About BORGI Hubmotor



The BORGI Hubmotor is an opensource, axial-flux, pancake style hubmotor which you can drop in between your cars rims and wheelaxle. In theory you can convert your car from gasoline or diesel to electric hybrid or 100% electric with it.

There are pros and cons for a hubmotor over any other normal motor design, but in general they offer a great simplification of the whole drivetrain of an electric vehicle. Hubmotors will allow you to get rid of all the components you normally have in your combustion-engine car, including drive-shafts, transmission axles and gearboxes. In the end this gives you less components you have to maintain and frees space for more batteries.

On the negative side, as you get rid of any gearbox, hubmotors have to generate all the torque by themselves, so they need to be quite powerful to get your vehicle rolling. The controlle sider is a bit more complex too as you basicly need one controller for each motor.

Axial-flux motors employ a different motor topology than your standard radial flux motor. They have a shorter flux path, generate less eddycurrents which in theory makes them create less thermal losses and higher efficiency ratings, thus higher power densities.

Super cool possibilities of hubmotors are that you can use them in 2 wheeldrive as well as 4wd configurations.

We will try to build more knowledge about axial-flux as well as other motors in the https://community.occupycars.com/c/production/other-motor-designs

How we started

The experimentation began with ordering a 8kw hubmotor from alibaba which turned out to be too heavy and bulky to fit it between the rim and the wheelaxle without rebuilding the whole wheel suspension assembly.

Our research led us to Axel Borg who showed a working axial-flux motor design, which he basically made from wooden parts, magnets and some copper wire. And he was so brave to put it into his motorbike and drive around with it. We were impressed and decided to build and experiment with that design.

The BORGI is clearly related to Axel’s design, and adapted to fit inbetween the wheelaxle and the rims of a VW Touran car. The name BORGI is a tribute to the incredible Axel Borg and his awsome DIY ingenuity.

What can it do right now?

So its not a wooden motor anymore. We translated it to cnc milled aluminum and 3D printed parts.
It fits flawlessly onto the wheelaxle of our VW Touran MK1, right where the brakedisc was sitting. Yeah right, we got rid of the rear brakedisc assembly. The plan is to go for electric braking, sounds crazy? Yes, but unless someone is calling you crazy you are doing something wrong right? So lets drive on and care about the braking later, for now this is a research project afterall.

It spins verry fast! we got it spinning around 10000 rpm, way too much for a driving application.
It would spinn even faster but we were scared about the thing desintegrating. The interesting thing was that we already pumped 20kw through the coils with no real heat development. We operated it with 72v and 300A and the result was 10000 rpm. We think that it wouldn’t be a problem to pump up to 1000A through the coils without destroying them, which would amount to over 60kw of peak power.
Many things can be improved, the coil configuration, magnet shape etc. Its kind of an open motor now, a kind of crude technology validation. It might need further enclosure for realworld driving. Liquid cooling could be added etc.etc. Lots of things to be done.
But it works and its simple to build. Its a beginning

Whats the next step?

  • controller:
    we need to build a controller which gets enough torque out of the motor to get the car rolling. As there is no gearbox between the motor and the wheel, the starting torque must be quite high to overcome inertia.
    Without a well fitting controller it is hard to validate the design thoroughly.
    Currently we drive the motor with a 3 phase sinusodial controller from kellycontrollers. Its not the optimal solution and it has startup characteristics which won’t unlock the full torque at motor startup.
    We are investigatiing the options for opensource motor controller we can adapt for the project.
    Currently the High Power VESC controller looks verry promissing:
    Thx RMK for the hint!

  • theory:
    To Do: we have to build more knowledge about the math behind axial flux motors
    Axial Flux motors