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do you want to fly with any batteries ?

aeropic

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B0B is ready!

B0B is a very simple way to fly your Mavic Mini without the DJI genuine battery but with the telemetry of voltage available on the RC.
Obviously there is some electronics behind this.

A PIC12F1840 microcontroler will emulate the I2C traffic needed by the ESC board of the Mavic mini to start the drone and to collect telemetry information.
The voltage of the cells is acquired by B0B via a resistor bridge.
The total voltage of the batt is displayed into the Mavic Mini temperature field. This is done on purpose just to remember you flight with B0B and not genuine battery.
The voltage is displayed like this :
820,0 °C ==> means 8,200 V
This value is then divided by 2 and displayed into each cell gauge.

The battery remaining capacity is estimated based on the total voltage and displayed on the screen. The estimation is NOT accurate and is clamped to a minimum value around 11%. Just enough to trigger the low batt warning
1f609.png
;-)
You'll have to flight "with tension" reading the total voltage of the batt. Don't go under 6.6V or the batt can be damaged (and the drone may lose power and eventually crash)
To be clear, as its name means B0B is a battery with no BMS.
You cannot use it to charge the batt from the DJI charger nor from the USB plug from the drone.
B0B is "stupid". it just fools the DJI firmware giving it just enough information to start the drone and display voltage . That is !
The battery is attached to B0B with a "sliding" 2x3pins connector. You can use a single B0B and own as many batteries you like. Two Samsung 2400mAh 18650 cells can be found for 10€ on ebay
1f609.png
;-)
the battery can be un attached and I charge it using the same connector to attach it + the middle point to balance it...
Only very few components are needed:
  • a PIC 12F1840 with a dedicated firmware
  • 2 resistors (1k and 1,8k)
  • a 3.3 LDO HT733 voltage regulator
  • a small capacitor
  • a battery connector
  • a PCB
  • 6 pins from a 2.54 pins connector
  • a 8 pins 2,54 female connector (to be installed on the battery)
To use B0B, the Mavic Mini firmware version shall be 1.0.0400 or below.
The battery type inside the firmware shall be set to type 2 or 3 (which means just a warning on the screen in case of low batt and no RTH. (you are just warned)
Should you want to keep the advantages of the latest firmware for the manual setting in video, there is the solution of "firmware module mixing"
1f609.png
;-)

BTW, why placing it on thingiverse? just because there is a 3D printed lock mechanism to avoid a disconnection of the batt ...
Of course the door can be closed and the batt is lighter than the genuine one (5 grams shaved in the mass budget)!

Should you be interested to build one, just PM me.. I get 8 spare PCBs and microcontrollers available
1f609.png
 

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It looks like the cells used in genuine DJI batteries are 18650 Samsung 25R cells (2500mAh, 20A rating). There are several other ratings for 18650 cells, such as Samsung 30Q (3000mAh, 20A) and Sony VTC6 (3000mAh, 20A). Has anyone tried using higher capacity cells to get a longer flying time? Most higher capacity cells are a few grams heavier so would put the drone's flying weight over the supposedly magic 250g limit.
 
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It looks like the cells used in genuine DJI batteries are 18650 Samsung 25R cells (2500mAh, 20A rating). There are several other ratings for 18650 cells, such as Samsung 30Q (3000mAh, 20A) and Sony VTC6 (3000mAh, 20A). Has anyone tried using higher capacity cells to get a longer flying time? Most higher capacity cells are a few grams heavier so would put the drone's flying weight over the supposedly magic 250g limit.
The biggest interest of B0B is the abaility to play with any batt you wish :cool:
I'm just in the process to connect it to some yellow 18650 cells found on ebay rated 35A peak and 2500mAh... Each for 3€ or so ... At that price I can take the risk LOL
Considering B0B with the genuine samsung cells is lighter by 5g than the DJI battery, this gives us a huge margin of 5+2 = 7 grams if we want to stay right under the 250g magic limit ...

Next time I wil try higher capacity such as the Sony VTC6.

I think we should make a forum of B0B's users and share our results :)
 
Can the MM make use of the higher max current rating? Any idea what current it can draw under heavy loading?
 
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Can the MM make use of the higher max current rating? Any idea what current it can draw under heavy loading?
The max current rating of a battery is related to the internal resistance of the cells. With a 'high' resistance, the battery will overheat under high current and part of the battery capacity will be lost by Joule effect.
The mini does not need a lot of current. As in average it drains a 2400mAh batt in 24 minutes this gives an average current of 6A with something around 10A to 15 A max...
 
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I will like to test with SONY VTC6 witch is my favorite battery in my Flashing lights hobby.
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