The motor plays probably the most important role in an electric skateboard build.
There are two main types of motor you can use in your board:
- Outrunner motor
- Hub motor
An outrunner motor is the classic design for a diy eboard. It means you require all the other mechanical bits listed in the parts list including a motor mount, pulleys, and timing belt. A hub motor does not require these extra parts as the motor is already in the wheel hub.
Choosing a Motor
There are two values you will come across when looking for a motor:
- Motor Velocity Constant – Kv
- Size – mm
The velocity constant is just the RPM of the motor per volt. Read the Wikipedia page on motor constants for more detail. But simply, a 200 Kv motor would run at 7,400 RPM optimum in a 37-volt system. As the Kv is the RPM per volt you would multiply 200 by 37. You can see how your batteries and ESC would come into play here, you need to choose the right voltage (batteries) and you need to choose a capable VESC that can handle that voltage.
You might think that a higher Kv would have a higher RPM (which it does) and therefore give you a faster top speed, but as you get higher Kv ratings the voltage gets smaller along with the size of the motor. This doesn’t work well for pulling a heavy human on a piece of wood as there is a lot less torque.
The sizing of motors is usually labeled with four numbers, for example, 6355. This is simply the length and height in millimeters with the first two digits being the length and the last two being the height.
What difference does the size make? Some motors have the same Kv rating but are different in size. Having a bigger motor allows for more electrical coils and therefore more magnetism, this provides more torque. Having more torque means quicker acceleration and better performance uphill.
When looking at motors, the specifications usually state the voltage range or the number of cells in series e.g. 6s (24V). Ideally, you don’t want to exceed the maximum rated voltage for a motor as it will start to overheat and become less efficient.
You don’t want to exceed the motor’s maximum current (A) load for the same reasons either.
Furthermore, you need to make sure you are giving the motor enough current and voltage to pull you along. You need to have enough torque to start and get up hills, and enough power to get you to top speeds.