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A 3D Printed Frame Assembly for a Quadrotor Drone - By : Thomas Desbordes, Patrick Terriault, Vladimir Brailovski,

A 3D Printed Frame Assembly for a Quadrotor Drone


Thomas Desbordes
Thomas Desbordes Author profile
Thomas Desbordes est étudiant à la maîtrise avec projet en génie aérospatial à l’ÉTS dans le cadre d’un partenariat avec l’École française Polytech Orléans. Il se spécialise dans la conception et fabrication aéronautique.

Patrick Terriault
Patrick Terriault Author profile
Patrick Terriault is a professor in the Mechanical Engineering Department at ÉTS. His researches include shape memory alloys, intelligent materials and systems, smart actuators and stents.

Vladimir Brailovski
Vladimir Brailovski Author profile
Vladimir Brailovski is a professor in the Department of Mechanical Engineering at ÉTS. He specializes in the design and manufacturing of shape memory alloy devices and in process engineering for additive manufacturing.

note3en

This article follows Designing a Drone Frame Assembly Using 3D Printing. It presents the printed frame assembly characteristics as well as avenues for improvement.

Preliminary Prototype Evaluation

Tensile and bending tests were carried out on standardized samples with the objective of acquiring the basic mechanical properties of nylon and fiberglass plies. The overall properties of the nylon/glass composite manufactured with the Mark One printer were determined in this way. These results were then validated by using more complex samples that were representative of the part to be manufactured, which were experimentally tested and compared with results from numerical simulations.

The lower plate of the chassis is thin (1.5mm), and it is subject to the weight of the batteries and payload. It was preferable to check the reliability of this part of the frame assembly, particularly since the plate in the current Dronolab version is made of composite material reinforced with very performant carbon fibers. A numerical model was built, and the plate was modeled with the help of ANSYS Mechanical APDL 15.0.

The batteries are held in place on the plate by straps attached to supports and rectangular slots (see Figures 1 and 2).

Battery Supports

Figure 1 Picture of Battery Supports Showing the Screws

Battery Bracket System

Figure 2 Schematic View of the Battery Bracket System

The battery is anchored at four points that are attached to the plate and we consider that its weight is equally distributed. The supports are not modeled, only the forces on the rectangular slots are taken into account, and they will have a tendency to bend the plate towards its center.

Moreover, a surface pressure is evenly distributed on the central portion of the plate and applied with the objective of simulating the weight of a payload. This value is progressively increased so that its influence on the structure could be observed if the drone had to support a heavy payload.

Finally, the support area pressure point, which was modeled by a ring around the screw hole, is restrained from any movement.

The stresses along the natural axis of the composite were determined for each layer. After calculating these stresses, maximum strain and the application of failure criteria, it was verified that the part did not break under normal working conditions. In fact, on ANSYS the integrity of the material is normalized to 1. So for a given criterion, if the value calculated by ANSYS is higher than one, the software will predict material breakage.

Results have shown that the lower plate will only break with a payload of 22 kg as designed (see Figure 3), but the drone never has a payload greater than 3 kg. Even if vertical acceleration is taken into account (2 kg F per motor, or an equivalent mass of 8 kg), a simulation shows that the lower plate, as designed, will not break.

 

Failure Criteria

Figure 3 Failure Criteria Calculated for each Payload Increment

 

Manufacturing and Testing Completed

After this validation, the part was manufactured (Figure 4a), and the printing lasted 39 hours. Tests were subsequently carried out to study the behavior of the frame assembly under conditions that simulated propellers maximum thrust, which can take place during lift-off. A comparison with the current Dronolab frame assembly (Figure 4b), under the same conditions, was also carried out.

First of all, the old and new drone frame assembly were mounted in an identical manner. The arms and batteries were installed (see Figure 5 a, b).

The drones were then placed hanging between two supports of the same height and in such a way that the arms could not move (Figure 5c).  Weights were used to increment a force in the frame assembly center to simulate the propellers thrust. A touch probe measured deflection at the center of the drone, for each increment of weight (see Figure 6).

Composite frame assembly

Figure 4 a) Composite Frame Assembly Manufactured by 3D printing, b) Original Frame Assembly

Frame assembly and Experimental Setup

Figure 5 Frame Assembly with the Drone Remaining Components a) New Frame Assembly b) Original Frame Assembly c) Experimental Setup

 

bend test

Figure 6 Drone Frame Assembly Bend Test

As a result of this analysis, several positive features were brought out regarding the frame assembly:

  • Structural mass was reduced by 25%. This feature will increase the drone range compare to the part currently being used.
  • Flexural rigidity of the new frame assembly is similar to that of the old frame assembly for payloads that are lower than 60 N, or around 6 kg, which is certainly the case in every instance except for take-off, which only lasts a few seconds.
  • The frame assembly production cycle was reduced from several weeks to a few days because of the reduction in the number of subcontractors needed to manufacture the frame assembly.
  • The frame assembly is now a one-piece unit and the long, laborious assembly stage is no longer necessary.

On the other hand, at a load higher than 60 N, the frame assembly manufactured in this project is less rigid than the current part — up to one and half times less, once the four motors are working at full power (about 80 N).

Avenues for improvement

In an attempt to improve the behavior of the composite frame assembly under extreme conditions, several solutions may be considered:

  • If one wishes to keep the same reinforcement material:

Triangular nylon filling was at 50% during manufacturing. 100% filling would add further rigidity to the structure for the price of purchasing an additional 16 cm3 of nylon, which corresponds to a 16% increase in nylon content compared to the actual part. It is also possible to increase the number of reinforced layers, which would also increase the rigidity of the part at the expense of a longer printing time and a larger quantity of added material, depending on the desired reinforcement.

  • If one wishes to change the reinforcement material:

The choice of the fiberglass was made because of the attractive ratio resistance/pricing, as well as the possibility of carrying out an isotropic filling. The Mark One machine offers the possibility of using aramid and carbon fibers; these materials may constitute very good choices due to their superior mechanical characteristics compare to glass (especially carbon). However, the manufacturing costs would be inevitably higher.

To maintain a similar printing time while improving mechanical properties, the most realistic solution would be manufacturing the frame assembly with the same number of reinforced layers, but using carbon with a 100% nylon filling.

We would like to acknowledge the support and generosity of the Dronolab student club. With thanks to their Captain, Jonathan Pierrat, and a special thanks to Victor Boutitie for his contribution during this project.

Thomas Desbordes

Author's profile

Thomas Desbordes est étudiant à la maîtrise avec projet en génie aérospatial à l’ÉTS dans le cadre d’un partenariat avec l’École française Polytech Orléans. Il se spécialise dans la conception et fabrication aéronautique.

Program : Mechanical Engineering 

Research chair : ETS Research Chair on Engineering of Processing, Materials and Structures for Additive Manufacturing 

Research laboratories : LAMSI – Shape Memory Alloys and Intelligent Systems Laboratory 

Author profile

Patrick Terriault

Author's profile

Patrick Terriault is a professor in the Mechanical Engineering Department at ÉTS. His researches include shape memory alloys, intelligent materials and systems, smart actuators and stents.

Program : Mechanical Engineering 

Research laboratories : LAMSI – Shape Memory Alloys and Intelligent Systems Laboratory 

Author profile

Vladimir Brailovski

Author's profile

Vladimir Brailovski is a professor in the Department of Mechanical Engineering at ÉTS. He specializes in the design and manufacturing of shape memory alloy devices and in process engineering for additive manufacturing.

Program : Mechanical Engineering 

Research chair : ETS Research Chair on Engineering of Processing, Materials and Structures for Additive Manufacturing 

Research laboratories : LAMSI – Shape Memory Alloys and Intelligent Systems Laboratory 

Author profile


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