Hi everyone,
I have a HGLRC Rekon 5" Long Range quad, and I'm planning to buy a Li-Ion pack to train for long distances after some weeks of training with LiPos on shorter distances.



I found this video, where he says at 44:50 that if you want to fly with a Li-Ion pack you must have a < 2000 KV, because the max Amp draw must be lower than 15 Amps. My Rekon 5 came with HGLRG Aeolus 2004 3000 KV motors (the green version of the motors). Does this mean I'll instantly damage the Li-Ion if I fly with this setup?

Is there a way to safely fly with a Li-Ion pack on my setup?

Thanks in advice.

You just need smooth throttle control.

Liion cells heat up when you have a high amp draw. Of course they dont immediately light up but it also degreases flight time. Betaflight has an option to scale your throttle down (in Pid tab on the bottom). Its not as efficient as using the right KV motors but you can safely use all your throttle. Another possibility is to use the throttle limit in the rates tab. This is the same like only using a part of your throttle. This leaves all headroom for the pid loop but helps you tame your throttle.
I would use the OSD elements for ampere and throttle position to determine your values

(04-Aug-2021, 01:00 PM)jasc Wrote: Liion cells heat up when you have a high amp draw. Of course they dont immediately light up but it also degreases flight time. Betaflight has an option to scale your throttle down (in Pid tab on the bottom). Its not as efficient as using the right KV motors but you can safely use all your throttle. Another possibility is to use the throttle limit in the rates tab. This is the same like only using a part of your throttle. This leaves all headroom for the pid loop but helps you tame your throttle.
I would use the OSD elements for ampere and throttle position to determine your values

Can I achieve the same effect by applying a curve to the throttle in the Taranis configuration?
In this way I could create two separate models, one for the LiPo and another one for the LiIon.

So the workflow would be the follwing:
1) Determine the max throttle sitck position that gives me 15~20 Amps max, using a LiPo
2) Set the curves in OpenTX in order to have the throttle level corrisponding to 15~20 Amps at the max stick position (maybe plus something more, in order to have more power when the battery will be at lower levels)

on 3000kv motors you could fly a lot configurations, these might be the best: 21700 3s1p / 18650 3s2p / 18650 4s1p / 21700 4s1p / 18650 5s1p

as kafie told, 18650 6s1p should work too
you can set a motor output limit in betaflight, but the key for good use of that battery is slow cruising and gently use of the throttle.

This is a test flight I've done today with a 850 mAh 4S LiPo. The max current was really high at the end of some of the recorded flights (150 A), even If I didn't do heavy punches.

Would this flight style be gentle enough to be used with a LiIon, or do I have to be even more gentle and/or add a motor output limit of 60% in BetaFlight?

That current seems really high. Are you sure your current meter is properly calibrated?

https://oscarliang.com/current-sensor-calibration/

Edit: In the video above, at idle on the ground, you current meter is showing ~4A, and about ~17A in cruise. I'm guessing the calibration is way off.

On the product page for those motors, on 4S, the max static current draw is ~17A, which would give you a max total draw of about 70A.

Thanks for the help.

I tryed to calibrate the current meter, and the values seem more reasonable now (I also added the mAh consumed in the OSD)

I did another test flight with a 850 mAh LiPo, and the current draw stayed always below 20 A (I even attempted some flips in the end).



With a 60% motor output limit I should be ok with the LiIon, but could it be safe to use it without the motor output limit and just trying to avoid abrupt maneuvers?

its more safe without any limit, the voltage range of liion is much bigger than on a lipo, to get all possible flighttime, you will probably need the upper throttle area in the end of the flight.

as example a 4s lipo is totaly empty at 12v, while a 4s liion is totaly empty at 10v. thats a huge difference and a downside of liion in comparison.

another example is a 6s liion, fully charged at 25.2v and empty at 15v. on the weight of a 6s liion - 300g - you will need a high throttle level close to 15v.

Hi Trial4life42,

_____________________________________________________________
Your quote:

if you want to fly with a Li-Ion pack you must have a < 2000 KV, 
because the max Amp draw must be lower than 15 Amps. 
_____________________________________________________________

Yeah, I watched the video, however... my experiences are a bit different.
It might be the difference between a 5 inch and a 4 inch lightweight; don't know...
But, I have run 18650 cells with much higher Kv motors without any issues.

I am an easy cruiser and normally maintain a smooth throttle at about 20-25 percent.
My experiences are as follows:

I did lower the Betaflight warnings, but I still fly until the quad drops from the sky, however,
the battery voltage has not been below 3.0 volts per cell. We had determined this was likely due to a
low voltage cutoff that is hard wired on some AIO FC boards. Joshua_A found a solution, but
up to this point I have not yet ventured to try the modification which involves bypassing the
onboard ESC regulator with a small jumper wire.

Yeah, I try to be close at the end of the battery, but I tend to push the batteries a bit. Just me, I guess.

Anyway, I have two 4 inch quads that I have flown with 18650 cells {2, 3, & 4 single cells in a holder}.
Using 18650 packs rather than using a holder will reduce the quad weight quite a bit which should yield
a little bit better Fly Times on both quads. 

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My Phantom-X running 1303 5000 Kv motors spinning 4 inch Gemfan 4024 Bi-blade props:
Using 2 18650 cells in a holder, my best Fly Time was 21 minutes and 20 seconds.
Using 3 18650 cells in a holder only yielded 17 minutes and 17 seconds.

The motors just too small for the extra weight of the 3rd cell.

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My Katana-LR4 Running 1504.5 3950 Kv motors spinning 4 inch HQProp T4x2.5 Bi-blade props:
Using 3 18650 cells in a holder yielded 21 minutes and 15 seconds.
Using 4 18650 cells in a holder yielded 21 minutes and 15 seconds. 

Again, the added weight trumps the additional cell capacity.

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I do have a 4 inch build in progress that will be using 1404.5 2750 Kv motors...we will see how it goes.

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All in all, I am satisfied these results. I also know that I could reduce the weight and improve these times.

So... 

Personally, I would NOT change the motors at this point. 

Just make the Betaflight changes, plug in an 18650 pack, and fly... NO fancy stuff, just easy cruising.

Since 18650 cells don't recover very fast, those throttle punches are simply out of the question.
Take off EASY, use just enough throttle to achieve the desired altitude, fly very easy...just enough throttle
to maintain flight. 

See how it goes before changing any hardware on the quad. 

-----//  NOW  //----

You can also limit the Kv in Betaflight {if you really want to}.
I would limit the Kv before I would limit the throttle.
I use my thumbs to limit the throttle