New Robot

As promised we have constructed a new robot that probably will be the one, or at least very similar to the final product. It is based on the Explorer robot from Nxtprograms.



Our requirements for the physical units was that it has to be able to rotate around its own axis (a requirement for the leJOS navigation classes) and that the IR sensor has to have a 360 degree field of view. A bonus with this model compared to others we have considered is that the IR sensor rotates directly on a motor. In earlier versions we had to convert between the rotation of the motor and the sensor, something we don't have to worry about anymore.


Aside from changing the sensor on top to our IR sensor, we have added a compass sensor and fitted the Ultrasonic sensor in front instead. We also slightly modified the top motor and sensor so that its rotational axis is between the wheels, something that will facilitate calculating the position of obstacles.

Today we have also done several tests to determine how accurate the navigation classes are, and the results are somewhat disappointing. For some reason navigation with the help of the compass sensor is actually less accurate than a simple tacho navigator that only uses the rotation of the wheels to navigate. Also, bugs with both classes severely limits the amount of methods we can use and still maintain a reasonable accuracy. For now we have settled on using Forward(), Backward() and Rotate(), which is accurate enough for our needs. Hopefully we (or leJOS, which is still in beta after all) will solve some of the problems and we won't limited to these forever.

/Josef and Peter

First test of the new sensors

So we finally decided to buy the sensors I told you about a couple of weeks ago.
We bought this from Mindsensors.com:
* High Precision Long Range Infrared distance sensor for NXT (DIST-Nx-Long-v2)
* Multi-Sensitivity Acceleration Sensor v3 for NXT - (ACCL-Nx-v3)
And this from HiTechnic.com:
* NXT Compass Sensor
* NXT Extended Connector Cable Set



And now they've finally arrived to Sweden :)
I've been able to test the Compass and the distance sensor so far, Josef still got the Acceleration Sensor at home and we will test it together when we meet in a couple of weeks.

Anyhow they look really good :) The accuracy of the distance sensor is very high, it gives you the distance in mm and it works good!



I put together a simple bot to test out the CompassNavigatorin LeJos.



We will do some more advanced stuff soon!

Useful sensors

This weekend I read the book Develop LeJOS Programs Step by Step by Juan Antonio Breña Moral. It was really good with alot of nice examples of how to do LeJOS stuff. It also included some information not directly connected to LeJOs, like Lego Mindstorms history for example, but this was really entertaining to read.



Anyhow the book included some useful links and one of the brought me to the company Mindsensors. I found a really nice sensor that could improve this project alot. The High Precision Long Range Infrared distance sensor for NXT (DIST-Nx-Long-v2) would allow us to calculate distances between 20 to 150 cm in millimeters!! Thats 10 times better than with the Ultrasonicsensor that only gives us the distance in cm.



I also read that the CompassNavigator in leJOS may take advantage of the compass sensor from HiTechnic. This would be really nice to have because (as i've understood it) the turns won't depend on the tachometer in the motor, instead it will look at the angle the compass returns i.e. it will rotate until it has rotated as much as needed.