Motor Mixers and Thrust Linearization

Table of contents

1. Motor Mixers and Thrust Linearization
   1. 0.4.0+
   2. Motor Output Mixer - Options for the controller’s motor output. New smooth variants change how the axes are mixed with throttle.
   3. Thrust Linearization - Compensation for inherent non-linearity of thrust and rpm of motor output.
   4. Suggested starting values for Thrust Linearization:

Motor Mixers and Thrust Linearization

0.4.0+

The new mixers and linearizations are independent functions but may be used together to provide a preferred fly-style. Code and ideas from Tyler Corleone and QuickFlash.

Motor Output Mixer - Options for the controller’s motor output. New smooth variants change how the axes are mixed with throttle.

• LEGACY is the mixer we have always had. (Note: for 100% legacy-mode, linear_throttle should be OFF and linear_thrust_high_output should be 0; However, pilots are welcome to use both Thrust-Linearization and Throttle-Linearization.)
• SMOOTH is a simple variant that applies smoother transitions to avoid mixer-output clipping.
• 2PASS is a SMOOTH variant that mixes yaw and roll/pitch separately in order to try to guarantee thrust linearity for roll and pitch and motor output linearity (almost RPM linearity) for yaw.
• mixer_laziness ON/OFF. When ON, requires Thrust-Linearization values configured (>0). Both SMOOTH and 2PASS can use an option called “laziness” that enables a smarter “clipping prevention” strategy, that is called lazy because it adds only the minimum required amount of offset to remain in the [0, 1] for each “motor group” (that is a group of opposite motors that can actually work in conjunction in order to obtain a certain amount of roll/pitch) instead of applying the biggest needed amount. In this way we avoid to add/increase the total thrust when not needed, obtaining a better “throttle authority”.
• mixer_yaw_throttle_comp compensate throttle for increased motor output during aggressive yaw maneuvers. This option applies only to 2PASS. LEGACY does not suffer from the issue. SMOOTH still suffers from the issue.

# get mixer

mixer_impl = 2PASS
Allowed values: LEGACY, SMOOTH, 2PASS
Default value: 2PASS

mixer_laziness = ON
Allowed values: OFF, ON
Default value: OFF

mixer_yaw_throttle_comp = ON
Allowed values: OFF, ON

Select the Mixer Implementation here:

Thrust Linearization - Compensation for inherent non-linearity of thrust and rpm of motor output.

• Two settings: linear_thrust_low_output for low motor output (low RPM) and linear_thrust_high_output for high motor output (high RPM). Use this tool to understand what you need to set (65/30 are good starting points for low and high output) https://www.desmos.com/calculator/ofaiocun0b
• Both values need to be != 0 (not zero) for TL being applied.
• linear_throttle gives you a linear throttle/thrust feeling. The hovering level will be lower (e.g. what before was 30% now could be 20%). This means that you need to be used to this before you can appreciate its advantages (more room on the upper part of the throttle)
• TPA is automatically disabled when TL is enabled because it already solves high throttle issues.

# get linear

linear_thrust_low_output = 65
Allowed range: 0 - 100

linear_thrust_high_output = 30
Allowed range: 0 - 100
Default value: 0

linear_throttle = ON
Allowed values: OFF, ON
Default value: OFF

For more information, please see all notes, graphs and discussions in the Pull Request: https://github.com/emuflight/EmuFlight/pull/398

To enable Thrust Linear, these three items must be set:

Suggested starting values for Thrust Linearization:

• When over-propping, lower these values some points.
• When under-propping, raise these values some points.
• Such will affect linear_thrust_low_output more. Tune values as needed based on P-Term overshoot or undershoot.

* Credit to Ryan Harrel (MiniQuad Bench Test), Ethan Bayer (Micro Motor Test Lab) for the thrust curve data from which these values were derived. Thanks to DrSchnickistein and EmuTestBandits for value recommendations.

@nerdCopter Tip: Recommend LEGACY or SMOOTH for cinematic aircraft. Recommend LEGACY or 2PASS+Laziness for racing and freestyle. Recommend tuned Thrust-Linearization (Use the table for deducing good values and tune as needed). Throttle-Linearization will depend on the aircraft and pilot preference as the throttle hover-point may be reduced too much on some craft.