Something is wrong with my copter build


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I have made a mistake here and I am not sure how to fix it. I followed the tuning wiki and it did not help this situation.
The copter is a 500, 6s with 15x4.5 in props on 5108, 700kv motors and 40 amp esc,s.
I have tried a cube on 3.6.9 and pixhawk on 3.6.10 with the same results
The throttle is too hard to control. I have broken 2 frames to date with these motors, so this test and log is tied to a trash can full of rock.
I have calibrated the esc’s but some advice on ESC’s would be good.
Any suggestions would be helpful and appreciated.

A bit hard to tell from the log what might be wrong because it’s tied down. Do you have a log from one of your crashes?

Also, what is the weight of the drone? I had a 5kg one that flew 15" on 400kV motors, so 700kV sounds like a lot to me since your copter looks a lot lighter.

I was going to say that 700kv seems high for 15" props… It should really be 300-400kv.

Can you be more specific on your specs? a 500mm quad shouldnt be able to fit 15" props…

What is the AUW?
Do you have a link to the motors?

I have an eCalc membership and I can crunch the numbers for you with enough information…

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Wrong motors. 700 kV is for smaller props and LiPo packs. If you want to spin 15 inchers on 6S you’ll need somehing between 330-400 kV.

Thank you all for the answers.
Lowering the prop size is what I was thinking too

I will look for another log file that had the crash landing
The weight is AUW 2kg

It may be a 550

I fly between 5,000 - 10,000 feet. Do you think going to 4s or smaller props is better?

that would be great!

Oh yeah those motors+props are definitely too much for 2kg.

I’d recommend trying 4S first, since you’ll get better flight time with bigger props, although you might want to monitor motor/esc temp carefully for the first few flights. You might end up having to get smaller props as well, since reducing your effective RPM by 1/3 might not be enough for a mere 2kg AUW.

On a side note, I’ve never seen a 50xx-size motor with such high kV before.

What ESCs are you using? Any chance they’re SimonK?

These super thin ‘pancacke’ motors are known to have sync issues with SimonK escs. Google ‘simonk sync issue’ and see if some of the videos look like what you are experiencing. I’m sure cheap motors have magnets not precisely spaced, too and that wouldn’t help.

In general, it looks like you are way over spec’d for 2kg.

I’ve never seen 50xx motors with that high of kv either. But that kv would be close for 4s.

However - at that altitude, you may want 6s for overhead power. I would also try a higher pitch. 4.5 is basically middle of the road. Try 5.5 pitch.

I’ve got a 650mm size copter w/ 700kv motors and use 15" or 16" props. 4s batteries. I’ve been flying it for years and have not had any problems with it. I built it back when higher voltage batteries were rare and pancake motors weren’t available yet…
I’ve flown it w/ a range of weights… No gimbal and 5500mah batteries up through a big gimbal and camera and 18000mah batteries.

So, it’s definitely worth trying 4s.

I have some 5010-750 Kv motors. Definitely not good on 6S.

I swing Tarot 15" folding props with 5010-530Kv motors on 4S and Tarot 16" folding props with 5010-350Kv motors on 6S.

I also have one rig with 2814-710Kv motors swinging Sail 13" x 4.4" props on 4S.

You power system is all wrong. Throttle is hard to control because those 700Kv motors are making hover thrust WELL below 50% throttle.

Ditch the 6S. Run 4s and 13" props.

Again everyone, thank you

This build is 1.6kg without a camera. I would like to tune it @ 1.6 then add an A5000 camera AUW 2.2kg.
@ekliptiko my esc’s are Favourite little bee 40 amp opto esc. If a calculation could be made at 7,500 feet that would be great.
I am replacing the props down to 13" & would like to stay with 6s if I can, what do you guys think?
I have made some obvious miscalculations with this motor and may ditch them to use 6s batteries because I have had better flight times with 6s in the past. As everyone has noted the KV on these is just too high.

It’s is super that I can get this good advice here. No product or store has this good of support for DIY.

Nothing inherently ‘wrong’ with 15" props, but might be overkill for only 2.2kg.

I think sticking with 6s is a good idea, and 700kv/13" will be clos(er). My intuition would be 550-650kv, but you already have the 700s. might as well try.

If you haven’t purchased new props yet, get a higher pitch (maybe 5.5). Regardless of kv rating, The motors will not have to work as hard up in the thinner air .

I tried 13 x 5.5" props and not much change. Still pretty scary at 20% throttle.
4s seems to be the next step.

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Quick 4s test 13x5.5 props
This did not work well at all.

If you run the motor test on MP, going up 10% at the time, what do you get?

Maybe the trim from the remote are bad, or your RC calibration

I cant find enough information on those motors for this to be reliable. I took a guess on the battery size. I had to make some assumptions, particularly with the max power of the motor (So just ignore the “map power over the limit of the motor” for now - This has little to no impact on hover throttle. I am pretty sure you would be over the limit, but I cant find any data on these motors, so we cannot rely on my 200W assumption which is likely low):

The main take away here is that your 750kv motors with 15" props are no good. 33% hover throttle is not good. This does not provide enough “under”-head (i just made that term up - the opposite of overhead, haha) for this setup to be controllable.

Dropping down to 4s is what it will take to make these 750kv motors work:

If you are looking at new motors, you can actually get pretty close just looking at the motor test data many motors provide. I recommend not purchasing motors that do not provide test data. Unfortunately, this typically means they cost a little more.

Have you seen something that looks like this? (this is the test data from

The goal is to have ~2-2.5 thrust-to-weight ratio. This should provide about equal throttle control both up and down, which is important on a hovering machine like a 'copter. Too much could mean it might not come down. Too little might mean it will struggle for control in adverse conditions like wind. That means we want ~2-2.5x the AUW in thrust at maximum, and we want the 45-55% thrust to be equal to the AUW.

Personally, I tend to spec my systems on the high side ~2.3-2.5 thrust-to-weight, and I have had good success doing so. I do not have alot of experience at the altitudes you are flying at, but I would assume that you might want to do the same to help account for the thinner air. And higher pitch props.

This is my process for selecting motors when tools like ecalc are not available:

  1. Take AUW and multiply by 2. (4.4kg in your case)
  2. Divide by number of props (4 in this case, obviously) results in 1.1kg for your copter
  3. Check motor voltage rating (4s vs 6s)
  4. Check motor test data for your prop size
    4a. check 100% for min 1100g thrust. I prefer to have a little over head.
    4b. Check motor test data at 50% for 550g (because we want the copter to hover at 50%, the thrust at 50% must be nearly equal to your AUW (2200/4)
  5. Select ESCs that are rated at or above the current draw for 100% condition

Beyond that, you can start to go down the rabbit hole and geek out over the efficiency rating (g/W). The higher the g/W number, the longer the flight time you will get on a particular battery.

Edit: I guess linking that motor might have been a little tricky of me. I think those would be a touch powerful for your AUW, but not too much.

They spin at 5%, 10% pretty fast

Alberto, We need to get the power setup squared up first. 15x4.5/750kv/6s is simply out of line.

yes, without the motor specs, we are just asuming. Its soudn strange to me too the 750KV - 5108, I think is a very fast spining for a 15" prop.

By the way, I use the arris 4010 for over 2 years, very good motors.

Good to know on the Arris motors. Ive been eyeing them myself. I always see them with good test data, but I dont see many people using them.