[RC Madman]

I put together a F450 to test out LP on a CC3D. My first test flight was on 4s and today I did another test flight on 3s and when I give full throttle the quad dips and wobbles while ascending? I checked to see if it was maybe the battery so I swapped it out and the same results. I put in a 4s pack and it acts normally?

[xpantz]

If you were giving it a bit of throttle then it might just be struggling a little on 3s.  You could try less prop.

Otherwise... if it's tuned for 4s then it will be a bit soft on 3s, so might just be PIDs for 3s.

[RC Madman]

Running 8x4.5 SF props with Sunnysky 980kv motors.

I will try adjusting the PID.

[TheOtherCliff]

On 930ish KV motors (2212) on 3s I run 10x4.5 props.

Also, if you tuned it on 4s, you need to retune it on 3s. 

[mazevx]

Maybe try out thrust pid scaling. Dont no how its named at LP...

[liftbag]

Definitely you need to retune your copter switching from 4S to 3S. The good news is that you can have two PID sets on two different Stabilization Banks, and switch according to the battery used.

[RC Madman]

Sorry guys I may not have explained the issue as clearly as I could. I don't believe this is a tuning issue.

I think it is something to do with the ESC's?

There is a lack of power when throttling up and the wobble is from a motor moving to slowly and the quad almost drops out of the air before regaining a little power and ascending.

When it ascends it is not at a normal 3s speed. Pretty slowly.

Also noticed it does this if I yaw as well. I used the Generic Quad X settings.

The ESC's are Hobbywing Xroto 20A flashed with the latest BLHeli firmware.

I guess the odd part to me is why does it fly fine on 4s and not on 3s?

I will be swapping out the ESC's as soon as I get them in the mail.

 

[TheOtherCliff]

With those motors, you need bigger props when on 3s and even then you will not generally have as much lifting power as when on 4s with smaller props.  For me, I have found that 900KV-1000KV motors on 3s need 10x4.5 props. 

On 3s you only get 3/4ths the RPM as when you are on 4s.

[RC Madman]

Here is some video with 10x6x3 props on it. 3s and 4s

10" props did nothing to improve the behavior.

[quadfather]

Here is some video with 10x6x3 props on it. 3s and 4s

10" props did nothing to improve the behavior.

To me that looks like a duff (or insufficient) battery.  With those props on 3S you should be hovering at around 1/3 throttle (depending on AUW).  What are your battery specs?

Like TheOtherCliff, I have 1045 props (two blades) on the same motors as you, and I hover just below 50%.

[RC Madman]

It's not a battery issue as this and the other 3s packs I have work just fine on my other 3 quads. 385mm with SS 1250kv and Avroto 770kv on 8" and 10" prop, Disco 550mm with Avroto 770kv.

The pack being used in the video is a Venom 3200Mah 20c pack. I also tested a Floureon 3000Mah 30c, Venom 5000Mah 35c and Glacier 4000Mah 30c pack with the same results.

Your correct in your thinking it "Should hover" at about 1/3 throttle but even small throttle inputs causes it to wobble and drop.

If the other video ever gets posted you will see the difference on 4s with the same setup.

I will try posting it here?

https://youtu.be/1wCFHoCkmi4

[TheOtherCliff]

Are you running unflashed ESCs?  Or flashed ESCs with an LVC set?  It could be an ESC Low Voltage Cutoff is set wrong.  Should be disabled or set to "NiCad".  That would explain one or other motor drop out at high power.

Also, I would measure the 3s pack voltage under full load.  It is so weak that it should be safe to do that.

I always use a lipo alarm for that, and it tells me if I over amp or run out of juice in flight.

[RC Madman]

They are flashed ESC's. They have BLHeli 14.1.0.3

I have a voltage alarm connected to the packs whenever I fly.

I tested this with 4 different fully charged packs with the same results.

I will double check the settings on the ESC's but pretty sure the low voltage is disabled and report back.

[RC Madman]

1 of them had "Low RPM protection" turned on while the rest did not.

I changed the settings and calibrated all of them again and the power is back. I will go test fly it to be sure.

Thanks everyone for the help and ideas.

[RC Madman]

Yep that was the issue. SOB! I swore I checked the ESC's to be sure they all had the same settings but I must have checked only 3 of them or maybe the setting did not load properly on that one ESC?

It flew OK. I need to tune it now. Some oscillations were present on the test flight using the F450 template.

Soon I will have 4 quads with LP running on them!