Autonomous Mobile Robots

My favorite books from Amazon

Centurion — Thu, 21 Jan 2010 22:12:06 +0000

PID controller for mobile robots, basic explanation

Centurion — Wed, 20 Jan 2010 22:14:27 +0000

I started a rticle about PID controller for mobile robots which I’m going to use for position control of my caterpillar robot. It is not finished yet and I’ll be glad to receive comments from you and suggestions how to make the explanation better. PID controller is rather popular type of controller to study but traditional explanation about how it works sometimes are much more sophisticated then algorithm itself. I’m not an expert in this area and I will be really glad if some one will check it out from academic point of view.

PID controller basics, for mobile robot direction control

Centurion — Wed, 20 Jan 2010 22:09:53 +0000

As I started to talk about PID control basics let me introduce you the main idea of this type controller and how it can be used practically.

PID is the abbriviation which stands for Proportional - Integral - Derivative controller, means that the controller consists of this three instances. You must remember that the controller is loop feedback type. What does it mean?

It means that to control one of the signals or instances of the system, for example speed or direction angle or position we need to measure this instance and compare the current value with the one we want to reach. This is done by calculating of error value. So, like in life we have to know the error/ difference between what we want to reach and where we are now.

How it can be done? Here we will turn to mathematics, in reality it is not very complex and can be easily understood if it is proper way explained. I will try to do this.

So lets imagine the situation when we have a robot and we want to turn to the required direction. What parameters we have to control in this case? There are not to many parameters, exactly there are only two parameters to control:

Rotation velocity(degree/second)
Angle (degree)

Which parameter in this case would be changed and which parameter would be used to measure the success?

So in this case we are going to control and change rotation velocity and measure if the angle we want is reached or not? How can we do this?

Lets say we can rotate robot for some time and measure the angle it reached, in this case we would need to rotate it very slowly with constant speed so we would not miss the desired angle. This will work but it is not very effective, especially if we want to turn quickly and precisely.

In this case maths come to us as a helper. So we are going to measure angle - lets call this variable θ and we are going to control rotation velocity - lets call it ω.

From the course of mechanics we can get the link between angle and angle velocity - other words our rotation speed:

ω=θ/t , where t is time in seconds

To be continue…

Mechanical Deisgn Section update

Centurion — Sat, 14 Nov 2009 23:22:50 +0000

My old walking robot is presented to you here. It has original design which I found once in the network, unfortunately I do not remember the link. Still I try to work on my present project of caterpillar robot.

Four legged walking robot

Centurion — Sat, 14 Nov 2009 23:19:27 +0000

Here is my first design of four-legged walking mobile robot with infrared sensor. It was able to move around the room and avoid obstacles.

Four-legged walking robot

One more picture:

Front view of the robot

Mechanical Desing Section update

Centurion — Tue, 28 Jul 2009 20:50:46 +0000

Here you will be able to find what does my mobile robot consists of and some ideas about future development.

What does my Mobile robot consist of?

Centurion — Tue, 28 Jul 2009 20:46:47 +0000

Well, I received a nice message yesterday at facebook with a question what does my mobile robot consist of?

So below you would find the full information about it:

Lets start:

Mobile platform - caterpillar mobile platform, very stable and easy to control
Main Controller - Arduino board Deciemila, nice and easy to program and use. I think to install one more for strategic level control, probably one more would be used for some tactical control. Allover 3 controllers are planed to be used, for the moment only one is used.
Motor Controller- Type SaberTooth, for 12V DC motor control - the RF version.
Communication between computer and mobile robot is made on the basis of Xbee shield for Arduino
9 V NiMh battery - will be changed to 12 or 14V one because more power is necessary.
HMC - magnetic compass with I2C protocol.
Two Hall sensors for velocity measurement, and two magnets for each caterpillar (get the linear velocity)… more magnets needed, and by using magnets it is necessary to recalibrate the compass.
Camera tower with two cameras, one wireless for operator, one for internal robots use… , IR distance measurer with I2C interface.

So these are all components at the moment.

Now the problem how to make them work together Please check the updates regularly, later I will publish algorithms for motion control of the robot by velocity(speed) and trajectory.

Caterpillar robot kinematics

Centurion — Wed, 15 Jul 2009 17:07:10 +0000

Caterpillar robot kinematics was added to “Control Algorithms” section.

Caterpillar robot kinematics

Centurion — Wed, 15 Jul 2009 16:57:32 +0000

Caterpillar robot kinematics

Development of New multiprocessor mobile robotic system

Centurion — Fri, 03 Jul 2009 12:37:44 +0000

One more article was added to “Books and Articles” section.