The following is the video featuring the robot detecting the lake, moving towards the lake and measuring the temperature.
Latest Entries »
Our presentation for the Line tracking and mars competitions.
Today we calibrated the camera, so we can convert the image coordinates to space coordinates relative to the position of the robot as presented in the figure:
The coordinates of a point in the image are related to the space coordinates for the equation:
We used an image where several point with known coordinates with respect to the robot were located. Using the coordinates in the image and in the space of these points, we found the matrix H, which is the linear version of the Pinhole Model. The results are appealing, using the known space coordinates we project the points in the image, as showed in the figure
After we moved the robot, we locate new points and we use their space coordinates to project them back to the image, the errors are acceptable.
We tested again our line tracking system, even using lines that wouldn’t be the first choice to test the system. The results are impressive! For a line of 3000 mm we obtained a measurement of 3012 mm and for a line of 915 mm we obtained a measurement of 908 mm.
The high speed video of the results:
After some tests, we concluded that the threshold used to determine whether or not we are at the edge of the mars platform should not be static. We implemented a dynamic threshold that updates every time we know we are in the table and the results are as desired. Here is the video:
We calibrated the temperature sensor for our Mars Rover comparing value showed by the sensor with a thermometer. We used ice, cold water and hot water and we obtained different values for the actual temperature and the sensor value as presented in the figure.
As we can see from the figure, the second order fit is accurate enough for our purpose and will give us good results in the range of temperatures we are expecting.
Go forward and avoid falling from the table.
The Mars Invader successfully avoided falling from the table by going backwards–turning the wheels by a relative 70 degree of the motor–moving forward during 3.5 seconds or until the edge is visible again–turning the wheels back to the aligned position.
Circular movement. We use the circular movement of the Mars rover to measure its rotation radius by setting the relative degree of angle for motor of rotation to be 70 and moving forward. We obtained a radius of 405 mm approximately.
Today we tested the final code for the Line tracking competition and the results are appealing. In the first case we used a line darker than the background and we obtained a measurement of 987 mm when the actual length of the line was 980 mm, so our calibration was accurate enough. This is the corresponding video:
After that, we used a line lighter than the background and again our measurement error was less than 7 mm, the video is here:
We are able now to focus in the mars mission.
On Monday we switched the middle sensor with a new one and calibrated 3 three sensors again by just shifting a constant value w.r.t. the nonlinear behavior of them. The data of result of testing on the table:
Position Left sensor Middle sensor Right sensor
On the center of black tape 34 29 33
On white background of table 41 37 39
Right boundary of black tape 36 34 35
Left boundary of black tape 40 36 39
on the center of green tape 35 30 33
The data which the sensors are on the left and right boundary is not reliable because these two positions are very sensitive. So based on other 3 cases we found out a steady shift of value: make left sensor as standard, middle sensor should be shifted by 4 upward and right sensor should be shifted by 2 upward.
From the latest hours of this afternoon’s experiment, we witnessed two main problems:
1. communication delay: sometimes there will be some delays in communication. From one experiment, the rover is going to the right a little and it correts it self. But it is always showing “case 4″which means slightly to the right even when it’s going way beond on the left side. After a while, it will show “on line” , “case 2” or “case 3″and “error”. It means the sensor actullay reads the data and the correct judgement is made. However, this message is held during the communication so the rover can not correct it in time.
2.unstable sensor reading: sometimes when the rover is not moving, the RCX will make changing judgement. Maybe this is because the sensor is reading different values each time and becasue the value is on the edge of our threshold, a small difference of 1 or 2 will make the decision different.
If these two problems don’t occur, then the rover will track the line all the way and will stop very soon after the tape ends.
Mars Invader 