How to make coils for the BORGI axial-flux Hubmotor (work in progress)
Picture of our coil making rig
The BORGI motor is a permanent magnet axial flux motor. Which means that the rotors (the spinning part of the motor) house permanent magents (Nd) and the stator has electromagnets. In contrast to the permanent magnets which you can just buy online, the electro magnets actually have to be made by yourself.
With the diameter of the copper wire, the length of the individual wires, the amount of wires in one coil and the amount of turns, you determine the physical properties of the coils. So this is a critical element in the motor build.
For the current build of BORGI (v001) we went with 0.1mm enamel copperwire.
We chose such a thin wire diameter because the thinner the wire, the less eddy currents occur in the wire while energizing it. This theoreticaly means less thermal buildup in the coils thus higher energy efficiency.
The coil as is in this version of the build consists of 210 individual strands of copper wire, each 4.6m long. Wound around a 3D-Printed coil template, you get a teardrop shaped coil which is 7mm thick.
You need 21 of them for one motor.
The coil winding process itself is a bit delicate as the individual copper strands are verry thin (0.1mm), almost as thin as a hair. The tricky part is actually measuring and cutting the individual wires to length and handling the wires in that process.
In theory you can manually measure and cut the wires to length and wind the coils with the help of a batterydrill or something like that. But we didn’t have much success with that method. The copperstrands are so thin that you easily crimp them or create tangles of unusable copper.
Furthermore you want a repeatable process which gives more or less equal results.
To achieve that, we have built a little machine which looks almost like a windmill, but its not a windmill. We should maybe call it “not a windmill”. It is basicly four arms rotating on an axis, driven by steppermotors controlled by an arduino. This gives us precise controll over the length of the wire we unspool from a bobbin.
For the BORGI Motor we need 210 strands of 4,6m long 0.1mm emaneled copper wire, which amounts to 966m of copper wire per spool. Thats an amazing 21 km of copper wire in the motor (21 coils)
We used individual bobbins with 1000m each and used the “Not a Windmill” to unspool exactly 966m.
You could also use bigger bobbins or you could build a machine with 21 bobbins unspooling on the coil template directly.
So the process looks like this:
- Unspool 966m onto the Coil Maker (Not a Windmill).
- Take the copper loops of one arm of the NaW while keeping it tensioned.
- Hooking it up to a “traktor” wire and feed the bunch through a teflon tube (this keeps your wires nice and safe in the tube, not allowing the wire to tangle and create knots).
- pull 25 cm of the wirebunch out of the tube and put heatshrink around it.
- mark the heatshrink as the start of your coil.
- start winding the wires onto the coil templates, while drawing them out of the tube (leave the 25cm start hanging out of the coil). You should have 8 turns around the coiltemplate.
- when you’re done with winding you should have 25cm if wire left on the end as well.
- put heatshring on the end of the wire as well and mark it as end.
- put insulating tape around the coil to keep the wires in place.
3D printing coil templates
We made these 3D printed coil-templates, which give us a defined and repeatable package for the coils
We will add more info as well as a How-To video of the full process soon. Also more infos on how to build the Not a Windmill. stay energized.