Pendulum Balance Robot

Using Arduino Project Guidance
16

I'm pretty sure you need to use an interrupt
attach the encoder to pins 2 and 4

Encoder encoder(2, 4);

        void setup() { 
            attachInterrupt(0, doEncoder, CHANGE); 
            Serial.begin (9600);
            Serial.println("start");
        } 

        void loop(){
            // do some stuff here - the joy of interrupts is that they take care of themselves
        }

        void doEncoder(){
            encoder.update();
            Serial.println( encoder.getPosition() );
        }