... | ... | @@ -47,10 +47,27 @@ In order to minimise the error we replaced the wide offroad wheels with slim whe |
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This time the robot ended 1 mm to the right and 1.5 mm in front of the initial position revealing an error of (80.18/80*100)-100 = 0.225 %. The robot’s pose values show that the robot have travelled 1.6 mm too far and 1.7 mm to the right (see fig. 5).
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![Skærmbillede 2015-06-01 kl. 09.32.02](http://gitlab.au.dk/uploads/group-22/lego/1283b932a5/Sk%C3%A6rmbillede_2015-06-01_kl._09.32.02.png)
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##### Fig. 5 - Screendump of the robot screen with values.
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These values are very close to the ones we noted on the paper grid layout.
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Compared to the previous experiment the error of 0.225 % is significantly smaller than 1.075 % from test 1 meaning that the slim wheels where more accurate for precision driving. However the same result may also be achieved with the wide wheels if the trackWidth and wheelDiameter values are properly adjusted.
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### Measurement and Correction of Systematic Odometry Errors in Mobile Robots
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There is two dominant errors [1] which can occur within the differential-drive mobile robots: Uncertainty about the wheelbase and unequal wheel diameters. |
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There is two dominant errors [1] which can occur within the differential-drive mobile robots: Uncertainty about the wheelbase and unequal wheel diameters.
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### Measuring the accurate wheel diameter and track width
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As our Test 2 revealed the importance of a precisely measured wheelDiameter we decided to use a caliper to get these values as accurate as possible. Doing these measurements would also reveal any possible deviations for the same type of wheels.
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![IMG_8677](http://gitlab.au.dk/uploads/group-22/lego/e449d916ab/IMG_8677.JPG)
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##### Fig. 6 - With the use of a caliper, we got the accurate measuring of the wheel diameter.
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The fat off road wheels were measured to be 5,6 + (1/10)*0,1 = 5,61 centimetres, but were likely to compress slightly under the weight of the robot, something that could not be measured using a standard caliper with the wheels mounted to the robot.
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The slim wheels we measured to 3 + (2/10) * 0,1 = 3,02 centimetres.
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While fitting the caliper to the slim wheels, we noticed that the right wheel was a couple of micrometres larger than the left, but that this wasn’t enough to actually make the caliper move.
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### Calculation of the true track width
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Since the true track width is measured from the centre of one wheel to the centre of the other, we could not use the caliper to measure it directly and therefore had to do some calculations.
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To calculate the true track width, we had to calculate the average wheel thickness. This was done by measuring the outer and inner track widths, subtracting them and dividing by two. |
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