There are two different types of Bluetooth app controlled motors on Aliexpress, a yellow-white version (left) which goes for 4-5$ or a light blueish gray-white version which goes for 7-8$ that is also the same as the red-black version which goes for 10-12$. When steps differ between the versions, the left image always shows the yellow version, right always shows the other one. They use different apps with different control options. 

The left one uses an app called „XP Block“ and the other one uses an app called „Power Box“, both available on the apple app store and apks for android are available here and here.

parts needed:

-n20 motor with 9v 3000rpm or 3v 1000rpm

-gear, same as the one on the normal motor

-2.54mm pin header at least 8 pins

-custom pcb pcb_9v_connector.zip or just a small piece of perfboard

-some wire

-black and housing colored filament

-1x AMS1117 5.0

-1x MB10F bridge rectifier diode - any other bridge rectifier diode will also work but I used this

-some small heat shrink tubing - any other electrical isolation will also work

-hot glue to secure everything in place and act as a strain relief for the cables

-2x steel axle - same as on the normal motor

-2x heat set inserts or 2x m3 hex nuts - depending on you housing choice

-2x m3x8 bolt

Instructions:

• Test that the motor works - this will be a big waste of time if you don’t test it and it turns out not working in the end - just do this first.

• Print all the normal parts of my 3dprinted monorail - use the housing with the hole for the button. You can also get these parts printed from a print on demand service like jlc3dp for a total cost of about 5$.

• open up the motor - unscrew the bottom screw and unclip the top

• unscrew the one (yellow) or two(gray or red) screws holding the pcb in place

• unsolder the battery and motor from the pcb - make sure to not let the two battery terminals touch

• remove the button and usb port from the pcb.

I first removed excess solder from the underside, used a hot plate to heat the board up and just remove the button and usb port.

 you can also use a hot air reflow station or just try and break and scrape most of the two components off the board or try to solder the wires directly to the board while these components still are attached, which is harder but requires no special tools.

• solder wires to the button you just removed (or another button if you broke it in the removal process)(you don't need to connect both side it just helps with stability).

• solder the button wires to the board, make sure to connect to both sides

• solder the 9v charge connector by inserting the pins into 9v_soldering_jig.stl and solder them to the pcb and the two cables

• solder the bridge rectifier diode to the end of the 9v connector cable and feed that into the ams1117 5.0 as show in the picture.

• solder the output of the ams1117 onto the main board - the outside pins are ground and one pin in from the 5 pins is the plus pin, just use the pictures as reference. Secure these components with hot glue so you don’t accidentally break something when handling this further. Here the two versions have slight variations, but both work as shown here (left yellow, right gray/red).

• extend the battery wire so that it is easier to assemble it into the monorail motor. If the battery looks damaged replace it now.

• Reattach the battery and the n20 motor.

• test again

assemble the printed parts. To insert the electronics into the housing first insert the battery on the side of the heat set insert, then slide in the main pcb, only then push the 9v connector into it’s side and secure the button to the other side with hotglue or other glue. You can remove parts of the main body of the monorail motor to make more space for the electronics, but this is not a requirement.

• put on the top cover and screw the two screws in.

done, enjoy you finished motor