Update PID tuning.md

docs/PID tuning.md

@@ -29,6 +29,24 @@ changing slowly (so the P and I terms aren't having enough impact on reaching th
 in the correction in order to reach the target sooner. If the error is rapidly converging to zero, the D term causes the
 strength of the correction to be backed off in order to avoid overshooting the target.
 
+##TPA and TPA Breakpoint
+
+* Note that TPA is set via CLI or on the PID TUNING tab of the GUI.  tpa_breakpoint is set via CLI
+
+TPA applies a 'P' value reduction in relation to full Throttle. It is used to 'soften' the P value at extream throttle which sometimes induces oscellation in the aircraft.
+
+An Example: With TPA = 50 (or .5 in the GUI) and tpa_breakpoint = 1500
+
+At full throttle, your P value is reduced by 50%
+at 3/4 throttle (say 1750), your P value is reduced by 25% (1/2 the differnce of 1500 and 2000 = 1/2 of 50% = 25%)
+at half throttle (1500), your P vallue is reduced by ~0
+
+So how do you use this?
+
+If you're getting oscillations starting at say 3/4 throttle, set tpa breakpoint = 1750 or lower (remember, this is assuming your throttle range is 1000-2000), and then slowly increase TPA until your oscillations are gone. Usually, you will want tpa breakpoint to start a little sooner then when your oscillations start so you'll want to experiment with the values to reduce/remove the oscillations.
+
+In theory, this should allow you to bump your PIDs a tiny bit more because now you can focus your PID tune to how you fly and not have to worry about bringing it down some to compensate for high throttle oscillations.
+
 ## PID controllers
 
 Cleanflight has 6 built-in PID controllers which each have different flight behavior. Each controller requires