Line Follower Sensor Spacing

RoboticsProfessor

If you space five sensors at just the right distance, you can always get patterns with·a single·one like:
00000
10000
01000
00100
00010
00001
...showing the black tape moving from left to right·under the array.

You can also move them closer together. Just enough that for a very brief period, two sensors can see the black line. This gives you more possibilities, like:
00000
10000
11000
01000
01100
00100
00110
00010
00011
00001

It seems the second choice offers more precision. What is your experience? Have you tried this. What do you think?

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Richard Vannoy

Programming and Electronics Instructor
www.RichardVannoy.info
·

Franklin

Since the sensors are not absolute there will be some slop in the transition from off to on and calibrating the sensors to be precise would be a pain. What would happen if the bot was at an angle to the tape?

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- Stephen

kwinn

I agree the second layout gives more precise positioning in relation to the line. I am not sure though if there is any benefit other than that. Are you aware of any?

RoboticsProfessor

My theory so far is that more precision is better. My students are actually trying both, so I'll let you know if there is much difference.

With BOE-Bot, it travels too slow for closer spacing to make much of a difference.

With 3PI, the sensor spacing is not adjustable.

I'm thinking next semester of taking some powerful 12 volt motors I have and using the close spacing to beat the approx 2 M/S that our 3PIs are doing.

kwinn said...
I agree the second layout gives more precise positioning in relation to the line. I am not sure though if there is any benefit other than that. Are you aware of any?

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Richard Vannoy

Programming and Electronics Instructor
www.RichardVannoy.info
·

RoboticsProfessor

I thought that would be a problem too. But so far, my line followers are tracking the line so well that they never get cocked enough to give a bad reading.

Franklin said...
Since the sensors are not absolute there will be some slop in the transition from off to on and calibrating the sensors to be precise would be a pain. What would happen if the bot was at an angle to the tape?

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Richard Vannoy

Programming and Electronics Instructor
www.RichardVannoy.info
·

Beau Schwabe

I think in your first set of data, the "inherent slop" would be 00000 in between each data set you provided. In which case if your code "sees" a 00000 condition as an ignore or do nothing, then you may not observe the unit operating out of place.

For example, instead of:

00000
10000
01000
00100
00010
00001

in actuality the data possibilities would look more like this....

00000
10000
00000
01000
00000
00100
00000
00010
00000
00001

The same number of data points as in your second set of data

I assume that in your second set of data with the sensors closer to one another that you ignore the data with the ODD number of data bits to confirm your position, This would have the same effect as assigning 00000 as a do-nothing with the first set of data with the sensors further away from one another.


What you do gain with having the sensors closer together is a faster reaction time or a need to react faster, but your resolution should not change in either position.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.