I, too, am curious about the 21700 Li-Ion cells and how they compare to the 18650 ones.
...or even other sizes...I have considered smaller ones to save some weight, but not sure how well that would work.

So I ended up testing the 3S 18650 pack this morning.

The good news is it flew great and I ended up with a time of about 37min and distance of 26km.
The extra thrust-to-weight really felt nice though.  Fun to fly and handled the wind better also.
I found I was cruising at about 33% throttle and 5A vs. 50% and 5A on 2S.

The bad news is I forgot to put the SD card in my googles, so I didn't get any DVR 
So, I'll have to redo that flight and actually get some video.

I change it up and test the 21700 on my next flight though.

I'm starting to think I need a new charger.  When you guys charge your cells, do they always go right to 4.2V?
The charger display shows all my cells at 4.2V, but when I measure them with a multimeter they're only at 4.15V.
I've measured with two different Fluke meters and a small battery checker and they all agree read 4.15V.
I'm using a Venom Duo Pro charger and as far as I can tell, there's no way to calibrate it.

All my flights so far have been drawn right down past 2.5V and I'm only using 2800mAh out of 3000, so I'm trying to figure out if my batteries are just getting old, or maybe my charger is to blame.

Amped mate, I feel for your poor wrists. My first attempt at just 15 minute flights and I'm cramping up like nothing else!

Well done mate! Your accomplishments spur us all on.

Cheers,
ph2t.

(12-May-2021, 01:31 PM)ph2t Wrote: Amped mate, I feel for your poor wrists.   My first attempt at just 15 minute flights and I'm cramping up like nothing else!

Well done mate!  Your accomplishments spur us all on.

Cheers,
ph2t.

Ha ha, appreciate the sympathy 
Ya, my hands definitely seize up and I need to let go of the sticks once in a while and shake them out!
Flying around a small area for that long is not very exciting!  
At the moment it's still around 4degC in the mornings, so I just sit in the truck and put some music on to help pass the time.

Here is the summary from my morning flight with the 27100 2S pack.
I'm still not getting the full capacity out of the battery, so not sure what's going on there.
Still, just shy of 38 min and 23.4 km ain't bad!

Current draw was about 1 amp higher at the same crusing speed due to the extra weight.
Considering the 18650 2S pack can still get +20km and +30min, I think I'd prefer it for daily flying, because AUW is light enough that you could still add a naked GoPro or Insta360 Go, if you wanted to, where as the 21700 2S or 18650 3S don't have any "wiggle" room at all.

   

Very interesting, thanks for sharing the results of your tests!

as for the voltage, yes they do charge to 4.2V but the Li-Ion Cells should be charged to 4.1v as thats normally their rated max voltage, and if you switch your charger to Li-Ion mode then it should stop at 4.1V. Some people do overcharge their batts a bit in hope to get a bit extra out, but I have found they struggle to hold too much over their max rated voltage which might be what you are seeing here.

Long term, overcharging batteries can have negative effects.

(16-May-2021, 11:24 PM)bffigjam Wrote: Very interesting, thanks for sharing the results of your tests!

as for the voltage, yes they do charge to 4.2V but the Li-Ion Cells should be charged to 4.1v as thats normally their rated max voltage, and if you switch your charger to Li-Ion mode then it should stop at 4.1V. Some people do overcharge their batts a bit in hope to get a bit extra out, but I have found they struggle to hold too much over their max rated voltage which might be what you are seeing here.

Long term, overcharging batteries can have negative effects.

Most new/high power Li-ions are rated for 4.2V. Check the manufacturer data sheets to verify, but the popular VTC6/6A and Samsung 30Q are both rated to 4.20V +/- 0.05V charge.

(17-May-2021, 04:46 PM)V-22 Wrote: Most new/high power Li-ions are rated for 4.2V. Check the manufacturer data sheets to verify, but the popular VTC6/6A and Samsung 30Q are both rated to 4.20V +/- 0.05V charge.

V-22, ok I'm glad you agree here, because I also went back and double checked the datasheet for the VTC6 cells that I'm using and the definitely state 4.2 max volts.

I should have a new motor arriving today to replace a janky one, so I'm going to retest the 3S setup again, with the actual DVR turned on this time

Took the 18650 3S pack out for a flight this morning and remembered to turn my DVR on this time
Winds were about 18km/h and temp was about 16 degC

Here are the results:
In hindsight, I should've kept it in the air one more second to hit the 40min mark
   

Mate. Daaaaaamn that’s a crazy flight time. I just hit 25mins on my hotdog with the 1204 5000kv motors - I thought the smaller motor would help but it looks like the 1404s are the way to go. After my attempt yesterday and video post I have gone over this thread again looking for insights to your wicked flight times. Could be my battery termination method or possibly the motors.

How is the voltage sag at takeoff looking for you? I can maintain above 4v on takeoff and am flying between 3-4A. I do need to calibrate the current sensor though - I never trust jhemcu to calibrate their current sensor, lol.

(22-May-2021, 12:05 AM)ph2t Wrote: Mate. Daaaaaamn that’s a crazy flight time. I just hit 25mins on my hotdog with the 1204 5000kv motors - I thought the smaller motor would help but it looks like the 1404s are the way to go. After my attempt yesterday and video post I have gone over this thread again looking for insights to your wicked flight times. Could be my battery termination method or possibly the motors.

How is the voltage sag at takeoff looking for you? I can maintain above 4v on takeoff and am flying between 3-4A.  I do need to calibrate the current sensor though - I never trust jhemcu to calibrate their current sensor, lol.

Ha ha, ya man I don't think I'll be doing many more of these park flying marathons... it's quite boring!  
I've been wanting to do a 5km out flight, but I'm working through some issues right now with my Ghost link.

I checked the DVR from this morning and it looks like the voltage drops immediately to 4.02V and stay's around 4V for the first minute and then falls pretty linearly from there.  For my setup I find 4.5-5A is a good cruising sweet spot.

The sag is a bit more on 2S 18650.  More like 3.95 after takeoff.  
I didn't see your video post! I'll have to go take a look!

My current sensor was way off at first too.  It's pretty dialed in now.

Challenge complete!!!   
Full flight video to follow later tonight!

   

(24-May-2021, 06:31 PM)amped_fpv Wrote: Challenge complete!!!   
Full flight video to follow later tonight!

Oh snap!!!  Congrats!!  

Here's the flight video for the final part of the Challenge !
I used the 2S 18650 pack for all the challenge flights to keep things consistent.

I was actually hoping to go for 6km on this flight, but I turned back because the video got pretty sketchy as you can see.
Video is now the limiting factor, because I know this build has the flight time and RC link to go much further than 5km.

When I reviewed the flight I actually realized I didn't following my intended flight plan.... I was using the wrong wind turbine as a landmark...
So I think I ended up with a big group of trees partially between me and the quad, which caused my video issues.
I hope this was was the issue, because it was kind of strange that the video didn't get gradually worse, it when pretty quickly from solid video to complete static.
I need to be extra careful now because all the trees have leaves on them!

This rig is so much more enjoyable to fly compare to the Nano, because I know that I've got plenty of reserve in the tank and I'm not stretching it to the limit.  Also, it's much more capable in the wind, so I don't have to wait for perfect conditions (ie. a tailwind on the home stretch, etc.) every time I fly for range.

Hi Amped,

CONGRATULATIONS !!!   GREAT JOB !!!  

I knew you could do it. NICE WORK !!

You are the FIRST to meet every single challenge requirement.