I saw this interesting 1S 3-inch FPV drone using 18650 Li-Ion cell for long range, and I had to give it a try. I will share my rather unsuccessful attempt and what you can learn from my experience if you want to build this too.

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Update ( Apr 2021): Good news, you don’t have to build it yourself right now, just buy it! HGLRC partnered with Dave-C to release a BNF model of this quad – the Rekon 3.

I love the idea that you can just snap a 18650 battery in this quad and fly for a very long time (20 minutes or more) :) And it’s super light too, only about 50g without battery. But don’t expect great flight performance, because it doesn’t. It’s slow and doesn’t have punch. It’s designed purely for staying in the air for a long time.

New to long range? Check out my tips on long range FPV flying.

Frame

Original design by Dave_C_FPV: https://www.thingiverse.com/thing:4769576

I am using this remix of the original frame, so I don’t need the battery tray (to save weight and cost): https://www.thingiverse.com/thing:4786123

The remixed frame needs battery contacts (with dimension 13.5×11.5mm), something like these: https://amzn.to/31n6iQc (Update: these have too much resistance, read my build update to learn about the issue)

Parts List

Recommended parts list:

• High discharge rate 18650 battery such as
  • Sony VTC5A
  • Sony VTC6
• FC: 1S AIO Whoop Flight Controller with built-in ESC (5A is fine), such as HGLRC Zeus5 1S AIO
• Small 5V Video Transmitter that can do 300mW or higher such as
  • HGLRC Zeus Nano VTX
  • Eachine Nano VTX
• 1202.5 11000-12000KV Motors, I think 1103/1104 should be fine too, but make sure they have M2 mounting, such as
  • HGLRC 1202.5 11600kV
  • Flywoo 1202.5 11500kV
• Nano FPV Camera such as the Caddx Ant
• 5V Step-up Voltage regulator
• 5V LC Filter
• Props: Gemfan 3018
• Crossfire Nano receiver
• 10V 1000uF Low ESR Capacitor (why use cap?)
• Light weight 18650 battery tray: https://amzn.to/31mdHzk

I used the following parts instead, simply because I already have them, not because they are better:

• iFlight Succex F411 AIO FC (don’t recommend, get the Zeus5 as recommended by Dave_C, or find another FC in this whoop FC round up)
• Mamba 1103 10000KV motors
• HQ T3x2x2 Props
• I didn’t use LC Filter for the VTX, video seems fine when hovering

Wiring Diagram

Credit to DaveC for this wiring diagram.

Build Updates

It took me around 6 hours to build this nano long range 3-inch, it was the soldering and figuring out how to mount everything in the limited space that took the longest.

Soldering these tiny components can be a bit challenging and requires steady hands and good solder tools :) Check out my recommended soldering tools here.

The weight is about 50g without 18650 cell.

My first attempt wasn’t successful though, the quad didn’t have enough power and couldn’t even lift off the ground. My first suspicion was the battery spring that isn’t good enough to deliver power from the 18650.

So instead of soldering the wire to the little tab, I soldered it right in the centre of the plate and the tip of the spring, the wires now have directly contact with the battery’s terminals, this should minimize resistance.

Or you could try this sort of battery contact which has much better performance, but i am not sure if you need to modify the frame or not: https://amzn.to/3tTTkWr (Keystone 209 1 Cell Leaf Spring Battery Contact, Nickel plated)

And that was kind of a success, the quad can now hover! It hovers at about 50%-55% throttle and it actually flies slightly better than I thought.

However, as soon as I move the throttle too quickly, the quad always drops out of the sky, and I could hear the ESC restarting chirp.

To investigate, I tried a normal 1S 300mAh LiPo on this quad, and it flies just fine! No more drop out.

So two possible causes for this problem I think:

1. the 18650 battery I am using isn’t good enough (unlikely)
2. the iFlight AIO FC can’t handle the voltage sag/fluctuations of the 18650 (more likely)

I am going to get some brand new VTC5A and try again just in case. In the meantime, I have also ordered the exact same HGLRC Zeus5 1S AIO FC that Dave_C used in his build, if the new 18650 doesn’t work then I will replace the FC.

Update (25/03/2020): I tried to update the ESC firmware tonight (downgrade actually, it was on 16.80, and I wanted to put 16.73 on it), but somehow it “bricked” the ESC, and now they won’t do anything when I plug in the LiPo, I also get “Flash Failed” error when I try re-flash them. Probably dead dead. Guess I will be replacing the FC after all :)

Stay tuned for more :)

Update (Apr 2021): I am just going to get the Rekon 3 BNF :) Don’t have the patience to mess with all this anymore.