QTI sensing at a higher distance from the ground

lakers78

I realize that this question has been asked before, but how can I possibly program the QTI sensors to read from higher off the ground?

My school project actually requires us to follow a track that is like a baseball diamond, with black lines and white foam for the bases.
The problem is that the foam bases are half an inch high, and the boe-bot is required to drive over each of the bases. For this reason, the lowest point on the boe-bot must be slightly higher than 1/2 an inch.

Yes, I have gone through the entire "Robotics With the Boe-Bot tutorial."

I do understand that the having the QTI sensors work at this range reduces their accuracy, and I am aware that light sources may or will interfere with the sensors.
However, I still want to attempt to program the sensors to do this, unless of course you have a better option.

Is this impossible? If not, how can it be done? Any other suggestions?

Thanks

Zoot

Yes it will work if you are using RCTIME rather than a "digital" on/off reading for the QTI sensor. You will just need to determine what thresholds work for deciding what areas are black/white/gray. In my 'bots I use a QTI about 1/2" off the surface to check for white (paper), surface (gray/brown), black (tape), and a cliff edge. The readings will increase in that order -- white or light colors giving the lowest RCTIME reading and a cliff giving the most (even more than black tape). Experiment and see.

I will add that the QTI sensor from Parallax is actually a few external components along with the actual QTI chip -- which is a combination IR emitter and detector. I bring this up because the little QTI board from Parallax has the resistor that limits the IR emitter output -- so it can't be changed without soldering (and voiding your warranty) if you need to increase the IR emitter's output. That said, the value on the board is generally OK up to nearly .7" (in my experiments, anyway), though reading the difference between white and gray becomes problematic (white/black or black/cliff is still not a problem at that distance).

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When the going gets weird, the weird turn pro. -- HST

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agfa

Maybe you could do it mechanically.· Instead of the having a fixed position sensor array, make it hinged or floating, so the distance to the surface is maintained by some sort of slide or wheels attached to the array.·· When it encounters an uneven surface or low profile obstacle it will lift·or lower·to accommodate it.· Like the riding lawnmowers that have floating decks with wheels to follow the contour of the lawn.


Just a thought.

dandreae

You can try adding a shroud around the base of your robot.· This will eliminate the light interference.

Dave

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Dave Andreae

Parallax Tech Support·