Vex SquareBot- movement programming problem

[Nathan]

Hi, I'm programming the Vex SquareBot in MPLAB IDE, and am having some problems programming the movement since one of the motors on the SquareBot is inverted. I tried this code:

void normal_operation()
{
	int R_Joy_Up    = 127;		// These hold the joystick values.
	int L_Joy_Up    = 127;		// Only R_Joy_Up & L_Joy_Up are used in tank mode.
	int R_Joy_Down  = 127;		// This probably isn't really needed, to be cleaned up after project completed.
	int L_Joy_Down  = 127;
	int R_Joy_Right = 127;
	int L_Joy_Right = 127;
	int R_Joy_Left  = 127;
	int L_Joy_Left  = 127;
	
	int temp;
	
	while(autonomous != 255)
	{
		R_Joy_Up = GetRxInput( 1,2 );
		L_Joy_Up = GetRxInput( 1,3 );
		
		if(L_Joy_Up > NEUTRAL)
		{
			temp = L_Joy_Up - 127;
			L_Joy_Up = NEUTRAL - temp;
		}
		else if(L_Joy_Up < NEUTRAL)
		{
			temp = L_Joy_Up - 127;
			L_Joy_Up = NEUTRAL - temp;
			if(L_Joy_Up <= 0)
			{
				L_Joy_Up = 253;
			}
		}

		autonomous = GetRxInput(1,5);
		drive ( R_Joy_Up, L_Joy_Up );
		PrintToScreen ( "L_Joy_Up: %d\n" , (int)L_Joy_Up );
		Wait(1);
	}

My code works fine, until I move the left joystick on the vex controller all the way to the bottom. The the motor suddenly reverses direction

Does anyone have any suggestions? I really appreciate the help

Thanks,
Nathan

[10scott10]

what is happening is that you are probably going below 0. when that happens it loops back to 255.
just put in an if statement to catch that before it changes speed. the same problem could cause it to go 255 to 0. so put in a if statement to catch that also

[Nathan]

Yep, your right! I found this out about an hour after I posted for help. I still don't understand why the value went below 0 though?

Thanks for your help,
Nathan