1S Tiny Octocopter

By Martin Flite on Sep 11, 2022

16  774  12

Betaflight resource remapping is so powerful that we can build an octocopter using an F405 (or above) AIO FC even without soldering pads dedicated for M5-M8. I would like to introduce my 1S octocopter using a JHEMCU GSF405A 1-2S AIO FC with an additional 1S 4-in-1 ESC.

To control ESCs (DShot) connected to pads on a FC which are not dedicated for motors, it is necessary to make those pins enable timer and DMA. However, all pins are not be able to be done. To find which pins are suitable, it is helpful to refer the spec sheet for the corresponding MCU of the FC. There are convenient copyies at the following link.


For JHEMCU GSF403A 1-2S AIO FC, I made resouuce remapping to TX4, RX4 TX6, and RX6 for additioinal motors. The original resource for motors and the above UARTs are the following:

resource MOTOR 1 B00
resource MOTOR 2 B01
resource MOTOR 3 A03
resource MOTOR 4 A02

resource SERIAL_TX 4 A00
resource SERIAL_TX 6 C06
resource SERIAL_RX 4 A01
resource SERIAL_RX 6 C07

As I wanted to arrange motor ordering for convenience, I made the following custom settings:

resource SERIAL_TX 4 NONE
resource SERIAL_TX 6 NONE
resource SERIAL_RX 4 NONE
resource SERIAL_RX 6 NONE

resource MOTOR 1 A02
resource MOTOR 2 A00
resource MOTOR 3 B00
resource MOTOR 4 C06
resource MOTOR 5 C07
resource MOTOR 6 B01
resource MOTOR 7 A01
resource MOTOR 8 A03

timer A00 AF1
timer A01 AF1
timer C06 AF2
timer C07 AF2

dma pin A00 0
dma pin A01 0
dma pin C06 0
dma pin C07 0

For concrete buildeing, some notes for parts are summarized as follows:

  • Frame : My original design for 40mm props. It is 1.5mm thick and weights 5.5g. This is a prototype.
  • AIO FC : JHEMCU GSF403A 1-2S 5A ELRS AIO FC. It is convenient for 1S use. I don't recommend it for 2S use.
  • 4-in-1 ESC : Racerstar Star4 4A. Sufficent for tiny quads. I bought it for $3.24 at RakonHeli online store.
  • Motors : Flywoo ROBO 1002 23500KV. They are great for 40mm props. I don't recommend them for 2" octocpters.
  • Props : HQProp HQ Micro Whoop Prop 1.6X1.6X4. Very quiet and accurate control.
  • Camera : Caddx Ant. Sufficent image quality for a analog light camera.
  • VTX : PandaRC NANO 16x16 VTX 5.8GHZ 25-400MW. Cheep, small and powerful.
  • Battery : GNB 1S 3.7V 500mAh 90C with XT30 connector. Light for octocopters.

As for PID tuning, Betaflight default setting is sufficent to get stable flight. This is only for 40mm props. As I tested 2" props with another frame, D terms needed to be set much higher than default.

Flight performance is powerful and stable. It hovers at 23% throttle with a 500mAh battery. Its flight time is up to 3 minutes. It can fly easily (hover at 31% throttle) even with two 500mAh batteries in parallel, so it is possible to enjoy longer flight time.

At the test flight, I cashed, but I could fly again. However, I noticed later that one motor did not have a propeller. Thus, I finally found a multicopter with Betaflight that can fly even when one propeller gets off or one ESC gets broken at accident.



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Jamesmichael   13 days ago  

rad so sick. how does it fly

Martin Flite   12 days ago 

Thank you.
With a lighter battery (~15g), it flies like a toothpick but less floaty and less efficient. With a heavier battery such as a 1100mAh one ( I made it from a cheep 6S battery), it flies much longer without losing aggressiveness. With a 18650 Li-Ion battery, It flies like a slow cruiser. For I don't use an action camera, it is very satisfactory and enjoyable.

Junnicutt   Sep 17, 2022  

for builds this unusual it'd be great to link to a dropbox file of a betaflight diff. I'm sure the write up is super helpful for people trying something similar but a diff can help with some of the more random little hiccups that can plague complicated builds like this. great job on everything. i love seeing stuff like this.

Martin Flite   Sep 17, 2022 

The link to the Betaflight diff file is the following:
Please note that I use GPS and softserial (LED_STRIP) for VTX.

Nikotttin   Sep 16, 2022  

I'd love to fly that one! Very nice build. The lower 4 in 1 is wrapped in heat shrink?
Do you have a wiring diagram ?
Thank you!

Martin Flite   Sep 16, 2022 

This 4in1 ESC is in heat shrink in stock condition.
You can find a wiring diagram at the following link:
Four soldering pads for RX4, TX4, RX6 and TX6 are in line, so they are very convenient for the additional ESC.

Nikotttin   Sep 17, 2022 

I'll build something like this just for fun :)

Martin Flite   Sep 17, 2022 

Good Luck!
Octocopters are very fun to build, but I think it is sometimes difficult to select appropriate motors. If motors are not appropriate, it is hard to adjust PID.

SQunX   Sep 13, 2022  

interesting concept.
I like it!

Martin Flite   Sep 13, 2022 

Thanks! I have made some octocopters from 35mm to 3.5" props this year. This is the most favorite one.

SQunX   Sep 13, 2022 

I like such odd projects.
I've done a X8 with 40mm props recently.

Martin Flite   Sep 13, 2022 

I also like odd projects. I think there remain many possibilities for multicopters.
I saw your X8 build. It is very small and cute.

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