Group 7
Lab Notebook - Lesson 9
Date: 07/05 2015
Group members participating: Ivan Grujic, Lasse Brøsted Pedersen, Steffan Lildholdt, René Nilsson
Activity duration: 5 hours
Goal
The goal of this exercise is to investigate how the method of odometry and the tachocounter can be used to keep track of position of a LEGO car with differential drive.
Plan
The plan is to follow the plan described in [1].
Odometry
| Attempt | Measured x | Measured y | Calculated x | Calculated y |
|---|---|---|---|---|
| 1 | -2.00 mm | -2.00 mm | 1.00 mm | -1.60 mm |
| 2 | -2.00 mm | 2.00 mm | 0.40 mm | -0.60 mm |
| 3 | -4.00 mm | 3.50 mm | 2.50 mm | -1.90 mm |
Calibration of wheel diameter and the track width
Initial square run with calibrated values
| Parameter | Value |
|---|---|
| Left wheel diameter | 5.539 cm |
| Right wheel diameter | 5.544 cm |
| Track width | 16.27 cm |
| Attempt | Measured x | Measured y | Calculated x | Calculated y |
|---|---|---|---|---|
| 1 | -10.00 mm | -13.00 mm | 1.30 mm | -1.30 mm |
| 2 | -10.00 mm | -10.00 mm | 2.80 mm | -2.80 mm |
| 3 | -13.00 mm | -15.00 mm | 3.00 mm | -1.80 mm |
Tweaking parameters according to square run with left turns.
| Parameter | Value |
|---|---|
| Left wheel diameter | 5.539 cm |
| Right wheel diameter | 5.544 cm |
| Track width | 16.4 cm |
5.5950.99 = 5.539 5.60.99 = 5.544
| Attempt | Measured x | Measured y | Calculated x | Calculated y |
|---|---|---|---|---|
| 1 | 5.00 mm | 5.00 mm | 0.60 mm | -0.60 mm |
| 2 | -1.25 mm | 2.50 mm | 1.90 mm | -2.10 mm |
| 3 | 2.00 mm | 3.00 mm | 6.30 mm | -1.80 mm |
| 3 | -1.00 mm | 0.00 mm | 1.80 mm | -2.30 mm |
Reversed square with right turns
| Attempt | Measured x | Measured y | Calculated x | Calculated y |
|---|---|---|---|---|
| 1 | 30.00 mm | 40.00 mm | 1.30 mm | 2.30 mm |
| 2 | -27.50 mm | -30.00 mm | 5.20 mm | 2.70 mm |
Final parameters
| Parameter | Value |
|---|---|
| Left wheel diameter | 5.539 cm |
| Right wheel diameter | 5.544 cm |
| Track width | 16.27 cm |
Position tracking by means of particle filters
The tests to performed to estimate the noise factors was performed at low speeds, on a wooden table covered by a single sheet of paper. The low speed reduces the noise factors because the wheel stops faster, and thus closer to the intended angle, also the low speed reduces the risk the wheel loosing grip of the surface. The wooden table covered by paper also reduces the noise factors, because the surface is homogeneously smooth, without any irregularities which could introduce errors.
The distance noise factor was determined by having the robot perform multiple forward travels of 500 mm. The average distance from the target was ~0.5 mm, thus the distance noise factor was estimated as: 0.5/500 = 0.001.
The angle noise factor was determined by two tests, both performed multiple times. In the first test, the robot perform four 360 degrees rotation. The second test was similar, but reversed the direction of the 2nd and 4th rotation. For both tests, the average deviation was 0.5 degrees, hence the angle noise factor was estimated as: 0.5/360 = 0.00138.
Conclusion
References
[1] http://legolab.cs.au.dk/DigitalControl.dir/NXT/Lesson10.dir/Lesson.html