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25 lines
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2.1 KiB
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25 lines
No EOL
2.1 KiB
Markdown
# INAV PID Controller
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What you have to know about INAV PID/PIFF/PIDCD controllers:
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1. INAV PID uses floating-point math
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1. Rate/Angular Velocity controllers work in dps [degrees per second]
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1. P, I, D and Multirotor CD gains are scaled like Betafligfht equivalents, but actual mechanics are different, and PID response might be different
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1. Depending on platform type, different controllers are used
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1. Fixed-wing uses **PIFF**:
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1. Error is computed with a formula `const float rateError = pidState->rateTarget - pidState->gyroRate;`
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1. P-term with a formula `rateError * pidState->kP`
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1. Simple I-term without Iterm Relax. I-term limit based on stick position is used instead. I-term is no allowed to grow if stick (roll/pitch/yaw) is deflected above threshold defined in `fw_iterm_limit_stick_position`. `pidState->errorGyroIf += rateError * pidState->kI * dT;`
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1. No D-term
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1. FF-term (Feed Forward) is computed from the controller input with a formula `pidState->rateTarget * pidState->kFF`. Bear in mind, this is not a **FeedForward** from Betaflight!
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1. Multirotor uses **PIDCD**:
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1. Error is computed with a formula `const float rateError = pidState->rateTarget - pidState->gyroRate;`
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1. P-term with a formula `rateError * pidState->kP`
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1. I-term
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1. Iterm Relax is used to dynamically attenuate I-term during fast stick movements
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1. I-term formula `pidState->errorGyroIf += (itermErrorRate * pidState->kI * antiWindupScaler * dT) + ((newOutputLimited - newOutput) * pidState->kT * antiWindupScaler * dT);`
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1. I-term can be limited when motor output is saturated
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1. D-term is computed only from gyro measurement
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1. There are 2 LPF filters on D-term
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1. D-term can by boosted during fast maneuvers using D-Boost. D-Boost is an equivalent of Betaflight D_min
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1. **Control Derivative**, CD, or CD-term is a derivative computed from the setpoint that helps to boost PIDCD controller during fast stick movements. `newCDTerm = rateTargetDeltaFiltered * (pidState->kCD / dT);` It is an equivalent of Betaflight Feed Forward |