Hi everyone,

Having a few issues with my GEPRC Phantom HD, and unsure if they are related.

Recently I have been seeing more battery sag with my GNB LiHv 4S 450mAH 80C batteries when doing any high thrust maneuvers or punch outs... These batteries are around 6 months old, probably around 20-30 cycles on them, always charged the day before flying and storage charged after use. Average internal resistance is around 20mOhms, which is apparently fine.

I tried ordering a new set of the exact same battery and even with the brand new set I am seeing the same voltage sag and power loss on punch outs.

I tried ordering a set of Tattu 4S 450mAH 70C lipos to see if they were better quality, unfortunately the internal resistance on these was 30-40mOhms when they arrived. They also have poor performance on any high throttle maneuvers and even performed worse (in my opinion) than the GNB LiHvs that I usually use.

Thinking that the internal resistance was really the issue, I ordered a set of the Tattu R Line 650mAH 4S batteries which have a 95C rating. 

When I tried flying with the 650mAH Tattu R Line the drone took off with minimal throttle input but continued to climb even after I lowered the throttle to 0. As the quad continued to fly off out of control I was forced to disarm the quad mid-air. Luckily it landed in the grass (learned from too many other crashes).

Thinking that this issue was due to the new R Line battery I tried putting one of the previous GNB 450mAH batteries back on to fly and found that one of my motors couldn't spin up properly. 

Done for the day I went home and replaced the motor (a skill I am learning too quickly).

I took the GEPRC Phantom HD out again today and was testing out the lower capacity Tattu 450mAH 4S battery and was again having issues controlling the power to the motors with the throttle, it seemed the power was either non existent or max with just a little bit of throttle input. After landing safely and removing the battery I checked the remaining voltage and was surprised to see it register only 3 cells, then 7 cells, then 4 cells... suffice to say I am losing confidence in this battery.

After narrowly escaping a crash with the Tattu battery I went back to the tried and true GNB LiHv 450mAH and flew one pack. I was not pushing the quad hard, just cruising around when suddenly the drone was spinning out of control towards the ground. Another motor failed mid-aid, but this time on a battery that Ive flown many many times before with no issue.

So with all this backstory my questions are:

1. Is there something that could be wrong with my drone that is causing the poorer performance in punch outs with otherwise fine batteries?
2. Is there something that could cause motors to blow at a higher rate than would be expected due to wear and tear?
3. Is there something that I need to change with regard to PID loops (never touched them before) or anything else in Betaflight to use the R line batteries on this drone?

I have the analog version of the quad and it is only rated for 3S....so I was wondering whether the same was true for the HD version. The web site says:

"Support 3S 450mAh-4S 450mAh battery(Don’t more than 4S 450mAh)"

Maybe that explains why it's continuing to climb w/o any throttle input when you are using 650mAh batteries? What's weird is that the web page for the replacement FC doesn't mention this limitation when using 4S...so why is it mentioned on the web page for the HD quad??

FWIW - I use either Tattu R-Line 550 3S, Tattu R-Line 450 3S, or RDQ 550 3S batteries with mine.

Thanks LJ Holland, I’ve learned my lesson not to go above 450mAH 4S on this quad, though I’d still like to understand why 4S 450mAH is the limit, how does the battery capacity cause this runaway throttle issue?

I also still want to understand why I am getting such bad voltage sag during punch outs now when I never used to get them before.

Gonna need some smarter folks than me to answer about the batteries. I think the punchouts with the bigger 4S batteries is probably the cause of the motor problems.

I have had great luck with the Tatuu batteries except for one that I ran down too low and ruined. That was my fault for leaving it connected while not paying attention. Other than that, they’ve worked great. My only comment is that these high C R-line batteries fall off quickly when they’re out of juice. When you get the low battery warning, you need to land Asap.

Can I change the motors out to something else that can handle the 4S better?

Currently has the GR1105 5000kV motors, would a larger size or lower kV reduce the frequency of these burn outs?

Well this all sounds a bit strange. Did you change to more aggressive props or perhaps start flying with more throttle? Because those are pretty much the only things that would suddenly induce sag where there before was none, if there isn't dirt or something in the motor that makes it harder to turn. Or of course old batteries sag more but not when they're this new.
For any given throttle level the prop gives the strain on the motor which in turn decides how much the esc much be able to deliver which then sets how much the battery must supply. A bit simplified but you get the point.

As long as the battery can give enough juice they don't really matter that much. MAh only increases weight and gives more flight time so there is no problem for the motors or esc to go to a billion mah 4s but you might find performance lacking

Regarding the fly-aways that sounds more critical and I can't say why because I've never had it happen but I doubt the extra weight from the 650 battery would cause it. What happens with the throttle channel in betaflight? Everything linear and nice? No twiches or big deadbands?

I changed to Avan Rush 2.5” props before ever flying it, and it flew well for 4-5 months, it’s just lately that the voltage sag has been terrible.

As far as throttle channel in betaflight I never touched it, kep it linear, no curve. Or is there some way for me to do a test in betaflight for what you are asking?

(25-Jan-2021, 01:44 PM)patlo911 Wrote: Well this all sounds a bit strange. Did you change to more aggressive props or perhaps start flying with more throttle? Because those are pretty much the only things that would suddenly induce sag where there before was none, if there isn't dirt or something in the motor that makes it harder to turn. Or of course old batteries sag more but not when they're this new.
For any given throttle level the prop gives the strain on the motor which in turn decides how much the esc much be able to deliver which then sets how much the battery must supply. A bit simplified but you get the point.

As long as the battery can give enough juice they don't really matter that much. MAh only increases weight and gives more flight time so there is no problem for the motors or esc to go to a billion mah 4s but you might find performance lacking

Regarding the fly-aways that sounds more critical and I can't say why because I've never had it happen but I doubt the extra weight from the 650 battery would cause it. What happens with the throttle channel in betaflight? Everything linear and nice? No twiches or big deadbands?

Funny....I tried Avan Rush 2.5 on the Phantom when I first got it because a reviewer said they flew well with the quad. I didn't like the way it flew at all - lots of prop wash and generally rough. At the same time, the original props were complete crap and fell off too easily because they weren't secured by screws. Someone here recommended HQ T65 Bi-Blade props. These flew much better than the Avans and are pretty sturdy...plus they have screws to keep them from falling off.

https://www.racedayquads.com/products/hq...7549953137

(26-Jan-2021, 02:30 AM)hutch08 Wrote: I changed to Avan Rush 2.5” props before ever flying it, and it flew well for 4-5 months, it’s just lately that the voltage sag has been terrible.

As far as throttle channel in betaflight I never touched it, kep it linear, no curve. Or is there some way for me to do a test in betaflight for what you are asking?

Nah it was just a long shot if you had hooked it up to betaflight to see in the channel tab that the throttle input matched your stick movements but that shouldn't suddenly change either so I'm out of ideas. The 650 4s should help with sag but why would they cause flyaways when it's just a few extra grams? Very strange. Sorry I couldn't be of more help.