REVR

What it does

Rapid Electric Vehicle Retrofit (REVR) is a new method for converting internal combustion engine (ICE) vehicles into hybrid electric vehicles (HEVs) that offers significant cost and time savings.

Your inspiration

I am concerned about climate change and my individual impact. ICE vehicles are responsible for over 20% of global emissions. I have wanted to help by getting an EV but they are too expensive and have considerable emissions impacts from their manufacture. My own car, a 20 year old Toyota is perfectly functional except for its petrol engine. Retrofits retain the carbon invested in cars and do not require a new carbon debt for a new car. Car retrofits for electric drive are not widely available to the general public and the present approach of replacing the entire drive train is slow and expensive.

How it works

REVR is a retrofit kit that incorporates all systems required for the conversion of a light ICE vehicle to hybrid electric. This includes airconditioning, heating, steering and braking boosters, controllers and batteries but the innovation is in the motors. How the axial flux motor works is not new. What is new is the shape and structure of the REVR motor. By having a flat axial flux outrunner motor with a large inner cavity it is able to mount directly between the cars wheel and disc brake. Since the disk brake and wheel mount to the rotor of the motor and are thus free to spin, the original axle and systems of the car, hydraulic braking and ICE are still able to work as well. The stator (stationary part) of the motor gets its torque leverage from the frame mounting points on the cars wheel hub. The motor provides direct drive benefits of high efficiency and low weight while taking only minutes to install with zero specialist knowledge.

Design process

I started from knowing nothing about motors, but I had a passion for CAD and tinkering so I took it on as a personal project during COVID. There is not much space inside the car so I focused on the large internal cavity inside the car wheels since this also does not vary too much between makes and models. After lots of research I stumbled upon an axial flux motor concept invented in 2009 called YASA used in a Rolls Royce airplane. I started my design from a small in-wheel hub motor and Iterated from there in Fusion 360. I employed freely available research magnetic flux modeling packages FEMM and MOTORXP and performed finite element analysis over hundreds of iterations to get to my final design. I underwent hands-on dimensions prototyping on my car to better understand how the motor could be installed. This included making a smaller motor using the same winding scheme from home wiring cable to validate the design. Many components used 3d printing and cnc technologies available at my university. Some components of the motor had to be manually melted and cast in copper from CAD shapes using lost-wax casting for me to remain in my budget. The key design constraint was size and cost-to-build, I wanted to use as many OEM parts as possible and limit CNC machining.

How it is different

This approach to ICE retrofits is lesser known and more recent advances in permanent magnets and battery technology have made it possible. While In wheel drives already exist, none target retrofitting and they are only made specifically for certain vehicles. The REVR motor provides the same or more power as the existing ICE. The motor mounting system and the design of the motor means it doesn't need to be ‘locked’ to the axle hub which then allows for hybrid use of the existing ICE engine. A retrofitted car can have two or four of these electric wheel motors as well as customisable wheel well battery size. This allows configurations for power and range. With the retained ICE motor, there is either backup range or more power again. Current retrofit services start at $50k and take weeks to complete due to the custom components required. REVR could cost as little as $5k without rebates and can be installed in under a day.

Future plans

I need to purchase a higher amperage controller to properly test the V1 prototype that is built. I have acquired quotes from Chinese manufacturers for various components of a future prototype design as well. The v2 prototype is in the design phase but needs to be finalised based on results from V1. I want to begin testing and better understanding how a motor performs in this new environment and how it interacts with the other systems in the car. My ultimate goal is to make an EV conversion toolkit that can be applied to any ICE vehicle and be implemented with minimal specialist knowledge.

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