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What is the TPA rate in BetaFlight?

Jun 28, 2024 HuYuan

When you adjust your PID in Betaflight, you will check a function, TPA rate. But some pilots will be curious about it, what is the TPA rate? When we adjust it, how it will influence our drone?

The TPA stands for Throttle PID Attenuation. TPA is a mechanism that dynamically attenuates a certain parameter in the PID according to the position of our throttle. The default attenuation of this mechanism is the D term. TPA allows an aggressively tuned multi-rotor (one that feels very locked in) to reduce its PID gains when the throttle is applied beyond the TPA threshold/breakpoint to eliminate fast oscillations.

Taking Betaflight 4.4.2 and 4.4.3 as an example, the default attenuation D term is the dampening. So why is this dampening attenuated? Because the dampening will amplify the gyroscope noise, and the high-throttle gyro noise of the drone is much larger than that of the low-throttle gyro.

These data can all be seen through black box data. For example, a gyroscope noise map, where debug is the original noise of the gyroscope. The brightest line below represents the interval with the highest noise. It gradually increases as we increase the throttle.

Only by correctly setting our TPA can we ensure the attenuation of the D term so that our high-throttle gyro noise will not have a very serious impact on our flight. Now Betaflight's latest version of the TPA is to attenuate the D term to prevent high-frequency noise from affecting the stability of our flight. Pay attention to the TPA rate option in the TPA throttle. TPA rate refers to the slope at which the P and D term is attenuated when your throttle value exceeds the starting point of TPA, such as 1350. For example, if we set the TPA rate to 0.65, then when the throttle is finally full, the P and D term will attenuate to the original 1 minus 0.65, which is 0.35, a ratio of 35%. Relevant instructions are also mentioned in Betaflight's Wiki: https://betaflight.com/docs/development/PID-tuning#tpa-and-tpa-breakpoint.

As shown in the figure below, TPA EFFECT on PIDs, when TPA breakpoint is equal to 1250, our throttle value exceeds 1250. Then use 0.6 as the slope to attenuate our PID value. Finally, at full throttle, it will decrease to 40%. That's 1 minus 0.6 equals 0.4, means 40%.

 

So how to adjust it specifically?

If your drone has obvious vibration in the high-throttle, but the PID performs well in the low-throttle, you can consider increasing the TPA rate to increase the slope, so that the attenuation will be greater at full throttle. If your drone with full throttle is relatively bumpy and the control and operation are not smooth, then you can reduce the TPA rate accordingly so that the PID term will not attenuate so much when the throttle is full.

By the way, we also receivced some beginner's contact, about where can find the black box analyze tool and betaflight files. Please check below links

Blackbox analyser: https://gitlab.com/bibitte/androidblackboxanalyser

Betaflight: https://github.com/betaflight/betaflight-configurator/releases/tag/10.9.0

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