MOBULA7 UPGRADE: More power with better battery connector

Introduction
In order to run 2s, the Mobula 7 comes standard with 2 x PH2.0 connectors that allow you to run 2 x 1s batteries in series. When running in series the strength of the connection is determined by the weakest link in that circuit. The strength of connection determines the maximum current that can pass and the voltage drop that results. Although it works this system has a very low current overhead from a design perspective - 2 x budget PH2.0 connectors with the dreaded 'folded' pin and very lightweight 26AWG wire. All this adds up to a lot of voltage drop when even reasonable current is pulled - something all will be familiar with on the mobula where you see voltage drop to scary levels (6v and below) during punches even when you have a full battery. Although it recovers almost immediately it does mean you don't get access to the battery's full voltage potential.

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This is the second article in my series of HappyModel Mobula7 upgrades, many of which can be used for the Trashcan too. Also to come are:

• Swapping to a much more durable frame​
• tuning betaflight filters more specifically for brushless whoops, 
• converting to run 'props out' 
• propeller upgrades. 
• receiver range improvement
• modding your 1s battery to be a proper 2s

All links will be updated here when completed. Many of these I've completed the work and am testing at present - it's starting to feel like a more complete little quad now. If you're looking for my review including setup it can be found here

JST connectors are very cheap, light and perfect for this application

How to improve the situation
Now that we are through the dreaded theory we can get on to the solution. To cut to the chase I will be moving to a true 2s battery connection with a JST connector and this is why:

• 1 x JST connector will allow much more current than 2 poor quality PH2.0 connectors
• 20-22AWG (guage) wire has a lot less voltage drop that the 26AWGwire included

As a bonus this makes it more durable. Although I used a 20AWG in this walthrough, I'd recommend these 22AWG ones because they are much more easy to solder and manage. In order to keep you motivated I'm pleased to say this makes a significant improvement to power and reduction in battery sag, more in the conclusions at the end. 

Why not XT30?
I'll address the elephant in the room - short answer is weight. The JST connector is lighter than the XT30 and has plenty of overhead on this quad considering it only has a 4x5a ESC (20a max). I've also had history of using both on my larger 1.9" ultralight build before too and the JST was not left wanting. The only reason I would go to XT30 over the JST in the future was if I needed more durability. (photos to follow shortly comparing weight)

Single male JST connector with 20AWG wire

XT30 with 18AWG wire (overkill)

2x PH2.0 connectors in series with 26AWG wires (stock)

New batteries
Going ahead with this mod means you'll no longer be able to use 2 x 1s batteries as before unless you make a harness of female JST to 2 x series PH2.0 I'd strongly recommend against this though as this adds weight and a lot of extra resistance. Assuming you have upgraded to the Eachine trashcan/mobula v3 frame as covered here (which is honestly the very first mod you should do) then there are 2 batteries I can strongly recommend:

GNB 2s 80c 300mah HV lipo. This is simply the best lipo in this size and fits the upgraded frame perfectly. It has excellent performance and minimal sag but you'll need to either use the xt30 connector on your quad or change the connector on the battery to JST. Note: RDQ, Happymodel and TBS use this same pack under their own brand. Note 2: for longer life I'd recommend charging to 4.2v per cell rather than 4.35 HV

Turnigy Nanotech 2s 45c 300mah lipo. This is a solid performer with a little more sag than the GNB but good nonetheless. It is almost half the price and is available in many places that the GNB doesn't ship to (including me in NZ). It comes standard with a JST connector.

If you do not have a balance charger, you will need one to charge these 2s batteries or ay other multicelled lipo battery. I use the hobbymate pro 2 duo (reviewed here) - a little more expensive but so versatile.

What to do with you 1s batteries you have left? I have an article coming to show you how to convert these to proper 2s batteries you can use with this new connector alongside the GNB or nanotech batteries.

How to install
Before I launch in with pics and steps I'll say although quick this is a fiddly install only because the solder pads are small in relation to the wires you will connect to them. I do have a method to confirm everything is safe but you have been warned!

1. First remove the canopy by unscrewing the 3 Philips screws with the screwdriver that came with the Mobula7

2. Take careful note of the pads and order the stock harness is wired to. I can't emphasise this enought

3. It's a little hard to see here but this shows the 26AWG stock connector vs. 22AWG JST and 20AWG JST. I used 20AWG but if I did it again I'd use 22AWG as it is lighter, and easier to manage with no real loss in performance.

4. Note I've soldered wires facing towards the board like the stock wires to help cable management. It's very easy to bridge here so strongly recommend testning continuity with your digital multimeter (I use this cheapie) which should read zero.

5. You can see roughly how I route my wire here to go between the two rear ducts. Screw the canopy back on

6. Voila you're ready to fly in a picturesque scene with plenty of bokkeh but you'll need to seem my note on batteries above.

Conclusions
I probably spoiled the suprise earlier but this mod is well worthwhile. I skeptical but really pleased to find the standard battery sag issue was instantly improved meaning I didn't have to guess at how much battery I had left as before finishing my flight. In addition I seem to have access to more power more quickly meaning response feels snappier. Also on long punches thrust seems to remain more consistent. If you have a good soldering iron and are a confident solderer I'd definitely recommend this one, particularly if you are running the v3/trashcan frame. On my year old 2s 300mah turnigy nanotech batteries I got just over 3 minutes of hard flying in a large area. During that time voltage did not dip below 6.8v and then only toward the end. Compare this to dips below 6.0v with the original setup in the first minute of light. This large voltage drop is less to do with the battery and more to do with the poor connection on the original setup hence the improvement to power. As a side bonus this should mean power will be more consistent to the VTX and receiver as well for more consistent performance. All in all I can recommend this mod but stick with the 22AWG wire and bear in mind the change in battery requirements.

Up next - easiest way to reverse motors (props out) without using BL_Heli Suite

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