I have a new build that was built to be a 4s quad.  It has a 50amp mamba stack and 2750kv motors.  The question, what would happen if I ran the quad on 6s and limited the throttle to ~66%.  The stack is capable of handling the increased voltage.  The throttle limit would keeps the motors from over spinning.  However, I may not fully understand how the electronics work.  Also, I know an ESC has a RPM limit but I think they are typically very high.

Anyways, what are your thoughts on the matter?

"But Josh, why are you doing this?"

1) It is a general question to understand more about these beautiful machines
2) It would theoretically yield longer flight times.

this should work very well.
I beleive you should add the 66% as a motor output limit, throttle limit doesnt limit the system/fc to use fullthrottle/max motoroutput.

Betaflight 4,2 release candidate have a graphical option to do motoroutputlimit, you can add the limit and choose on which voltage the output should be limited.
if you plug in a 4s the motor output wont be limited, plugin a 6s lipo the flightcontroller will add the limit. pretty usable nice feater. it would be possibel with a older bf version but more work. the 4.2 release candidate is very nice, would recommand it.

https://github.com/betaflight/betaflight.../4.2.0-RC2

If you motor is not meant for 6s power, then you don't want to run it on 6S, even with limits. Because 6S voltage is still going into the motor coils (as far as how I understand ESC).

sure they arent rated for 6s but as for quality motors like t-motor, brotherhobby, emax... this work very well, i know a racer allways buy 4s kv versions run them scaled on 6s, he doesnt get more motorheat or power, lifetime isnt decreased.
adjusting the pid would be needed for sure.

xD

Understandable that some motors can handle higher voltage that intended. People were doing this when 6S started because 6S motors were not ready available.

I guess you take your risk when you do this.

All very good points. Thanks for the input from everyone.

It all makes me wonder if I would even get long flight times. I have a 1550mah 4s pack and some 2200mah 3s packs. I seem to get roughly the same flight times off of those. It makes me want to dive deep into the testing and find the perfect mix for my flight style.

the 3s 2200mah lipo have a littlebit more energy wh, a 1650mah 4s would be the same.
as the energy of the two lipos are near, probably both provide the same poweroutput. as voodoo described the voltage as a risk, the more traditional sort to get more power would be use a bigger 4s pack 1800mah to get a near performance to 6s, 1800mah would be comparable to a 1200mah 6s lipo.
if the battery and esc can handle the current a motor produce on lower voltage there wont be a benefit for a settup with more cells.

Ok.

Thank you everyone. I very much appreciate all of the input.

I had a different response that I deleted as my understanding of ESC's was incorrect. 

There are ways to do this safely. Here are two videos of how to do it. Betaflight 4.2 makes this easier.

Joshua Bardwell video


DrainMan FPV video

(19-May-2020, 12:42 AM)kingstar Wrote: There are ways to do this safely. Here are two videos of how to do it. Betaflight 4.2 makes this easier.

I looked at the release notes and searched in Github. Which function in BF4.2 do you mean? Link?

i guess there is no link or description about, i didnt find it to post here.
if you have a quad bf4,2 you can find the option on bottom of the pids or rates tab.

(19-May-2020, 05:54 PM)hugnosed_bat Wrote: i guess there is no link or description about, i didnt find it to post here.
if you have a quad bf4,2 you can find the option on bottom of the pids or rates tab.

Mark talks about the Motor Output Limit (Attenuation %) at 06:56 into his video below...

Just now got to the video. It was great. That guy knows his stuff. Thanks again.

(17-May-2020, 08:05 PM)voodoo614 Wrote: If you motor is not meant for 6s power, then you don't want to run it on 6S, even with limits. Because 6S voltage is still going into the motor coils (as far as how I understand ESC).

That's where motor output comes in, I saw a video, I'll see if I can find it, but he started buying all his motors with the upper KV amount and just limits the motor output. Imagine two cars racing, and the race has a 4000rpm limit on engines (I know that's probably not a thing)  would you rather have a car that's engine tops out at 3900rpms, or car well tuned speedster, that can easily hit 5000rpms, but was tuned down to not exceed 4000.  The one car will screaming at full throttle trying not to come apart, where the speedster can floor it and the car feels like it's on a Sunday drive at the park.  Never mind, I found the video, dude can explain it better...lol. 

4S motor + 6S battery + output limit

At best its a dangerous bandaid.
You gain none of the 6S motor efficiencies.
You get the 6S extra noise and voltage spikes.
Its great to show "you can", but I would not do this on daily driver.