Transverse Flux Motor V6

This is part of a larger project I started in some free time over the last summer. I was on co-op with a company working on a hybrid system. Being exposed to the industry made me realize that what i thought was the gradual and eventual transition it hybrid and electric vehicles isn't happening as fast as I thought. I always had an interest in electric vehicles because of their emissions potentials and because they are quiet. I decided to get back into electric vehicles. My school has a few electric vehicles and hybrid electric teams. I have tried attending meetings with all of them and talking with team leadership about team vision and plans. While I believe the teams are doing some really cool work, I find myself incompatible with the team cultures and operation models.

I instead decided to design my own electric vehicle. Cars are cool but I already have a car, so I don't really need a second one. Cars are also very challenging to build them road legal, let alone finding someone to insure you. For a while I rode a 1982 Honda moped and loved it. Eventually I sold it when I moved and I've really missed it. In my area, you don't need a motorcycle license for a moped and they are required to be inspected. They are also much easier to be insured. So I started sketching and brainstorming for a small electric moped.

I want to design everything myself; battery, BMS, motor, motor controller, frame. This post focuses on the motor design I settled on and the first version of the model I developed. I began by reading research papers. There is a lot on forums about motor design but much of it lacks solid engineering fact behind it; research papers provided the detailed information. Traditional laminated core in-runner motors I decided were too complex to build, even though they were the most common. They require a lot of reliance on outside vendors to cut the laminations, and a ton of time winding the slots. I wanted something simple and easy.

Reading research papers about various motor designs, I found something called a transverse flux motor. Originally an in-runner motor, I decided an out-runner with a Halbach array would give the highest torque density. After playing around with 6 different sizes and configurations, I finished a small scale model of the motor described. This motor only has two phases as that is all that is required. It is designed much like out-runner motors found in model aircraft.

Finished transverse flux motor

Finished transverse flux motor with rotor removed, only one phase is shown.

 Each phase has only one large coil. Interlaced around it are small horseshoe shaped laminations. They alternate inside and outside the coil, causing a reversed polarity on each horseshoe. The two phases are offset by halve a phase so no offset would be required in the magnets in the rotor. The light grey annulus is the mounting surface for the motor. The horseshoe laminations key into this mounting structure and and spaced apart by plastic insulators. The two phases are held in place by a lock nut on the back of the mounting structure.

Cross section of the phase, blue lines show where the copper winding would be

 The rotor is made of a single tube of plastic, slotted internally to space out the permanent magnets. Its a very unconventional design and difficult to prototype, but it is the best way I could think of doing it without laminating it. On the rear end is a cap with the main bearing in it. This bearing seats on to the stator via the phase lock nut. A small aluminum ring is pressed into the opposing side of the rotor to prevent possible collapse or deformation of the plastic tube. This design really needs a second bearing for support at one end or the other.

Motor rotor, note the complex fin shapes in the plastic tube and the single, large bearing

I ultimately rejected this design because of the complexity of the rotor, and the wiring of the leads out of the phase. With how I wanted to build it, large or small, there was virtually no space to run the power leads from the rear most phase to the mounting flange. I eventually decided to move to an axial flux motor design. There are many documented cases of axial flux motors performing to very high standards while there are virtually none of transverse flux motors preforming at high levels.

My designs for axial flux motors will be featured in future posts.