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.
RC rate is the setting that controls the speed at which your quad rotates on a given axis (pitch, roll or yaw) for the TX stick travel. Betaflight ties RC Rate for Roll and Pitch together with a separate setting for Yaw.
Think of RC rate as the stick sensitivity setting, if you increase RC rate, your quad will respond more aggressively to your stick inputs.
High rate will make your quad more responsive and twitchier, small movement on the stick would produce big movement in the quad.
Exponential, or Expo, 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 abit like having the combined effect of RC Rate and RC Expo.
By increasing Super Rate, it allows you to have relatively moderate stick sensitivity around mid sticks 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, but you have to play around with RC Rate, Expo and Super Rate back and forth to achieve the desired curve while still maintaining the desired full-deflection rate that you like.
How to Tune RC Rate, Expo and Super Rate?
This is really a personal preference, it’s all about finding what suits you the best.
With any new quad, I always tune RC Rate first. Just cruise around (no flips or rolls), and make sure the quadcopter respond quickly enough to the sticks.
Then I increase or decrease Super Rate until I am happy with the speed of rotation for acrobatics. Note that Super Rate also affects your centre stick sensitivity, so you might need to fine tune your RC Rate afterwards… You might need to go back and forth a few times to get the right feel :)
You can aim for a max rotational rate desirable to your. For me it’s around 900 to 1000 deg/sec. If the sticks are still too twitchy, you are lower RC Rate and increase Super Rate to dame the response around mid stick, yet maintaining the same max rotation speed.
Finally, if you are looking for more precision around mid stick, you might want to add some RC Expo.
Different flight controller software has different ranges and number scaling in PID, rates and expo, so the same numbers don’t necessarily give the same results on a different quad.
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 from two of my quads:
- RC Rate, Pitch/Roll = 0.82, Yaw = 0.86
- Super Rate, All = 0.80
- RC Expo, All = 0.03
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.
- Sep 2015 – Article created
- Mar 2018 – Article updated