5.9. Running the relay algorithm

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From the course by Moscow Institute of Physics and Technology

Building Arduino robots and devices

135 ratings

Moscow Institute of Physics and Technology

Building Arduino robots and devices

135 ratings

For many years now, people have been improving their tools, studying the forces of nature and bringing them under control, using the energy of the nature to operate their machines. Last century is noted for the creation of machines which can operate other machines. Nowadays the creation of devices that interact with the physical world is available to anyone. Our course consists of a series of practical problems on making things that work independently: they make their own decisions, act, move, communicate with each other and people around, and control other devices. We will demonstrate how to assemble such devices and programme them using the Arduino platform as a basis. After this course, you will be able to create devices that read the data about the external world with a variety of sensors, receive and forward this data to a PC, the Internet and mobile devices, and control indexing and the movement. The creation of such devices will involve design, the study of their components, the assemblage of circuit boards, coding and diagnostics. Along with the creation of the devices themselves, you will perform visualization on a PC, create a web page that will demonstrate one of your devices, and figure out how an FDM 3D-printer is configured and how it functions. Besides those keen on robotics or looking to broaden their horizons and develop their skills, the course will also be useful to anyone facing the task of home and industrial automation, as well as to anyone engaged in industrial design, advertising and art. The course does not require any special knowledge from the participants and is open even to students of upper secondary school. Programming skills and the level of English allowing to read technical documentation would be an advantage, but this is not obligatory. The entire course is dedicated to practice, so the best way for you would be to get hold of some electronics, follow the illustrated examples and experiment on your own. The kits can be purchased here: kits.cyberphysica.ru. Taught by: Alexey Perepelkin, head of Robotics department in the Laboratory of innovative educational technologies at MIPT Taught by: Dmitry Savitsky, researcher in the Laboratory of innovative educational technologies at MIPT

From the lesson

Week 5.

Let’s turn one wheel and then two wheels at once, and the robot car will start moving. It’ll be moving along the line or under your control. It could as well be just messing with your hand with which you are trying to control it.

Meet the Instructors

Алексей Перепелкин
Руководитель направления развития цифрового творчества
Центр инновационных образовательных технологий МФТИ
Дмитрий Савицкий
Научный сотрудник
Лаборатория инновационных образовательных технологий МФТИ

Before we install the sensors on the robot, let’s get back to our diagram,

where we shall mark that we have the

line sensor that distinguishes white and black colors, as well as their shades,

which it sees as grey reading them as basic analog signals.

We will also have a function that will

inform us about the color of the background under the sensor.

We are now going to realize the algorithm, which we devised when we were talking about our robot moving along a line.

Let’s now interconnect these two functions.

Okay, I am back. Now we know everything that would help us set our robot in motion.

We only need to improve our robot a bit by adding the path and the code.

Speaking of the robot,

I have installed 2 sensors as close

to the borderlines as I could,

because if they are too far from them, the robot will move until

it hits the line with one of its sensors, and it will go off the path.

Do we need this? I don’t think so.

After that, it will lean back and go in zigzags.

No, we certainly don’t need that.

That’s why I’ve placed the sensors next to the line.

As for the path,

I have drawn one in a simple graphic editor.

I want to it to look like a race track with some straight sections,

swift and sharp turns, and so on.

You can find the sample in Additional materials or draw your own track,

and then type “broadsheet print” in the search engine, find a printing office,

call them and ask if they print on banner fabric.

When they print it, you’ll have your own track.

Now let’s deal with the code.

I have taken one of our previous sketches as the basis, the one where we already experimented with the robot’s movement.

I have then corrected it a bit.

Firstly, I have added macrodefinitions for the sensors’ pins, as well as

several other macrodefinitions, which will help us make the code more readable.

These parameters we shall be transmitting to the function of sensor readings.

This marks the border between the black and the white,

while these ones are the set speeds for the forward and backward rotation of the motors.

Remember, what we had in our diagram?

I have also determined the function of sensor readings.

We could have done without it, but with the further improvement of the program, the code could

become less readable, that’s why I have decided to create a separate function for this.

Here it is.

It will be returning a boolean value, true or false,

depending on the color of the background under the sensor.

As parameters, it takes “right” or “left” to determine which sensor

readings to perform.

What happens is,

if we receive “left”, we will read off the value from the pin,

to which the left sensor is connected. If it’s higher than the threshold value,

the sensor will return us the “false” value, or “true” if that’s not the case.

The same happens if we receive “right”,

but already for the right sensor.

Now we have a function to control the motors, and a function to do the reading of the sensors.

We also know how to connect them, and we will do so in our code.

According to our table, if both sensors show “white”,

i.d. the lineSensor function returns the “true” value,

the robot moves forward.

Otherwise, if the right sensor shows “black”,

i.e. lineSensor (right) returns the “false” value, the robot will turn right,

and the right wheel will turn backward, while the left wheel will turn forward.

The third case we need to look at is when the right sensor

shows “white”, and the left sensor shows “black”.

In this case, the robot will turn left.

Finally, if by any chance both sensors show us “black”,

or any other unexpected situation happens, the robot will just stop.

That’s it.

Let’s see how it works, but before that, let’s read the sensor values once again in order to

determine the borderline between the black and the white.

What do we see?

In my visualizer program, we have these boxes with the max and the min values, which are very convenient,

so I can see that the values change from 37 to 485.

I am not even going to work with trimming resistors – I will just

determine that the borderline between the black and the white is at the value of 200,

as mentioned in the code.

If I had 400, I would change one of the macrodefinitions.

Now let’s see if the robot is going to move in the way we had described.

Before uploading the program, don’t forget to start the Port Monitor

or its visualizer, otherwise you will experience problems with the upload.

[MUSIC] Let’s see

what we have here.

[MUSIC] [MUSIC]

[MUSIC] [MUSIC]

[MUSIC] So,

at a first glance, we have set our robot in motion and it moves along the line, so our main task has been completed.

However, there are a lot of drawbacks.

Firstly, when the robot turns, it moves discontinuously.

Secondly, it’s obvious that

at different battery charge levels,

the same strictly set values will lead to a different result,

i.e. we will always need to change the invariables which determine the speed, for instance.

Anyway, we will be talking about an alternative way later,

which has its own advantages.

[END]

[END]

[END]

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