# Failsafe Landing bug in PX4 1.14? Source: https://forum.modalai.com/topic/2533/failsafe-landing-bug-in-px4-1-14 Category: General Questions (https://forum.modalai.com/category/2/general-questions) Posted: 2023-08-04 12:21:56 UTC by hmlow Replies: 20 · Views: 6759 ## hmlow · 2023-08-04 12:21:56 UTC Hi devs I'm encountering an odd behavior with PX1.14 (SDK 1.0). Indoor flight with VIO. GPS antenna not attached. PX4 is configured to transit to Land when a link loss (not RTL) is encountered. 1. Takeoff the aircraft and move horizontally somewhere away from the takeoff point. 2. Close QGC application to simulate loss of link. 3. The aircraft goes into Land mode - but while the aircraft is descending, it translates in the direction of the takeoff point as well until it touches the ground. 4. Verified this by simulating loss of link at various positions relative to the takeoff point and it always translates in the direction of the takeoff location. I'm certain that this behavior wasn't present in 0.9.5. Failsafe Landing ought to be completely vertical. Anyone with any idea what is happening? ## Reply by hmlow · 2023-08-05 05:01:00 UTC After further testing, i can confirm that this behavior does not occur to failsafe landing only but **normal Landing mode** as well (ie. operator select flight mode). ## Reply by hmlow · 2023-08-08 16:18:31 UTC (in reply to hmlow) Anyone encountered this too? ## Reply by hmlow · 2023-08-14 14:58:06 UTC Hi Can i seek some assistance pls to look into this issue? Its a safety hazard when the aircraft translates in position while descending. I believe the same behavior is present on the Starlingv2 as well. Much appreciated. ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-14 19:21:34 UTC (in reply to hmlow) @hmlow We will try to replicate with a Starling ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-14 19:21:56 UTC (in reply to hmlow) @hmlow Do you have any logs that you can share? ## Reply by hmlow · 2023-08-15 09:13:25 UTC (in reply to Eric Katzfey) @Eric-Katzfey Yes pls refer to this ulg log: [horizontal translation while landing](https://1drv.ms/u/s!AuFM2Kf1Pu9rlUC02TyiQp3v_iqp?e=BIfnFl) I did a couple of landings in Land flight mode. The first and second landing was from a positive and negative x position (NED) with respect to the Home location, respectively. You will be able to see that during the descend, the aircraft translates in the x-axis toward the home location without any stick inputs from me. There are local position setpoints generated during the descent/translation, which suggests that it is a programmed behavior. I did a couple of more landings at various positions/orientations with respect to the Home location after that. ## Reply by hmlow · 2023-08-17 16:14:50 UTC (in reply to Eric Katzfey) @Eric-Katzfey Any luck? Does the log make sense to you? ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-17 17:21:56 UTC (in reply to hmlow) @hmlow We did a quick check with HITL simulation but in that case the landing is perfectly straight down every time. So we need to have our flight team recreate this with a real drone to see if it can be replicated but that will take a few days for them to get to it. ## Reply by hmlow · 2023-08-17 23:11:09 UTC (in reply to Eric Katzfey) @Eric-Katzfey Thanks keep me posted ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-17 23:32:55 UTC (in reply to hmlow) @hmlow Our flight team was able to recreate the issue today. Now we just need to figure out what is causing that to happen. ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-21 16:38:17 UTC (in reply to hmlow) @hmlow This seems like a fundamental bug in PX4 when dealing with EV modes so we're working with the PX4 developers to figure out who and how this will be addressed. ## Reply by hmlow · 2023-08-21 22:52:45 UTC (in reply to Eric Katzfey) @Eric-Katzfey thanks for the update. At least the issue has been identified. Looking forward to some fixes in the near future.. ## Reply by hmlow · 2023-08-29 01:11:22 UTC (in reply to Eric Katzfey) @Eric-Katzfey hi. Any progress on this? Thanks ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-29 14:36:51 UTC (in reply to hmlow) @hmlow Not really. I don't think anyone in the px4 community has time to assist on this so it's going to be up to ModalAI to fix it. Unfortunately, I can't offer any estimate on when we will be able to resolve this yet. ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-30 22:04:17 UTC (in reply to hmlow) @hmlow I have been able to recreate the issue in HITL with the Gazebo simulator so that should help with testing and investigation on this issue. ## Reply by hmlow · 2023-08-31 15:42:56 UTC (in reply to Eric Katzfey) @Eric-Katzfey that's good. Looking forward to the fix ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-31 21:54:12 UTC (in reply to hmlow) @hmlow This fixes it in HITL: ```$ git diff src/modules/navigator/mission_block.cpp diff --git a/src/modules/navigator/mission_block.cpp b/src/modules/navigator/mission_block.cpp index 565b2f2150..ac36732214 100644 --- a/src/modules/navigator/mission_block.cpp +++ b/src/modules/navigator/mission_block.cpp @@ -664,8 +664,8 @@ MissionBlock::mission_item_to_position_setpoint(const mission_item_s &item, posi return false; } - sp->lat = item.lat; - sp->lon = item.lon; + sp->lat = static_cast(NAN); + sp->lon = static_cast(NAN); sp->alt = get_absolute_altitude_for_item(item); sp->yaw = item.yaw; sp->yaw_valid = PX4_ISFINITE(item.yaw);``` ## Reply by Eric Katzfey (ModalAI staff) · 2023-08-31 21:55:46 UTC (in reply to hmlow) @hmlow But that probably only works for VIO mode. Not sure what it would do in GPS mode. So it isn't a fix that will be acceptable for general use. So it still needs more work but that is the heart of the issue. ## Reply by swickliff · 2025-03-07 16:03:44 UTC (in reply to Eric Katzfey) @Eric-Katzfey Has any testing been done with this fix in GPS mode? ## Reply by Eric Katzfey (ModalAI staff) · 2025-03-07 16:36:35 UTC (in reply to swickliff) @swickliff No, it hasn't. Supposedly all of this is fixed in latest mainline but we haven't tested it. But we do have a mainline build available to try: http://voxl-packages.modalai.com/dists/qrb5165/dev/binary-arm64/voxl-mainline-px4_1.16.0-1.0.0-202502271326_arm64.deb