Phoebe is an ARRMA-RC Raider BLS rc car that I’ve spent the past 4 years off and on making semi-autonomous.


Phoebe came stock with an arrma-rc BLS ESC & Motor combination. This is a sensorless brushless motor, which is not ideal for a robot, and I’ve been on the hunt for a suitable sensored replacement.

From the specs, the motor is:

Shaft Length13mm
Shaft Diameter3mm
Motor Speed4000kv

The ESC supports 35A continuous, 50A peak, with either a 7S NiMh (8.4V), or 2S LiPo (7.4V).

Any replacement motor, to fit on the car, needs to match the physical dimensions. To keep a similar performance (I don’t care to replace the gearbox - I might as well buy a new platform if I do so), I also want it to have a similar speed as the stock motor.

Control System Mounts

Attaching to Phoebe

There are 4 screw holes - 2 on each side. They are symmetrical.

  • It appears that the first 2 set are 24 mm from the back.
  • The next set are 83 mm from the first
  • Allow at least 5 mm vertical clearance from the screws to the bottom of the control system platform
  • From the screw holes to the bottom of the chassis for Phoebe is 34 mm.
  • m3 screws.
  • The holes aren’t threaded - use nuts + lock washers on the other side to hold them in.
  • The batteries for the electronics will likely be 16mm thick.


  • The stock ESC is 54 mm long, 38 mm wide, and 21 mm tall.
  • The (m3) screws are 46 mm apart (center to center)
    • 17 mm from one edge
    • 21 mm from the other (this one is the side with the cable leading to the switch)
  • It should be mounted opposite the side the facing the micro USB port for the raspberry pi

PWM Servo Driver

Phoebe uses a SunFounder PCA9685 PWM Servo Driver to interface a raspberry pi 3 to the servo and ESC.

  • It is 62 mm long, 26 mm wide.
  • The (m3) screws are 19 mm apart (centers inset by 3.5), and are 56 mm apart.

Raspberry Pi 3 B+

  • Mechanical drawings for a raspberry pi 3 b+
    • Length: 85 mm
    • Width: 56 mm
    • Screws:
      • m3 screws
      • 49 mm width between screw holes.
      • 58 mm length between screw holes
      • Inset 3.5 mm from width of board.
      • Trailing screws are inset 3.5mm from length of board.
    • The micro USB/Power input is 8 mm wide, and the center is 10.6 mm from the edge of the board.
      • Doing some math, the center of the power input is 4.6 mm from the nearest screw hole - the nearest edge of it starts 0.6 mm from that screw hole.
      • It is ~1.5 mm tall. The hole in the side of the mount should allocate 15 mm width + 10 mm height for the cable.
      • In other words, the hole for the mount should start just past the screw holes and continue for 15 mm. It should allow sufficient height plus/minus for the micro usb cable.
    • The USB A ports extend approximately 2 mm beyond the length of the board.

Last updated: 2020-06-12 16:34:13 -0700