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- determine and limit the disturbances which make the prediction uncertain to a degree that make the experiment unfeasible;
- identify a model of the system that is suitable for the long term prediction that the algorithm requires.
SUMMARY OF CHANGES
- Implemented a simulator in C for Linux. This is integrated with the code used on cars (ca2). It simulates the cars dynamics and the behavior of the Camera Positioning Systems (CPS). Besides being very useful to verify the system model, it makes easy to test changes to code and the controller before applying those changes to cars.
- Implemented a script to visually debug cars behavior. It works both with the simulator and test-bed experiments data.
- ca2: grouped utility functions in a separate folder that is shared with the simulator. This makes the code more modular.
- ca2: partially implemented a Kalman filter in the attempt to remove part of the measurement noise of cameras. The model must be refined for it to prove its real effectiveness.
- ca2: implemented a new target detection algorithm that allow the car to work with the path with lots of points.
- ca2: steer controller has been reworked, the monodimensional speed has been substituted by the one read from the encoder, the PD has been calibrated and a compensator has been added.
- ca2: modified paths to add compensator directives (See #COMPENSATOR DIRECTIVES).
- ca2: implemented a new filter for the heading measure to cancel the effect of leaps (See #HEADING FILTERING).
- ca2: set the limit of steer input to (-100,100) since the curvature radius saturates above it.
- CPS: fixed a bug that affected the initial target dectection for cars that were not tracked by computer 0.
- CPS: now compute and send also the 2D speed of the cars. This is likely to be needed for the predictor in the future. See also section #CPS MEASURED 2D SPEED.
- CPS: implemented linear error correction for the computation of camera position. This visibly improves the path following of cars. See section #CAMERA MEASUREMENT ERROR CORRECTION.
Note about CPS usage. Since CPS now compute and send the 2D speed to cars, AndreaCPS is not compatible to previous ca2 versions. Viceversa my ca2 is not compatible with previous version of CPS. This is because the communication protocol between CPS and ca2 is now a little bit different. In general I would suggest using AndreaCPS instead of KevinCPS or LeoCPS. This because of the bug that involved the initial target detection. I did not check CPS versions that are previous to KevinCPS but it is likely that those versions do not have this bug since computer 1 and 2 do not send their information to computer 0 before sending them to cars.
CURRENT LAB PROBLEMS
- Cameras should be screwed to the metal support. Now every time they move, the whole calibration procedure must be done again. An extrinsic calibration (at least) should probably be performed again after this job.
- The two chargers close to the whiteboard seem to have some wiring problem. Sometimes the led is green while cars are connected (i.e. they're done charging) but it turns red when you move the wires.
- Sometimes the connection between computers and cars is lost. There are 2 main cause.
- There are 2 critical functions in the CPS code in main.cpp that occasionally takes up to 300-400ms in computer 0. This does not happen (or happens extremely rarely) with computers 1 and 2. I think the fault may simply be the computer's hardware because computer 0 is the slowest among the three. The two critical functions are flycaptureGrabImage2() and cvWaitKey(). The CPS currently prints a warning when one of this two functions takes more than 0.1s (the car's clock). I changed the CPS so that computer 1 now sends the data to cars so that the connection is always active, still this kind of delay makes cars tracked by computer 0 to receive out-of-date information.
- Sometimes car 2 becomes unreachable to ping tests while moving. This causes the time between two clock cycles to reach even 1-2 seconds. I never found the same problem with car 1 and 3. Most of the times this happens, there is no timeout of the recvfrom() function which receives the data from computers. This suggests that the problem resides in the on-board computer more than in the connection. The reason could be originated by both hardware (the motherboard of car 2 is an older and slower model with respect to car 1 and 3) and software (out-of-date operating system or some background program that takes too much resources).
- Car 2 cannot handle high engine voltages for a long time. After about 2 minutes at constant PWM 200 the car's speed dropped exponentially. This does not happen with cars 1 and 3. Substituting the h-bridge and the battery did not help. Anyway, a motor controller that is not very stressful does not cause troubles.
- The encoder of car 1 often does not give signal at the beginning when the car starts running. It starts working only after about 10 seconds.
- There is a point on the part of path8CL tracked by camera 4 (the one closest to the computers and the door) in which there are "jumps" of the measured position even if the tracking of the car does not pass from a camera to another. I am not sure if this is the problem of the camera itself or of the calibration that must be redone.
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TROUBLESHOOTING
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CURRENT LAB PROBLEMS
- Cameras should be screwed to the metal support. Now every time they move, the whole calibration procedure must be done again. An extrinsic calibration (at least) should probably be performed again after this job.
- The two chargers close to the whiteboard seem to have some wiring problem. Sometimes the led is green while cars are connected (i.e. they're done charging) but it turns red when you move the wires.
- Sometimes the connection between computers and cars is lost. There are 2 main cause.
- There are 2 critical functions in the CPS code in main.cpp that occasionally takes up to 300-400ms in computer 0. This does not happen (or happens extremely rarely) with computers 1 and 2. I think the fault may simply be the computer's hardware because computer 0 is the slowest among the three. The two critical functions are flycaptureGrabImage2() and cvWaitKey(). The CPS currently prints a warning when one of this two functions takes more than 0.1s (the car's clock). I changed the CPS so that computer 1 now sends the data to cars so that the connection is always active, still this kind of delay makes cars tracked by computer 0 to receive out-of-date information.
- Sometimes car 2 becomes unreachable to ping tests while moving. This causes the time between two clock cycles to reach even 1-2 seconds. I never found the same problem with car 1 and 3. Most of the times this happens, there is no timeout of the recvfrom() function which receives the data from computers. This suggests that the problem resides in the on-board computer more than in the connection. The reason could be originated by both hardware (the motherboard of car 2 is an older and slower model with respect to car 1 and 3) and software (out-of-date operating system or some background program that takes too much resources).
- Car 2 cannot handle high engine voltages for a long time. After about 2 minutes at constant PWM 200 the car's speed dropped exponentially. This does not happen with cars 1 and 3. Substituting the h-bridge and the battery did not help. Anyway, a motor controller that is not very stressful does not cause troubles.
- The encoder of car 1 often does not give signal at the beginning when the car starts running. It starts working only after about 10 seconds.
- There is a point on the part of path8CL tracked by camera 4 (the one closest to the computers and the door) in which there are "jumps" of the measured position even if the tracking of the car does not pass from a camera to another. I am not sure if this is the problem of the camera itself or of the calibration that must be redone.
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TROUBLESHOOTING
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- Router It happened to me once that the computers kept connecting and disconnecting to the local network making impossible to estabilsh a connection between them and with the cars. When this happened, removing the internet cable from the router (the one that is plugged to the wall) fixed the problem.
- Motherboard You can test if a car's motherboard is working by connecting it to the screen and turning the car on. If it doesn't, usually the cause is the power supply unit (PSU). Try substituting that piece.
- Brainstem ca2 console displays the message "Host-Stem Link: DOWN". Sometimes the baudrate of the brainstem resets itself for no apparent reason, so first try to set back the baudrate as explained in section "Hardware Reset Procedure" in the main page of the lab wiki. If you cannot make it work, proceed with an hardware reset (described in the same section). Note that if you do not have to configure a brand new card, there is usually no need to load the tea scripts again.
- Engine When a car is particularly slow, check that h-bridge connections to the power and the motor are solid.
- Encoder gives no signal, check that the serial cable is connected in the proper way (you can find the h-bridge datasheet http://www.acroname.com/robotics/parts/S11-3A-EMF-HBRIDGE_datasheet.pdf and encoder datasheet in the electronic components catalog on the shelf).
- Steer is biased towards a direction. The steer cannot be set straight only mechanically. You must set the offset parameter in RoboCar_Lib.tea.
SOFTWARE
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SUMMARY OF CHANGES
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- Implemented a simulator in C for Linux. This is integrated with the code used on cars (ca2). It simulates the cars dynamics and the behavior of the Camera Positioning Systems (CPS). Besides being very useful to verify the system model, it makes easy to test changes to code and the controller before applying those changes to cars.
- Implemented a script to visually debug cars behavior. It works both with the simulator and test-bed experiments data.
- ca2: grouped utility functions in a separate folder that is shared with the simulator. This makes the code more modular.
- ca2: partially implemented a Kalman filter in the attempt to remove part of the measurement noise of cameras. The model must be refined for it to prove its real effectiveness.
- ca2: implemented a new target detection algorithm that allow the car to work with the path with lots of points.
- ca2: steer controller has been reworked, the monodimensional speed has been substituted by the one read from the encoder, the PD has been calibrated and a compensator has been added.
- ca2: modified paths to add compensator directives (See #COMPENSATOR DIRECTIVES).
- ca2: implemented a new filter for the heading measure to cancel the effect of leaps (See #HEADING FILTERING).
- ca2: set the limit of steer input to (-100,100) since the curvature radius saturates above it.
- CPS: fixed a bug that affected the initial target dectection for cars that were not tracked by computer 0.
- CPS: now compute and send also the 2D speed of the cars. This is likely to be needed for the predictor in the future. See also section #CPS MEASURED 2D SPEED.
- CPS: implemented linear error correction for the computation of camera position. This visibly improves the path following of cars. See section #CAMERA MEASUREMENT ERROR CORRECTION.
Note about CPS usage. Since CPS now compute and send the 2D speed to cars, AndreaCPS is not compatible to previous ca2 versions. Viceversa my ca2 is not compatible with previous version of CPS. This is because the communication protocol between CPS and ca2 is now a little bit different. In general I would suggest using AndreaCPS instead of KevinCPS or LeoCPS. This because of the bug that involved the initial target detection. I did not check CPS versions that are previous to KevinCPS but it is likely that those versions do not have this bug since computer 1 and 2 do not send their information to computer 0 before sending them to cars
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.
DISTURBANCES ANALYSIS
In this section a quantitative analysis of the disturbances in the system is attempted. In order to deal in an easier way with the assumption of monotonicity and with the coupling between the steer and the motor input, the model is linearized and the lateral and the longitudinal components are separated. The coupling effect is seen as a disturbance. In the following the coordinate system will be relative to the path as represented in Figure coord_sys.jpg. In other words, y represents the position along the path while x the lateral distance from the path.
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