! Your next step will be to add some sensors to your robot, so that it can get some information about its surroundings.

Report

Add a large comment at the start of your program for Challenge 1. This should explain who you are, what your program was supposed to do, and how well it did it. This report can be quite short, but it must provide enough information so that we can make sense of your program. An example is shown below:

/*   RoboRugby*08     Team 2: Joe Bloggs, Jane Doe, Dara Murphy.     Challenge 1 report.

We planned to have our robot start in the small scoring area, facing towards ...
We wanted it to travel straight to ... and then ...
...
Finally, we wanted it to stop in the other scoring area, facing the wall.

We found it quite difficult to achieve this perfectly, as the robot seemed to blah blah blah. We settled on a compromise turning time, blah blah blah.
However, blah blah blah...

The basic algorithm is:
Drive forwards for ...
Turn left through ?? degrees; etc., ...

We connected the motor on the left side of our robot as motor 1,
and the motor on the right side as motor 2.                         */

Submit your report and program by e-mail, to roborugby@ee.ucd.ie. Add the entire .ic file as an attachment - NOT in the body of the e-mail. The deadline for submission is 9am on Friday 25 January. We suggest you do it now - one team member can write the report while the others work on adding sensors to the robot. However, the entire team will be assessed on the basis of this report, so you should all check that you are happy with it before you submit it.

When you have finished, be sure to save a backup copy of your work. Copy it onto a memory key, or e-mail it to yourself. It is important to get into the habit of keeping a backup copy of all your hard work - losing your competition program later in the semester could be a disaster! Ask for help if necessary.

Adding Sensors

The next step is to add some sensors to your robot, to give it some information about its surroundings. Small switches can provide information about collisions with the walls or other obstacles. An optical sensor can detect the white lines on the table. Next week, you will use this information in your programs, to control how the robot behaves.

Bump Detection

In bag Y, you should have a set of five small switches, called micro-switches. These are mounted on Lego bricks, in various configurations, as shown:

The switches are operated by a metal lever - three have short levers, and two have long levers. You can use these switches to detect when your robot hits an obstacle, such as the wall or another robot. For this exercise, you only have to detect collisions at the front of your robot, but you may need to watch your back in the competition! With a switch on each front corner you can tell which corner of your robot has hit an obstacle, which will help you to decide how to get away from the obstacle.

You can detect collisions over a larger zone by building a Lego bumper. The picture shows an example, using bent beams or lift-arms, with the short-lever micro-switches mounted behind. Another beam across the front restrains the moving parts, and stops them swinging too far forward. It also ensures that a switch will be operated even if the robot hits a narrow obstacle in the centre.

Add switches

Fit two switches to the front of your robot. We recommend that you use a Lego bumper - it need not be as complicated as the one shown.

Connect the switches to two of the digital input ports on the Handyboard. These are the ports numbered 7 to 15 at the front of the Handyboard, as shown below. We suggest that you avoid port 8, as it will be needed for another sensor later. Keep a record of the port to which each switch is connected.

Each port has three terminals, two together at the front and one further back, as shown below (left and centre). In the Handy-Board circuit, there is a 47 kohm pull-up resistor connecting the input terminal to the +5V supply, as shown (below right). This means that the voltage at the input terminal will be high (5V) if nothing is connected.

The switches are connected between the input and 0V terminals (dashed lines above). Each switch is normally open (open-circuit), so the voltage at the input terminal will be high, as if nothing was connected. When the lever is pressed, the switch is closed (short-circuit), so the voltage at the input will be low (0V). The Handyboard maps the low voltage to binary 1, and the high voltage to binary 0.

To test the switches, use the interactive mode in Interactive C. With your Handyboard connected to the computer, type the command digital(9) - replace the number 9 with the number of a port where a switch is connected. This command gets a binary value from the port - either 0 or 1. You should see the result in the upper part of the window.

What value do you get when the switch is not pressed? What value do you get when the switch is pressed? Repeat these tests for the other switch.

Line Detection

The RoboRugby table surface is mostly matt black, with reflective white lines. It will be useful to be able to detect these lines, and perhaps to follow them. You can do this using an optical sensor of the type shown below left. You will find one in bag Z. See the optical parts page for details of how it works.

The sensor emits infra-red light and can detect reflected infra-red light. It works best when the reflecting surface is 5 to 10mm from the sensor. Use insulating tape to install the sensor temporarily on your robot, somewhere near the front. It should be facing downwards, close to the table, but not so close that it hits the raised lines around the scoring areas.

To use it, you should connect it to one of the analogue input ports on the Handyboard, as shown above right. Ports 0 and 1 are not available, and ports 4 and 5 have been modified for other sensors, so you should use port 2 (as in the picture) or 3 or 6.

The analogue ports measure the voltage of the input signal, in the range 0 to 5V, and convert it to an integer in the range 0 to 255. To test your sensor in interactive mode, just type analog(2) (or similar - use the correct port number). The result should be in the range 0 to 255, depending on what is in front of the sensor.

Try it with the sensor "looking" at a sheet of white paper, and then looking at something dark, or with nothing near the sensor. If all is well, there should be a significant difference between the numbers that you see.

Tidying

Before you leave the laboratory, please put all your Lego parts and your robot into the large plastic box provided.

Disconnect the white cable from the Handyboard, and make sure that the Handyboard is switched off. These two steps are necessary to prevent the Handyboard battery from being discharged over the next few days. We will charge these batteries for a few hours before the laboratory session next week, but there will not be time to re-charge them fully if you let them discharge completely!

If you were working at a desktop computer, you can leave the interface and charging unit on the desk. If you were using a laptop computer, please disconnect the interface and charging unit from the computer, and put it and the power supply unit into the box with everything else.

Lab Session 1

Introduction