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Changes for page Ball Physics

Last modified by Soeren Domroes on 2025/01/30 12:18
From version 5.1
edited by stu104225
on 2020/03/04 17:18
Change comment: There is no comment for this version
To version 16.1
edited by Sascha Hoppe
on 2023/07/11 10:12
Change comment: Renamed back-links.

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1 +Projects.Pinball Project - Winter Term 201920.Project Documentation.WebHome
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1 -XWiki.stu104225
1 +XWiki.rtadmin
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1 -The **ball physics model** is meant to do things ... [TODO]
1 +The **ball physics model**'s main objective is to provide a point in time to the controller, when the ball is predicted to be hittable, in order to not let the ball fall into the drain.
2 +The code for what is described in this section can be found in the files "physics.cpp" and "physics.h".
2 2  
3 -\\
4 4  
5 5  
6 -
7 7  {{toc/}}
8 8  
9 9  == Ball trajectory ==
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10 10  
11 11  ----
12 12  
13 -The trajectory of a ball can be modeled to be parabolic.
14 -\\\\\\like so: .... [TODO]
12 +The trajectory of a ball can be modeled to be parabolic. From two point //p// and //p_old// with corresponding timestamps, the velocity //v// is computed.
13 +For a future point in time //t//, with //t=0 //being the timestamp of// p//, we can then approximately predict the corresponding ball position using the following formulas.
15 15  
15 +[[image:attach:Bildschirmfoto von 2020-03-07 12-21-22.png]]
16 +
17 +The incline of the playfield causes a vertical acceleration, which is modeled via a gravitational pull with the factor //g = sin(6°) * 9.81 m/s²//.
18 +The value of 6° is the incline of the playfield  measured on the physical device.
19 +
20 +== Prediction ==
21 +
22 +----
23 +
24 +The controller calls the function //full_prediction// passing it two subsequent ball positions with timestamps. From these a ball trajectory is inferred as described above.
25 +Along the trajectory future times are stepwise tested for whether the corresponding predicted position is in the flipper range.
26 +Once a position inside the flipper range is found the search is continued both forwards and backwards in smaller steps in order to find a good enough estimate of the first and last possible time to hit the ball.
27 +If the trajectory does not intersect the flipper range within a certain prediction frame (see below "**Prediction parameters**") a value far enough into the future is returned, that will be overwritten by subsequent predictions.
28 +
29 +With the current configuration the controller uses the middle point in time between the first and last possible time in order to be most positive to hit the ball.
30 +The computed velocity is also passed to the controller and used is some more advanced  tactical decisions like catching balls.
31 +
16 16  == Configuration ==
17 17  
18 18  ----
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19 19  
20 20  === Prediction parameters ===
21 21  
38 +(% class="wrapped" %)
22 22  |=(((
23 23  Parameter
24 24  )))|=(((
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31 31  )))|(((
32 32  window size for prediction - How far
33 33  
34 -into the future are predctions calculated at most.
51 +into the future are predictions calculated at most.
35 35  )))|(((
36 36  70ms
37 37  )))
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51 51  10
52 52  )))
53 53  
54 -with the default values up to 7 predictions are calculated if the ball is not predicted to be in flipper range roughly within the next two frames.
71 +When setting the PREDICTION_FRAME keep in mind that predictions, that reach multiple frames into the future, are likely to be overwritten, when new frames arrive and new predictions are calculated.
72 +Nevertheless it is reasonable to calculate predictions beyond the next frame in case a ball is not recognized on the next frame.
55 55  
56 -\\
74 +With the default values up to 7 predictions are calculated if the ball is not predicted to be in flipper range roughly within the next two frames.
57 57  
58 -So this number is also the worst case number of predictions calculated during the reverse search part of the prediction process.
76 +The REFINEMENT_FACTOR is also the worst case number of predictions calculated during the reverse search part of the prediction process.
59 59  
60 60  \\
61 61  
62 62  === Flipper range ===
63 63  
64 -The model of the area, where the the flippers can hit a ball is computed from a set of five points. These points are set to real world coordinates in meter
82 +The model of the area, where the the flippers can hit a ball is computed from a set of five points. These points are set to real world coordinates in meters
65 65  
66 -and should not need further adjustment after the camera is correctly calibrated (see [[doc:World Coordinate System]]).
84 +and should not need further adjustment after the camera is correctly calibrated (see [[doc:Projects.Pinball Project - Winter Term 201920.Project Documentation.World Coordinate System.WebHome]]).
67 67  
68 68  The values for the left flipper are set to be symmetrical.
69 69  
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113 113  
114 114  Since the trajectory prediction does not consider collisions in general, we need a different kind of predictions for the inlanes,
115 115  i.e. the path feeding a falling ball from the playfield to the flippers, behind the slingshot.
116 -A ball is considered to be in an inlane, when it is in a rectangualar area, with one edge given by the begin of the flipper
134 +A ball is considered to be in an inlane, when it is in a rectangular area, with one edge given by the beginning of the flipper
117 117  and the other by a point at highest, outermost position of the angled part of the inlane.
118 118  
137 +In this area the vertical acceleration is deactivated in the prediction, since it would cause the prediction to assume the ball would slide into the wall.
138 +Though in reality there is still some acceleration, a simple linear prediction has shown to be practical in this less critical area.
139 +
119 119  [[image:attach:physics_inlane.png]]
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1 -71401643
1 +71401594
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1 -https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/PP18/pages/71401643/Ball Physics
1 +https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/PP18/pages/71401594/Ball Physics