[theDoctor]

We're using unsigned ints. The values when we have strange behavior go above 32766. That's just the last number I wrote down when I was testing the arm.

This is most of our arm routine. (Probably more than you wanted to see--sorry.)

 static unsigned char enable = 0;
 
 void arm_positioning(void)
 {
 	static short use_manual_control_shoulder = 1, use_manual_control_elbow = 1;
 
 	if(arm_sw_freeze == 1)	//Make the arm stop moving
 	{
 		enable = 0;
 		use_manual_control_shoulder = use_manual_control_elbow = 0;
 	}
 
	if(oi_shoulder_sw_fwd)
 	{
 		cylinder_fwd = 0;
 		cylinder_rev = 1;
 		shoulder_target = Get_Shoulder_Pos();
 		use_manual_control_shoulder = 1;
 	}
 	else if(oi_shoulder_sw_rev)
 	{
 		cylinder_fwd = 1;
 		cylinder_rev = 0;
 		shoulder_target = Get_Shoulder_Pos();
 		use_manual_control_shoulder = 1;
 	}
 	
 	
 	if(oi_elbow_sw_fwd)
 	{
 		arm_motor = 127 + arm_speed;
 		elbow_target = Get_Elbow_Pos();
 		use_manual_control_elbow = 1;
 		enable = 1;	//Allow arm to move again, if it was turned off.
 	}
 	else if(oi_elbow_sw_rev)
 	{
 		arm_motor = 127 - arm_speed;
 		elbow_target = Get_Elbow_Pos();
 		use_manual_control_elbow = 1;	
 		enable = 1;	//Allow arm to move again, if it was turned off.
 	}
 
 	// manual positioning, but no movement commanded; hold cylinder in place
 	if (!oi_shoulder_sw_fwd && !oi_shoulder_sw_rev
 		&& use_manual_control_shoulder)
 	{
 		cylinder_fwd = 0;
 		cylinder_rev = 0;
 		enable = 1;
 	}		
 
 	if (!oi_elbow_sw_fwd && !oi_elbow_sw_rev
 		&& use_manual_control_elbow)
 	{
 		arm_motor = 127;
 		enable = 1;
 	}		
 
 
 	if(!use_manual_control_shoulder && !use_manual_control_elbow)
 		position_arm(shoulder_target, elbow_target);
 
 	printf("Manual FWD: %d REV: %d, Shldr Trgt: %u, Elb Trgt: %u, Shldr: 0x%04x, Elbow: 0x%04x\n",
 	oi_shoulder_sw_fwd, oi_shoulder_sw_rev, shoulder_target, elbow_target, Get_Shoulder_Pos(), Get_Elbow_Pos()); 
 	printf("Shoulder Pot: %u, Elbow Pot: %u, Cylinder Values FWD: %d REV: %d\n", 
 	Get_Shoulder_Pos(), Get_Elbow_Pos(), cylinder_fwd, cylinder_rev);
 
 }
 
 
 
 void position_arm(unsigned int shoulder_target, unsigned int elbow_target)
 {
 	//This gets changed a few lines later if enable is on.
 	arm_motor = 127;
 	cylinder_fwd = cylinder_rev = 0;
 	
 	if (enable)
 	{
 		if(Get_Shoulder_Pos() < (shoulder_target - SHOULDER_DEADBAND))
 		 {
 			cylinder_fwd = 1;
 			cylinder_rev = 0;
 		}
 		else if(Get_Shoulder_Pos() > (shoulder_target + SHOULDER_DEADBAND))
 		{
 			cylinder_fwd = 0;
 			cylinder_rev = 1;
 		}
 		else
 		{
 			cylinder_fwd = cylinder_rev = 0;
 		}
 
 
 		if(Get_Elbow_Pos() < (elbow_target - ELBOW_DEADBAND))
 		{
 			arm_motor = 127 + arm_speed;
 		}
 		else if(Get_Elbow_Pos() > (elbow_target + ELBOW_DEADBAND))
 		{
 			arm_motor = 127 - arm_speed;
 		}
 	}
 
 }
 
 unsigned int Get_Shoulder_Pos()
 {
 	return Get_Analog_Value(robot_shoulder_pot);
 }
 
 unsigned int Get_Elbow_Pos()
 {
 	return Get_Analog_Value(robot_elbow_pot);
 }