Reader Question Submission #2
We received this question: "If I want my tribot to turn 90 degrees, how come I have to code the motors to spin in opposite directions each for 180 (or a bit more) degrees? I mean, why 180 degrees if I am turning the robot 90 degrees?"
Click on the image at left. If you take the NXT stock wheels (2.25 inches in diameter) and calculate their circumference, you get approx. 7 inches. Now, assume those wheels are mounted on a bot as shown, with a distance of 5 inches between them and you want the bot to spin a quarter-turn in place (left wheel spins one direction, right wheel spins the opposite direction).
When the Bot makes a quarter turn, each wheel has traveled 3.925 inches (along the path indicated by the red circle). If 7 inches = 360 degrees, then a simple calculation shows that 3.925 inches is approx 201 degrees - not 90.
The bot as a whole has made a 90 degree turn, but the wheels have turned substantially more.
Did this help? Can someone verify my math and that I've done this correctly?