We’ve begun testing some Brushless Outrunner Motors for the Metroboard Electric Skateboard. Unlike an Inrunner Brushless Motor, an Outrunner houses its magnets on the body of the motor, and the body spins with the motor shaft. These have become popular for use on Electric Skateboards (e.g., Boosted Boards), because of their small size, light weight, and high power density. However, they are typically designed for use on RC Airplanes to drive the propeller so adapting them for Electric Skateboards requires some customization for them to work successfully.
For example on an RC airplane, the load on the motor is fairly constant, so you can get away without using Hall (Magnetic) Sensors to drive the brushless motor, but with an Electric Skateboard the load is quite variable including starting from rest with a heavy load which can result in jerky motion without the use of Hall Sensors. So far the smoothest possible ride, we plan on using these motors with Hall Sensors. The manufacturers of these types of motors don’t typically build them with Hall Sensors, so we are developing a custom part that will fit over the motor and house the Hall Sensors.
The other challenge is keeping a Brushless Outrunner Motor clean and protected from the environment. Unlike an Inrunner Brushless Motor, Outrunners typically aren’t sealed very well and have large cutouts in both their face cap and end cap. In an RC Airplane, these cutouts allow the Propeller to cool the motor by blowing air onto the motor windings during flight. However, the environment for an Electric Skateboard is much more harsh, with road grime and street pebbles getting flung in the area of the motor which could potentially damage the exposed windings. Also the spinning body of the outrunner motor is a potential safety issue for the customer, so you really need some kind of protective shell around the motor to protect it against the elements and the customer’s fingers!
The main advantages of the Brushless Outrunner Motor is it’s small size (63 mm Diameter x 74 mm long) vs our current Inrunner Brushless which is (80 mm Diameter x 125 mm long), and weight (1.8 lbs vs 4.8 lbs). We hope to offer this type of light weight high power motor within the next 6 months on the Metroboard Electric Skateboard, so stay tuned for future updates!
We also plan on offering upgrade kits to existing customers, so they won’t miss out on the latest improvements to the Metroboard Electric Skateboard!