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154 lines
8.7 KiB
Markdown
154 lines
8.7 KiB
Markdown
# Multicopter Racer Setup
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This page describes how to setup and configure a multicopter racer for optimal performance (in particular for [Acro mode](../flight_modes_mc/acro.md)).
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Keep in mind that racers are fast vehicles, specifically designed to be overpowered!
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You should already have some experience, or let someone with experience help you.
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::: tip
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Many things described here can also be applied to improve the flight performance of other types of multicopters.
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:::
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::: info
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A racer usually omits some sensors (e.g. GPS).
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As a result, fewer failsafe options are available.
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:::
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## Build Options
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A racer usually omits some sensors.
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The minimal configuration is to use only a gyro and accelerometer sensor.
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::: info
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If the board has an internal magnetometer, it should not be used (small racers are particularly prone to strong electromagnetic interference).
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:::
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Racers typically do not have a GPS as it adds some weight and is prone to damage during crashes (a GPS + external magnetometer must be placed on a GPS mast away from high currents to avoid magnetic interference, which unfortunately means that it is easy to break).
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There are however some benefits in adding GPS, particularly for beginners:
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- You can go into position hold and the vehicle will just stay in one place.
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This is handy if you lose the orientation or need a brake.
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It can also be used to land safely.
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- [Return mode](../flight_modes_mc/return.md) can be used, either on a switch or as RC loss/low battery failsafe.
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- You will have the last position when it crashes.
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- The log contains the flight track, which means you can review the flight (in 3D).
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This can help to improve your acrobatic flight skills.
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::: info
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During aggressive acrobatic maneuvers the GPS can lose its position fix for a short time.
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If you switch into [position mode](../flight_modes_mc/position.md) during that time, [altitude mode](../flight_modes_mc/altitude.md) will be used instead until the position becomes valid again.
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:::
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## Hardware Setup
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The following paragraphs describe a few important points when building the vehicle.
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If you need complete build instructions, you can follow the [QAV-R 5" KISS ESC Racer](../frames_multicopter/qav_r_5_kiss_esc_racer.md) build log.
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### Vibration Setup
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There are various mounting approaches to reduce vibrations.
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For example, the flight controller can be mounted with vibration dampening foam, or using [O-rings](../frames_multicopter/qav_r_5_kiss_esc_racer.md#mounting).
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While there is no single best method, you will typically have fewer problems with vibrations if you use high-quality components (frame, motors, props) as for example used in the [QAV-R 5" KISS ESC Racer](../frames_multicopter/qav_r_5_kiss_esc_racer.md).
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Make sure to use **balanced props**.
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### Center of Gravity
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Make sure that the center of gravity is as close as possible to the center of thrust.
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Left-right balance is usually not a problem, but front-back balance may be.
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You can move the battery until it is correct and mark it on the frame so you will always place it correctly.
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::: info
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The integral term can account for an imbalanced setup, and a custom mixer can do that even better.
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However it is best to fix any imbalance as part of the vehicle setup.
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:::
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## Software Setup
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After having built the racer, you will need to configure the software.
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Go through the [Basic Configuration Guide](../config/index.md).
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In particular, set the [Airframe](../config/airframe.md) that most closely matches your frame (typically you will choose the [Generic 250 Racer](../airframes/airframe_reference.md#copter_quadrotor_x_generic_250_racer) airframe, which sets some racer-specific parameters by default).
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These parameters are important:
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- Enable One-Shot or DShot by selecting the protocol for a group of outputs during [Actuator Configuration](../config/actuators.md).
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- Set the maximum roll-, pitch- and yaw rates for Stabilized mode as desired: [MC_ROLLRATE_MAX](../advanced_config/parameter_reference.md#MC_ROLLRATE_MAX), [MC_PITCHRATE_MAX](../advanced_config/parameter_reference.md#MC_PITCHRATE_MAX) and [MC_YAWRATE_MAX](../advanced_config/parameter_reference.md#MC_YAWRATE_MAX).
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The maximum tilt angle is configured with [MPC_MAN_TILT_MAX](../advanced_config/parameter_reference.md#MPC_MAN_TILT_MAX).
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- The minimum thrust [MPC_MANTHR_MIN](../advanced_config/parameter_reference.md#MPC_MANTHR_MIN) should be set to 0.
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### Estimator
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If you use a GPS you can skip this section and use the default estimator.
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Otherwise you should switch to the Q attitude estimator, which works without a magnetometer or barometer.
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To enable it set [ATT_EN = 1](../advanced_config/parameter_reference.md#ATT_EN), [EKF2_EN =0 ](../advanced_config/parameter_reference.md#EKF2_EN) and [LPE_EN = 0](../advanced_config/parameter_reference.md#LPE_EN) (for more information see [Switching State Estimators](../advanced/switching_state_estimators.md#how-to-enable-different-estimators)).
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Then change the following parameters:
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- Set [SYS_HAS_MAG](../advanced_config/parameter_reference.md#SYS_HAS_MAG) to `0` if the system does not have a magnetometer.
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- Set [SYS_HAS_BARO](../advanced_config/parameter_reference.md#SYS_HAS_BARO) to `0` if the system does not have a barometer.
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- Configure the Q estimator: set [ATT_ACC_COMP](../advanced_config/parameter_reference.md#ATT_ACC_COMP) to `0`, [ATT_W_ACC](../advanced_config/parameter_reference.md#ATT_W_ACC) to 0.4 and [ATT_W_GYRO_BIAS](../advanced_config/parameter_reference.md#ATT_W_GYRO_BIAS) to 0.
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You can tune these later if you wish.
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### Failsafe
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Configure [RC loss and low battery failsafe](../config/safety.md).
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If you do not use a GPS, set the failsafe to **Lockdown**, which turns off the motors.
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Test RC loss on the bench without props attached by turning off the remote when the vehicle is armed.
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Make sure to assign a [kill switch](../config/safety.md#kill-switch) or an [arming switch](../config/safety.md#arm-disarm-switch).
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Test it and train to use it!
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### PID Tuning
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::: info
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Make sure to calibrate the ESCs before doing any tuning.
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:::
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At this point you should be ready for a first test flight.
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Assuming the vehicle is able to fly using the default settings, we then do a first pass of [Basic MC PID tuning](../config_mc/pid_tuning_guide_multicopter_basic.md).
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The vehicle needs to be **undertuned** (the **P** and **D** gains should be set too low), such that there are no oscillations from the controller that could be interpreted as noise (the default gains might be good enough).
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This is important for the [filter tuning](#filter-tuning) (there will be a second PID tuning round later).
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### Control Latency
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The _control latency_ is the delay from a physical disturbance of the vehicle until the motors react to the change.
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:::tip
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It is _crucial_ to reduce the control latency as much as possible!
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A lower latency allows you to increase the rate **P** gains, which means better flight performance.
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Even one millisecond added to the latency makes a difference.
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These are the factors that affect the latency:
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- A soft airframe or soft vibration mounting increases latency (they act as a filter).
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- [Low-pass filters](../config_mc/filter_tuning.md) in software and on the sensor chip trade off increased latency for improved noise filtering.
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- PX4 software internals: the sensor signals need to be read in the driver and then pass through the controller to the output driver.
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- The IO chip (MAIN pins) adds about 5.4 ms latency compared to using the AUX pins (this does not apply to a _Pixracer_ or _Omnibus F4_, but does apply to a Pixhawk).
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To avoid the IO delay attach the motors to the AUX pins instead.
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- PWM output signal: enable [Dshot](../peripherals/dshot.md) by preference to reduce latency (or One-Shot if DShot is not supported).
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The protocol is selected for a group of outputs during [Actuator Configuration](../config/actuators.md).
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### Filter Tuning
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Filters trade off control latency and noise filtering, both of which impact performance.
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For information see: [Filter/Control Latency Tuning](../config_mc/filter_tuning.md)
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### PID Tuning (Second Round)
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Now do a second round of PID tuning, this time as tight as possible, and also tuning the thrust curve.
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:::tip
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You can use the approach described in [Basic MC PID tuning](../config_mc/pid_tuning_guide_multicopter_basic.md) to tune the frame, but you will need to use the [Advanced Multicopter PID Tuning Guide (Advanced/Detailed)](../config_mc/pid_tuning_guide_multicopter.md#thrust-curve) to understand how to tune the thrust curve.
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### Airmode
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After you have verified that the vehicle flies well at low and high throttle, you can enable [airmode](../config_mc/pid_tuning_guide_multicopter.md#airmode) with the [MC_AIRMODE](../advanced_config/parameter_reference.md#MC_AIRMODE) parameter.
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This feature makes sure that the vehicle is still controllable and tracks the rate at low throttle.
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