# Axial vs. Radial air gap motors

I’m working on a rare treat- a little history/research project I’m pretty excited about, but one little thing sparked my curiosity- the difference between an axial air gap motor (the Agni and Lynch design) and a radial air gap motor like the Mars.

In the process of trying to learn the difference, I stumbled on this site: MyOwnHybrid, the tortured tale of a guy, Vasco Névoa, building a car from the ground up. I’m using his amazing drawings to show the difference between an axial and radial air gap. Interestingly, what threw me, was the “air gap” part. What they’re describing as axial or radial is the space between the rotors.

Axial means, essentially, on the same axis. Radial means perpendicular to the axis… take a look.

This is an axial motor.

…well, an axial air gap motor. Note that the space between the two rotors is, well, axial- if it was a rotor, it would be rotating on the same plane, from the same center, as the other rotors.

Now, here’s a radial air gap. Motor.

These drawings are just awesome. But look, see the gap? It’s now perpendicular to the rotors- simple as that.

The big deal with the Agni motors, if you go and try to order one, is the issue of ordering a reinforced motor or not. I had no idea what this meant. As you can see from the drawing, in an axial design the force on the rotor wants to pull it in, together, and so there’s all sorts of funky torque acting on it. The solution is to bridge it, as much as possible, to keep it from twisting. The radial is, by design, a more balanced structure. The force to pull the rotors together is pulling directly outward from the center.

Crap. I’m actually starting to feel like I understand this stuff a little. Scary.