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About

I'm sure most of you've have seen video of my fixed wing UAV flight ranging various type of models from previous years to current ones, you might notice that all of my flight have consistent flight pattern where my UAV plane first have to perform close range or localized waypoint (zig zag pattern) before it went off for a long journey. Most autonomous UAV builder and owners simply launched their planes and go straight away on their journey to their next distant waypoint but for me i usually let it fly above my head first at least passed between 2 to 4 close range waypoint before it heads out for its long journey.   Why do i need to do that?  The first 3 to 4 waypoints after launching then loitering around over my head at closed range within L.O.S (Line Of Sight) range is called 'Pre-Check Waypoints'.  You don't find much about the term 'Pre-Check Waypoints' online neither at drone/UAV community forum because not many people wanted to waste battery power, time and resources to let their flight models to such flight pattern. The 'Pre-Check Waypoints' is a procedure i came out of my own ideas based on my experienced flying my home DIY made UAV planes used as redundancy UAV health check to ensure the plane are safe enough to be complete departure away from the based after checking its flight parameters in the air.

 

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The 'Pre-check Waypoints' protocol

What does a 'Pre-check Waypoint' flight pattern do?  Its actually a simple 2~4 waypoint or more performed at close proximity above the home base executed after launching the UAV platform.  The waypoint loitering  size usually around 70m radius between each waypoint visible enough for the operator/user/pilot to see line of sight and close enough for both radio controhow to precheck waypoints 67l and radio telemetry frequency to connect with the UAV model.  The waypoint pattern plotted random or zig zagged within visual range above the base usually having sharp angular or polygonal turning point where plane have to bank hard on each opposing waypoint.  The reason such waypoint created before fully depart away from home base is to check if the UAV platform is 'healthy' or 'fit' enough to perform the mission by observing its flight characteristic, handling and check for any abnormalities as it fly above us, so i can decide if it safe enough to let it fly or push the abort mission button.

Below are list of task of things to watch out once UAV launched in the air then started to loiter close by waypoints:

If all above passed though rough observation and monitoring via GCS then the UAV is good to go.  As mentioned before for any autonomous platform regardless if its fixed wing, multirotor, single rotor (helicopter) or rover (ground based)  i always sacrifice a bit of power and runtime doing a simple waypoint route before launching long distance autonomous mission so i could do a quick last minutes performance checklist.  Normally most people will check their UAV platform status while its on the ground but not after launching it.  Health status of UAV on the ground and in the air offer difference results because once its start to pump the power all onboard hardware goes 100% and that is the moment where critical failure started to show up.   Normally once in the air my UAV have to passed these health checklist as listed below.
**Note i usually used android 3DR - TOWER and DROID PLANNER apps to monitor my ARDUPILOThow to precheck waypoints 46 driven flight controller onboard fixed winged UAV.

Based on my experience despite having all green check list as shown above doesn't mean your UAV platform will have a guarantee zero risk flight throughout the mission, there are always about 20%~30% chances it will shown signs of impending failure a few seconds or minutes into 'operational' autonomous flights. On perfectly build UAV platform most failure comes due to fail to take time to calibrate, degraded hardware performance and fail to plan ahead into unexpected weather.   Here are several true scenario happened to me which led to lost several of my UAV fixed wing and also multirotors despite they are 100% build and tuned perfectly from the start of their life span.

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Scenario 1:

If you've been following my twitter for about half decades ago i did build fixed wing big FLY DREAM aka BIXLER which have same the same UAV as Drifter UAV setup that runs on APM MINI PRO, it was also consider the last plane that have both full FPV + UAV capable hardware with proven longer radio MAVLINK connection over 20km on 433Mhz due to its isolated telemetry antenna located at the rear tail.  The plane have been through just 5 how to precheck waypoints 45cycle of autonomous flight in just a month.  The last flight was on windy Saturday morning with slightly more thermal than usual.  On the ground the GPS, gyro, compass, RSSI indicator, servo, battery and other parameter was healthy as usual.  Went into successful hand launch and made 4 way point closed proximity flight as 'Pre-check Waypoint' protocol so i could observe plane flight condition visually line of sight and on my GCS app via smartphone.  During the first 3 waypoint flight it went ok but on the 4th waypoint the plane flew slightly 'crabby' or should i say drifted side swerving its tail pointed into head wind...but lousy judgment says it was ok to continue the flight so i ignore the windy condition on that day.  Once its already exit the  'Pre-check waypoint' to the next waypoint to continue mission the plane started flying sideways like a crab for the rest of the flight when viewed via FPV goggle as it pointed its head towards the head wind and confirmed by compass heading onboard. FPV signal lost at 11km and last MAVLINK signal was at 20km when it suppose to do a U-turn home...i did waited for 1 hour for its returned but to no avail. My prediction was i guess it stalled somewhere in the ocean as it try to banked against the wind because my previous experience with BIXLER type plane actually not really good at recovering itself when its already started to stalled itself due to immense dihedral wing tip design. Lesson learned; do not over confident on your platform, bail out from the flight if it shows indication that it couldn't handle abnormal wind pattern.  I should have bail out immediately when it shows signs of struggle on 4th waypoint.  *Note that i did try to activate RTH mode on my GCS when my MAVLINK radio but didn't worked well.


Scenario 2:
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Its my 450 size 3DR APM quadcopter;  Been through more than 50x cycle of successful flight most are FPV + aerial photography while 40% are autonomous waypoint flight. Usually its build for aerial photography and basic mapping works but on that fateful day during the first close proximity waypoint flight the current shown on FPV's OSD MAVLINK layout shows spike of unstable current consumption on as it passed second waypoint then followed with compass error reading.  I ignore it thinking it was a temporary glitch out of 0.001% probability but i was wrong.  On the 5th waypoint it flew away and never to return..even FPV video signal was lost at just 500m range.  1 year later when flying micro FPV racing quad around the beach with friends a fisher man sat near us and told us he caught a red and white rusty 4x prop drone in their net and gave to their young cousin to tinker around. It was about 3km from the base where i flew. Ouch! 


Scenario 3:

Ironically this one happened during the early development of third unit Z-84 V3 which gone terribly wrong but manage to recover back safely.  The Z-84 V3.0 was on its third day of autonomous test flight conducting grid style waypoint test, has the same basic components build like its predecessor the Z-84 V2.0.  On ground test leaving it for about 30 minutes the GPS lock, compass, battery, servo and other hardware's/sensors worked well just like previous test day.  But on third day; after launching the plane entering how to precheck waypoints 28the 3rd waypoint the GPS lock started to dip from 9 to 6 satellite lock. Again ignoring it was a temporary fluke.  The flight expected to do a grid style waypoint test to 'stress test' the platform like i always did, however the GPS module started to deteriorate from 6 to almost 0 satellite after 15 minutes into the flight.  When its hitting 0 satellite it automatically started to do loiter flight mode in circle as default fail safe procedure but unfortunately due to windy condition it got pushed sideways and started to drift off-set 30 meters every 20 seconds until it was flown outside 1km range which is at that time was outside my MAVLINK radio GCS range...the antenna was not configure well at that time because it was still at beta test build.  The Z-84 GPS started to gain lock at random times but as it try to return home the flaw repeated itself again and again causing the plane to veered further beyond 3km.  I had to chase the plane down the highway driving my car to locate the plane where about parallel to the direction of the wind and pointing my ground station antenna to get signal locked hoping some signs via GCS apps. It was 15 minutes worth of havoc trying to locate the plane in the air  until the last 20 minutes i heard my GCS apps voiced that it has full GPS locked and on its way to return back to home base and it did flew back about 7 km away from where it suppose to.  I drove back, waited for its arrival and manage to catch the signal back on my 9X + FrSky controller and landed manually with just 15% power to spare.  Upon inspection my GPS module was overheating like it was baked inside an oven, after further investigation the current power supply that powered the GPS was faulty. The GPS module was replaced with different model from different vendor.  Lesson learn; don't ignore even the smallest flaw in the air.

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Parameters to observe

Once its launched and fly in 'Pre-check Waypoint' pattern you immediately check some critical parameter you'll need to observe via 'Line Of Sight' (LOS) and also through your handheld monitoring devices or known as your GCS (Ground Control Station) eg: tethered tablet, smartphone or computer that run program such as Mission Planner, TOWER, Droid Planner or other compatible UAV apps that displayed all health telemetry.

Here are list of basic parameter need to observe after launching the UAV:

So above are my basic list of atributes to monitor during the 'Pre-Check Waypoints' flight for all my fixed wing UAV and also applicable for multirotors.  Sometimes the attributes to look out can be more than what i've listed above depends on how complex a UAV features and function was build into it for example camera gimbal , Lidar sensor, deployment servos (cargo UAV), airspeed sensor and etc; because of all this bulk feature there are reason why i prefer keep my UAV build with more simpler features and function so there will be less thing to worry about (less components to break down) which makes its easy to narrow down troubleshooting the problem due to less parts onboard.  Simplicity always the best!..or should i say "less is more".

 

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List of my active UAVs (autonomous mission flight)

Below are list of currently active fixed wing that uses that above flight pattern protocol for further reading and reference:


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Summary

The 'Pre-Check Flight' have saved me from 'mission gone wrong' by helping me do detect hidden symptom, ensuring safer and confident mission flight.  This protocol should have been part of fundamental knowledge of handling any UAV platform to ensure that all flight parameters are fully check, monitored and confirm the health parameter are within acceptable range/level while UAV flying close proximity in the air before letting the UAV drone to continue on long range autonomous mission. So before you launched your UAV platform into unknown territory it is best to do a simple close proximity flight (Pre-check Waypoint) so you can observe and monitor its health parameter before its cleared for long autonomous journey.

** PS:  Before we end this article; oh btw remember the last article?...yeah got the C-FLY DREAM drone!  Coming soon shortly on my next review. hehehe!

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