We are trying to incorporate the NXT into other uses and want to use the NXT Servos to control some speed controllers. We have gotten it kind of working. When we push forward we cant just hold down the controller forward. We have to step it forward, one push at a time, almost like a button. then when we want to go backward we have to step it all the way back down to stop then step it further backward for reverse. We would like it to be a smooth transition for forward and reverse, similar to using the speed controller that came witht he NXT. Any ideas?

I suspect the NXT motor’s encoder doesn’t give you absolute position of the axle. Just like any other optical encoder it’s up to software to convert the encoder signals into absolute location. A typical encoder will give you a direction signal and a pulse every time the shaft has rotated x degrees.

I don’t know the details of the software you’re using so you’re on your own there. If this is for FTC RobotC might well do some of this for you.

We are using labview and the 2008 FTC Template code to run the servos, then using the PWM outputs of the servos, connected to a speed controller.

I think there might be a terminology problem that’s keeping people from understanding what you are trying to do. Servos I am familiar with don’t have PWM outputs; they have PWM inputs. If you want to connect a speed controller, you should not also connect a servo.

Also on the terminology front, the NXT’s motors aren’t servos, they’re just motors with encoders built in. They run on an I2C interface.

Ok I understand the confusion. We are using the NXT with the Servo Controller for Tetrix. The servo controller has a pwm output. We are using the output from the Servo controller and putting that as the input on other speed controllers. The speed controllers are powered independently from a 12v supply. We are doing this because we believe the motors we are trying to power are to large for the hitechnic motor controller.

Did that clear up what we are doing?