我的飞控是Foxeer F722 V2 飞控，看到它支持INAV，但是我忘了检查是否支持气压计（因为很多飞控都支持，就想当然的以为它也支持），结果发现它是没有气压计的。气压计可以检测高度，这个在自动返航(RTH)时很重要。上次测试时我不知道没有气压计，就执行了RTH，但飞行器没有任何反应。飞行器高度一直都是“0米”。我猜测可能是没有气压计的原因，所以RTH失败。为了弄清楚这个问题，我查阅了官方资料，这部分的内容如下：
官方文档：
inav/Navigation.md at master · iNavFlight/inav (github.com)
NAV RTH – return to home mode
Home for RTH is the position where vehicle was first armed. This position may be offset by the CLI settings
nav_rth_home_offset_distanceandnav_rth_home_offset_direction. This position may also be overridden with Safehomes. RTH requires accelerometer, compass and GPS sensors.If barometer is NOT present, RTH will fly directly to home, altitude control here is up to pilot.
If barometer is present, RTH will maintain altitude during the return. When home is reached, a copter will attempt automated landing. An airplane will either loiter around the home position, or attempt an automated landing, depending on your settings. When deciding what altitude to maintain, RTH has 6 different modes of operation (controlled by nav_rth_alt_mode and nav_rth_altitude cli variables):
- 0 (NAV_RTH_NO_ALT) – keep current altitude during whole RTH sequence (nav_rth_altitude is ignored)
- 1 (NAV_RTH_EXTRA_ALT) – climb to current altitude plus extra margin prior to heading home (nav_rth_altitude defines the extra altitude (cm))
- 2 (NAV_RTH_CONST_ALT) – climb/descend to predefined altitude before heading home (nav_rth_altitude defined altitude above launch point (cm))
- 3 (NAV_RTH_MAX_ALT) – track maximum altitude of the whole flight, climb to that altitude prior to the return (nav_rth_altitude is ignored)
- 4 (NAV_RTH_AT_LEAST_ALT) – same as 2 (NAV_RTH_CONST_ALT), but only climb, do not descend
- 5 (NAV_RTH_AT_LEAST_ALT_LINEAR_DESCENT) – Same as 4 (NAV_RTH_AT_LEAST_ALT). But, if above the RTH Altitude, the aircraft will gradually descend to the RTH Altitude. The target is to reach the RTH Altitude as it arrives at the home point. This is to save energy during the RTH.
可以看到，官方说没有气压计的话，高度无法控制，飞行器将会直接返航，而不是先爬升高度。高度需要人为控制。这说明飞行器还是可以自动返航的，而不是没有反应。因此我还需要再做一次测试。
2022.07.15 外出测试，结果发现，没有气压计的话，RTH等模式是无法启用的，即遥控器拨杆切换到RTH模式或者定点模式的话，飞机是没有任何反应的，类似于这个功能不存在一样。飞机还会照样接受控制，但这两个模式完全无效。
不知道是GPS的问题，还是说没有气压计就压根不会启动RTH，需要我更换一个飞控后再做测试。
2022.07.20 准备换飞控测试时，想到可否外置气压计呢？于是找到了这个模块，才一块多，觉得可以买回来安装上测试一下。又看到有一个教程，说到没有气压计时，需要使用以下命令之后才能实现无气压计返航，视频地址：INAV4.1调参教程（三）：定高定点和自动返航_哔哩哔哩_bilibili。
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set inav_use_gps_no_baro=ON |
这样才能没有气压计时启用返航，否则是无效的。
