In this section of the tutorial I will explain the construction of the robots chassis(base, motors etc).
For designing the robot chassis I used Google SketchUp, which is a free 3D modelling software. I didn’t include much detail in the model like the electronic components, wires etc.
The robot uses differential drive as its steering mechanism. When the sensors sense the black line the corresponding motor is stopped until the sensors are back on the white surface. Thus, the robot is able to stay on the line.
Before building the chassis, you will have to add 0.22uF decoupling capacitors across the motor terminals. This not only increases the life of the motors but also reduces noise in the circuit. This is an optional step.
Now lets move on to building the actual chassis. To make the base of the robot you will need a 9cm x 8 cm HDPE Plastic.
Paste the following template onto your 9cm x 8 cm HDPE plastics sheet and cut drill holes through the grey dots.
Make sure that you print the template to size (8cm x 9cm). To print the template to size, save the template in your PC. Once saved, right click on the template and select ‘Edit’. The template should open in Paint, where you have to click on the Print option under the File menu to print the template to scale. This is only for Windows users.
Once the holes are drilled, attach the L-Brackets to the base with the help of screws. The L-Brackets will be used to mount the motors to the base. You may also use other materials like clamps and rubber bands instead of L-Brackets if you can’t find the right L-Bracket for your motor.
Next you will have to mount the DC motor to the L-Bracket. The DC motors I used are rated as 100 rpm, 12V and 250mA.
As I told before, I bought the wheels from a local store. The wheels I used had a diameter of 7.5 cm. To attach the wheel to the shaft of the motor, I forced the shaft of the motor into the extended shaft of the wheel and tightened the setscrew.
You can also use ‘mini’ CDs’ as wheels and reduce the cost of your robot by 3-5$. The mini CD’s have a diameter of 8cm - perfect for our robot.
Screw the 2cm spacers to the base through the holes, previously drilled. These spacers will be used to attach the sensor module to the chassis.
Screw the four 2 cm spacers to the other side of the base. These spacers will be used to mount the main circuit board.
Stick a strip of Velcro to the base as shown in the image
The Velcro will be used to attach the 9V battery so attach another Velcro strip to the battery.
This completes the chassis construction; the next part is the electronics.