3DR Solo with LiIon 9000mAh battery | up to 30min flight time

Someone did a comparison of (1) stock, (2) APC 11", and (3) MA 10.5" 2 blade here on a 'normal weight' solo... (elsewhere there are tests showing the 3 blade MA is worse for efficiency).. The 2 blade MA's were best... The 11" was very close behind... The stock was 3rd (about 8% worse than the the others..

See Solo Props: APC, MA & Stock. Battle For Power..

My observation is that with a heavier batt pack the 11" props take the lead for me.. But I can't quantify by how much (not much really I suspect- maybe just a few Watts, translating into a few 10's of seconds extra flight time perhaps).. So it could be that MA 2-blade and APC 11" options are so similar efficiency wise (within 1%) it hardly makes any noticeable difference, allowing for experimental error etc. So then it comes done to preferred flying characteristics (smaller props = more nimble, larger props = more stable??)

Thanks, like a few others here, I am lugging around a Sony APS-C mirroless camera on my Solos. The 11" props may be a good choice to handle the weight. Will give both the MAS and the APC 11s a workout.
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Obviously - Wattage (power) stays constant to maintain a hover throughout a flight... So at the start if the pack is at >16 volts, and at the end the pack is ~10-11v then there has to be an approx 50% increase in Amp (current) draw so as to keep power constant.
In my tests (although I did have issues in calibrating my shunt resistor current measure), I was drawing about 20A at the start, and just under 30A at the end (the limit for the Sanyo 4s3p pack).
I appreciate the detailed reply. From my experience or others comments for the LiIon, there is an amp limiting issue. I run 800kV motors and have seen a reduction for amp draw peak, hover or in between. IIRC, with stock weight hovering is around 16A and then peak (full throttle hole shot) at around 40A with stock battery from circa 2016 memories.

I really don't have any foundational experience to the why's and what's for battery choices. I'm a RTF'er rather than a DIY'er I am listening to conversations here to gain a perspective to make a choice. Again thank you for your reply. I just want the best solution available...with no compromises.
I just saw the new posts and would like to share my thoughts.

In general bigger propellers are more efficient because they have a higher aspect ratio (same principle as with wings). But of course it depends on the airfoil used of each propeller model. It depends also how you test them (static hover vs forward flight). Some propellers might be more efficient in hover but inferior during forward flight. 3-bladed propellers are in general worse from an efficiency stand point of view. They have the advantage that in order to get the same thrust as a 2-bladed counter part you can spin them at lower rpm which results in a lower speed of the blade tip which reduces the risk of stalling the propeller blade. 3-bladed props "grip" the air better, are probably more responsive (might as well have to do with the lower momentum of inertia of 3-bladed props) and thus safer but less efficient. That is why you see them on a lot of racing drones. But the aspect ration of 3 bladed props is not good that is why they are less efficient. In order to make a 2 bladed propeller with the same thrust as a 3 bladed one you can make the 2 bladed propeller bigger with a higher aspect ratio.
In general the efficiency of propellers is worse in hover than in forward flight (also known as translational lift) Why so? Because in hover the airspeed of the air that goes into the propeller is close to 0 m/s. In forward flight the drone is slightly tilted forward thus the airspeed of the incoming air is higher. Generally a propeller has its best efficiency range when the airspeed of the propelled air is 15-30% higher than the air coming in. Hover is a pretty inefficient flight state because the speed difference of the incoming and leaving air is huge. This is also the reason why low pitch propellers are better suited (more efficient ans safe) for hover flight. Here is how to calculate the speed of the leaving air: rpm/60 * (pitch * 2.54 / 100 ) [m/s]
If the drone is tilted 20° forward and has a flight speed of 10m/s the airspeed of the incoming air is sin(20°) * 10m/s = 3.4m/s
Lets assume 8'000rpm and a 4.5" propeller pitch. This results in an airspeed of the air leaving the propeller of ~15 m/s.

In my opinion the original 3DR Solo with camera and gimbal is already on the heavy side. Even more so with the 4S3P mod battery. Thus bigger propeller make certainly sense (if they are well designed). Unfortunately I have never tested bigger propellers with the Solo.
I run Master Airscrew 2 bladed because they are quieter than the stock propellers and in my experience a tiny bit more efficient. The original propellers tend to make a loud noise which people on the ground don't like and unfortunately enough people I meet when flying have a dislike against drones because of their privacy concerns. (Note: I always try to fly responsibly, I don't care about spying on other people, just want to fly the drone and film some nice landscapes, objects) If they only knew what is going on on their smart phones or their computers ... (or they know, but just want to be angry ...)

What I generally do with propellers:
- from the factory mold some tend to have rough edges. I use a 400-600 grid sandpaper and make the surface smooth (helps with noise and efficiency)
- balancing the propellers is inevitable

4S3P vs 4S2P
In general be aware the the energy output of the battery cells under heavy load is less than rated. A heavy load cell with "not so high mAh" could deliver as much energy as a light load cell with "very high mAh". It all depends on the load and the internal resistance of the cells. Thus on paper a 3450mAh cell might look much better than a 3000mAh cell but since the 3450mAh cell has a higher internal resistance it looses more energy during flight. Thus in reality the difference is smaller. Take also into account that the cells internal resistance increases over time.
Although I have never flown a 4S2P battery I would imagine that the Solo would fly "better" but shorter. If your flying style does not include crazy abrupt maneuvers then this works for sure with the Samsung 30Q (you might also try 21700 cells). Lets assume to get 2600mAh of the 30Q cells under load, thus a 4S2P 30Q pack could deliver about 75wh (2.6Ah * 3.6V * 8) of energy which would be about the same as the stock pack but the drone would be lighter thus it would fly a bit longer. So if you don't care about the maximum flight time and prefer a quieter, better flying Solo then I would use a 4S2P battery.
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talking about Warning, Battery differential: xxxxxmV
"to disable cell differential checking, comment out this line and it will no longer check the cell voltage to provide that warning" - OpenSolo/OpenSolo
shotManager.py is located on drone in /mnt/rootfs.ro/usr/bin

I can edit it but can't save, can downalod, edit, save, but cant upload via WinSCP

I think it needs to be done somehow differently. Can someone point out please?

[update] found this:
But what exactly to do?
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@makatanav I think the problem is that you don't have root access to write on this part on the Solo onboard computer IMX6 (which runs some old Linux). You need to establish a SSH connection to the Solo and then you need to gain root access (with sudo). Though I m not sure if you can login directly as root through the SSH connection. I don't remember. According to this site:
3DR Solo (Developer Information) — Dev documentation the root password for the IMX6 is: TjSDBkAu
A SSH connection is a remote command line of another computer on your computer. Through that you can fully control (with root access) the other computer.

Edit: Here it is described (you gain directly root access on the Solo): Accessing Solo | 3DR Solo Development Guide
You can replace the file on the Solo with some commands or edit the file on the solo with the command line editor vim or nano (I guess one of those must be installed)

After you establish the SSH connection you type in the terminal:
nano /usr/bin/shotManager.py

This should open the file on the Solo in your computer. You can edit it and safe it. Job done.
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You're looking in the wrong place. I'm not sure how you dug into that one but you're trying way too hard. That's the ro system that it will revert to when reset.

Connect to the solo with WinSCP (, user root, pw TjSDBkAu). Then simply navigate to /usr/bin/. The file you're looking for is in there. You can edit the file and save to the copter directly in WinSCP.
You're looking in the wrong place. I'm not sure how you dug into that one but you're trying way too hard. That's the ro system that it will revert to when reset.

Connect to the solo with WinSCP (, user root, pw TjSDBkAu). Then simply navigate to /usr/bin/. The file you're looking for is in there. You can edit the file and save to the copter directly in WinSCP.
thanks, will check and inform back.
I wrote on 3DR facebook group and Jon Brotherton provided the info.
Have wrote some questions also directly to you in this forum, but haven't got answers :)
thanks, will check and inform back.
I wrote on 3DR facebook group and Jon Brotherton provided the info.
Have wrote some questions also directly to you in this forum, but haven't got answers :)
I don't do private message support for random people on the forum. That's an impossible time commitment rabbit hole I don't go down. Post questions in the forum so I or anyone else here can help when able.
tested mine 4S3P 30Q on 10" MA and 11"APC
the same environment
16.5V down to 12.4V
10" MA - 21:20 min
11" APC - 21:15 min
10" MA gain altitude faster than 11" APC and seamed smoother, soo looks like will stay primary with 10" MA
(my 3DR weights ~2kg)
Hi everyone

I would like to share my experience with building a custom LiIon battery for 3DR Solo and have correct battery % display on the App and Artoo controller. My goal was to build a battery that lasts longer than the original one without any performance cuts. There are several ways to do a battery mod in this thread. Please read careful what you need to do for your mod. Not all writing bellow is important for you! The italic writing is contend that I discovered during the process of all this. It represents to me a less optimal solution. I leave it there for knowledge. If you do this mod you need to take great precaution! If done not properly you can endanger yourself, other people and property! I'm not taking any responsibility in any way for damage that may result!

1. Choosing the right cells
When flight testing my 3DR Solo the maximum amp draw it could produce was 46A in stabilized mode giving full throttle. This kind of flying style isn't suited for Solo in my opinion but the battery should be able to deliver the power needed. Looking at 18650 cells and knowing each cell weighs 45-48g there are two options to make a battery pack. The original Solo batter weighs 492g.

a) 4S2P which weighs around 370g cells only
b) 4S3P which weighs around 550g cells only

In hover and slow cruising Solo consumes 15-20A. From this I knew that there would be 18650 cells that will deliver the required amount of power. Having a look at different cells and comparing them here Battery test-review 18650 comparator

Samsung 18650-25R 2500mAh 20A continuous discharge
Samsung 18650-30Q 3000mAh 15A continuous discharge
Sanyo 18650GA 3500mAh 10A continuous discharge

I decided the 30Q would be the best option for a 4S3P pack considering the cells become less power full with time as IR increases. And they hold voltage better under load than the 25R. I m sure the GAs will work good as well and they would give even better flight time. Other 18650 cells are suited as well for sure.

2. Building the 4S3P LiIon battery
The battery is a 4S3P. Build it accordingly. I used a spot welder but if careful and fast soldering should work as well with no problem. Cover the LiIon battery with tape or shrink tube. I used XH balancing cables. The 4S3P 30Q battery weighs 593g, 100g more than the Solo battery. Internal resistance of each cell of the pack is 6-7 mOhm which I m very happy about! Make sure not to short anything during the process! I did not use plus pole paper prodection rings on the 18650 cells. Which I will use in future.

3. Getting battery telemetry
3DR Solo uses smart BMS in each Solo battery which will give battery telemetry to Solo and ground station. There are different ways to get this information.

a) Don‘t have telemetry: Solder the battery connectors directly to the Solo board. You need then to use a LiPo alarm and/or timer. It works but it is not what we want.

b) Using the Solo BMS: It will give all the telemetry. And allows to use your own battery. However there is a 5200mAh capacity limit coded in the BMS. That means if you use a 8000mAh battery the Solo BMS will report 0% battery after 5200mAh used in flight although there are still 2800mAh left. In Software hack down bellow I show a way to get around it.

c) Use your own smart BMS: Solo uses SMBUS v1.1 specification. Found here: SMBUS Spec.pdf Any BMS that support this can be used. The available SMBUS BMS are either too big and heavy or have too little amp support. And they are expensive. Unfortunately this does not seem the way to go.

d) Use a power module: A power module allows to use any battery and to use your own RTL parameters. There is no 5200mAh limit. And it saves weight. The Solo BMS with connector weighs around ~60g. The power module only ~20g. This is my prefered method. It requires very difficult soldering.

Taking apart a Solo battery
I would like to thank the kind user from Solo Hack group on FaceBook who sent me defective batteries.
The Solo batteries are made very well and difficult to take apart. It is impossible to take it a part and put it back together! With a bench grinder I removed as much plastic around the battery where the two half's connect and then it is quite easy to open. Underneath the battery where the sticker is and where it is glued to the plastic, there is a protective aluminium plate on the LiPo cell. You can use a flat screw driver and go between the plastic and the cells and you wont do any damage. Be careful with the open battery (shorting it)!!! Unsolder all cables from the Solo LiPo in order to reuse them. There are several videos on YouTube that show you how to open a Solo battery.

Soldering connectors to the Solo BMS
Soldering your favourite connectors to the Solo BMS battery leads is easy. Be careful that you solder the balancing cable the right way around! AN1 stands for ground and P+ is positive pole. For an image check this post here: 3DR Solo with LiIon 9000mAh battery | up to 30min flight time
After that connect a 4S LiPo battery to it and check if it works. If successful cover it with shrink tubing or insulation tape.

Charging the LiIon battery with the Solo BMS and charger
To say it short: It simply works!
I discharged the LiIon battery completely down to 2.8V per cell (at least 8300mAh used) and was able to charge it completely with the Solo BMS and charger! And the Solo BMS reported a full battery. If you don't trust the Solo BMS and charger you can use your normal RC battery charger. If you charge the battery externally and plug it in to the Solo BMS it will report that last battery stage it was at. Eg. if you just flew one battery empty with this BMS and you plug a fully charged battery to the same BMS it will report an empty batter. Voltage and amps are correct though. To prevent this plug the unit to the solo charger a couple of minutes for the Solo BMS to adjust or connect to Solo and set BATT_CAPACITY parameter to the specific value of the battery you want to fly with.

The battery is strapped with a walkro to Solo. Does not look nice but it holds. Because of the metal case of the 18650 cells the compass needs recalibration. Even after swapping one LiIon battery for the other. At least with the stock compass. I don‘t know how it is with the Here compass. I imagine it to be better. After calibration it works just fine. If you change from LiIon to the original battery you have to calibrate it as well. The Solo BMS with your battery is recognized as a normal Solo battery. However in the case of LiIon batteries, they have lower voltage level and can be discharged to a lower voltage (2.5V vs. 3V LiPo per cell). Thus Solo with LiIon battery will trigger RTL and low battery alarm too early. How to prevent this see section Software hacking below below.
If RTL is triggered just press pause, A or B. After that you have to monitor the voltage with the App in order to have an idea about battery life. This needs some experience with battery discharge curves to be able to tell. I recommend flying down to 11.6-12V (2.9-3V per cell) with LiIon batteries and 14V (3.5V per cell) with LiPo batteries. Tests have shown that Solo flies even with 10.9V.
If you charged the battery externally and the Solo BMS is reporting 0% capacity from the last flight but you still want to fly it, you have to move and hold the left stick to the centre and down and Solo will arm. You wont see any information on the Artoo controller - just the battery warnings. But on the App all the information is there.

How to install a power module
For pictures see this post (I cant fit more pictures to this post): 3DR Solo with LiIon 9000mAh battery | up to 30min flight time

PRO: It works! With correct battery % on artoo and in Solex
CON: The soldering job is very difficult

I managed to solder cables to pins 47 and 49 (the standard power module input pins on the Pixhawk Cube). It seems that on the Solo board these pins are not used at all and no traces are leading from the plug either. This means that in order to use a power module you need to solder to these pins! The soldering job is very tiny and difficult! Please consider very thoroughly if you want to do this! The cables I had were too thick. I had cut half the stripes in half to get a fine enough wire. To lead the wires out under the Pixhawk Cube it was required to make some space. I did a quick and dirty job by using the soldering iron and melting the plastic (350°C) of the Pixhawk Cube. Worked well.

Pin 47 = Current sensor
Pin 49 = Voltage sensor

Connect these pins to the power module which will have 6 Pins. Solder the power module to the power input on the Solo board and solder your plug system at the battery input input of the power module.

Power module pin output:
Pin 1 VDD 5V do not connect
Pin 2 VDD 5V do not connect
Pin 3 BATT_VOLTAGE_SENS_PROT connect with pin 49
Pin 4 BATT_CURRENT connect with pin 47
Pin 5 GND no need to connect
Pin 6 GND connect to ground on Solo board eg. on the battery input

I used this power modul: mRo Hall Sens Power module ACSP7 (Next Gen)
This looks great too: 100A / 200A Hall Sensor PM for Pixhawk / APM
Others work as well for sure ...

Each power module model is different to what settings have to be set in parameters. The ACSP7 uses these parameters (to be set in Mission Planner or QGroundControl): ACSP7_config.pdf You have to do a calibration in Mission Planner with a multimeter/wattmeter and measure voltage (important!) and amps. Amps should be measured under load to calibrate. Ideally 10+A.
That's it! Solex will display the values from the power module and the Pixhawk will calculate battery percentage based on used mAh and BATT_CAPACITY and this percentage will be displayed in Solex and artoo. No need to change it or flash artoo! With Mission Planner you can change the the RTL voltage and RTL remaining capacity paramters as you wish.

My settings for this LiIon battery:

The battery percentage in Solex and artoo (no need to flash it) is calculated based on used mAh. The formula is: (BATT_CAPACITY - used mAh) * 100 / BATT_CAPACITY RTL here is based on voltage (safer if the battery ages or you fly with a non fully charged battery). If you start flying with a half full battery Solex will report a full battery. But who goes out on the field with a half full battey anyway? The messages on artoo that it will RTL @ 10% is wrong, it does not really matter. I changed it to "RTL soon - battery is criticaly low". If you wish to have this slightly modified artoo firmware let me know.

Disabling RTL (only use with great care, no need to do it with Solo BMS or power module)
In order to prevent RTL kicking in at 520mAh or under 14V left I disabled some features in Arducopter (see here: 3DR Solo - ArduCopter Master Upgrade — Copter documentation). For this connect Solo network via computer/phone/tablet with Mission Planer or QGroundControl and change following parameters:



With these settings Solex and artoo will play low battery alarm after you reached the programmed thresholds, which is a bit annoying. But RTL will not kick in! Use voltage to land!

Artoo software hacking for battery % when flying with a Solo BMS

Make it RTL when you want
FS_BATT_ENABLE is triggered by a set voltage (FS_BATT_VOLTAGE), used mAh (FS_BATT_MAH) or at a specific percentage of battery remaining (artoo ?). I found out that the SMBMS sets at every boot of the drone the BATT_CAPACITY parameter on the pixhawk. You can change the parameter BATT_CAPACITY with Mission Planer / QGroundControl but after a reboot the changes are gone. The SMBMS has a coded capacity limitation of max. 5200mAh what ever the battery is. The Solo BMS learns at every discharge what its capacity is. But it is never more than 5200mAh. When flying with BATT_CAPACITY = 5200 it does a BATT_FAILSAFE at ~4900mAh which is not what we want. To overcome this connect Solo before flying with Mission Planer or QGroundControl and set BATT_CAPACITY to what ever your high mAh battery is (remember the discharged mAh under load is a bit less than printed). This value will stay until you power Solo off. To overcome the manual changing of the parameter I wrote python script on Solo that Solex can trigger from commands at every connect and overwrites BATT_CAPACITY written to the Pixhawk from the SMBus. This means no more RTL at ~4900mAh used and no need to manually change parameters before flight. The 5200mAh limit means as well that the used mAh in flight ae never more than 5200mAh. This resulst that on the App or Artoo the % is still after 5200mAh used capacity. In the 8000mAh example the 5% would stay still at 35% ((8000-5200)/80).

Making artoo display correct battery % (but not Solex!)
Artoo code reads mavlink messages and one of these messages is the battery percentage coming directly from Pixhawk and Solo battery. However this is not correct with a higher than 5200mAh battery.
I took the mavlink volt and ampere readings and calculated a battery % based on them. It does calculate for the voltage drop under load and compensates it to give a smoother output. The voltage range is set to 16.8V - 11.6V. The percentage comes down to personal preference and safety.
Flashing artoo is quite easy: documentation/flash-custom-firmware.md at master · OpenSolo/documentation · GitHub

Settings on Pixhawk:

Now it does:
- RTL does work at a set voltage or used mAh (thouhgh no more than 5200mAh)
- No need to tweak or setup anything before flight /script runs automatically)

This video shows overriding BATT_CAPACITY parameter and RTL at 12.4V.
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As I have no code from Solex, the app does show the percentages and alarms according to SMBus battery percentage. Nothing to be done here. As not every custom battery is the same it does not make sense to do anything here.

Here is a video of the Solo hovering 30:20m not in ground effect with the new battery. AUW 1650g, average power consumption 228w, 500 m.a.s.l, 1°C.
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Here is a video of the Solo hovering 23:28m not in ground effect with LiIon battery, gimbal and recording GoPro 4 Silver. AUW 1948g, average power consumption 285w.
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Fun and safe flying!
Please let us know when someone in the group is going to go in to business providing a plug and play battery superior to what 3DR originally came out with at a comparable price. I have about 15 dead batteries. And I am not a do it yourself kind of guy.

Fingers are crossed and let us know. :)
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Please let us know when someone in the group is going to go in to business providing a plug and play battery superior to what 3DR originally came out with at a comparable price. I have about 15 dead batteries. And I am not a do it yourself kind of guy.
Fingers are crossed and let us know. :)

In USA there is or will be an option (by info on facebook 3DR Solo group):
Please let us know when someone in the group is going to go in to business providing a plug and play battery superior to what 3DR originally came out with at a comparable price. I have about 15 dead batteries. And I am not a do it yourself kind of guy.

Fingers are crossed and let us know. :)
I understand you but to be honest I think there is no way around a bit of DIY with non standard batteries. Especially with the Li-Ion batteries who influence the compass in the Cube.
Using the BMSOne opens up the use of any and all batteries that fit the battery bay.
Add a 3D printed cover and its hard to know the difference.
I have one Solo I am fitting the BMSOne internally so it is just an XT60 and balance connect, slide cover on and fly.
I am no longer limiter to 5200mAh either as makatanav has stated.
Time to move on from the standard Solo batteries.

IMG_2470.JPG IMG_2490.JPG
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I need help!
how to defeat such a critical message...voltage failsafe critical ≥ low?
mro ACSP5 power module.MP_failafe.gifMP_batt.gif
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Have anyone tried the 4S2P configuration?
I guess you would have to use the 25R because the 30Q would only give you 30A max on a 2P config.
I want to be able to put the batteries back inside the solo battery plastic chassis. From may drawings here it fits perfectly.
Any comments?

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