USB connection problem

Hello,

I have a new kind of problem which i could not understand.

i have written a stand alone app to rotate motor at a fix speed.

but it only works when i connect VESC tool to it with USB.

otherwise the motor starts to cog and the motor vibrates very badly.

The code is shown below.

// FixSpeed thread
static THD_FUNCTION(FixSpeed_thread, arg);
static THD_WORKING_AREA(FixSpeed_thread_wa, 2048); // 2kb stack for this thread
 
void app_FixSpeed_init(void) {
 
	// Start the example thread
	chThdCreateStatic(FixSpeed_thread_wa, sizeof(FixSpeed_thread_wa),
		NORMALPRIO, FixSpeed_thread, NULL);

	
}
 
static THD_FUNCTION(FixSpeed_thread, arg) {
	(void)arg;
 
	chRegSetThreadName("APP_FixSpeed");
	//Set initial RPM
	static float pid_rpm = 2000;
	static float final_rpm = 6000;
	chThdSleepMilliseconds(500);
 	timeout_reset();

	for(int i=0;i<final_rpm;i++)
		{
		mc_interface_set_pid_speed(i);
		chThdSleepMilliseconds(5);
		timeout_reset();
		}
	for(;;) {
		
		mc_interface_set_pid_speed(6000);
		// Run this loop at 500Hz
		chThdSleepMilliseconds(2);
 
		// Reset the timeout
		timeout_reset();
	}
}