Disassembly Attempt

Disassembly Attempt

I wanted to disassemble the motor for two reasons:

1. To see how it was made.

2. To possibly add inertia internally.

The motor was super-easy to get out of the chassis. I did not even have to remove the skid plate. Unfortunately, that's where easy ended.

I began disassembly by removing four M5 screws and four M8 screws from the fan-side endplate. This did not allow anything to come apart, but I did notice the rotor would no longer turn!

When everything moves freely, the motor turns over with relatively little torque, maybe 15 pound-inches to start it moving and then only 5 pound-inches to keep it rotating.

Once all 8 screws are removed, you can remove three shims on the fan side that total 0.9mm in thickness (nominally 0.3mm each). These are held in by an internal snap ring.

After a bit of experimentation, I realized that the rotor was being pulled into contact with the stator when the M8 screws were removed. These screws need to be drawn up tight in order to pull the stator away from the rotor. I also realized the 3 shims set the rotor/stator clearance gap. The thicker these shims are, the closer the magnets get to the stator coils. So removing shims would decrease the performance of the motor. (The competitor in me considered fitting thicker shims. But because I could not find any toleranced manufacturing drawings, I did not know what the limits might be and did not want to catastrophically find out.)

As you can see, there's a pulley for a toothed belt that needs to be removed. I could not get the jaws of a conventional bearing puller behind it. The pulley is made with sheet metal sides pressed onto the center section. I tried using a battery terminal puller (very flimsy) and it began to bend the pulley's metal sides.

Then I tried a hot air gun and penetrating oil. No luck.

Then I machined some 6mm thick aluminum plates to pry against. No luck.

The next attempt was gentle heating with a propane torch. Nothing moved. I envisioned making a more complicated “puller.”

I likely would have destroyed the pulley in the process and EM no longer sells them. In fact, EM even changed how the pulley attaches in subsequent years for this model.

What's Inside?

While searching the internet for motor disassembly instructions (there aren't any), I learned that an axial-flux motor can be very difficult to disassemble. In the case of the HPM48-5000, a special fixture is required, as is a hydraulic press. Furthermore, suitable precautions must be taken when putting the motor back together as it can energetically “self-reassemble” due to the very strong magnetic attraction.

The photo below, posted by Frank at VESC-Project.com, satisfied my curiosity.

Another source states that the OD of the rotor is smaller than the OD of the stator coils. So, I'm guessing there may be room for extra inertia to be installed right inside the motor. If it would be possible to locate an inertia ring directly inside the 5.7's motor, it might have about the same inertia as the external disk I envisioned - but with only one-fourth the mass.