Page 48 - The Unofficial Guide to Lego Mindstorms Robots

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A serious problem occurs if the same bumper is quickly hit twice. Suppose the bumper on input 1 is hit once. It begins
e xecuting its sensor watcher code by reversing the direction of the motors.
The robot travels backwards for half a second, th en output A reverses direction and the robot spins in place. Suppose, now, that
the bumper on input 1 is triggered again, before output C's direction is reversed again. The sensor watch er routine will begin
ag ain, reversing the direction of both the motors. Hank, therefore, will begin spinning the other direction instead of moving
backwards.
T hen output A's direction reverses, and the robot moves forward. Finally, output C's direction reverses, and the robot spins in
place again, instead of moving forward.

T here are two solutions to this problem. First, you can be more explicit about controlling outputs. Instead of just reversing the
output directions in the sensor watcher routines, you could specifically set the directions and turn on the motors. This technique
is shown in Hank's first program, in Figure 2-6. It doesn't matter if the sensor watchers are interrupted before they finish,
because the directions of the moto rs are always set explicitly. The other solution is to structure your program differently. If
your sensor watchers don't have any delays built into them, for example, they will be much less likely to be interrupted.

Online Resources

T he Art of LEGO Design

ft p://cherupakha.media.mit.edu/pub/people/fredm/artoflego.pd
This is an outstanding paper about building with LEGO parts. It includes helpful tips on making strong structures and using
gears. The paper is written by Fred Martin, one of the people at the MIT Media Lab whose programmable brick work formed
the basis of the RCX. I highly recommend this paper, especially if you are having trouble getting things to fit together.

Fred's 6.270 Ho me Page

http://lcs.www.media.mit.edu/people/fredm/projects /6270/
For a deeper treatment of many aspects of small mobile robotics, read the course guide for MIT's famous 6.270 class. In this
class, students build robots from the ground up. The 6.270 Robot
Builder's Guide was written by Fred Martin; it is a real bonanza of information and advice.

Doug's LEGO Technic Tri-Star Wheel ATV and Robotics page

http://www.net-info.com/~dcarlson/
Doug Carlson's fascinating page is full of pictures of his implementations of the tri-star design, synchro drive, and the Killough
platform. For sheer mechanical finesse, this page is hard to beat.