Using 3D printing to help flying taxis take off

Challenge

They have long been a feature of sci-fi depictions of the future, but flying taxis are real — and could be in our skies in the next few years. Rooftops in prime locations around the world have already been sold in anticipation of using them as landing sites for air taxis.

But for this transport revolution to happen, there needs to be both technological breakthroughs and regulatory changes.

Sheffield motor manufacturers Magnomatics has been working with the University of Sheffield Advanced Manufacturing Research Centre (AMRC) on the first of those.

They conducted a project to prove that additive manufacturing can be used to build highly complex electric motor casings with the right combination of weight and power to allow air taxis to take off vertically.

Background

In order to be able to take off and fly efficiently, every element of an air taxi needs to be lightweight, and that includes the motor casing.

Usually electric motors have fins on the external surface that maximise the surface area to exchange heat. This project was to determine if it is possible to integrate ducting channels into the wall of a motor casing instead. This would force the air to be in contact with the motor for the longest as it passes through the wall and is directed by the integrated ducting. This results in an improved heat transfer that enables more effective cooling of the motor.

For this to work, the whole motor casing would have to be additively manufactured as one single piece, rather than made up of many different parts. All the ducting interior had to be self-supporting as there would be no access to remove the support structures.

Innovation

To produce a single-piece aluminium motor casing like this is extremely complex. In the same way that huge cathedral ceilings are never flat, there could be no horizontal features inside the motor casing, as they could not be supported.

Incorporating all the features of the motor, including the air ducts, while adhering to these limits proved a challenge. The casing is a single object with thousands of surfaces and planes. The CAD modelling came very close to the practical limits of what it can handle.

The designers at the AMRC conducted a series of simulations looking at how air moves through the casing. They then printed a polymer model to test the integrated sensors that measure the temperature and airflow.

One of the advantages of using additive manufacturing for this casing is that the internals of the motor can be completely sealed from the external environment, eliminating dust or sand and contributing to the longevity and reliability of the motor.

Another advantage is that, unlike traditional casings which only cool the cylindrical portion of the casing, this casing seamlessly integrates the non-drive end plate and the axial casing into one complete structure. This contributes to the conductive heat transfer and also the entire casing stiffness to support the high mechanical loading.

Result

Eventually a 3D-printed design for the motor casing was produced that met all requirements. Sensors were integrated in locations not possible with conventional manufacturing methods.

In the new product the airflow through the integrated ducting is generated by the impeller mounted on the rotor shaft. The design allows the airflow to contain particles of dust, snow, and rain during operation. These are allowed to freely pass through the ducting without any significant negative effect on the motor longevity, because they never interact with the internal motor components.

Further testing showed that the product has a torque density twice as good as anything else on the market, and an effective heat transfer coefficient of 250 watts per square meter per kelvin. Both of these features are crucial for a wide adoption of the technology.

The air-cooled machine is significantly lighter than water-cooled alternatives without the requirement for mass heavy ancillaries like pumps, radiators, pipes and coolant fluid.

Therefore the new design is smaller and lighter than previous versions — weighing under 15kg and achieving up to a peak torque density of 32Nm/kg — with higher efficiency, high reliability and low maintenance.

Impact

This project showcased the ability of additive manufacturing to produce a much lighter part with a high torque density. It can give UK manufacturing confidence in using this technique for metal. Additive manufacturing was the only way to produce a single part of this complexity.

Magnomatics gained a lightweight, compact product that offers all the advantages of mechanically geared motors without the risk of jamming. The company is now working towards the next level of air taxis.

Another gain for the organisation was a student who worked on this project on placement from the University of Sheffield. He is now a full-time member of staff for Magnomatics, travelling the world presenting his findings and attracting significant interest in the technology.