I would like to know how I can go about calculating what speeds on the motors correspond to different turning angles for the Sabertooth 2x12. I am using the simplified serial protocol and am able to move the rover forward and back at different speeds, but I do not know how to determine what motor speeds correspond to different angles. For example, If I want the rover to turn at 60 degrees, what commands do I send? Short of trying all of the commands and physically measuring the angle, I’m at a loss.
Since the Sabertooth has no feedback information, I believe your only option would be by trial and error.
There are some other motor controllers such as the Roboclaw by Basic Micro, that allows you to have encoders on the motors and connect the encoders up to the controller and get some feedback. But again may need some trial and error as you sill typically have to take into account that on most of these rovers you turn by skidding the wheels, and so just because the wheel moved a distance of X may not fully imply the rover moved that far.
Kurt is entirely correct. Without feedback, you’re only left with trial and error - and that cannot necessarily be reproduced on different surfaces (especially if the traction under one wheel is different than the traction under the others). The way around this is to use a compass; this would ensure the robot turned a specific number of degrees, and of course you could also use it for navigation. If your robot will encounter rough terrain, consider a compass with tilt compensation. robotshop.com/magnetic-sensors-compass.html
