public void prePhysicsTick(PhysicsSpace space,float tpf){
            if(isPressedFarward)
            {
                if(throttle+tpf*2<1)
                {
                throttle +=tpf*2;
                }
                else{
                throttle = 1;
                }
                
            resetInput = true;
            }
            else if(isPressedBackward){
                if(throttle-tpf*2>-1)
                {
                throttle -=tpf*2;
                }
                else{
                throttle = -1;
                }
            resetInput = true;            
            }
            else
            {                 
                if(throttle-tpf*2>0)
                {
                throttle -=tpf*2;
                }
                else if(throttle+tpf*2<0){
                throttle +=tpf*2;
                }
                else{
                throttle = 0;
                }
            }
        for(PropulsionUnit x:propulsionUnits){
            if(lastThrottle != throttle)
            {
                if(throttle==0){
                x.activate(throttle, false);
                lastThrottle = throttle;
                }
                else{
                x.activate(throttle, true);
                lastThrottle = throttle;
                }
            }
        x.update(tpf);
        }     
        
    }