The electronic speed controllers (ESC) have as their main purpose to control the amount of power applied to the motors as a function of a control signal. In our setup the power comes directly from the battery (via a power distribution lead) and goes to the motors. The PWM control signals in our setup come from the controller when the airframe is tested without the autopilot, and from the autopilot in the complete installation.

A second function offered by the ESC is to provide 5V power to components requiring 5V (e.g., the autopilot and the mobile node). This function is commonly referred to as BEC (battery eliminator circuit). However, the maximum current supplied by a typical ESC (e.g., all of the below) is 2A or less, which is close to the maximum power consumption for our autopilot and mobile node. Additionally, if the BEC circuit in the chosen ESC overheats, it may affect the performance of the ESC (shutdown?). Therefore, instead of using the BEC in ESCs, we use an external BEC (voltage regulator). The BEC functionality in each of the ESCs has to be explicitly disabled - see installation notes below.

Installation

In the installation, the ESCs should be placed as far as possible from the compass to minimize electromagnetic interference. Also, if they are used toward the top of their power range (> 50% of rated power), they should be place in the airstream from the propellers. Therefore they can be placed as close to the motors as practically possible while still being connected to the power distribution and the autopilot/controller board.

Since we used an external, high power BEC, we have to disable the BEC functionality. This is achieved by disconnecting (the connector allows the removal without cutting it, although cutting it is acceptable) the middle wire from the three control wires going to the autopilot/control board.

Setup

The ESCs have to be programmed, as they are general purpose and settings for airplanes would be unsuitable for multirotors. The following settings work well for multirotors:

• Brake: Off - hopefully not needed, but if it is, it may help a bit.
• Timing: High - our motors have 12 or 18 poles and can benefit from the high timing.
• Acceleration: High - motors of multirotors should be as responsive as possible.
• Battery type: Ni-XX - although we use LiPO batteries, we rely on the autopilot failsafe to bring the multicopter down safely rather than on the ESCs cutting off.
• Cutt-off-voltage: low (irrelevant for Ni-XX batteries
• Direction - do not change in software - change it via wire swapping

Components

• ​Turnigy Multistar 30 Amp Multi-rotor Brushless ESC 2-4S (USA Warehouse). This is our preferred ESC. Specifications:
  • Constant Current: 30A
  • Input Voltage: 2-4 cells Lipoly
  • BEC: Yes (Switching) [Remove middle wire to disable]
  • BEC Output: 5.5V/4A
  • PWM: 8 KHz
  • Max RPM: 240,000rpm for 2 Poles Brushless Motor
  • PCB Size: 41mm x 24mm
  • Discharge Plugs: Male 3.5mm Bullet Connector
  • Motor Plugs: Female 3.5mm Bullet Connector
  • Weight: 29g

• ​Turnigy Multistar ESC Programming Card (USA warehouse) the programming card corresponding to the ESC above. Only 1-2 needed to program all ESCs.

• ​TURNIGY Plush 18amp Speed Controller (US Warehouse) we also considered this ESC - it does not have connectors either on the input or output. It is also lower performance (BEC, max Amp), and at this time we do not consider it viable. Specifications:
  • Cont Current: 18A
  • Burst Current: 22A
  • BEC Mode: Linear
  • BEC : 5v / 2A
  • Lipo Cells: 2-4
  • NiMH : 5-12
  • Weight: 19g
  • Size: 24x45x11mm

• ​HXT 4mm to 6 X 3.5mm bullet Multistar ESC Power Breakout Cable this is OK, although one with eight leads would be better . Unfortunately, the one with eight leads does not seem to be available.

• ​Hobby King Octocopter Power Distribution Board is an interesting (neater than the cable distribution). The main problem is that the power output is limited at 10A per port.