Can’t achieve the amount of flight time that I should be

Hardware Multirotors
1

I’ve been modifying/adjusting my quad to get good performance and it just continuously keeps going badly.

Basically flight always goes super well for about 2-4min before something goes wrong. The copter gets wobbly, and then quite rapidly loses altitude. Not quite just dropping from the sky, but definitely close. Almost like it’s losing battery, but I just don’t think that’s the case. Hoping someone here can give me some pointers.

I got a new frame based on some recommendations here actually. The new frame is a 500mm carbon fiber setup. Very sturdy. A little on the heavier side but not too bad.

It’s a quad setup using the SunnySkyA2212 980KVs (SunnySky A2212 Brushless Motors – SunnySky USA )

I suspected there might be an issue with the original battery. It’s a 50c 3s 3200mah battery. I’m flying with 10in props.

Thought maybe the battery was faulty, so purchased two add’l Ovonic 3s 50c 3000mah batteries.

Using PixHawk FC, with a Raspberry Pi CPU. 30a ESCs.

It feels really heavy. But the scale I use to weigh it says it’s 1.1kg. I don’t know how much I trust the accuracy of that though. It feels more like it’s probably closer to 2kg.

First day I got the new batteries, I used 1 and I was able to fly for about 4min. Took her pretty easy since I had a gut feeling the problems weren’t solved. After about 4min in, it started going… what I would call topsey turvy. Just started wobbling mid flight. Was able to keep enough control of it to land (barely).

So in my head I’m thinking, we’ll maybe 4min of flight is about right for only 3ah. Did some calculations using ecalc multi rotor calculator and it was coming out at about 5.5min of flight. So cool, maybe if I run the two new batteries in parallel to double that to 6ah. This should double my flight time. Ecalc was netting around 9min mixed flight time. And the extra battery only added 196g, so not too bad. Knew it wouldn’t be double flight time, but maybe 80% extra.

So got that all setup and yesterday took flight. Was airborne for all of 1:42 before it started going topsy turvy again from about 20m altitude.

At this point, I’m figuring it maybe is heavier than what I believe it is. So maybe 12in props versus 10 would give me the extra thrust I need. Or maybe go to an X8, and split the batteries back up, 1 for each set of 4 motors.

Or it could be a faulty motor (doesn’t seem like it though). So maybe a faulty ESC. Maybe an incorrect parameter in ArduPilot. Honestly I’m a bit lost at this point because my flight time with the current configuration should be much longer.

2

What props and an accurate take-off weight? And as always provide a link to a .bin flight log. Just hovering is fine but whatever you have.

3

Hey Dave. The props are just cheap plastic 10x4.5 props, but I had the same result from 10in master airscrew props as well.

The accurate takeoff weight is 1.8kg.

It wouldn’t allow me to upload the .bin file here directly (said it was over 4.4mb which is odd). Here’s the file in a g-drive link. Please let me know if that works for you. And thank you for your help!

4

I would call this a flying overstuffed Turkey. It would have to be on 4S with this configuration and that weight. On 3S it would have to loose 600g or more of stuffing.

5

There’s no voltage/current sensor - the voltage is quite essential so work on that first.

You said quad but there’s 8 motor outputs configured
Frame: OCTAQUAD/X

Before the instability motors are all working fine, even if a bit overworked - then Motor3 appears to lose thrust and is commanded to maximum. This has more of a detrimental affect that it really should, because setup and tuning is lacking. The attitude control is poor and oscillations set in.
This could be an ESC losing sync, a bad motor wire (bullet connector) or even the prop slipping.

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Earlier in the flight there is a definite difference between clockwise and counter-clockwise motors, so check for twisted motor mounts and get all the props operating on the same plane.

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6

Yea that’s the issue, there’s no stuffing to drop :joy:. The RPi CPU maybe since I’m not even really utilizing it at the moment. But that won’t give me 600g.

Guess I could go to a smaller frame, but that’s a shame with the money/time spent on it. Honestly I thought a 4s would be too much voltage for the motors on my setup.

7

What would you recommend?

Well maybe there’s a more deep rooted issue here then. When I originally completed my build, I had some issues with the motor ordering, so the sequence was off. My motors are ordered based on the DJIX, versus the standard order. I’ve selected just the standard quad in my initial setup with Mission Planner :man_shrugging:. Maybe I need to check my firmware again.

Would moving to 4s versus 3s as Dave suggested solve for this?

Can you explain more of what you mean by setup and tuning is lacking?

I used the initial setup and configured all the parameters best I could manage my way through it as a newbie.

It’s definitely not a prop slipping. Had that issue 2 flights prior to this one, so ensured that was fixed. I have suspected a faulty ESC already. Maybe it’s time to pony up for some new ones.

Very insightful! Thank you. I thought this might be an issue but I tried to get the motors as evenly on the same plane as possible. It’s because the new frame has an odd design because the arms do not have a fixed orientation. Basically the tubing can be rotated within the housing, so the motor could end up at a slightly different angle than the rest. I’ve taken my level out and got them as close as I could. Frustrating.

Thanks for all the help!

8

The motors are OK at 4S. Are the ESC’s? Even at 4S you wouldn’t want it to weigh any more than 1.8kg so you will have to go down in capacity.

And of course set if for quad-X or whatever quad frame suits.

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9

Actually I dont know the voltage range of the ESCs… just they’re 30a max.

The frame is setup to support x8. Would it be more efficient to go that route maybe?

10

Not more efficient; you loose some efficiency with a co-axial motors. You use them when you want relatively high thrust with a smaller frame footprint. What frame is it?

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11

It’s a 500mm carbon fiber frame

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12

With that frame as a quad I would have went with lower kV motors (~700-750), 11-12" props and 4S power.

13

What about just using 11-12” props with those motors? Maybe buy a few more minutes of flight time. Plus with the 4s power like you mentioned earlier, just with lower capacity to keep the weight similar.

If I did go with the setup you just mentioned, what’s a realistic flight time expectation?

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14

I think those motors will be lucky to swing bigger props, flight time would go down.

ecalc is your friend.

A subscription is less than the price of a set of cheap props, and could save you hundred$ in bad choices.

15

Thanks Shawn! I actually have a premium subscription to ecalc and have grown quite familiar with it. Those are the flight time estimates I mentioned above. That’s another reason why I know there’s something malfunctioning/not 100% optimized (most obvious statement of the day but eh)…

16

With those 2212 motors 9x5 is as big a propeller as you can go on 4s before you start overheating them.

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17

Not much. Take a step back and reconsider the build. If you want longer flight time build it for 6S power. Of course then all components will change.

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18

Would you have a recommendation on motor, prop combo for the setup I’m looking to achieve?