Line followers use 2-8 reflectance sesnsors for detecting the line.
http://www.pololu.com/product/975
This product has swift movement and turns, it uses 5 sensors 3 in middle and 2 on sides, but does the middle one is neccessary in any way? Or does it is just consuming one extra ADC pin?
I am looking for a perfect sensor array for line following robot.
How big it’s the line?
The middle could be used as positive feedback that the bot it’s over the line, so it can go forward at full speed. To be smooth you use a large line and slow speeds, more sensors could help to get how much the bot it’s off line
These reflectance sensors
These reflectance sensors from pololu are really cool. I don’t know about the “behind-the-scene circuitry” that’s going on in the sensors, but the thing is, these sensors can easily provide “positions” of the robot while following a line. How do they do that? It’s not just go left or go right while following a line. There’s a tecnique called PID in which the robot tries to stay as close as possible to the line-following track. You can find a detailed walkthrough on how these sensors work and how you can integrate them into your project here.
Regarding your topic question : How many sensors are needed for a line follower ?
If you are planning for a similar high speed demon, I suggest you go with at least 5 because you don’t want to drift too far away from the track as inertia will always look to drag the robot away from the track on sharp turns. A higher number of sensors is directly proportional to more effective “sensor” and “positional” readings. But the real question is : How smart is your code to handle the sensor values and motor speeds effectively? Luckily, if you stick around with the QTR sensors, half the work is cut out for you.
Moving on to your question about the sensors on the 3Pi Robot : Yes, the middle one is not absolutely necessary, but it is premanufactured in that way so as to offer flawless line following capabilities. Through the middle sensor, the robot easily gets the a more “detailed” information on the track through a better “positional reading”. But the same middle sensor could be replaced by 2 other sensors for a total of 6 sensors, and so on. Do find some time to go through the above link if you are incredibly interested in this topic.
The perfect array sensor for a fast line following robot would definitely be the QTR Array Sensor. But you can also make use of any home-made IR sensors using photodiodes, and incorporate your own code. There are many techniques for successfully executing a super fast line following routine through a robot, out of which the most popular has to be PID, in my opinion.
Do visit the link I posted above to get a better idea on how the Pololu QTR sensors work, for now, with Arduino. If you want a more detailed documentation on the product, it’s a better idea to look through the Pololu Page. You should easily find a full indepth description on the 3Pi Robot and QTR sensors there. Please find some time to go through the code and hardware setup Pololu themselves have provided, so that you will be benefitted from a thorough study.
The other bit you need for speed is
distance. The farther ahead of the base you can get the sensors the faster you can run. I have even seen arrays that don’t have a simple straight line of sensors, but, a V shape inverted or not. If all you want to do is follow a line, 2 sensors will work. I have heard of similar setups calld bang-bang sensing. It works pretty good at low speed. I suppose I would still opt for more sensors.
