Volvo 240

Playing with Robots

Legged Robots

In these pages I have gathered some information on a hobby mobile robot I started. Most of my time, however, has gone into the robot prototypes I am developing as part of my PhD work. Initially, the aim of this hobby robot was to build a mobile robot that would be able to negotiate obstacles without hitting them. Basically though, it gave me the oppurtunity to learn about electronics and microcontrollers - that I find really exciting. I've tried to write a bit about all the various stages and components involved as the robot progressed.

Robot General Description:

The robot is comprised mainly of the body. The robot has three wheels, two of which are attached to the rear axle, while the third is the wheel at the front, that can turn. So the robot has the general form of a tricycle. The body is made mobile by two motors, one of which drives the rear wheels, while the other turns the front wheel about the vertical axis. The motors can tell how many revolutions they've made using the encoders.

The robot will be equipped with an infrared proximity sensor, which is still actually under construction. This sensor will allow the robot to realise when it's getting too close to an object, and then stop and take measures to avoid it.

The power source for the robot was chosen to be batteries, as it is important that the robot is autonomous (i.e does not require electrical wires feeding power to the robot, which restrict its motion). Specifically, rechargeable AA size batteries are being used at the moment.

Rechargeable batteries were preferred over ordinary batteries for the simple reason that in the long run they're cheaper, although a bit expensive to buy at first. At this stage eight such batteries are being used in series, to increase the total voltage.

I preffered eight AA size NiCd batteries over two similar 9V batteries (although much lighter and smaller) becuase the AA batteries hold a lot more charge than the 9V's. Below is a table with the charge the respective batteries can store. As can be seen, AA size batteries capable of storing more or less charge can be found. Obviously, the greater the storable charge, the higher the price... I use the 700mAh.

Type NiCd 9V rechargeable NiCd 1.2V AA rechargeable
mAh 100 700-2100

Finally, there is one of the most important components on the robot, the microcontroller. This component is a bit like a very small (smaller than the size of a persons little finger) computer and is responsible for the communication between all other components (motors, encoders and sensor), as well as the control of the motors.