QTR-8RC vs. QTRX-MD-13RC for 30mm Line

I have developed two line following robots using your older QTR-8RC and newer QTRX-MD-13RC sensors and Arduino Uno. Both robots perfectly follow 19mm (electrical insulation tape) lines. However, the line width of the next competition arena is 30mm. I also noticed that QTR-8RC and QTRX-MD-13RC sensors have different sensor pitch (9.525 mm vs. 8mm).
So which sensor (QTR-8RC or QTRX-MD-13RC) would you recommend for this 30mm line?
What are the ideal line widths for QTR-8RC and QTRX-MD-13RC sensors?
What are the maximum line widths that QTR-8RC or QTRX-MD-13RC sensors can handle?


In general, both of those line widths should be fine for either of the reflectance sensor arrays you mentioned. For the most part, as long as the line is wide enough that it does not get “lost” in between sensors, it should be able to follow the line smoothly.

There isn’t really one ideal line width, and in practice you probably won’t see much of a difference, but theoretically, you would probably want each edge of the line to line up directly under a sensor. For example, for the 8-sensor array this would happen with a line with of ~8mm and every 16mm beyond that (8, 24, 40, 56)~ 9.5mm and every 19mm beyond that (9.5, 28.5, 47.5, 56, 66.5). The 13-sensor array has a sensor right in the middle, so that changes it to be multiples of ~19mm (19, 38, 57, 76, 95, 114)~ 16mm (16, 32, 48, 64, 80, 96).

The maximum line width I would generally recommend would be the distance between the first and last sensor (~56mm and 114mm~ 66.5mm and 96mm for the 8- and 13-sensor array respectively). However, if you wanted to follow a line wider than this, you could probably just account for that by adjusting your program so your robot aligns with one edge of the line instead of trying to follow the center.


Thanks Brandon for the reply.

Yes, you are right. I want edges of the line to line up directly under two sensors, or at least line up closer to two sensors on either side.

I think for 8-sensor array, this would happen with a line width of 9.5mm and every 19mm beyond that as sensor pitch is 9.525mm, not as 8mm and every 16mm as you said. Kindly correct me if I am wrong. Similarly, for 13-sensor array, this would happen with a line width of 16mm and every 16mm beyond that as sensor pitch is 8mm. Again, please correct me if I am wrong.

As the line width of the course is 30mm, I thought of using 13-sensor array. With this sensor array, I think three sensors would be directly over the 30mm line whilst two sensors on either side would line up closer to the edges of the line.

I hope this kind of sensor arrangement would help for a smoother run.

Look forward to hearing your thoughts.


Oops! Yes, you are correct, I mixed up the pitches in my previous post. I am glad you caught that!

In practice, I expect both of those sensors to work well for a 30mm line, but the 13-sensor array gives you a slightly tighter alignment to the edge of the line like you described.