In this article I will explain what Setpoint Weight and Transition are, and how you should tune these settings in Betaflight. I will also touch on the different flight characteristics of “derivative of error and measurement”, which are closely related.
Take a look at my PID explained article if you haven’t already, where I will also show you how I tune my PID.
To understand the setting “Set-point Weight”, it helps to get a basic understanding of what the “Derivative of Error” and “Derivative of Measurement” are. Here is a basic introduction to what “derivative of error”, where i also explain why excessive D gain causes oscillations.
Derivative of “Error” vs. “Measurement”
During the development of Betaflight, we once were given an option to either use “Derivative of Error”, or “Derivative of Measurement”. These are the two methods of deriving D value in the PID controller, and they can greatly affect your quad’s flight characteristics, specifically in terms of smoothness and responsiveness.
I will refer to these two methods as “Error” and “Measurement” in the rest of the article.
D term on Error gives you sharper stick response but rougher motors, while Measurement gives you softer stick response with smoother running motors.
You may have seen RC command without interpolation in a blackbox log, it looks like a jagged trace as shown in the image below which is completely normal by the way. This is what we believe that can make the most noticeable difference between Error and Measurement.
The reason that Error feels so direct and twitchy could be that RC command is stepped. Because every step is a big change in Setpoint which creates a sudden error, and this causes what is called a “D term kick”.
Every D term kick gives the motors a sudden push, and you can get lots of “D term kicks” from moving your sticks because you are basically changing your set-point rapidly and constantly. This makes the control feel very snappy and responsive, but also rougher.
D term from measurement avoids “D term kick” as mentioned above, therefore it feels less snappy but smoother.
Which one is better?
The main difference between the two can be noticed when you are moving your sticks rapidly e.g. doing acro moves or bank turns etc. However, there is little to none difference when you are not moving the sticks.
It’s been suggested that racers might prefer Error and freestyle pilots might prefer Measurement, anyway, I am sure everyone has a different preference.
But why do we have to choose when we can have the best of both worlds? That’s why Setpoint Weight was introduced.
Setpoint Weight Explained
“Setpoint Weight” in Betaflight is a sliding scale between the two D term methods we mentioned above, so you can have it exactly where you want it between smoothness and responsiveness.
- Setpoint weight of 1 = error
- Setpoint weight of 0 = measurement
You can actually set Setpoint weight way higher than 1, up to 2.55, which will make stick response ultra fast and movement more crispy. The downside of going high on Setpoint Weight is every time you move your stick, it produces a sharp movement, which is often described as being “robotic”, “twitchy” and “stiff” which is undesirable in FPV Freestyle.
What I also found is that Setpoint Weight can affect your Rates and Expo a little as you pass 1, so you might want to fine tune those settings too.
Tuning Setpoint Weight
Setpoint Weight only has an effect when you are moving your sticks, they don’t do anything when your sticks are idle, so make sure to do lots of acro moves when tuning Setpoint Weight.
My personal recommendation is to play around between 0.3 to 2, remember there is no wrong value as long as you like it.
Setpoint Transition Explained
“Setpoint Transition” works on top of “Setpoint Weight”, it’s like a percentage scale of how fast you want to transition from one stick movement into the next one.
In simple words, high transition value (close to 1) will make the quad accelerate into the next move more aggressively, while low transition value (close to 0) will feel slower, mushier, but smoother between stick movement.
Setpoint Transition can “fix” bounces!
Note that low “Setpoint Transition” value can decrease the influence of “Setpoint Weight” when the stick is returning back to the centre.
Putting it more simply, lowering Setpoint Transition can give you a nicer, smoother stop. If you are getting a bounce-back when doing a flip or roll, try lowering your transition value :) It’s kind of like adding D gain except you won’t introduce vibration in your motors.
Tuning Setpoint Transition
Again, Setpoint Transition only has an effect when you are moving your sticks, they don’t do anything when your sticks are idle.
When tuning, I recommend leaving Setpoint Transition at 1, and tune Setpoint Weight first. Also tune your D term to minimize prop wash, and finally use Setpoint Transition to minimize the bounces. This will allow you to have the lowest possible D term, yet gives you smoother and cleaner stops at flips and rolls.
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