Converting the Eachine Racer 250 to APM Controller

A while back I wrote about buying the Eachine Racer 250, which used a CC3d controller.  Well I got tired of trying to figure out this controller and decided to switch the controller over to an APM.  I used the Hobbyking Micro APM, but you can get the same hardware from Banggood.

This started out easily enough, but there were a few hurdles along the way.

Step 1 Disassemble the Eachine

Take the top deck and battery alignment plates off as shown in the figure 1.  Be careful when removing the power connector for the 5.8 GHz video transmitter as it can be easily damaged.  Use an old coffee cup to store the parts while you work on the rest of the project.

Figure 1

Step 2 Mount the Micro APM

The Micro APM will easily go into the CC3D mounting standoffs as shown in figure 2.  Note that you will have to remove one standoff that supports the battery alignment plate as it blocks the USB port.  Figure 3 shows the APM mounted from the top

Figure 2

Figure 3

Step 4 Wire Up the APM

Here is where it gets a little tricky.  The servo wiring from the APM to the receiver is done as per normal.  The Ardupilot.com website shows how it needs to be done.  This is easy.

Next, you need to supply power to the APM so you will need to make up a cable that goes from the Eachine 5V and ground power pads (green arrow Figure 4) to the power input connector of your APM (magenta arrow, Figure 4). You will need a 6 pin connector to attach to the APM.

Then, we come to the tricky part.  The connections to the motor speed controls are shown by the red arrow in Figure 4.  You have to make a new cable here.  The motor numbering IS NOT THE SAME for APM and CC3D.  The cable will need to be set up as follows:

APM            Eachine

5V                5V

Gnd              Gnd

Motor 1        Motor 2

Motor 2        Motor 4

Motor 3        Motor 1

Motor 4        Motor 3

Figure 4

Step 5 Reaasemble the Eachine

Now you can reassemble the battery alignment plate, top deck, and secure any loose wires.  You are ready to fly again after the usual ESC calibration, radio, compass, gyro calibration are done.

Figure 5 Reassembled Eachine Racer 250