Designing Lightyear One: In-wheel motor testing

Wiebe Janssen — Lead Motors Engineer
Last time I introduced you to our in-wheel motors, and what using them means for our design. Not all has been said about that topic, and with new developments and tests to share, it’s time for a closer look.

 

Building a motor from scratch

Finding the perfect in-wheel motor is not easy.  We demand the perfect balance between efficiency, weight and torque, and after initially looking at off-the-shelf in-wheel motors, we decided to build one in-house, with selected partners.

Building a motor from scratch, like searching for one of the shelf, starts with defining your requirements. Most importantly: requirements for a functional architecture and system for better powertrain efficiency, to maximize both range and solar kilometers. Torque and power density too remained essential factors. Next we had to find the right electromagnetic technology. Not only did the technology have to fit our performance requirements, we also wanted the motors to fit within our more slender tires. Once we defined what we wanted and what we needed, we could finally begin developing design solutions that integrate electromagnetic performance, mechanical casing design, cooling capabilities, braking interfaces and control inputs.

A more technically detailed interview with Wiebe about the latest in-wheel motors testing for Lightyear One.

To create a motor suitable for a solar car, you need to understand what drives performance and efficiency. The mechanical possibilities and limitations of an in-wheel motor are pretty straightforward, but electromagnetic behavior is not so easy to predict and has a considerable impact. The performance of an electric motor hinges on the interaction between all the technical disciplines mentioned before. For example, because we want as little friction as possible we aimed for more slender wheels. This did however limit the packaging space for the motors. We had to create flat motors, and because we wanted to minimize weight there was also a direct constraint on the width of the motor.  Taken together we were challenged to maximize torque by packing the electromagnetic components into the wheel as efficiently as possible. Given the current technology, these are demanding requirements. These same challenges cropped up when we designed the cooling, the casing, the brake interfaces, and all other components of the system.

How to reach your goals

Lightyear has set ambitious goals for delivering its first car. Thinking of ways to make sure we reach these goals, while building a first version of a Lightyear in-wheel motor and all the risks associated with it, is challenging. It forces you to approach problems differently. It means quickly solving the hard problems that you would most likely address at an easier pace in a more conservative environment. That is what makes working at Lightyear great: Starting from scratch, creating a concept design, and then working towards the actualization of a first product is absolutely thrilling. Working here means that, every day, you get the chance to work in a unique environment with a combination of highly motivated and talented people, experts and industry partners. But more than that, it is a chance to help develop a novel EV-platform.

 

In my previous blogpost I laid out how the in-wheel motors fit Lightyear One: In-wheel motor technology enables you to drive off-road with one individually controlled motor on each wheel. This makes it possible to drive Lightyear One anywhere. But there is more to it than that. Using in-wheel motors also frees up space, so other designers have more freedom to define the architecture of the car.

But when all is said and done, and all designs have been made and realized, it’s time for the moment of truth. Testing the motor. The spinning motor test was a special moment; seeing a concept design become reality. With the initial tests we achieved basic functionality, mainly using electromagnetic principles.

Our focus now is on performance validation and mechanical integration. We are preparing for a more elaborate testing round to prove the motor’s integral performance. Of course there are always things to improve. For the next design iterations, the objectives are to continue reducing the weight of the motors, and to further improve performance, efficiency and integration.

 

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