AP_ServoRelayEvents: allow mavlink command of rcin scaled functions #25241
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Allow other modules to get and store the PWM value for a specific scaled value and re-apply it later.
Allow `MAV_CMD_DO_SET_SERVO` and `MAV_CMD_DO_REPEAT_SERVO` to be used on a servo output set to an RCINnScaled function (i.e. k_rcinN_mapped). Scaling is applied so that a commanded servo PWM of <=1000 maps to SERVOn_MIN, a PWM of 1500 maps to SERVOn_TRIM, and a PWM of >=2000 maps to SERVOn_MAX. Linear interpolation is performed between ranges.
IamPete1
reviewed
Oct 16, 2023
| // mapped channels are set up with a -/+ 4500 angle range by | ||
| // SRV_Channel::aux_servo_function_setup | ||
| int16_t angle_scaled = constrain_uint16(pwm, 1000, 2000); | ||
| angle_scaled = (angle_scaled - 1500) * 9; // 1000 ... 2000 -> -500 ... 500 -> -4500 ... 4500 |
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Suggested change
| angle_scaled = (angle_scaled - 1500) * 9; // 1000 ... 2000 -> -500 ... 500 -> -4500 ... 4500 | |
| angle_scaled = (angle_scaled - 1500) * (4500/500); // 1000 ... 2000 -> -500 ... 500 -> -4500 ... 4500 |
The compiler will evaluate it to 9 in any case and I think this makes it a little easier to understand.
tridge
approved these changes
Oct 16, 2023
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Allow
MAV_CMD_DO_SET_SERVOandMAV_CMD_DO_REPEAT_SERVOto be used ona servo output set to an RCINnScaled function (i.e. k_rcinN_mapped).
Scaling is applied so that a commanded servo PWM of <=1000 maps to
SERVOn_MIN, a PWM of 1500 maps to SERVOn_TRIM, and a PWM of >=2000 maps to
SERVOn_MAX. Linear interpolation is performed between ranges.
This allows control of servos/hardware with reasonable/safe scaling applied by firmware and allows more functionality from mission scripts.
In our use case we have a variable aperture controlled by a hobby servo for releasing crop seeds. The scaling is controlled by the mechanical geometry and programmed in the autopilot firmware so that SERVOn_MIN is fully closed and SERVOn_MAX is fully open. By setting the servo function to an RC scaled value, we can have straightforward controls from both an RC controller programmed to send 1000-2000 on a knob and mission scripts with that same range without danger of going overrange and damaging the mechanism or servo. This concept should extend logically to many other types of actuators one may wish to attach which don't fall under e.g. camera or sprayer headings.
Tested on SITL (on top of master) and on a real copter (on top of Copter-4.4.1).