(08-Feb-2021, 06:40 PM)Joshua_A Wrote: So let’s collect: There are three ways to fix the 7volt cutoff (I think)...
1). Move to three cell
2). Buy an ESC with BLHeli_32 (this “fix” is unverified, although if there’s someone who can verify this, let me know )
3). Remove the Voltage regulators power resister (this has been done -with success- although I presume it’s tricky to find the right resister...)

(08-Feb-2021, 11:46 PM)iFly4rotors Wrote: 3) Good luck with that. In my opinion this is very risky, so I won't be doing it. 

    If a manufacturer has implemented a Low Voltage Cutoff in hardware, then don't buy those boards for long range.
    Thing is, I am not sure how to tell without actually testing the board.

As i'm in the same boat for my 7" sub250g build using a 2s Li-Ion pack, and wanting to use a board that has a cutoff in place that you can't change, i looked more deeply into how difficult it is to modify the voltage regulator. I found out it actually isn't too difficult to do. 

I made a video so others might feel more confident in doing this modification. It's also reversible:



Cheers to the board, often have find very useful information here - hope i can contribute something with this myself.

Excellent work!!
I'm pleased to see we both came to the same conclusion, here's my guide. [Great minds think alike, I guess]

(06-Apr-2021, 05:41 PM)Joshua_A Wrote: Excellent work!!
I'm pleased to see we both came to the same conclusion, here's my guide. [Great minds think alike, I guess]

Indeed so it seems   Actually during my research i found this thread, but not your solution. Good job as well!

(06-Apr-2021, 05:58 PM)Felias Wrote: Indeed so it seems   Actually during my research i found this thread, but not your solution. Good job as well!

  Yeah, I think you can thank my organization "skills" for that, I try to fix this soon...

Hi Felias,

I am interested in your sub-250 7 inch build. Have you started a build thread yet?  If so, what is the link?

One of my 7 inch projects is a quest for a sub-250 gram craft.

Also, the Quest250-LR is  the sub-250, 30 minute, 10K distance challenge. The battery comes into play here. Presently, a 2S 18650 pack seems to be the best power source. This is where the low voltage cutoff comes in. While this looks to be a pack voltage issue, it is NOT. It is a per cell voltage issue; regardless of the number of cells. The cutoff is a PER CELL rating, NOT a total pack rating. Consequently, moving to 3S DOES NOT solve the issue; it only obscures it.

Great video Felias, thank you!

(07-Apr-2021, 02:24 AM)iFly4rotors Wrote: The battery comes into play here. Presently, a 2S 18650 pack seems to be the best power source. This is where the low voltage cutoff comes in. While this looks to be a pack voltage issue, it is NOT. It is a per cell voltage issue; regardless of the number of cells. The cutoff is a PER CELL rating, NOT a total pack rating. Consequently, moving to 3S DOES NOT solve the issue; it only obscures it.

Are you sure about this? I haven't seen the problem with 3S, only on 1S and 2S. Can you point me to an example?

(07-Apr-2021, 03:07 AM)V-22 Wrote: Great video Felias, thank you!

Are you sure about this? I haven't seen the problem with 3S, only on 1S and 2S. Can you point me to an example?

Hi V-22,

Good to hear from you again.

All my flight data specifically bears this out. I will get it all together for you and post it again here. I have noticed through this whole Low Voltage thing that the perception is total voltage, but it is NOT, it is a per cell voltage. I will assimilate my actual flight data and post it here. I have NEVER, to this date, been able to draw down a pack...any pack or cell count, down below 3.5 volts PER CELL...regardless of the cell count of the pack.

I will collect it, assimilate it, and post my data. Give me a day. 

Again, good to hear for you.

(07-Apr-2021, 03:17 AM)iFly4rotors Wrote: Hi V-22,

Good to hear from you again.

All my flight data specifically bears this out. I will get it all together for you and post it again here. I have noticed through this whole Low Voltage thing that the perception is total voltage, but it is NOT, it is a per cell voltage. I will assimilate my actual flight data and post it here. I have NEVER, to this date, been able to draw down a pack...any pack or cell count, down below 3.5 volts PER CELL...regardless of the cell count of the pack.

I will collect it, assimilate it, and post my data. Give me a day. 

Again, good to hear for you.

Are you referring to the warnings in the OSD, or the FC shutting down and the quad falling out of the air?

(07-Apr-2021, 03:17 AM)iFly4rotors Wrote: Hi V-22,

Good to hear from you again.

All my flight data specifically bears this out. I will get it all together for you and post it again here. I have noticed through this whole Low Voltage thing that the perception is total voltage, but it is NOT, it is a per cell voltage. I will assimilate my actual flight data and post it here. I have NEVER, to this date, been able to draw down a pack...any pack or cell count, down below 3.5 volts PER CELL...regardless of the cell count of the pack.

I will collect it, assimilate it, and post my data. Give me a day. 

Again, good to hear for you.

   Hummm, interesting 
I have had NO problem discharging my packs to <2.8 volts cell, regardless of the input voltage or number of cell used (although I'd like to note: 1} this was ONLY after the voltage regulator modifications and 2} the pack is almost all the way discharged, per mAh, so there not a lot left in the pack).

  With that out of the way, did you attempt the voltage regulator modifications?
If not do you have any lvc set in betaflight? 
What esc firmware are you running?
Li-ion or lipo?
What are your discharge rates for the batterys used in the test?
I'm curious...

(07-Apr-2021, 04:02 AM)V-22 Wrote: Are you referring to the warnings in the OSD, or the FC shutting down and the quad falling out of the air?

Hi V-22,

I am referring to the quad dropping out of the air.  I am NOT a battery conservationist; I Fly-Till-I-Die.  When I start getting warnings, I fly closer to the launch point so I don't have to walk so far; then I just fly around in a smaller area and in line where I know I can find it when it Drops Out of the Sky. If I could fly the battery dry...zero volts...I would; at least a few times, just to see.

Hi Joshua, 

I have not yet done the voltage regulator mods, but that will be one of the first things that I do when I get back to building.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The follow is a sampling from actual flight log data at the end of the flight.
Various quads, but only the 3S and 4S runs and I didn't duplicate the information.

Total Pack Voltage /  per cell voltage ( VPC )
                    
GNB 3S 1100 mAh:       9.72  /   3.24  
GNB 3S 1100 mAh:     11.4    /   3.8
GNB 3S 1100 mAh:     10.4    /   3.46
GNB 3S 1100 mAh:     10.2    /   3.4

GoldBat 4S 650 mAh:  13.8   /   3.45   << Even the 4S dies at 3.45 VPC, but the Pack voltage is still 13.8 !!!
 
The quad drops from the sky before the per cell voltage reaches 3.0 volts regardless of the pack voltage.

Now, tell me how the cell count or pack voltage makes any difference. 
It simply Does NOT, it is clearly the Per Cell Voltage. 

Increasing the Cell Count did NOT make a difference in the per cell voltage nor the battery draw down.
That is NOT the answer and does not resolve or change the situation. 

So, that regulator is working on a per cell voltage, definitely NOT a per pack voltage. 
If you think about it, that is the only logical way since you can run a wide variety of cells per pack with varying voltages.
Trying to set the regular for various pack voltages is simply not logical, but per cell is.

It does, however, make sense to bypass that regulator; which I WILL do. 

I also believe that there might be some boards out there with the regulator set to a lower value; I just haven't found any.

Well, you case gets tricky...
First, how far have you discharged your packs, per mAh? (I've had packs that seemed to cutoff early, but in reality were almost entirely discharged, per mAh, and in turn, Wh.)

Next, are the motors still spinning at cutoff? (I have also had a quad cutoff, even though there was a LOT of power left in the battery, my conclusion was simply; the quad was too heavy, at lower voltages not enough thrust was produced).

What quad(s) did you use in your testing?

Also, would you mind posting a video (LOS), of the quad at cutoff?

Are those resting voltages after the flight, or the min voltage from the flight summary screen?

If resting voltages, then you're drawing them pretty close to 3V under load.

By fall out of the sky, does the video just go dead and the motors stop? Or they just slow to the point where they can't provide enough lift to keep the quad in the air?

Is this all on the same quad? Is there a LVC set it BLHeli?

I'm just trying to figure out what's going on because I don't think what you're seeing is typical.

All the regulator is doing is taking a higher voltage and providing a fixed lower voltage to bias the FETs. All it sees is the total input voltage, and has no way of knowing what the per cell voltage is.

(07-Apr-2021, 02:24 AM)iFly4rotors Wrote: Hi Felias,

I am interested in your sub-250 7 inch build. Have you started a build thread yet?  If so, what is the link?

One of my 7 inch projects is a quest for a sub-250 gram craft.

I've just finished the design and soon will upload a video of it in detail. So far i only shared a few glimpes in my latest project update video:


(will bring you directly to the right chapter)

I'll share all design files on Thingiverse when i upload the design video. I plan to build it next week already (though video will come a little later).

Will be posting a build thread as well soon.

The data is a summary from multiple quads having different components, but the results are extremely consistent regardless of the build.

The data presented is battery voltage physically measured after the flight. Even though a battery will regain some voltage, I don't believe that a battery drawn down to 2.5 volts would recover to 3.5 volts; just too much to rebound to.

I would need to go back through the videos to try to determine everything else. If I recall correctly, the video is generally, but not always, still alive. I say this because I almost always have a final screen. I will also say that the OSD readings NEVER match the measured values. I have done battery calibrations, but can't seem to find the magic spot. I can get the initial voltage pretty close and have been working on the amp draw, but so far the ending battery voltage is always off by quite a bit.

I haven't gotten to fly for a while so I don't have recent data. Hopefully, that will change pretty soon.

I want to try that regulator by pass that Joshua has discovered just as soon as I can start building again. That will be the real test, to see if I can draw the batteries down lower with a modified FC. I am glad that a HIFIONRC board was used as I use it a lot and might have one in the parts bin.

Thanks for all of the help.  

(07-Apr-2021, 06:49 PM)Felias Wrote: I've just finished the design and soon will upload a video of it in detail. So far i only shared a few glimpes in my latest project update video:


(will bring you directly to the right chapter)

I'll share all design files on Thingiverse when i upload the design video. I plan to build it next week already (though video will come a little later).

Will be posting a build thread as well soon.

Great video and awesome builds! You can tell a lot of work went into those frame designs. Looking forward to some flight videos!