This tutorial explains the differences between RC Rate, Expo, Super Rate, as well as Throttle Expo and Throttle Mid, how these settings affect the performance of a quadcopter, and some tips on how to set them up.
You might be also interested in PID tuning.
The combination of RC Rate and Super Rate determines “max angular velocity” – how fast the drone is allowed to rotate (measured in degrees per second). Expo changes the sensitivity in centre stick. Note that while Super Rate changes max velocity, it also has an effect on centre stick sensitivity too.
Still don’t get it? No worries, let me explain in a bit more detail.
RC rate changes the sensitivity of your sticks. High rates makes your quad rotate more with less stick deflection.
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 spins faster, as you can see an increase in deg/sec figure. This allows you to do faster flips and rolls as well, but usually we use “super rate” to control how fast we want our flips and rolls to be, we will talk about super rate shortly.
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), while retaining the maximum rotation speed at the ends of the stick.
Expo is a percentage value. 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 speed.
As you increase Expo, the sensitivity around mid stick is reduced so you have to push the stick further to reach the same 50% of max rotational speed. 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) changes your full-stick-deflection rate as well as your centre stick precision. It’s like having the combined effects of RC Rate and RC Expo.
By increasing Super Rate, it allows you to have relatively moderate stick sensitivity around mid stick for “normal flying maneuvers”, and yet super fast roll and flip at the stick end points.
It gives you more flexibility over tuning and control. It must be adjusted together with RC Rate and RC Expo to achieve the desired curve and stick feel.
Actual Rate & Quick Rate in Betaflight
These are two new types of rate system in Betaflight.
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.
What RC Rate, Expo and Super Rate to use?
This is really a personal preference, it’s all about finding what works for your flying style. I use these rates/expo on my freestyle quad:
- RC Rate – 1.3
- RC Expo – 0.25
- Super Rate – 0.68
To find your own rate and expo, here is what you can do.
I always adjust RC Rate first. Just cruise around (no flips or rolls), and make sure the quadcopter respond quickly enough to the sticks when doing turns. Not fine adjustment, but general stick movements.
Then I increase or decrease Super Rate until I am happy with the max rotation speed (doing flips and rolls). You can also check in the GUI, what deg/sec you prefer. For me I prefer around 800 deg/sec. Note that Super Rate also affects your centre stick sensitivity, so you might need to fine tune your RC Rate afterwards…
Now you can do some precise/smooth flying with very little movement around mid stick. Adjust RC Expo until you find a good balance between precision and responsiveness.
You might need to go back and forth a few times to get the right feel :)
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.
Pro Tip: Applying Expo on the radio (TX) reduces your stick resolution, therefore ONLY set Expo in the flight controller software whenever possible!
To give you some examples, here are the Rates and Expos I used to use:
- RC Rate = 0.80
- Super Rate = 0.65
I don’t use expo for smooth flying, to avoid overreacting in close situations.
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
As your flying skill improves, and you become more comfortable performing aggressive maneuvers, you will probably increase your rates. As you do, you will also probably want to adjust (increase) the 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.
- Sep 2015 – Article created
- Mar 2018 – Article updated
- Mar 2021 – Added info about new feature in Betaflight: Actual Rate and Quick Rate