2s35: the Ultimate 18650-Powered 3.5"–4" FPV Drone

The 2S35 is a long-range, ultra-lightweight, and budget-friendly FPV drone designed around the highly accessible 18650 Li-ion battery standard. Capable of spinning 3.5-inch or 4-inch propellers on a 2S (7.4V) configuration, this drone focuses on maximum flight time and efficiency rather than aggressive acro performance.

By utilizing standard 18650 cells (like the Sony/Murata VTC6 or Samsung 30Q), you get an extremely durable battery pack that can be charged with standard chargers and swapped out in seconds. The frame and canopy are fully 3d printed, making it easy to repair and customize.

Frame & Hardware

1. 3D Printed Parts: (Download from MakerWorld)
2. 1x 2S35 Canopy and 1x frame
3. use PLA+
4. Hardware
5. M2 screws 6-8mm long
6. 4x M2 heat inserts
7. Batteries: 2x High-drain 18650 Li-ion cells (>15A e.g., Murata VTC6, Samsung 30Q, or Molicel P28A).

Electronics & Propulsion

1. AIO Flight Controller/ESC: 15A to 25A 1S-2S AIO board (25.5x25.5mm mounting pattern, e.g., BetaFPV Toothpick AIO or DarwinFPV 15A AIO)
2. Motors: 1303.5 to 1604 Brushless Motors (4000KV - 5000KV recommended for 2S efficiency).
3. Propellers: 3.5-inch or 4-inch bi-blade or tri-blade props (e.g., Gemfan 3520 or 4024).
4. FPV Camera and VTX: DJI O4
5. Receiver: ELRS Nano RX (or system of choice).
6. Battery Contacts: 2S 18650 battery holder

Tools Needed

1. 3D Printer (FDM)
2. Soldering Iron & Solder (plus flux)
3. Hex Screwdrivers (M2 size)
4. Wire Strippers / Flush Cutters
5. Heat Shrink tubing or Electrical Tape

Download the STL/3MF files from the MakerWorld page.

Print Settings:

1. Walls: 6
2. Infill: 25%
3. Layer Height: 0.2mm
4. Support: Tree

Before touching any electronics, prepare the mechanical foundation of the drone.

Clean the 3D Prints: Carefully peel away all support material from the TPU canopy and the battery tray. Use flush cutters to clean up any stringing inside the camera mount and battery bays so everything fits snugly.

Install Heat-Set Inserts: Using a soldering iron heated to around 200°C–220°C, gently press four M2 brass heat-set inserts into the designated holes on the frame/canopy structure. Let the plastic cool and solidify for a couple of minutes.

Mount the Battery Tray: Position the 3D-printed battery tray onto the carbon fiber frame. Secure it firmly in place using two short M3 screws.

Motor Installation

1. Bolt the four brushless motors to arms using M2 screws.
2. Crucial Check: Ensure the screws do not protrude too far up into the motor base, or they will pierce the copper stator windings and destroy your motor.

Solder Motor Wires

1. Route the motor wires neatly along the frame arms toward the center stack.
2. Cut them to length, strip the tips, and solder them directly to the motor pads on your All-In-One (AIO) Flight Controller.

Wire the 18650 Battery Tray (2S Series Configuration)

To get a 2S (7.4V) output from two separate 18650 cells, they must be wired in a series loop:

1. The Bridge: On one side of the battery tray, solder a jumper wire directly between the Positive (+) terminal of Bay 1 and the Negative (-) terminal of Bay 2.
2. The Main Leads: On the opposite side of the tray, solder your main positive wire from the remaining Positive (+) terminal to the AIO Power (+) pad. Solder your main ground wire from the remaining Negative (-) terminal to the AIO Power (-) pad.
3. Double-check the polarity molded into the 3D-printed frame before soldering!

Wire the Peripherals

1. Solder your RC Receiver (RX) to an open UART on the AIO board (GND, 5V, TX, RX).
2. (Optional) If you are adding a GPS module for long-range rescue capabilities, solder it to a secondary available UART.

Stack DJI O4 and AIO

1. Place your DJI O4 Air Unit directly on top of the AIO board.
2. Connect the digital video cable between the Air Unit and the AIO flight controller.
3. Use rubber anti-vibration grommets and M2 screws to secure both the AIO and the DJI Air Unit down to the central frame stack.

The final step encloses the electronics and secures the sensors.

Route the Antennas: Tuck your Receiver antenna, the DJI O4 antenna and your optional GPS module into their dedicated cutout slots inside the canopy.

Mount the FPV Camera: Mount the DJI camera into the front camera cage of the canopy (M2 screws)

Note on Camera Fit: The canopy housing is designed natively for 20mm wide cameras. If you are using a stock DJI O4 camera without a wide-angle lens mod (like the Flywoo wide lens), there will be a slight gap on the sides. You can use minor plastic spacers or M2 washers to shim the fit if necessary.

Secure the Canopy: Lower the canopy over the entire stack. Align it with the frame mounting holes and secure it using short M2 screws threaded directly into your previously installed heat-set inserts.

Ensure no wires are pinched under the canopy before tightening completely!

Connect to DJI Assistant: Plug a USB cable into DJI O4 and open DJI Assistant 2 (Consumer Drone Series)

1. Activate and Update O4
2. Bind with your DJI Goggles

Connect to Betaflight: Plug a USB cable into your AIO board and open the Betaflight Configurator.

Basic Setup:

1. Set up your receiver protocol (e.g., CRSF for ELRS).
2. Configure your video settings and peripheral ports.
3. Check motor directions in the "Motors" tab (without propellers attached!).

Insert Batteries & Test: Pop two charged high-drain 18650 batteries into the slots, ensuring correct polarity alignment. Check that your video feed works and that the receiver binds to your radio transmitter.

Attach Propellers: Screw your 3.5" or 4" propellers onto the motors. Ensure you match the correct orientation (Props In or Props Out) based on your Betaflight settings.

Find a Safe Spot: Go outside to an open grassy area.

Maiden Flight: Arm the drone and hover gently. Because 18650 cells have lower sag capabilities compared to traditional LiPo batteries, manage your throttle smoothly. Enjoy cruising times that can easily exceed 10 to 15 minutes of peaceful exploration!