UPDATE: There is a follow up post on how to remove the stiff wires alltogether.
I have been building micro brushless quadcopters like my pepperFIISH for a while now. Over the last builds it became more and more clear that one of the weakest spots are actually the motor wires: Most of the small brushless motors come with stiff, single strand copper wires covered in heat shrink tubing. Most of the time this wire breaks due to vibration directly at the soldering spot at ESC pad. Often this is due to previous damage caused by minimal cuts occurring while stripping the isolation but it also happens to perfect solder joints.
The root of the problem is the single stranded and stiff wire. Replacing it with a flexible multi strand silicone cable helps a lot. In this tutorial I am going to show you how to replace these cables. Along the way you will also learn a nice trick to remove the cable isolation without leaving cuts on the wires. I am going to write this tutorial based on a Racerstar BR1103B motor but in principle this can be applied to all motors. If you use bigger motors make sure to use the proper sized silicone wire. Measure the single stranded wire thickness and use this AWG chart to lookup the best matching AWG size. I measured the wires of the 8000KV BR1103B to be 0.22mm in diameter and the perfect match would be 31 AWG. This is not common and as thicker wires are generally better I choose 30 AWG for this motor.
You will need the following items:
- Motors of your choice: Racerstar BR1103B
- a sharp (!) wire cutter: this one is a real bargain
- heat-shrink tubing: 1.5mm from this set
- matching silicone wire: 30 AWG (this one is good, only 0.8mm OD)
- a soldering iron and some solder
 Cut the wires
Even though removing the wires altogether and soldering the silicon wires directly to the motor coils would be the cleanest solution, we are going to cut and attach the wires on the outside as this saves us a tremendous amount of work (disassembly of the bell, removal of glue, messing around with the tiny coil wires,…).
Start by cutting the wires at a distance you feel comfortable with. I usually cut the wires at 1cm distance but you might want to start with some more length. Just make sure to remember the exact length where you cut it, it will become important in one of the following steps.
 Overstretch the isolation
Now comes a handy trick: Remember, the isolation is heat shrink tubing, mechanically stretched heat shrink tubing contracts on application of heat. We are going to exploit this property in order to get clean wire ends without cut marks. Take a tweezer or pliers and gently pull and overstretch the isolation 4-5 mm as shown in the next picture:
 Cut the isolation
Now cut the wires again at the same distance you did the initial cut. If done properly you will only cut the (overstretched) isolation as the wire does not extend to that distance
 Apply heat
Now apply some heat to the wire ends. You can either use a hot air gun or a gas lighter for this:
The overstretched heat shrink tubing will now contract and expose some millimeters of the bare wire!
 Tin coating
Cut three 5 cm long pieces of your silicone wire and strip 2mm of the isolation. Use your soldering iron to tin the silicon wire and the bare wire ends of your motor.
Cut any excess wire and solder the single ends together.
 Heat shrink tubing
You’re almost done. Cut 5mm long pieces of heat shrink tubing and use heat to shrink them in place. Your final result should look similar to this:
Repeat this three times for the other motors and you are done! Or five if you are building a hexacopter 😉
In order to prevent the point of cable attachment from breaking due to vibrations, make sure to attach this spot to the frame. I use thin pieces of duct tape or multiple turns of thin thread for this.