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18650 Cell in Tello instead of original battery

gdanas87

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Hello guys, I just got the Tello a few days ago. I have been building diy quads for quite some time, with open source firmwares such as ardupilot, iNav and fc's like apm, pixhawk, and omnibus F4 but that's another story. The reason I bring this up is because I have switched over to lithium ion cells on all my quads (homemade 3S2P packs) and never looked back to lithium polymer batteries!!! The good thing about lithium ion 18650 cells that I use is that they can provide enough power since i dont fly racing quads and my amperage needs are quite low, they have a better weight to capacity factor and they are a bit less dangerous to use (if used properly). The main cell I use on my builds is a sony vtc6 konion 3120mah cell that can provide up to 30A current (that is more than enough for the tello, i guess). It weighs 47grams (yes, much heavier than the tello battery, I know) but hear me out:
I made a flight test yesterday, with "dummy" weight to emulate the all up weight of the tello "if" it would be flying with my 18650 cell. The all up weight (auw) would be the empty tello (51G) plus the 47 gram battery=98grams (that's 20 grams overweight compared to original tello setup). I made a test flight (hover only) inside the house, recording video continuously to test the max flight time. The tello autolanded @ 7:30 minutes. The motors were ofcourse working a little harder but right away after the autoland I felt them and they felt a tad bit warmer than they usually do after a 12min flight with the original auw. Not hot however.
So, results are:
1100mah (for the auw of the "theoretical" 18650 setup)=7 minutes flight time
3120mah (and the auw of the 18650)= calculated at 19 MINUTES!!!

The thing is, that to fully take advantage of the 18650 cell capacity, I usually run them down to 3V per cell under load in my big quads. Typical lipos however (like the one in the tello) are run down to 3.5V-3.6V under load, then you better be in the ground by the time the voltage is at these levels. Usually, anything lower than 3.3-3.5 per cell will put considerable life altering damage to the battery. That is not the case with li ion 18650 cells, people even run them down to 2.5V per cell and they work ok.

I understand the tello fw has some type of voltage cheker and triggers the low battery alarm and autolanding sequence when the battery hits a certain voltage while in flight. I am guessing that is the 3.5V-3.6V mark. Does anyone have any idea how that can be altered to 3.0V so we can take full advantage of the li ion 18650 cell capacity and achieve a 17-19ish minute flight time on the tello? That would be amazing!!! Ofcourse I will have to also use an "old" useless tello original battery to steal the board and dummy rig it to my 18650, but thats easy.

Dowsides of this:
-Motors will die quicker: even if succesful, considerable shortening life span of the motors, since brushed motors don't "live" that long anyway, and a continuous flight time without rest, for more than the manufacturer has designed them for, and at temperatures higher than they usually work at (remember, in my test i noticed the motors were a bit warmer, but not HOT), will make them live much much less. I am prepared to replace them though, I wouldn't mind if the ryze "advertised" 40hr life span was shortened by 50% because of my proposed battery hack.

-Reduced max thrust: all motors, brushed or brushless, have a certain kV rating. That is, for example if a motor has a 10,000kV rating, that means that if you send 1V of electricity it will try to sustain 10krpm. Under that theory, the original tello battery is a HV lipo from what i have seen, so max thrust at 4.35V 100% charge would be much higher than that of my 18650 4.2V 100% charged cell. Thrust would also be much lower (even if we manage the battery alarm trigger fw hack) around the low mark of the li ion, since 3.0V would generate considerably less rpm than the 3.5V-3.6V expected of the original tello battery upon alarm triggering!!! Fingers crossed that supplied thrust at the 18650 low-voltage levels is enough to safely fly and land. The "suspected" decreased 100% battery thrust i suggest, will not be an issue for flying, probably would make it barely noticeably more sluggish than the stock tello.

-The new "hacked" battery cannot be charged through the tello: Since its a 4.2V max battery, it will be damaged or even overheat/catch on fire, if it is charged through the tello (the tello charges the battery up to 4.35 volts since its original battery is a HV lipo).
I await your ideas and suggestions
 
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volate!lo

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Hello guys, I just got the Tello a few days ago. I have been building diy quads for quite some time, with open source firmwares such as ardupilot, iNav and fc's like apm, pixhawk, and omnibus F4 but that's another story. The reason I bring this up is because I have switched over to lithium ion cells on all my quads (homemade 3S2P packs) and never looked back to lithium polymer batteries!!! The good thing about lithium ion 18650 cells that I use is that they can provide enough power since i dont fly racing quads and my amperage needs are quite low, they have a better weight to capacity factor and they are a bit less dangerous to use (if used properly). The main cell I use on my builds is a sony vtc6 konion 3120mah cell that can provide up to 30A current (that is more than enough for the tello, i guess). It weighs 47grams (yes, much heavier than the tello battery, I know) but hear me out:
I made a flight test yesterday, with "dummy" weight to emulate the all up weight of the tello "if" it would be flying with my 18650 cell. The all up weight (auw) would be the empty tello (51G) plus the 47 gram battery=98grams (that's 20 grams overweight compared to original tello setup). I made a test flight (hover only) inside the house, recording video continuously to test the max flight time. The tello autolanded @ 7:30 minutes. The motors were ofcourse working a little harder but right away after the autoland I felt them and they felt a tad bit warmer than they usually do after a 12min flight with the original auw. Not hot however.
So, results are:
1100mah (for the auw of the "theoretical" 18650 setup)=7 minutes flight time
3120mah (and the auw of the 18650)= calculated at 19 MINUTES!!!

The thing is, that to fully take advantage of the 18650 cell capacity, I usually run them down to 3V per cell under load in my big quads. Typical lipos however (like the one in the tello) are run down to 3.5V-3.6V under load, then you better be in the ground by the time the voltage is at these levels. Usually, anything lower than 3.3-3.5 per cell will put considerable life altering damage to the battery. That is not the case with li ion 18650 cells, people even run them down to 2.5V per cell and they work ok.

I understand the tello fw has some type of voltage cheker and triggers the low battery alarm and autolanding sequence when the battery hits a certain voltage while in flight. I am guessing that is the 3.5V-3.6V mark. Does anyone have any idea how that can be altered to 3.0V so we can take full advantage of the li ion 18650 cell capacity and achieve a 17-19ish minute flight time on the tello? That would be amazing!!! Ofcourse I will have to also use an "old" useless tello original battery to steal the board and dummy rig it to my 18650, but thats easy.

Dowsides of this:
-Motors will die quicker: even if succesful, considerable shortening life span of the motors, since brushed motors don't "live" that long anyway, and a continuous flight time without rest, for more than the manufacturer has designed them for, and at temperatures higher than they usually work at (remember, in my test i noticed the motors were a bit warmer, but not HOT), will make them live much much less. I am prepared to replace them though, I wouldn't mind if the ryze "advertised" 40hr life span was shortened by 50% because of my proposed battery hack.

-Reduced max thrust: all motors, brushed or brushless, have a certain kV rating. That is, for example if a motor has a 10,000kV rating, that means that if you send 1V of electricity it will try to sustain 10krpm. Under that theory, the original tello battery is a HV lipo from what i have seen, so max thrust at 4.35V 100% charge would be much higher than that of my 18650 4.2V 100% charged cell. Thrust would also be much lower (even if we manage the battery alarm trigger fw hack) around the low mark of the li ion, since 3.0V would generate considerably less rpm than the 3.5V-3.6V expected of the original tello battery upon alarm triggering!!! Fingers crossed that supplied thrust at the 18650 low-voltage levels is enough to safely fly and land. The "suspected" decreased 100% battery thrust i suggest, will not be an issue for flying, probably would make it barely noticeably more sluggish than the stock tello.

-The new "hacked" battery cannot be charged through the tello: Since its a 4.2V max battery, it will be damaged or even overheat/catch on fire, if it is charged through the tello (the tello charges the battery up to 4.35 volts since its original battery is a HV lipo).
I await your ideas and suggestions
You can change the % for low voltage alarm in Tello (red light flashing, and no longer taking off I think) but you can't change the threshold for landing. Its in the firmware. Mine does it between 6 and 8%. Because it doesn't use a fixed % I guess its triggered by touching a floor voltage.

There is video on some FB group of a guy who modded Tello to accept some other batteries. Can't remember if it was an 18650 but I think he ended up with 13min instead of 9min on his stock batteries. My tello does 13min on stock batteries...
Don't forget you are ruining the leek lines, and creating weak spots where Tello might break easier on a crash.
 

gdanas87

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You can change the % for low voltage alarm in Tello (red light flashing, and no longer taking off I think) but you can't change the threshold for landing. Its in the firmware. Mine does it between 6 and 8%. Because it doesn't use a fixed % I guess its triggered by touching a floor voltage.

There is video on some FB group of a guy who modded Tello to accept some other batteries. Can't remember if it was an 18650 but I think he ended up with 13min instead of 9min on his stock batteries. My tello does 13min on stock batteries...
Don't forget you are ruining the leek lines, and creating weak spots where Tello might break easier on a crash.
Thank you so much. Yes it will definately not be as sturdy as stock, since I will have to remove some plastic from the top of where the battery usually sits! Is there any chance you remember what the fb group name is for the video you mention? I have looked all over the place (google, youtube, fb) and can't find any mention of an 18650 battery mod. Only a typical 1S lipo mod on youtube where the comments are disabled. This proposed mod of mine will have to wait quite some time, since I get about 12mins with video recorded continuously on the stock setup/battery. I don't yet want to ruin a perfectly good (and new) tello and its battery!! :D
 

gdanas87

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Thank you so much. Yes it will definately not be as sturdy as stock, since I will have to remove some plastic from the top of where the battery usually sits! Is there any chance you remember what the fb group name is for the video you mention? I have looked all over the place (google, youtube, fb) and can't find any mention of an 18650 battery mod. Only a typical 1S lipo mod on youtube where the comments are disabled. This proposed mod of mine will have to wait quite some time, since I get about 12mins with video recorded continuously on the stock setup/battery. I don't yet want to ruin a perfectly good (and new) tello and its battery!! :D
BTW I recorded video of the "dummy weight flight" and the "stock flight" with my phone and the pitch the motors/props make, is quite a bit higher (expected) in the dummy weight test!!! hmm... Maybe the motors are being strained more than I thought? The temperature of the motors after each flight however, is about the same (7mins dummy weight, 12mins stock weight). So if it flew longer as expected with the li-ion 18650, the motors could get hotter.
 

Mike Shock

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Hello guys, I just got the Tello a few days ago. I have been building diy quads for quite some time, with open source firmwares such as ardupilot, iNav and fc's like apm, pixhawk, and omnibus F4 but that's another story. The reason I bring this up is because I have switched over to lithium ion cells on all my quads (homemade 3S2P packs) and never looked back to lithium polymer batteries!!! The good thing about lithium ion 18650 cells that I use is that they can provide enough power since i dont fly racing quads and my amperage needs are quite low, they have a better weight to capacity factor and they are a bit less dangerous to use (if used properly). The main cell I use on my builds is a sony vtc6 konion 3120mah cell that can provide up to 30A current (that is more than enough for the tello, i guess). It weighs 47grams (yes, much heavier than the tello battery, I know) but hear me out:
I made a flight test yesterday, with "dummy" weight to emulate the all up weight of the tello "if" it would be flying with my 18650 cell. The all up weight (auw) would be the empty tello (51G) plus the 47 gram battery=98grams (that's 20 grams overweight compared to original tello setup). I made a test flight (hover only) inside the house, recording video continuously to test the max flight time. The tello autolanded @ 7:30 minutes. The motors were ofcourse working a little harder but right away after the autoland I felt them and they felt a tad bit warmer than they usually do after a 12min flight with the original auw. Not hot however.
So, results are:
1100mah (for the auw of the "theoretical" 18650 setup)=7 minutes flight time
3120mah (and the auw of the 18650)= calculated at 19 MINUTES!!!

The thing is, that to fully take advantage of the 18650 cell capacity, I usually run them down to 3V per cell under load in my big quads. Typical lipos however (like the one in the tello) are run down to 3.5V-3.6V under load, then you better be in the ground by the time the voltage is at these levels. Usually, anything lower than 3.3-3.5 per cell will put considerable life altering damage to the battery. That is not the case with li ion 18650 cells, people even run them down to 2.5V per cell and they work ok.

I understand the tello fw has some type of voltage cheker and triggers the low battery alarm and autolanding sequence when the battery hits a certain voltage while in flight. I am guessing that is the 3.5V-3.6V mark. Does anyone have any idea how that can be altered to 3.0V so we can take full advantage of the li ion 18650 cell capacity and achieve a 17-19ish minute flight time on the tello? That would be amazing!!! Ofcourse I will have to also use an "old" useless tello original battery to steal the board and dummy rig it to my 18650, but thats easy.

Dowsides of this:
-Motors will die quicker: even if succesful, considerable shortening life span of the motors, since brushed motors don't "live" that long anyway, and a continuous flight time without rest, for more than the manufacturer has designed them for, and at temperatures higher than they usually work at (remember, in my test i noticed the motors were a bit warmer, but not HOT), will make them live much much less. I am prepared to replace them though, I wouldn't mind if the ryze "advertised" 40hr life span was shortened by 50% because of my proposed battery hack.

-Reduced max thrust: all motors, brushed or brushless, have a certain kV rating. That is, for example if a motor has a 10,000kV rating, that means that if you send 1V of electricity it will try to sustain 10krpm. Under that theory, the original tello battery is a HV lipo from what i have seen, so max thrust at 4.35V 100% charge would be much higher than that of my 18650 4.2V 100% charged cell. Thrust would also be much lower (even if we manage the battery alarm trigger fw hack) around the low mark of the li ion, since 3.0V would generate considerably less rpm than the 3.5V-3.6V expected of the original tello battery upon alarm triggering!!! Fingers crossed that supplied thrust at the 18650 low-voltage levels is enough to safely fly and land. The "suspected" decreased 100% battery thrust i suggest, will not be an issue for flying, probably would make it barely noticeably more sluggish than the stock tello.

-The new "hacked" battery cannot be charged through the tello: Since its a 4.2V max battery, it will be damaged or even overheat/catch on fire, if it is charged through the tello (the tello charges the battery up to 4.35 volts since its original battery is a HV lipo).
I await your ideas and suggestions
Your exploration is very promising indeed!
 

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