Litchi: Question and caution

Jack Daw · Jun 5, 2018

Was flying a Litchi mission downtown last night. Video signal went out with some ways left to go. Fine: I expected that. It came back up again as my MA was about 20 feet in front of an office tower window (a Google office, no less), and flying towards it. Luckily, I had time to pull it back manually and then send it home.

My question: Do Waypoint missions allow for use of obstacle avoidance? If I hadn't seen it in time, would it have crashed into the side of the building?

My caution: Don't always trust Google maps to tell you where the buildings lie, and how tall they are. In cities with building booms, like mine, they can be out of date very quickly.

lisadoc · Jun 5, 2018

Jack Daw said:
My question: Do Waypoint missions allow for use of obstacle avoidance? If I hadn't seen it in time, would it have crashed into the side of the building?

To answer your two questions: Yes. And no.

If you have OA set in your settings, it will operate even in waypoint missions. So even if the Mavic is out of range/signal, it should avoid those obstacles if they are in the flight path. In real life, the sensors need to be able to see the obstacle in time. For a building, that's generally not an issue. For something smaller (like a branch), you never know.

Pro Tip: if flying a waypoint mission out of RC range and with OA sensors enabled, be sure that you're not flying into the sun low on the horizon along the flight path. You may send your Mavic out with the setting sun to your back, and it may never return... due to the fact that it thinks it's going to hit an obstacle when flying home.

Logger · Jun 7, 2018

If you are using Focus POI and have POIs scatted along the mission there is a good chance the Drone will not be pointing in the direction of travel. Don’t expect OA to work when it is not facing forward.
Having OA set on limits max mission speed to ~22mph. With it off it is ~ 33 mph.
As Lisa mentioned OA can get fooled by the sun when iit is low in the sky.
For these 3 reason I always fly my Litchi Missions with OA off. The trade off is it is incumbent on me to ensure I correctly plan the mission to clear all obstacles and that I set RTH height appropriately as well.

lisadoc · Jun 7, 2018

Logger said:
Having OA set on limits max mission speed to ~22mph. With it off it is ~ 33 mph

For "long" missions, especially ones where you need to fly a significant distance to get to the target area, this can dramatically reduce the overall mission time, as the Mavic can "cruise" at higher speeds to get to your first point of interest (and back).

Pro Tip #2: If you've set the higher cruise speed and expect to lose RC signal, you might wish to reconsider, as without an uplink in Litchi, the Mavic will retain the last known speed it had before losing signal (as well as gimbal angle), meaning that you may get to your film location and speed around the area you want to film at full cruise speed (~ 33 mph), and then head on back. It also means that your calculated mission time (as shown in Mission Hub), will actually be far less than expected, as it whips around your mission course at full speed.

Pro Tip #3: The same goes for losing signal at slower speeds (with opposite effect). If you are flying a mission, ended up going slow, then lost signal, expecting to speed up to move to another area, and then return, you'll have a much longer mission time than calculated, as the aircraft retains the last, much slower speed. You may be in for a not-so-welcome surprise if you were counting on the extra battery to RTH or finish the mission.