Pointing the sensors

By | January 10, 2011

How do you decide where to point the sensors?

I haven’t seen too much discussion on where to point the sensors. The few images I’ve seen show the mouse laterally centered with the diagonal sensors pointed at the pegs for an orthogonal as well as diagonal cell. What is not clear is where the mouse should be longitudinally.
I think the longitudinal location should be a function of the turn radius (and vice versa). The further forward the sensors look, the sooner the mouse can detect the side openings. However, this also means that when it finishes a turn, it may be looking too far forward to do correction or see the pegs.
The other design choice is what should the sensor angle be?
For the sake of this discussion, imagine that a sensor pointed forward (along the longitudinal axis) has an angle of 0 deg. and a sensor pointed directly towards the wall (along the lateral axis) has an angle of 90 deg.
As the sensor angle decreases, the emitter energy reflected by the wall decreases which means that the detector response goes does. Also, as the sensor angle decreases, a change in the mouse angle has a larger effect on the detector’s response.
So, my design target has been to put the mouse in the middle of a cell and then locate the sensors such that they can see the longitudinal peg and maximize the angle of the sensor. Since nothing is for free, as you maximize the angle of the sensor, you have to move it further away from the center of the mouse which means you are increasing the sensor’s rotational inertia contribution.
For the longest time, I wondered why people were crossing the diagonal sensors i.e. the sensor on the left side of the mouse looked at the right wall and vice versa? The answer turns out to be that they were trying to minimize the rotational inertia! Since light drops off at 1/distance^2 (Peter has some graphs in one of his blog posts), this means they were trading off sensor performance also.
As they say, mouse design is full of compromises.
You might want to move paper cut outs of the mouse along with pieces of paper showing the sensor location and angle through a maze to get an idea of different sensor angles. Alternatively, you might be able to do this with a CAD program – my CAD skills are too limited for me to have tried this.

One thought on “Pointing the sensors

  1. Rodrigo Forrequi


    I’m a currently embedded developer on Microchip PIC/AVR word, now coming to ARM, and trying to working on my Mac. Your web site help me a lot, give to me the direction on ARM on Mac. Thank’s for share yours experiences and problems.

    About your micromouse, look at my blog my GUI Bot. It’s a kind of basic micromouse. The wheels are very nice.


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