EDF brushless motors are selected primarily on the cell count and the EDF jet unit planned to be used.
Selecting EDF Brushless Motor Size
From knowing the EDF unit, motor can diameter can be determined. The diameter of the can is restricted by the fan units maximum allowable diameter. Common values can be found on the EDF unit page for maximum diameter. It is always best to select the largest allowable diameter for best performance.
The motors can length will be selected based on the general wattage required. Longer cans will typically support more wattage.
Motor Shaft Size
Brushless motors used in EDF jets come in many different shaft sizes. Limiting your selection of motors is the motor shaft diameter. Some EDF units have a couple adapters to fit more than just one shaft size. Be certain the motor you select has the proper shaft size.
Selecting EDF Brushless Motor KV
The KV value is the most tricky selection to make. KV is the value of unloaded RPM created per volt. If this number is too high, you may burn your power system components up. If the number selected is too low, the ducted fan unit may not produce enough thrust for flight. The KV value is determined by your fan type and voltage used. If the fan you use has a high number of blades, a lower KV value is required. A lower number of blades would require a high KV value.
Generally, most EDF units will run between 35000 RPM and 50000 RPM. The following chart is a general guide line for cell count vs kv range. Please understand the range provided is quite large however the range required for your fan unit may be much smaller requiring a very specific KV value.
|LiPo Cell||KV Range|
|3 cell LiPo||3000-4500kv|
|4 cell LiPo||2300-3400Kv|
|6 cell LiPo||1500-2300Kv|
|8 cell LiPo||1150-1700Kv|
|10 cell LiPo||940-1350Kv|
|12 cell LiPo||770-1120Kv|