Hi everyone, here's a noob question! First, some background: I have just completed a build of a RCExplorer style TriCopter, and flashed ArduCopter firmware 3.1.3 on my APM 2.5 flight controller. I ran the Wizard and calibrated compass, gyro sensor, RC radio, etc. Did the ESC calibration, and all seemed fine. On first attempt out in field I concluded I needed to reverse elevator channel on my Turnigy 9XR radio, and most importantly, I need to go into the Mission Planner terminal window and set REV_CH7 to -1, as the back motor servo was turning in the wrong direction.
After these fixes, I attempted to lift off again, after verifying a successful GPS fix before arming and taking off. It was a success! Very stable even with default ArduCopter 3.1.3 parameters. I tested Loiter mode, and it seemed to move fine with Super Simple mode enabled. I enabled RTL, and it went straight for home position, waited five seconds, and landed fine, handling the rather strong wind this day. I took another short flight, flying higher this time and using Loiter mode, did a 360 panorama over the site, then RTL back.
However, on my third flight attempt, I flew at a low altitude away, then enabled RTL. It raised up to, I presume, 15 meters, and began heading back. It then put in a Rudder input on my TX, turning it towards me to get the camera to record in the direction it was heading, as it was heading RTL in a backwards orientation. Immediately after I put in the rudder input (`well, it actually did turn around first), it tumbled down out of sky and crashed on the ground. So, my question is: Are you supposed to stay away from the sticks during RTL? Or is there another factor that I should look for, in order to explain what happened? Maybe I accidentally moved the throttle input as I moved the rudder control? Any ideas?
All in all, I am pleasantly surprised about the simplicity in getting this capable controller up and running with relatively little effort. After reading and searching on forums I was prepared to go through more problems than this to get it up in the air. Now I just have to test, test, test to understand how the controller actually works and behaves. There are many parameters to possibly adjust, and fail-safe behavior to configure and test out. I read about sync issues with SimonK firmware on the ESCs and the ArduCopter controllers. I am thinking about trying an auto calibration procedure, but I am not sure if I it would be risky to do so? My motors are 750kv DT750 motors and I am using HobbyKings F-20A ESCs flashed with the latest 2014-03 SimonK firmware. Anyone here using similar equipment?
Replies
You did put a new battery in for each flight?
Thank you for the reply. No but each one was just a minute or two, tops. When I got home, the charger charged 1019mAh in the pack, and it was a fully charged new 2200mAh Turnigy nano-pack pack to start with, so I think we can rule out low battery.
No not quite, you might easily have had a brown out and once home the battery recovered a little. I will leave it to a better qualified person to examine the logs.
Thank you for the reply. Here are the logs for that days, including all three mini-flights (the crash is obviously the last one)
logs.zip
Hi. none of the three last log files I tried contains what you described - or RTL.
Maybe your logging was somehow terminated ?
Sorry, I think I attached the wrong logs. It should have been yesterdays logs,
I used RTL on all three flights. I disarmed and disconnected the battery once in between. I found the two log sets for yesterday and attached them as "logs2.zip".
Here is also a video of the event, both as recorded on ground and with the onboard camera. I enable RTL at the point where it starts rising and going back, in a backwards direction. Then it turns around, which is my rudder input - then it just falls out of the sky!
https://www.youtube.com/watch?v=ZDLutkFGlAs
logs2.zip
You did not log ACC, so it's hard to see if vibrations did something, but if you plot BarAlt vs Alt - you will see a great difference. not a good sign 20 vs 130m .. most of it builds up the first time when you release yaw, - maybe a very different pressure around the APM when you yaw ? (just guessing)Are APM close to/beneath propellers ?
This alone would not cause the crash.
Your ThrOut was reduced to only 130 , it seems that was done as a response to the uncommanded rapidly climbing BarAllt - I could guess the Y3 most likely got unstable at such low throttle - falling while level, if APM is on top of a plate, there could be a pressure drop around it - further increasing it's sensed altitude (max 130m) - and so the motors remained at minimum speed.
I do not think ThrOut of 130 is flyable for you Y3 does not maike it easier - too bad you did not have RCOUT logged.
Consider increasing THR_MIN - or just test THR_MIN at safe altitude. To do so , set MOT_SPIN_ARMED to 130 too, and - at safe altitude, in STAB, lower throttle stick, be ready to increase it in case of trouble.
I would guess it's not flyable at 130. (remember to test with same payload/dummy weight as you operate)
Thanks for the analysis of the logs! The APM is located in the center of the Y3, on the top plate, attached with velcro tape. I attached a picture of the build here. Btw, if I enable ACC and RCOUT logging, can I leave them enabled without any negative side effects for the time being?
I have a case for the APM unit. However, I have not taped anything over the barometer to protect it from wind, it's just the case protecting it. Do I need to take any further action with it?
I will try to test your suggestions with regards to minimum throttle levels as soon as I have suitable flying conditions. The upcoming days are going to be quite windy, I'm afraid.
DSCF7366.JPG
-Do log ACC, at least while testing - with only 3 motors to calculate - there will not be any reduced performance,.
-You will most likely discover that your vibrations are over the limit, check here:
http://copter.ardupilot.com/wiki/vibration-damping/
- Let the cables have some slack, the way they are mounted, can conduct vibrations as well.
-I am not familiar with the the case you have, bu usually - there's a piece of foam inside.
All conectors(openings) point up, in case of rapid descent, the pressure inside would drop. I am not sure if the descent or vibrations did that, but you can reduce this effect by having a plate on top of APM too, (sandwich it) - be sure the top plate do not touch cables/case and conduct vibrations.
Start with testing vibrations. , and verify that min throttle is able to keep it steady.
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