Hi,

It as been some time since I posted my last blog.  Work kept me busy for most of the time. But I also experienced some difficulties that affected my motivation. However, I’m not willing to surrender yet. I will discuss the difficulties I experienced, maybe this will help me to find solutions for them.

First, I thought I had improved the position of the compass sensor when I replaced it last time. There were no more disturbances from the motors. But during testing I found out why. The brick was influencing the compass sensor in such a strong way that the influence of the motors was pushed to the background. But still the sensor didn’t give me good readings. I moved the compass sensor to the top of a pole I placed on my robot. This is very ugly but it does the trick (I hope).

Second, my son needed some of the parts back that I borrowed from him. FreeRover was destroyed while he removed them. Luckily there is BrickLick. I put my son on sale on BrickLick, so that problem is solved as well 😉

The third problem is in compass disturbances. I anticipated this problem but I still did not solve it.  What happens is this. Suppose a situation were there are no disturbances to the compass. Its reading is more or less accurate. When I start moving the robot the combined output of the gyro and compass sensors by the Kalman filter is better than the output of the sensors on their own. But when I move the robot to a place where there is a magnetical disturbance and hold the robot there the Kalman output is good in the beginning but then it drifts of to the disturbed compass reading. I do understand why, the filter knows both the compass and the gyro cannot be trusted totally, also it knows there is some process noise (ie the position can change due to movements of the robot). So when it gets a false compass reading it still takes this reading into account because it cannot know were the errors came from, it might as well be a false gyro reading or a movement of the robot. I hoped to make the filter smarter and to detect false compass readings, when there is a large change in compass reading that is not in line with the gyro reading I ignored the compass reading. However this proved to be more difficult than I thought. As sensor readings are frequent, disturbances do not show as large changes, they come in slowly and cannot be detected because they are within the range of sensor noise.  I do not have a solution for this yet.

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