RC India

I have a quad with emax frame. I use to fly it on a 3S lipo 1500 mah. One cell died.. now it only shows 2 cells. And total of 8.2 voltage. Will this be able to fly the quad..say 2 min or so.. earlier with 3s it use to fly 4-5 min.
Any help would be really appreciated.

IT WONT U WONT HAVE ENOUGH PUNCH TO PUSH IT

Oh...that means it wont lift..

1. On paper, if we know the maximum current draw of your motor and a known minimum C rating of your battery(hint:maximum instantaneous current you have ever seen during punch outs), we may get a rough idea of whether to give it a try or not.

2. Your motors, ESCs, camera, vtx, etc. must be rated for 2s volt. The only risk I can think of is battery being dead, not being able to provide the required current altogether. If you have any means of knowing the in-flight battery voltage(via. telemetry or OSD), you may still give it a very smooth hover for no more than 1 or 2 seconds to get a idea of the voltage sag.

I have never tried this though. Just my first thought. If you're trying any way, please do post the result. Just curious to know:)

Regards,
Raj Gunaseelan James

Sent from my CP8676_I02 using Tapatalk

Emax Nighthawk 250 V1
4 x DYS 2204 2400kv
4 x DYS 20A BL Heli ESC
Naze32 REV6 6DOF version
CC3D mini Power Distribution board
Hobbywing 3A UBEC

Battery is 35C 3s 1500mah.. one cell dead now

Its better to just buy a new battery..

The video below shows that the  motor pulls a max of around 155 Watt on a dys 5045 propeller on bench test(don't know if it's a 2 blade or a 3 blade one).

https://youtu.be/_gAR6uBnbwI

So, if we use a 5030 2 blade prop, ESC will be safe(Some dys ESCs like XM20A V2 support 3s and 4s only. Ensure your particular model supports 2s). Worst case: 6.6V @ 155W = 23.5A. On a two blade 5030 flexible prop like the gemfan ones, max power should be well below 155W. (Do you have any 5030 2 blade props lying around?)

This brings us to 23.5x4 = 94A required current. This is the absolute max required. I expect we may not pull 94A at all. A motor on bench test pulls more current than on a quad.

Assuming that the 1500mAh 35C rating is correct(which may or may not be true), we have 35Cx1500mAh=52.5A for a "3 cell" battery. Depending on the battery brand, age, wear, etc. this number will be very less.

The numbers do not look promising. But, there are way too many factors and assumptions that we can't possibly model mathematically.

If you have plans to use the 2s LiPo for any other application, I would suggest not to try this.

Otherwise, why not give it a try? At least, now that we know you won't hurt your ESCs and the motors, you have nothing to lose either way. At max, the motors will try to spin and the battery gets killed. Just use a voltage alarm to let you know when to stop pushing it hard and you can still save the LiPo.


Regards,
Raj Gunaseelan James

Sent from my CP8676_I02 using Tapatalk

Nice analysis. It's better to keep the lipo for some future use. Pushing it hard may leave it dead for ever.

Gave it a try today. while doing this there were no props. Multimeter was connected to the battery to check the voltage drop. Little raise brought down the terminal voltage from 7.8 to 7.1... motors were spinning good. there was no heating of battery too. and the motors sounded rock solid. but I got the feeling that the quad wont lift with the props ON. Also didn't want to kill the battery. so stopped the experiment.

Nice try. Its exciting to experiment and good to know the limits of our setup. Thanks for the update Tony sir.

Regards,
Raj Gunaseelan James