| ... | ... | @@ -18,18 +18,37 @@ The plan is to follow the plan described in [1]. |
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## Odometry
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For this exercise the standard base vehicle from Lesson 6 is used together with the PilotSquare.java program provided in this lesson.
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The parameters of the LEGO car in this program is defined as the following.
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| Parameter | Value |
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| ------------------------- |:---------------:|
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| Left wheel diameter | 5.5 cm |
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| Right wheel diameter | 5.5 cm |
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| Track width | 16 cm |
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The program makes the car drive 20 cm straight forward, turn 90 degrees to the left and repeat this 4 times in order to get back to the initial position.
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A special piece of paper with multiple grids on it is used to measure the accuracy of the system. This is shown in the following image.
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Optimally, the LEGO car should end up in the exact same position as prior to the execution of the program. However this is not the case due to both **systematic** and **non-systematic** errors.
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The result of the 3 test runs are summarized in the following table.
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| Attempt | Measured x | Measured y | Calculated x | Calculated y |
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| -------- |:-------------:| -----------:| ------------:| ------------:|
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| 1 | -2.00 mm | -2.00 mm | 1.00 mm | -1.60 mm |
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| 2 | -2.00 mm | 2.00 mm | 0.40 mm | -0.60 mm |
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| 3 | -4.00 mm | 3.50 mm | 2.50 mm | -1.90 mm |
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"Measured" x and y is the physical error measured by a ruler and "Calculated" x and y is computed error displayed in the LCD on the NXT.
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The **Non-systematic** involves variations in the surface and the internal uncertainty of ~2% [2]. These errors are difficult to cope with. However the **systematic** errors involves incorrect definition of the LEGO car parameters and these can be corrected by calibration which is described in the following.
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## Calibration of wheel diameter and the track width
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#### Initial square run with calibrated values
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| Parameter | Value |
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| ... | ... | @@ -86,11 +105,23 @@ The plan is to follow the plan described in [1]. |
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| Track width | 16.27 cm |
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## Position tracking by means of particle filters
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Why this behavior?
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Quantization error in tacho counter in each step of the trip.
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Orientation of back wheel.
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500 mm kørt distance. Afstand fra mål ~0.5 mm = dist_err = 0.001
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Rotation error ~0.5 degrees. 0.5/360 = 0,00138
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## Position tracking by means of particle filters
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Hastighed ændret fra 5 til 15
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Distance noise factor = 0.005
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Angle noise factor = 2.5
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## Conclusion
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| ... | ... | @@ -98,6 +129,7 @@ Rotation error ~0.5 degrees. 0.5/360 = 0,00138 |
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## References
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[1] http://legolab.cs.au.dk/DigitalControl.dir/NXT/Lesson10.dir/Lesson.html
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[2] http://lejos.sourceforge.net/nxt/nxj/tutorial/WheeledVehicles/WheeledVehicles.htm
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### Code
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| ... | ... | |
