全文转载自：RC Rate, Expo, Super Rate Explained
This tutorial explains what RC Rate, Expo and Super Rate are, and how to tune them for optimal FPV drone flying. I will also touch on Throttle Expo, Throttle Mid and TPA and how these settings can affect the performance of a quadcopter.
You might be also interested in PID tuning.
RC Rate determines “max angular velocity” – how fast the drone is allowed to rotate (measured in degrees per second). Expo changes the sensitivity around centre stick. Super Rate is like the combination of both RC Rate and Expo, it changes max velocity, but also has an effect on centre stick sensitivity just like Expo.
Don’t get it? No worries, let me explain in a bit more detail.
RC rate changes the slope of the rate curve linearly through out the whole stick range, and how fast the quadcopter rotates at full deflection. If you’re familiar enough with computers you can think of this as mouse sensitivity.
High rate will make your quad more responsive but at the same time, twitchier. Small movement on the stick would produce big movement in the quad. Increasing RC rate also makes the quad spin faster, as you can see an increase in deg/sec figure. This allows you to do faster flips and rolls as well.
Bear in mind that the maximum angular velocity can be limited by your motors. When the motors reach their physical limitation and simply cannot spin any faster, you have reached the maximum angular velocity even if you set it to a much higher value in Betaflight, which is just a theoretical number.
RC Expo is also known as Exponential, or simply Expo. It reduces the sensitivity near the centre of the stick where fine controls are needed (for Roll, Pitch and Yaw), but it does not change the maximum angular velocity at full stick.
Expo is a percentage value, it goes from 0% (0) to 100% (1). At 0% the increase in rotational speed between minimum and maximum stick input is linear, imagine the curve as a “V” shape with no stick input being the center. At 50% stick input, your quad will rotate around the given axis at exactly half of the maximum rotational velocity.
As you increase Expo, the sensitivity around mid stick is reduced so you’d have to push the stick further to reach the same rotational velocity. Imagine that Expo changes the “V” shape to a “U”, the higher the expo percentage, the flatter the “U” is around the middle.
Super Rate (aka Super Expo in other firmware) increases the max angular velocity as well as the sensitivity around center stick.
By increasing Super Rate, it allows you to have relatively moderate stick sensitivity around mid stick for “normal flying maneuvers”, and yet snappy roll and flip at the stick end points.
Super Rate is like having the combined effects of RC Rate and Expo, actually with Expo and RC rate you can mimic the effect of super rate:
So why use Super Rate? We can just use RC Rate and Expo right? Yes, sort of, but having Super Rate gives us more flexibility in achieving the stick feel we want.
Actual Rate & Quick Rate in Betaflight
These are two other rate systems in Betaflight: Actual Rate and Quick Rate.
With “Actual Rate”, you can enter exactly the max rotational speed, and center sensitivity value – it’s a lot more clear and less confusing for new comers to be honest than the old rate system.
And “Quick Rate” is the mix of the the traditional rate and Actual Rate. You still enter Rates and Expo but you can set the max rotational speed value directly.
If you are new to all these, I’d recommend using the default Betaflight rate system for now, until you know what is actually going on, then explore other rate system so you don’t get confused. And honestly it really doesn’t matter which rate system you use, there are many online rate converters to calculate these values for you.
How to Tune Your Rates?
Tuning rates is all about “feel” really and it’s just a personal preference.
Start with default Betaflight values: RC Rate 1.0, Super Rate 0.7, Expo 0 for all 3 axes.
When I tune my rates, I always adjust RC Rate first. Do some flips and rolls, if the quadcopter is spinning too slow then bump up RC Rate until you are happy with it. Write down the max angular velocity (deg/sec) in Betaflight Configurator. For my freestyle rig, I usually have around 700-800 degrees per second.
Now just cruise around (no flips and rolls), and make sure the quadcopter responds quickly and predictably to your sticks when doing turns. If it’s too sensitive to make precise movement increase Expo. But if it’s too slow to react (not sensitive enough), then you need to decrease Super Rate. But to compensate you also need to increase RC Rate to bring the max angular speed up.
Expo is not always needed, as you get the same effect from having Super Rate. But if you still find little movement around mid stick too sensitive, then increase Expo until you find a good balance between precision and responsiveness.
Pro Tip: Applying Expo on the radio (TX) reduces your stick resolution, therefore ONLY set Expo in the flight controller software whenever possible!
You might want to go back and forth a few times until it feels perfect to you. Note that your pitch, roll and yaw rates do not need to be identical. Many freestyle pilots actually prefer higher roll and yaw rates but lower pitch rate, it’s all personal preference.
Different flight controller software has different ranges and scaling in PID, rates and expo, so the same numbers don’t necessarily give the same results in a different firmware. You should be able to find online converters if you want to migrate to a different FC firmware.
To give you some examples, here are the Rates and Expos I used in the past:
- RC Rate – 1.3
- RC Expo – 0.25
- Super Rate – 0.68
- RC Rate = 0.80
- RC Expo = 0.00
- Super Rate = 0.65
Expo is set to zero here on purpose, this is to avoid overreacting in close situations and actually gives you overall smoother result.
Aggressive Acro Quad:
- RC Rate, Pitch/Roll = 1.80, Yaw = 2.00
- Super Rate, All = 0.64
- RC Expo, Pitch/Roll = 0.20, Yaw = 0.15
Tiny Whoop Rates
- Roll Pitch: RC Rate 1.2, Super Rate 0.75, Expo 0
- YAW: RC Rate 1.3, Super Rate 0.80 Expo 0
- If using acro mode, enable crash_recovery, there are some settings (get crash_ in CLI) you might want to tune first to avoid false self-centering.
As your flying skill improves, and you become more comfortable performing aggressive manoeuvres, you could try to crank up your rates. And you will also probably want to use a bit more expo to maintain accurate fine control.
There is no right or wrong Expo and Rate values, as long as it suits you. For example, I have shaky fingers, so my expo might be a bit higher than others. :p
Having consistent rates on all your quads is actually very important because of muscle memory. Especially for yaw and roll, you can train yourself to control these movements instinctively with consistent rates.
When you change rates, it can take you longer to get used to the different feel depends on how experienced a pilot you are. So having consistent rates help you moving from quad to quad without surprises.
Throttle Mid and Expo
Lastly, next to RC Rate and Expo, we also have Throttle Mid and Throttle Expo.
Throttle Expo changes the shape of the throttle curve, it flattens out the curve around “Throttle Mid” and allows for softer throttle response and maximum stick resolution around this throttle level.
Throttle Mid changes where in the throttle curve you want to apply the Throttle Expo. By default it’s set to 50% throttle (0.50), but in my opinion this should be set to your normal cruising throttle. This is where you will need the most throttle resolution and it should make it easier to control your altitude.
Throttle Mid won’t do anything if you set Throttle Expo to 0, because your throttle curve will be a straight line regardless what throttle mid is set to.
I personally prefer to use a tiny bit of throttle expo (<0.10) to get a better resolution and smoother throttle control. It’s especially useful for proximity flying.
You can also setup throttle curve in your transmitter for more precise throttle control.
TPA & TPA Breakpoint
TPA lowers PID values by a certain percentage, the more you increase throttle, the lower PID becomes. It helps reduce vibration associated with high throttle.
TPA breakpoint determines where in the throttle PID should begin to be reduced. You should normally set this slightly below the throttle level where you start to get vibration.
See this article for a more detail explanation of TPA.
- Sep 2015 – Article created
- Mar 2018 – Article updated
- Mar 2021 – Added info about new feature in Betaflight: Actual Rate and Quick Rate
- Sep 2022 – Updated screenshots, updated Rate Tuning instructions