[chbot] Lego NXT question

[Richard Jones]

Robo Sumo is on 18th Feb 2009, and here is a picture of my second Lego Sumo
robot, this one is called Gnasher after the Beano character. Here is a pic
of gnasher in the sumo ring. The ring was pristine a couple of days ago and
is showing battle scars already!

http://homepages.ihug.co.nz/~rjtp/LegoSumo/gnasher.JPG

Now I have a little problem that an NXT expert may be able to advise on.
When I program the dual motor control to turn fully at 50% power unlimited
time, the motors turn at half rate for a few seconds and then run up to
about full speed. The robot still turns on the spot so I suspect that the
speed is still accurately controlled, just at the wrong rate. Anyone have
any ideas? I've simplified the program to a single motor control block and
changed my NiMh cells for alkaline cells. My nxt kit is less than 2 months
old so I'm not keen to void the warranty yet by taking it apart. When I
load the same program into a different NXT with different motors, the
motors turn indefinitely at the slow rate as expected. Any suggestions much
appreciated.

Happy New Year to everyone.

Richard