Dual Battery Mod

[Gimpster]

Well, I've only owned my P3A for almost two weeks and got bit by this bug for a little more flight time. Cracked open one of the batteries and modded away. Weather is poor today for flying, but I'll just be using a single ~300g 2650 mAh pack I typically use on a fixed wing plane.

I have a pair of the CF side saddles I see FPV Customs uses on the way for running dual 1.3-1.6's, but for the single pack I'm just going to make a balsa leg saddle for the single pack.

This was a long thread to make it through, but thanks everyone for posting a lot of great data.

As my DJI batteries degrade, I'll reconfigure this.

 

[MVodhanel]

This could be big![emoji41]

I get a little frustrated working with this DJI battery manager. I find myself wanting to find the firmware designer and do really bad things to him. I don’t find myself cussing so much any more. It took a while, but my dignity is coming back now that I have left my catatonic, fetal position. The reports of thumb sucking, etc are greatly exaggerated, so please cut me some slack…

Yeah, ever notice how the transmitter shows you cell, voltage recovery when you land? The color goes either from orange or red back to green? Some of that is battery recovery, for sure. Some of it could be voltage drop if your wires aren’t of sufficient size while under load. The bigger the load, the more apparent this effect will be.

When I added the load of the equivalent of a second smart battery without the circuitry, the copter no longer flew smooth as silk. It became choppy and the transmitter voltage drop was more pronounced. Btw, the extended batteries are feeding directly to the ESC board, bypassing the battery manager, so the battery manager was getting an assist. Also, Btw, I didn’t attribute this behavior to voltage drop immediately, hence my replacement of the motors and downward spiral into catatonic, oh never mind….

I wired my entire bird using 14-gauge wire. Gauge chosen walking that fine line of weight vs capacity and the observation that DJI used 14 for internal connections. However, the DJI (presumably, highly engineered) connections were very short, less than an inch. Mine not, and sometimes as long as 6 inches. DC does not travel very well. Even 6 inches will make a difference. This is the very reason AC was developed, for long runs (Btw).

So, I re-wired using 10 gauge from Radio Shack (yes sir, I went in there) I have 12 gauge, silver plated strand ordered, that is what I am going to standardize on. I am also going to start to use 5% silver solder, rosin core. This is over-kill designed to hedge my bet to remove conductivity as an issue and find the middle ground on weight. So I will be re-wiring once again when I have everything. It is just as well, this test with the RS 10 G produced the new knowledge about how to run the battery manager in this new mode. It will probably influence my (hopefully) permanent wiring job.

So, guys before me, the ones whose shoulders I stand are the ones that have been extending flight successfully by connecting after the battery manager. Nobody bothered to document this fact, unfortunately. I spent months trying to extend trying to work with the battery manager. It is a lot easier being able to use the same switch, etc…. The reason this works, I speculate is the fact is that it is after the manager, and the manager doesn’t get to see the electron flow provided by the extension batteries. Electricity will always follow the path of least resistance.

OK, to describe a little better, in this context, what I discovered: I created a connection very similar to the connection the extended battery has after the battery manager to the primary battery. The connection must be left open normally, otherwise the copter will start up. The copter needs the battery manager to arm, however.

So, I start the copter the normal way and it arms itself and initializes. The amperage helping circuit is simply a male/female plug I just connect at this point. It is 12 gauge wire. Knowing that electricity is going to follow the route of least resistance, how would you guess the real power is going to flow? This is also going to take a load off of that poor battery manager. It should stay nicely powered to keep the copter armed and informed of the voltage?

Copter lands, I pull the plug and turn the copter off. I want you to note that I was able to, for the first time, use a single battery, a Hyperion HV 5200 that I split into two 2s’s wired in series and I was able to fly it down to 3.33 volts. Before this, I did nothing but cuss at China… There is no reason this wouldn’t be appropriate for dual battery configurations. My next wire job will just have a switch, I think. What do we call the switch? (The screw DJI switch?)

 

[Gimpster]

Try not to laugh too hard, but I got out the spruce ply + balsa and made a little battery tray this afternoon. I'll sand it down and paint it white tomorrow. I made this so I could fly with the two aux batteries before the CF mounts come, but I actually like how it lowers the center of gravity and stiffens the landing gear.

The 1300 and 1600's just will just slide in (going off published dimensions) and hug the rail and I'll notch slots for velcro. A couple baby 2S's just to give an idea. If I like how it flys, I might draw it up and print it on the 3d printer at work.

 

[Gimpster]

I know I'm really johnny come lately to this thread/Phantom in general.

Alright, so I took my first flight with one ~330 gram 2650mAh battery on my tray. The battery is about 2 years old now, many flights on my Slick 3D plane. Internal resistance is still within limits though, and I tend to take care of my batteries. I ordered some of the lighter 1300-1600's, but not here yet. I have no intention of buying LiHV's as I have no other use for them.

While I flew, I put my LCD battery meter on the 2650 so I could watch it from behind. After the flight each cells voltage was pretty dead on with the DJI battery, so I'm happy about that.

I had to just hover in my garage due to rainy weather. Never got more than 2-3 feet off the ground. Messed around in atti mode, yawed around and goofed around. Balance is CLEARLY less than optimal with this battery, so I'm sure that doesn't help hover time

Flight: HealthyDrones.com - Innovative flight data analysis that matters

Battery: ZIPPY Flightmax 2650mAh 4S1P 45C (AR Warehouse)

Somewhat interesting, but I used the stop watch on my phone and my phone says I was up 22:43 vs. 21:20 on healthydrones? When I clicked the battery info on the app it was in the 22:xx's too. Not sure how they calculate flight time. EDIT: I see why now, I landed not long after taking off the first time to re-secure the LCD battery meter to it counted it as separate flights.

Comparing to other flights where I just hovered, I'm pretty happy to have maybe an extra 3-4-5mins flight time (depending on conditions). I mean I have an investment of like 2 hours of my time, 1 dollar in wood and 30 bucks of batteries on the way. No way in hell I would pay $150-250+ for this though, but I understand not everyone is comfortable soldering stuff. Added bonus of now being able to charge my DJI batteries with my much nicer LiPo/LiHV charger through the XT60.

When I first got my Phantom, I did a very similar hover in my garage but only to 50% battery. I thought it would be interesting to chart both of those in Excel to compare the first half, I attached a screenshot of that graph. Not a big surprise to me that the initial sag is diminished, and also it just seem like the power is less eratic with > 1 battery. Red line = +1 battery

Charting like that you get some good trend lines too to estimate flight time.

Earlier in this thread a poster (sorry, it was so many pages back I forget who...) posted some good weight vs. power usage info, and that will certainly help me make my decisions going forward.

 

[nix240z]

When I tried to mount my batteries low near the landing gears, I was getting compass errors even after many compass calibrations.

 

[Gimpster]

Interesting. I will keep my eye on that when the weather clears up and check.

When I tried to mount my batteries low near the landing gears, I was getting compass errors even after many compass calibrations.

 

[MVodhanel]

I ran a test with a dual battery configuration on my custom copter and was reminded that the dual setup works pretty well. I have attached pictures of battery screens showing results. The percentage system allows a pretty thorough discharge of both batteries.

Then I ran the same test with the load assist circuit (AKA ‘Screw DJI Switch’) and was reminded of how I got there in the first place. There was no comparison between the two flights in terms of stability. I could actually take my hands off the transmitter, and relax. I was testing in my basement. The copter was much more stable. The flight times were comparable.

As I mentioned earlier, this method is something I would only recommend for those that truly understand what it is. I see some potential safety benefits (but make absolutely no claims) of having a better powered drone with a shut-down logic with less to go wrong.

I plan on using this method and will post here if I find any safety issues as I use it.

 

[MVodhanel]

When I tried to mount my batteries low near the landing gears, I was getting compass errors even after many compass calibrations.

Nix, the compass is in the landing gear, right - rear. It is really finicky about anything metallic like wires, etc... You probably have something too close to it. Just relocate it, and you should be good.

 

[nix240z]

Nix, the compass is in the landing gear, right - rear. It is really finicky about anything metallic like wires, etc... You probably have something too close to it. Just relocate it, and you should be good.

Yes, I moved it after a few calibrations and no go...

 

[Ed209]

I ran a test with a dual battery configuration on my custom copter and was reminded that the dual setup works pretty well. I have attached pictures of battery screens showing results. The percentage system allows a pretty thorough discharge of both batteries.

Then I ran the same test with the load assist circuit (AKA ‘Screw DJI Switch’) and was reminded of how I got there in the first place. There was no comparison between the two flights in terms of stability. I could actually take my hands off the transmitter, and relax. I was testing in my basement. The copter was much more stable. The flight times were comparable.

As I mentioned earlier, this method is something I would only recommend for those that truly understand what it is. I see some potential safety benefits (but make absolutely no claims) of having a better powered drone with a shut-down logic with less to go wrong.

I plan on using this method and will post here if I find any safety issues as I use it.

View attachment 52313 View attachment 52314 View attachment 52315

Nice custom frame. Did you build yourself? What's the normal weight without any batteries? I was thinking of doing something similar but seems that it would be hard to get it lighter than the DJ shell. Those times were with what battery?

 

[hebs]

Earlier in this thread a poster (sorry, it was so many pages back I forget who...) posted some good weight vs. power usage info, and that will certainly help me make my decisions going forward.

I should have much more accurate results soon. It appears that my initial predictions were too conservative- might be something to do with the way that the battery manager limits current (I didn't know this during my initial tests), this means that my flight predictions are short:

DJI battery & 2x MultiStar 5200 batteries

Predicted flight time was 28min 28sec
Actual flight time was 37min 19sec


Sent from my iPad using PhantomPilots mobile app

 

[Gimpster]

wow, impressive!

I should have much more accurate results soon. It appears that my initial predictions were too conservative- might be something to do with the way that the battery manager limits current (I didn't know this during my initial tests), this means that my flight predictions are short:

DJI battery & 2x MultiStar 5200 batteries

Predicted flight time was 28min 28sec
Actual flight time was 37min 19sec


Sent from my iPad using PhantomPilots mobile app

 

[MVodhanel]

Nice custom frame. Did you build yourself? What's the normal weight without any batteries? I was thinking of doing something similar but seems that it would be hard to get it lighter than the DJ shell. Those times were with what battery?

That is my Lite Foot project at : Lite Foot In case it may seem rude of me posting such a link here, really, it is not. This thread inspired that project. I would have posted it here, but it would have hurt too much making it fit the dual battery mod theme as I have done in the past. You are right about it being difficult to make something lighter than a stock P3. It takes exotic materials. The end result can be a P3 that is more like a piece of equipment designed to be kept in service. That is what Lite Foot is.

I have actually neglected my own thread. This thread has the most up to date info on Lite Foot. Lite Foot does beat a standard P3 in weight, but not by much, and gets a reliable 22 minute flight time as a result. And this is a quiet bird because of the weight. But now I am working on the extended version and I am coming up with stuff, so I like to get posted here for the extended flight community. I will update Lite Foot later.

The P3 has been a success on so many dimensions, one doesn't have to look any further for the perfect drone. It is a shame the manufacturer is not easier to work with, or one that may be trusted. Be that as it may, the drone is out there in quantity like the people's car the VW bug. It has already been shown that their firmware is comprised of portions open source code. I did ask on the DJI forum where I could find their source a while ago. I am still waiting for an answer (no, I did not expect to get the source - I made my point I think)

Anyway, just looking at some of these facts may eventually wear DJI out and cause them to open the P3 up and cut this proprietary nonsense out. They can focus on their other products. They can continue making P3 parts. Aftermarket suppliers can make P3 improved parts. If DJI doesn't bend, we crack. They are not as smart as they think they are.

Open source firmware, aftermarket frames... The P3 compatible....

 

[Ed209]

That is my Lite Foot project at : Lite Foot In case it may seem rude of me posting such a link here, really, it is not. This thread inspired that project. I would have posted it here, but it would have hurt too much making it fit the dual battery mod theme as I have done in the past. You are right about it being difficult to make something lighter than a stock P3. It takes exotic materials. The end result can be a P3 that is more like a piece of equipment designed to be kept in service. That is what Lite Foot is.

I have actually neglected my own thread. This thread has the most up to date info on Lite Foot. Lite Foot does beat a standard P3 in weight, but not by much, and gets a reliable 22 minute flight time as a result. And this is a quiet bird because of the weight. But now I am working on the extended version and I am coming up with stuff, so I like to get posted here for the extended flight community. I will update Lite Foot later.

The P3 has been a success on so many dimensions, one doesn't have to look any further for the perfect drone. It is a shame the manufacturer is not easier to work with, or one that may be trusted. Be that as it may, the drone is out there in quantity like the people's car the VW bug. It has already been shown that their firmware is comprised of portions open source code. I did ask on the DJI forum where I could find their source a while ago. I am still waiting for an answer (no, I did not expect to get the source - I made my point I think)

Anyway, just looking at some of these facts may eventually wear DJI out and cause them to open the P3 up and cut this proprietary nonsense out. They can focus on their other products. They can continue making P3 parts. Aftermarket suppliers can make P3 improved parts. If DJI doesn't bend, we crack. They are not as smart as they think they are.

Open source firmware, aftermarket frames... The P3 compatible....

YES!!! I don't know how I missed your thread but that is exactly what I was thinking about doing. Using CF materials to build a lighted drone with P3 guts. Much respect! I'm curious how good that would do with a heavy battery fitted. Perhaps a Multistar 5200. I know that goes against what you were trying to accomplish but my goal is to use the proven extra battery along with the DJI battery. I got 39:45 with my P3A using the 5200 and DJI bat. Shaving off a whole 120g is huge! I might have to put some time and energy into this.

 

[FredzMaxxUAV]

I should have much more accurate results soon. It appears that my initial predictions were too conservative- might be something to do with the way that the battery manager limits current (I didn't know this during my initial tests), this means that my flight predictions are short:

DJI battery & 2x MultiStar 5200 batteries

Predicted flight time was 28min 28sec
Actual flight time was 37min 19sec

You actually flew with 2x aux 5200 batteries attached? Wow

 

[hebs]

You actually flew with 2x aux 5200 batteries attached? Wow

I have nearly 10 times now. It's a bit slow to accelerate and stop but it seems to cope well and the motors are only slightly warm on landing.

Iv used duel 4000s & 4400s even more often (video of me landing on my tank in a previous post).

I may try duel 6600s but I know that I'm getting close to the birds limits.


Sent from my iPad using PhantomPilots mobile app

 

[hebs]

That is my Lite Foot project at : Lite Foot In case it may seem rude of me posting such a link here, really, it is not. This thread inspired that project.

I missed that thread before as well...... I may have to give up my family now that I have seen your project. I didn't realise that carbon fibre was within reach of my abilities. Dangerous

Awesome work MVodhanel!


Sent from my iPad using PhantomPilots mobile app

 

[FredzMaxxUAV]

I have nearly 10 times now. It's a bit slow to accelerate and stop but it seems to cope well and the motors are only slightly warm on landing.
Iv used duel 4000s & 4400s even more often (video of me landing on my tank in a previous post).
I may try duel 6600s but I know that I'm getting close to the birds limits.

I fly single LiHV 4000s, 5200s and 6600s (Hobbyking), mounted under VPS with Dual Lock. I get about the same results as yours with dual (up to 35-36 minutes). I honestly think running these as duals is killing the bird. Running them with singles is already pushing to the limits. And you're getting almost no extra time... In warm weather, people have reported up to 40 minutes with single 5200. This is all to 10%.
Just my opinion.

 

[MVodhanel]

I missed that thread before as well...... I may have to give up my family now that I have seen your project. I didn't realise that carbon fibre was within reach of my abilities. Dangerous

Awesome work MVodhanel!


Sent from my iPad using PhantomPilots mobile app

Yep! Amazon will deliver tools and materials directly to your door. Please do not indicate to family where you learned any of this...

 

[MVodhanel]

YES!!! I don't know how I missed your thread but that is exactly what I was thinking about doing. Using CF materials to build a lighted drone with P3 guts. Much respect! I'm curious how good that would do with a heavy battery fitted. Perhaps a Multistar 5200. I know that goes against what you were trying to accomplish but my goal is to use the proven extra battery along with the DJI battery. I got 39:45 with my P3A using the 5200 and DJI bat. Shaving off a whole 120g is huge! I might have to put some time and energy into this.

Sounds good to me. In fact I realized I haven't updated my battery inventories in a while so I ordered a couple of MS 5200 and the next step up 6xxx, a couple of those as candidates to split and try as extended flight single mode. My load bypass circuit now makes this possible. Before I thought of doing that, any time a larger primary battery were used in place of the standard battery, only 4,480 mah of it could be used. So there are new, single battery power to weight ratios to try.

One thing I have learned is that the P3 is really weight sensitive. Just taking 120 g's off the copter got me 22 minutes, a quiet bird that literally loafs in the air. It moves like a 911 (turbo - no lag or over steer) and is like a rock. Now I am adding batteries and heavy gauge wire harness and gaining incremental time in the sky, but I am losing stuff too. I guess I am going to view this copter as having two modes, a sport mode, and a extended flight mode....

I also need to build a true ultra-light P3 without the fancy feet (and cool Indian name) and really see what this P3 can do with one, standard battery. It might surprise us all. Btw, there is no turning back once you start making custom copters. Fair warning...