3D Printed, Endurance Micro Quad

This post outlines the build of a micro quad that’s been designed with endurance in mind. I designed and 3d printed the quad parts to fit micro DC motors, prop gears and all relevant electronics, with reduction of weight being a prime objective.

Micro quad overview
Micro quad overview

Motors & Prop Setup

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One way to build an endurance quadcopter is to use large diameter slow-swinging props. A few cheap quadcopters use a geared design where a very small, high-RPM motor swings a much larger prop through a single reduction gear. This setup offers good efficiency and low weight.



One drawback of course is that the brushed DC motors have limited lifetime due to the wearing out of the commutation brushes, but at $1.50 a piece this is hardly an issue. The motors in this micro quad design have 8mm diameter and together with gearing and prop shafts are listed here. The props themselves are listed here.

Motor and prop holder assembly
Motor and prop holder assembly

Frame

I custom designed and printed the micro quad frame around the motor and prop setup described above. The diagonal is 200mm (7.87 inches). It has a 3d printed mount on each corner that holds together the motor, the prop and the arm that attaches it to the main fuselage. The first iteration of the design featured all-3d printed arms that were fused together to form the frame. The arm in the latest iteration is revised and made of carbon fiber tube. The tube itself is part of an old carbon fiber arrow. The motor mounts needed several remodeling iterations, in order to ensure that the motor and prop shaft mounted in precise distances so that gear meshing would be ideal.

First iteration of the micro quad design
First iteration of the micro quad design

The main fuselage has a hollow form to maximize torsional stiffness. In addition, it features four mounts for the carbon fiber studs of the motor arms. The fuselage design though offers room for improvement and especially for weight reduction.

Read also:  Balancing bot using Neuroevolution
Micro quad main fuselage
Micro quad main fuselage

Electronics

The quad uses an STM32F4-based brushed quadcopter controller board from Eachine. A 2S, 300mah LiPo battery provides power to the controller and the motors. The controller gets signal from a Radiolink R6DSM micro receiver over SBUS. One thing that proved frustrating with the particular controller was that it came with an old version of Betaflight. This caused conflict with the ground station, and a lot of the features of the board seemed not to work. Unfortunately there is very little information on the internet for this controller. After a lot of trial-and-error, upgrading to the latest Betaflight through the ground station did the trick and I was able to fully configure the board.

Main fuselage showing hollow core and electronics (no RC receiver is included in the image)
Main fuselage showing hollow core and electronics (no RC receiver is included in the image)

Testing

The all-up weight of the quad is 85g. I’ve done some testing in indoor flight, and found that in level flight it performs surprisingly well, being not only stable but also quite snappy. That is, for the rather large prop size! Flight time is a pleasant surprise as well: The battery starts losing voltage at around 9.5 mins of hover. At that point the throttle needs to be pushed further to maintain hover. At this point I landed the drone, but I’m sure it would handle another half a minute for a total of 10 mins flight time. Re-designing the frame for weight savings could potentially offer another couple minutes of flight time.

Conclusion

This post went over the design, 3d printing and assembly of a micro endurance quadcopter. The design was based on geared props driven by micro brushed DC motors. Overall the result is a stable and responsive aircraft that is suitable for indoor or outdoor flight in good weather conditions.

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