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 [DPRG] Meeting re-cap Message index sorted by: [ date ] [ thread ] [ subject ] [ author ] Previous message: [DPRG] Robomo Next message: [DPRG] tutebot brain breadboard layout question Subject: [DPRG] Meeting re-cap From: David P. Anderson dpa at io.isem.smu.edu Date: Wed May 10 16:13:17 CDT 2000 ```Howdy Clay writes: > At the end of the meeting Clay Timmons > re-programmed his robot from the last contest > to run a 4 meter (157 inch) square course. This is part of a > test/calibration procedure developed by the University > of Michigan called UMBmark. A drain in the floor > made for a less than level surface. The course > was setup to run around the drain to avoid the dip in > the floor. Clay taped a large piece of graph paper to the > floor to record the test results. The X and Y > positions for each of 5 clockwise runs were recorded. > (all values in inches to the nearest .1 inch) > X Y > run 1 +0.4 +6.0 > run 2 -1.2 +8.9 > run 3 -2.8 +10.6 > run 4 -3.7 +9.3 > run 5 -1.0 +4.3 > > Testing was not very rigorous but it will > serve as an intial benchmark to compare > with future improvments. Cool! I especially like the graph paper chart of the results! Your robot has a UMB "center of gravity" error of these five clockwise runs of X error = (0.4-1.2-2.8-3.7-1.0)/5 = 1.66 Y error = (6.0+8.9+10.6+9.3+4.3)/5 = 7.82 The next step is to run the same course counter-clockwise five times and collect the same data. Going around the square both clockwise and counter-clockwise allows wheel base errors to be separated from wheel size errors, and this is the really nifty thing about this benchmark. If the errors for the clockwise and counter-clockwise runs are symmetrical (i.e., X becomes -X and/or Y becomes -Y) then the calibration error is in the definition of the robot's wheel- base, the distance between the two drive wheels. This number should be tweaked. Increasing it will cause the robot to revolve slightly further, decreasing it will cause it to revolve slightly less. If the errors for the clockwise and counter-clockwise runs are not symmetrical (X and Y remain the same sign) then the calibration error is caused by a slight difference in size between the wheels, and those numbers should be adjusted. Borenstein suggests that a small constant be added to the size of one wheel and subtracted >from the other. Ideally the errors for the five runs should scatter evenly around X,Y = 0,0. In this case, the calibrations are as accurate as they are likely to get, and the variation in error is caused by random bumps and irregularities in the path across the floor. This is sort of like firing a group of shots at a target to see the spread of the pattern when sighting-in a rifle scope. Here are the errors from my robot SR04 when it was last calibrated last summer: dpa ----------------------------------------------------------------------- SR04 Calibration 06 Jul 99 clockwise: X error Y error 1.0 -1.5 -2.5 1.75 2.0 -1.5 -0.75 -0.75 ---------------------- Average error -.05 -.5 (UMB "center of gravity") counterclockwise: X error Y error -1.5 -2.0 -2.5 -1.0 -2.0 -1.5 -2.5 0.0 -3.5 0.0 --------------------- Average error -2.5 -0.9 (UMB "center of gravity") ``` Previous message: [DPRG] Robomo Next message: [DPRG] tutebot brain breadboard layout question Message index sorted by: [ date ] [ thread ] [ subject ] [ author ] More information about the DPRG mailing list