Advanced Line Following Robot - Step 3: The Mechanics

The Mechanics

 

Nothing too complicated here. The robot uses differential drive as its steering mechanism. From my experience differential drive is one of the best steering mechanisms for line following robots. Almost all of the fast line followers I have seen use differential drive or a variation of it. It is easy to understand and implement and at the same time quite cheap (only needs two motors). And above all writing a PID control for the differential drive is both simple and easy. When the robot’s left or right sensor senses the line, the corresponding motor is slowed down and the robot stays on line.

The chassis is quite intriguing. The chassis is completely closed. All the parts – motors, circuit board, sensors – are placed inside the chassis. This is done so because by keeping the sensors enclosed in the chassis, you will be shielding them from any ambient light thus avoiding any interference from the surrounding light sources. With this setup, I can calibrate the sensors once at home and use the robot in outdoors, indoors and in the competition

Photobucket
The sensor board is mounted inside the closed chassis and is completely shielded by external light


Designing
I used Google SketchUp for designing the robot. Google sketchup was used because it is easy to learn and it is available as a free download.

Construction
The robot is built in plywood. Plywood was used because it is easy to work with – cutting and drilling holes in plywood is easy and requires no special tools. Moreover it is quite light(keeping the robot light has many advantages). I used plywood of 3 mm thickness.

Photobucket
This picture shows the plywood cut into pieces.

Then I drilled four holes to mount the L-Brackets to attach the sides.

Photobucket
The robot's base


Photobucket
The L-Brackets attached to the base.

Photobucket

Photobucket
The sides attached to the base.

The top piece is then attached to the chassis. A hinge is attached in its front end.
Photobucket


The front piece is attached to the top through the hinge. The front piece is attached to the hinge so that, the front piece may be opened for calibrating sensors, changing batteries, etc.

 

Photobucket

I added a similar hinge to the back and attached the back piece as shown. Such an arrangement is made so that the back piece can be opened and the main circuit board can be accessed easily.

Photobucket

Photobucket



Then I drilled two holes for the motors on the sides. Make sure that the holes are correctly aligned or the robot's wheel will not be aligned and the robot will not go straight even on straight tracks.

Photobucket



Then I mounted the motors and the wheels. The motors I used had a nut around the shaft, which enable me to drill a hole in the side of the chassis (as seen in the above picture) just enough for the shaft to go through it and tightened the nut from the other side (as seen in the picture below).

Photobucket


Mounting the wheels was even easier. The wheels I used had a set screw which I used to mount it to the motor's shaft.

Photobucket

 

Then I drilled three holes of diameter 3mm at the back of the top peice and cut a 3cm by 8 cm peice for the LCD as shown in the next picture.

 

Note: As you can see in the picture, I have used polarized connectors for the DC motors. It is always a good idea to use polarized connectors for DC motors because if you connect them the other way around, then that motor will be turning back instead of turing forward and it will take a lot of time to figure out whats happening(this happened to me and it took me more than an hour to figure out what had happened. For more than an hour I thought there was some problem in the algorithm !)