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
I know the source of your problem, I've seen this before on one of my copters. The barometer is very sensitive to light. When you yawed, it's likely that sunlight came through just right and hit the barometer, causing the reading to spike. This causes the copter to think it needs to drop a lot of altitude. This is a well-documented issue with an easy fix. Just put some foam over your barometer and it shouldn't happen again. This is why you can see that the GPS altitude remains constant while the barometer altitude goes up a hundred or so meters. I hope this helps.
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.
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