All entries for Tuesday 07 November 2006

November 07, 2006


I guess my promise of writing up things on the 1st of November didn’t really materialise but I thought i’d take a stab at it now.

My PhD’s in the Warwick Automation Research group, we’re on the second floor of the International Manufacturing Centre, overlooking Computer Science and Maths.

One of our projects and the area i’m involved in is the design of autonomous robots.

At the moment we’ve got one of these:

Ransomes Spider lawnmower

and we’re getting a ride-on purely electrical lawnmower (EPlex II) courtesy of Ransomes in a fortnight’s time.

The aim is to turn both in to autonomous robot platforms that can then be adapted to perform specific tasks like keeping a golf course cut and helping farmers with pasture management.

To start with, we’ve got four of these (though one’s refusing to work properly):

Sick PLS

They are proximity laser sensors. Nifty devices, not little or light though. They scan the 180 degrees in front of them and return you sets of 180 values (one for each degree) twice a second over rs232. Each value represents the distance at that position. It only functions in an x-y plane but gives enough information to make a reasonable last-ditch safety system preventing the robot from colliding with obstacles.

We are toying with the idea of using a single Sick PLS sensor to map out the ground ahead of the robot. This could be used to aid the eventual vision system.

The first problem i’m focussing on is that of getting accurate positioning information for the robot. While GPS can give us a rough position (assuming we can see a couple of satelites) as we can’t rely on having differential gps correction signals available, we need to incorporate other methods.

One of the possible methods is to attach magnetic strips and sensors to the Spider’s wheels and drive chain in order to get odometry information that can be used to ‘fill in the gaps’ (or be used with a Kalman filter) to better calculate the robot’s position.

Another possibility is borrowing an idea from the world of computer mice. Modern optical mice are pretty neat little devices. Wikipedia have a little section on optical mice . Essentially, they involve tiny cameras (normally only 15-20 pixels square) at very high frame-rates (1000fps+). They compare successive pictures from the cameras to figure out how far and in which direction you’ve moved.

I’m currently investigating doing just that but with a high-speed camera mounted perpendicular to the ground off to the side of the robot. This has the advantage that it, as a sensor, could be move from one platform to the other with ease. At the moment, i’m looking in to methods such as optical flow in order to work out movement.

I went to Abbey Fields this afternoon to take lots of photos of grass. That got some odd looks.

I’ll let people know how experiments are going at the end of the week.

Most recent comments

  • yeah agree with jules need some cover may b some plants or rock work or those fry will quickly b eat… by carl on this entry
  • well by the time u get this they should of hatched lol …. id put some cover in ur tank looks abit … by Jules on this entry

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