5.5. Robot car

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Del curso dictado por Moscow Institute of Physics and Technology

Building Arduino robots and devices

149 calificaciones

Moscow Institute of Physics and Technology

Building Arduino robots and devices

149 calificaciones

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

De la lección

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.

Conoce a los instructores

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

Now we know how to control DC commutator motors.

It’s time to start assembling our robot car, which will be our first mobile robot.

We already have all the control electronics, a power source,

motors and wheels.

What’s missing?

We have 2 motors and 2 wheels, so we shall need a third support.

For this purpose, we will use a ball like this one, which will allow the robot to move and

turn about the axis which passes through the wheels.

We need a frame, which we shall assemble from familiar components.

We will use some new details to mount the ball bearing and the motors.

Besides, we will need to power our device.

In the experiments with motors, we were powering the controller from the computer.

Here we will be using the same battery compartment, which powers the motors.

We have 4 batteries of 1.2 V each,

but 4.8 V will not be enough for Arduino.

Therefore, we shall need a voltage up-converter.

Let’s see in detail how our power will be organized.

Wires come from the battery compartment to the voltage up-converter.

Wires also go through the same terminal block and then directly to the Motor Shield.

In other words, 4.8 V is applied to the motors without any conversion.

From the converter’s output, the wires go to the Vin controller and the ground.

With the help of a trimming resistor, we will apply from 7 to 9 V there,

which is permissible for the controller.

Let’s set suitable voltage for our controller.

[NO SOUND] [NO SOUND] I have

set the voltage of approximately 9 V, which is more than enough for the Iskra.

In the end, we get this beautiful device.

Before we teach it to move, let’s see

how our previous Motor Shield test sketch works with it.

[NO SOUND] I have connected the power supply with a simple wire, since we don’t have a

separate switch yet.

[SIGNAL] We can hear the motor accelerating.

The voltage is not yet enough.

[NOISE] Let me say a couple more words

about the assembly.

I have deliberately decided to not direct your attention to the assembly of the robot, for

you can experiment as you want with it.

Let me remind you that our task is to make the robot move along a straight line.

It can turn into a race along the line,

if the speed becomes important for us.

Things influencing the robot’s dynamics will be playing a central role then:

say, wheelbase width, ground clearance height,

center of gravity position of the battery compartment, etc.

However, now it’s not that important for us, since we only need a test robot car,

which will be able to move.

Let’s finally get down to programming the robot’s movements and see

what new things we have in the program.

First, we have added a macrodefinition for the pins of the second motor – “enable input”.

Naturally, we have set them as outputs

and started both motors.

By the way, if you upload this code and the robot doesn’t move forward,

don’t worry, as this all depends on how you connected the motors.

You can either switch the wires in the terminal blocks or switch high to low.

We are starting both motors at their maximum speed.

Then we create a 1.5-second delay to see what’s happening and next we

change the direction to “full astern”.

Next comes a delay again, after which we start one motor in the “full ahead” direction

And the other one in the “full astern” direction so that the robot would rotate.

Afterwards, we are performing the same actions, but vice versa, so that the robot would rotate in the opposite direction.

By the way, you can turn the robot in different ways -

turning about the robot’s axis is not the only way.

You can follow a curve when both wheels are turning forward: one should turn

slowly and the other one fast.

[NOISE]

[NOISE] You must have already noticed

that the robot doesn’t always follow

a straight line and it turns at different spots, meaning that

its turning angle is always different.

This is natural, and without feedback, i.e without monitoring how the wheel

actually turns, we won’t be able to follow a perfectly straight line.

Even identical motors of the same manufacturer can differ a little

bit from each other, and we come across this quite often.

Think about it: would we want to

add new lines to our code every time we need to change some of our

parameters, be it the speed or the direction of motor rotation?

I don’t think so.

That’s why we need to create a definite function to control our motors.

Let’s call it “drive”.

We will be communicating two parameters to it: the speed

of the left and the right wheels.

We can also set their direction simultaneously by changing the sign of these parameters.

Thus, if we set the -100 value, for instance,

The wheel will be turning backwards with the speed of 100.

Then we need to make sure that the motors operate with correct values,

because the “drive” function can be called with an automatically

calculated parameter, so we will need to ensure that

it falls in the permissible range from -255 to 255.

Otherwise, the “right” analog will react in a way that we can’t predict.

Next, we need to determine whether the parameter comes with a plus or a minus sign.

Thus, if it’s a plus sign, we will be rotating the motor forward,

and backward if it’s a minus sign.

We need to do the same for the right motor,

and then set the speed for both of them.

Furthermore, the “right” and “left” parameters need to be absolute, meaning that we shall go for their absolute values.

Now we can simply call this function

by setting the speed for the right and the left wheels.

Let’s conduct a small experiment by turning both wheels forward at their maximum speed, and then backward

at a different speed for both.

By the way, we can’t say for sure if 80 will be enough to set the motor in motion.

But let’s see.

Now let’s turn the motors in the opposite direction at different speeds.

We need to make sure that this works though.

[NOISE] In fact, all the three actions are performed.

Naturally, 80 is not enough to turn the left wheel backward,

but that’s not a problem.

Let’s do a mini-summary of what we have achieved here

And look at our main circuit.

We have new executors here: the collector and the DC motor

together with the gear reducer and the wheel.

The wheel is controlled not just by the signal sent from Arduino,

but through an agent, which in our case is the motor driver.

We control the motor driver by sending basic digital and analog

signals, which make the wheels turn.

We took two motors with wheels and built a robot car,

which is a more complex executor.

In spite of its complexity, it’s still controlled with the help of the same micro circuit.

We have also created the “drive” function, thanks to which we

don’t have to think anymore about the combination of signals coming to both motors -

we simply need to set the speed for the right and the left wheels.

We also tested how our robot car moves in different directions,

and no feedback was needed for this.

We just had a set of commands to make the robot car move in different directions.

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