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diff --git a/digital/asserv/doc/parameters.txt b/digital/asserv/doc/parameters.txt new file mode 100644 index 00000000..e2a7c894 --- /dev/null +++ b/digital/asserv/doc/parameters.txt @@ -0,0 +1,81 @@ +================================== + How to measure robot parameters? +================================== +:Author: Ni + +Scaling factor +============== + +The scaling factor will be used to convert between asserv steps and +millimeters. We will look at the left counter as this one is not corrected. + +Select a flat, clean and long (2 to 10 meters) surface, then position the +robot precisely on a starting line. Draw a parallel line at the other end and +measure distance between the two lines. + +Now, reset the robot counters and start monitoring left counter value. Drag +the robot as linearly as possible until it reaches the final line. While +doing this, remember any counter overflow or try to calculate how many +overflow is expected (with a wheel diameter estimation). + +Position precisely the robot on the finish line and write down the left +counter value. + +The scaling factor is given by:: + + distance (mm) / augmented_counter + +where ``augmented_counter`` is the counter value prefixed with the number of +overflows. + +Keep the right counter value as well as it can be used for the next measure. + +Right wheel correction +====================== + +As wheels can not be exactly the same, we will introduce a correction factor. + +Do the same measure as for the scaling factor, but we need the left and right +counters values. + +The correction factor is given by:: + + left_augmented_counter / right_augmented_counter * 2^24 + +The ``2^24`` factor is used to have a 24 bit floating point number. + +Now, it is time to check your measures. Ask the robot to drive a distance and +check it. + +Encoders footing +================ + +This is the distance between the encoders wheels, used to compute robot angle. + +Place the robot precisely on a line. + +Now, reset the robot counters and start monitoring counters values. Make a +large number of turns (about 10) and position the robot precisely on its +starting line. While doing this monitor counting direction, and any counters +overflow or underflow. + +Write down the counters values and the number of overflow. + +A counter was counting backward, so you will have to handle negatives numbers. + +For example, if the current counters values are 0x1234 and 0x2345, if the +first counter was counting upward and the second one backward, and each +counter has overflowed 3 times, this gives, in the 24 bit two's complement +notation, 0x031234 and 0xfc2345 (0xfc = 0xff - 3). The second number +represents -0x03dcbb (0x1000000 - 0xfc2345). + +Now make the difference between the two augmented counters values, or the sum +of their absolute values, this will give the total distance in steps travelled +by the two encoders to do the number of turns. + +The encoders footing is given by:: + + difference / 2 / pi + +The ``2`` divider is there because we summed the distance traveled by both +encoders. Then we divide by ``pi`` to get the diameter. |