Motor start question

[SuperSharpShooter]

If the copter is started off on a surface that isn't completely flat, Is it normal for the motors on the lower side to start spinning, while the ones on the high side don't spin at all, until the lower side takes begins to raise up. Only then do the motors on the high side begin to spin.

This has caused me quite a few flips on takeoff. It seems that quite often that by the time the motors on the high side spin enough, the copter has already flipped itself onto that side from the force of the lower ones.

How would changing the min or starting PWM affect this behaviour? Basically when armed if I give throttle, I want all the motors to begin to spin at the same time (with the lower ones spinning more obviously), which I'm pretty sure will stop this behaviour. I have my ESCs calibrated to 1125/1950.

[bluuu]

yes, it's normal

You can change min pwm to higher value.
To take off you can do more "agressive" - higher throttle.

[SuperSharpShooter]

It just flips onto its side too often on takeoff as it is and I think this issue should be fixed since i'm sure it's easily preventable. No other platform I've used does this.

I've always taken off slowly because of this, and haven't been game to ever take off aggressively as I would expect more serious damage to be caused.

[chschmid]

Morning Glen

The behaviour you describe is unknown to me. I take off with my hexa from uneaven ground very often. How far off level is your copter @ start when you run into a flip? In what mode are you taking off usually when a flipp occurs?
Can you provide some more information about your machine and maybe a pict or a Video.

Cheers
Christof

[Max]

Hi Glenn, this sounds strange. AQ should not flip itself... even if the high side motors don't spin up very fast, the AQ should reduce output to the low side motors so as to prevent a flip. Christof asks good questions. If you're taking off in PH mode, it might be trying to fly to a new position before it's fully airborne (I always take off in manual for this reason).

Another question, what does the HUD look like before takeoff (in QGC or Android GCS), does it show the correct angles? You can also check the diagnostic telemetry view and watch ACC Magnitude and MAG Magnitude values. They should be around 9.8 and 2.0, respectively, regardless of AQ orientation.

-Max

[SuperSharpShooter]

Hi guys, thanks for looking at this.

Generally if the ground is flat enough that all of the motors spin up evenly when throttle is applied, it will take off without issue and once in the air it handles without any problems. It's just if the copter is on anything from about a 5 or so degree lean that I have problems, and even then it's not something I can predict. Sometimes it will lift the lower side up, and then take off OK, and other times, it will flip towards the high side. I take off very very slowly and try to get all motors spinning before giving it any significant throttle as a result. Normally if it flips once, it will flip again, so I generally power cycle it if it flips once.

I've only ever taken off in manual mode.

I've got a log here which shows a tip onto the high side at takeoff, but yesterday I reworked the FC platform as I think when the dome was fastened, some wires were transmitting vibrations through to the platform. I think that vibrations are where pretty much all my autoquad problems have come from. I've only managed to get one flight in since then, and I took off from a perfectly flat surface for that one, and it flew ok. I guess the next few flights will tell as to whether this change has solved the problem or not.

309-AQL shows the flip, and 311-AQL is the flight after reworking the equipment platform. The equipment platform which holds the FC weighs 150g and is attached to the rest of the frame with four small 1cm square pieces of latex foam. I use motors 0,1,2 and 7,8,9.

[chschmid]

Hi Glen

Looking at 311.log it seems that Motor 9 shows a stange behaviour at startup. Your spoolup seems to produce a lot of vibrations. After liftoff (at 4000) the vibs are much less.
Can you post a screenshot of the HUD as Max suggested. One shot when the Hexa sits level and one shot when it is on not even startposition.

Cheers
Christof

[SuperSharpShooter]

Thanks for pointing that out. It looks like motor 0 has a similar output to 9, but does this mean that it is the cause or is just acting as a result of the vibrations? I will get some screenshots of the HUD and do some more testing tomorrow.

[SuperSharpShooter]

I've just taken it out again now, and it still seems to be getting that weird noise in the logs on the motor outputs during spoolup. I took off from an uneven surface, and it worked OK this time.

What's everyone else doing for vibration isolation for the FC? I have balanced the props perfectly, but there is a possibility that one of the motors is bad somehow.

Here are the screenshots of the HUD at level and on the slope I took off from.

[chschmid]

Hi Glen

It should not be a problem to take off from this sloping position. And your level is ok. It is hard to tell what went wrong. My best guess is to apply power quite quick to lift off.

Cheers
Christof