SUB100g 5inch Ultra-light quad

By kera on Oct 07, 2023

15  0  15

An efficient quad is lightweight and equipped with large propellers. Until now, I've been building the following machines based on ready-made frames:

  • 3-inch with a 1-cell 2400mAh battery: Offers good flight time (22 minutes) and minimal maneuverability.
  • 4-inch with a 2-cell 550mAh battery: Provides sufficient flight time (9 minutes) and high satisfaction in terms of maneuverability.

This time, I decided to take on a more extreme setup.
I aim to keep the weight below 100 grams. This aligns with the drone regulations in my country, Japan.

Regarding the frame construction, I found that using carbon plates would inevitably add some minimum weight, making it impossible to achieve a 5-inch machine. So, I opted to create the frame by cutting carbon fiber rods and using 3D-printed parts for connections.

As for the motors, I went with lightweight and affordable 1104 4500kv motors. I chose these motors based on their official test data for 1s 5-inch props, which suggested they could handle 5-inch propellers.

After assembling everything and conducting test flights, I found that the angle mode was not feasible, possibly due to frame flex and extreme lightness causing issues with the accelerometer. However, in acro mode, although some vibrations remained, it was possible to fly, and I managed to hover indoors for about 7 minutes.

Based on these results, I confirmed that when building a sub-100g efficient machine, 3-inch or, at most, 4-inch setups are the limits. If a manufacturer were to produce a highly precise and lightweight 5-inch frame in the future, there might be room for improvement. However, in my personal efforts, this is about the extent I could achieve.

flight test video(youtube)



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daro   Jan 26, 2024  

how does this work, wouldnt the motors get superhot?

kera   Feb 01, 2024 

The motors get hot, but they didn't reach temperatures high enough to cause damage. I'm using 6A ESC, and it might be because I've built it in a way that doesn't allow too much current flow.

Apeian   Nov 27, 2023  

Hey...another avenue you can look down is using gears. The old Blade 180qx used large props with brushed motors. Take a look at my old build here -

Going to take some more serious 3d designing though for the Brushless motor mounts, custom gears, etc... ;)

You could borrow some of the work already done on this from other modders:

minati3748   Nov 29, 2023 

heat treated Pla (annealing PLA will cause the part to shrink along the x- and y-axis and grow in the z-direction, so you have to compensate by scaling the model in your slicer non proportional. For me the following values worked the best to get an accurate scale after annealing

kera   Dec 05, 2023 

Your build and design truly impressed me!

Even in Japan, where I reside, I remember there were geared toy drones released about 9 years ago.

It's highly informative!
However, I doubt I can achieve such precision in design and manufacturing with my current skills😂

riyan234a   Oct 19, 2023  

the new Transformer 5" Ultralight adopts a lot of the same design philosophies with larger props and more payload capacity. It can fly upwards of 20 minutes on a 4 cell Li-Ion battery pack and in ideal conditions it's got a range of over 4 to 5 miles. In this guide I'll walk..

dafunk   Oct 11, 2023  

Awesome ! !
I hope you try to push the 5" further. Maybe replacing 3D parts by rigid aluminum hardware ?
7hHow does it sound? I guess it can barely be heard

kera   Oct 11, 2023 

I'm thinking it would be great if I can make further improvements.

Aluminum sounds good, but I don't have the manufacturing equipment for it...

Is it about the flight noise? It's very low-pitched and quiet. I plan to upload a video later.

dafunk   Oct 11, 2023 

Yes it was about flight noise. I built a 7'' 250gr (without lipo) back in the days and it was astonishingly silent.

If you are open to suggestions here is a link for inspiration
If it was me, I would use the screws of the motor in combination with 'stainless steel paper clips' that I would reshape so that screws, rods and motors are joined by metal/carbon only. Also 'eating' some of the carbon with a file to make sure the 'paper clip' grabs thee rods firmly.

when you try to flex the quad by holding the motors, do you feel whether it's the rod that flexes first or the 3d printed joint ?
Also many flight controller batches have been 'polluted' by bad gyros. You can make sure yours has a mpu6000 by typing 'status' in the betaflight client.

I love how every gram counts to the extent that the props are screwless :)

kera   Oct 19, 2023 

Thank you for the wonderful links! They are very helpful in understanding how the parts are connected.

I noticed that when I bend the quad, the 3D printed parts are the first to flex. There's also some distortion due to the parts not gripping the rods securely.
I agree with your opinion that the parts should have a firm hold on each other. This is an area that needs improvement.

Yes, as you mentioned, the FC I'm using is equipped with an MPU6000.

Thank you for your valuable insights!

Rice_Bowl   Oct 11, 2023  

Thats looking great my guy!

Felias - eyefly   Oct 09, 2023  

hey there! Whats the weight of the frame alone? I've also designed a sub100g 5" 3s Li-Ion with DJI Mavic Mini motors in the past using my tubular designs ( Maybe i can help you out, and also learn something from you regarding most efficient motor/prop combination. If you like hit me up on my Discord, ( Greetings, Nic

kera   Oct 11, 2023 

The frame alone weighs approximately 20g. The 3D printed parts are around 11g, and the carbon rods are about 9g.

I joined in Discode. Thanks!

I checked Your designs! fantastic!🥰

JoeShu   Oct 08, 2023  

Interesting! That's a really light-weight build, how did you secure the prop? Just press fit?

kera   Oct 11, 2023 

Thanks! It's just press fit

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