Problem:
My Hexacopter “spools up” on its own with only minimal throttle applied. I get the slow rotation at 0% throttle after arming, which is fine. When I apply just 5 or 10% of throttle and hold at that position (not enough to take off yet), the hexa will slowly (over a period of a few seconds) ramp up the speed of the motors as if I was increasing the throttle myself. Left unchecked, I’ve seen this ramp up actually produce enough thrust to lift off. I don’t like this behavior and would prefer to have manual control instead. I’m not sure if this is the ESC’s doing this, my radio, or the Pixhawk. I suspect the ESC’s?
Build:
Tarot 680Pro Hexacopter
SunnySky 380kv motors with 13" props
6000mah 6S Lipo
Hobbywing 30A ESC’s (hobbywing.com/product_show.asp?id=285)
3DR Pixhawk
3DR Compass/GPS
Taranis X9D Plus tx with X8R rx
What I’ve done so far:
I’ve messed around with the “Start Mode” settings on my ESC’s by trying them in “normal”, “soft”, and “very soft” modes. No noticeable difference observed in these modes.
I’ve performed a full ESC calibration
I’ve performed a full radio calibration
Conclusion:
I’m not sure if there’s a setting for this behavior in MissionPlanner I’m missing or if I potentially missed a programming option for my ESC’s somehow? Either way, this behavior has led to a couple of minor crashes already since it can be quite erratic. If half way through the automatic ramp up I cut the throttle to 0%, everything slows down to the normal arming speed. The moment I apply just 1% throttle, the hexa will resume where it left off during the ramp up. It’s like going from 0% throttle to 25% instantly - very twitchy. I’ve also ran into issues when landing on uneven ground. The hexa looks like it will tip so I apply a little throttle to move to a slightly better spot and instead of getting a little throttle, I get 25-50% instantly. Mix in the fear factor of watching an expensive drone you’ve poured time and money into over months and the nerves alone are enough to cause you to mistakenly give that 1% throttle at the end, which has been enough to cause it to want to take off again just about.
Hoping someone has seen this before and is able to guide me in the right direction. Can post flight logs if anyone feels they are necessary.
The simple solution is to ‘take-off’ assertively. Slowly trying to lift off usually leads to tip over. You can for your first flight try taking off slower* to make sure everything seems ok-ish, but really, as stated, you need an assertive throttle up.
Sounds like you’re taking off in one of the assisted modes (AltHold, PosHold, Loiter, etc) plus you have an issue with rc throttle calibration. I’d personally look into rc calibration. Specifically make sure that when at half throttle on your Tx, the pixhawk sees this as 1500 on the rc calibration screen in Mission Planner. The reason I’m thinking your issue is in this area is that in one of these assisted modes you need to push past 50% throttle to get a take off, but lower than 50% you get slow rpm. If it thinks half throttle is at the bottom of your throttle throw then…
[quote=“billbonney”]The simple solution is to ‘take-off’ assertively. Slowly trying to lift off usually leads to tip over. You can for your first flight try taking off slower* to make sure everything seems ok-ish, but really, as stated, you need an assertive throttle up.
Taking off assertively is working quite well actually. I suppose I need to ditch the idea of slow, smooth take-off’s.
It just feels like something is wrong when I move throttle to 10% (which isn’t enough to take off), and without touching anything else, watch as the motors spin up faster and faster until it almost wants to take off on it’s own. My preference would be that I am in full control over the output of the motors via the throttle stick.
[quote=“pauljatherton”]Sounds like you’re taking off in one of the assisted modes (AltHold, PosHold, Loiter, etc) plus you have an issue with rc throttle calibration. I’d personally look into rc calibration. Specifically make sure that when at half throttle on your Tx, the pixhawk sees this as 1500 on the rc calibration screen in Mission Planner. The reason I’m thinking your issue is in this area is that in one of these assisted modes you need to push past 50% throttle to get a take off, but lower than 50% you get slow rpm. If it thinks half throttle is at the bottom of your throttle throw then…
Just an idea.
Sent from my Kindle Fire HDX using Tapatalk[/quote]
Thanks for the suggestion, Paul. I’m actually taking off in stabilize mode however. What I’m dealing with is actually a 2 part problem. My hexa had more than a 2.5:1 power ratio before I just installed another battery, gimbal, camera, and vid tx. With the extra weight, things are feeling less “twitchy” for sure.
My main problem remains however. Move the throttle to 5 or 10% and let go. Watch as the hexa spools up on it’s own over 5 or so seconds to near take-off power. Taking off assertively like Bill suggested definitely works, I just wish there was a way to have the throttle 100% reflect motor output.
[quote=“nysethe”][quote=“pauljatherton”]Sounds like you’re taking off in one of the assisted modes (AltHold, PosHold, Loiter, etc) plus you have an issue with rc throttle calibration. I’d personally look into rc calibration. Specifically make sure that when at half throttle on your Tx, the pixhawk sees this as 1500 on the rc calibration screen in Mission Planner. The reason I’m thinking your issue is in this area is that in one of these assisted modes you need to push past 50% throttle to get a take off, but lower than 50% you get slow rpm. If it thinks half throttle is at the bottom of your throttle throw then…
Just an idea.
Sent from my Kindle Fire HDX using Tapatalk[/quote]
Thanks for the suggestion, Paul. I’m actually taking off in stabilize mode however. What I’m dealing with is actually a 2 part problem. My hexa had more than a 2.5:1 power ratio before I just installed another battery, gimbal, camera, and vid tx. With the extra weight, things are feeling less “twitchy” for sure.
My main problem remains however. Move the throttle to 5 or 10% and let go. Watch as the hexa spools up on it’s own over 5 or so seconds to near take-off power. Taking off assertively like Bill suggested definitely works, I just wish there was a way to have the throttle 100% reflect motor output.
Regards,
Erik[/quote]
OK in stabilize mode, THR_MID comes into play. Take off and adjust the value of this parameter to give you a hover at mid throttle. That might help. Out if ideas after this sorry.
It’s fly-by wire system, so this will never be true. The problem when you are on the ground is that the control loops are operating outside of there normal range. This can result in what seem like bizarre behaviour. When flying in stabilize the throttle control should feel as though you have direct contact with throttle. Without a computer controlling the throttle, the quad won’t even fly.
The issue is your perception of how it should be, which is counter to the way it really is.
Anyway, as long as you are flying, and it’s behaving as you expect in the air, thats good!
This seems to be a new feature and I too think it’s a horrible one.
Go to your advanced parameters and change MOT_TCURVE to 0 / disabled. Unlike others have stated, you can get a linear curve.
If anyone is still looking for a solution , please look at the manual provided with the esc. And in the programming mode you need to set the startup mode to normal.
In my case, turn on the rc controller , and put the throttle to max. Turn on the pixhawk, wait for the startup tone. Now restart the pixhawk, and press the safety switch of present .
Wait for the musical tone in the escs.
Then , some beep tones will start . Wait for the tone - B-BBBB ( 1 long beep 4 short beeps) . Then immediately put the throttle in the rc , to down. Then wait for 1 beep and then push the throttle to max again .
