MTSU Students Retrofit Hub Motors (Converting an Accord into a plug-in Hybrid)

[NeilBlanchard]

It would be hard to see how a gear reduction drive train could be retrofit onto a typical drum brake rear wheel?

[niky]

Too complex. The whole point of the MTSU design is to integrate seamlessly into the rear hub.

[serialk11r]

Originally Posted by niky

Too complex. The whole point of the MTSU design is to integrate seamlessly into the rear hub.

I don't see how adding that thing to the rear hub is any simpler than putting a ring gear on the wheel and bolting a support to the spindle. Universal fit across rim sizes. Or, you could add a gear to the hub instead, and rather than put all those electromagnets around the hub, have the electric motor more or less directly attached to the spindle.

Having separate components that are commercially available drops the cost as well, and so does using low torque high speed motors.

[niky]

You're putting a ring gear to mate with a motor mounted on the suspension? Problematic if the wheel flexes or starts wobbling... and adding that mechanical component to a relatively robust electric-only system would simply be adding something to break.

The prototype looks messy, but the idea is that it will be sold as a completely sealed package.

[serialk11r]

Originally Posted by niky

You're putting a ring gear to mate with a motor mounted on the suspension? Problematic if the wheel flexes or starts wobbling... and adding that mechanical component to a relatively robust electric-only system would simply be adding something to break.

The prototype looks messy, but the idea is that it will be sold as a completely sealed package.

Sure, you're adding something to break, but a ring gear that deals with low torque can easily be designed with a high safety factor and one can use "compressible" (like bump stops) mountings to deal with minor flexing.

But I still don't see how it'll be so easy to integrate a hub motor into undriven wheels with no shafts to attach things to. You have to keep brake rotor functionality. There will be an equal amount of custom attachments required except fully integrating the motor into the hub will make said attachments more difficult to manufacture.

[niky]

The premise given is that you install it between the brake and the wheel, but it looks like it actually replaces the brake. The half of the motor on the strut side is stationary, just like the brake calipers or shoes are stationary, while the half on the wheel side moves with the hub. Simplicity itself.

[serialk11r]

Originally Posted by niky

The premise given is that you install it between the brake and the wheel, but it looks like it actually replaces the brake. The half of the motor on the strut side is stationary, just like the brake calipers or shoes are stationary, while the half on the wheel side moves with the hub. Simplicity itself.

I don't consider replacing the brake simplicity, because that involves making a rather specific hub motor for every car. Besides, reduced braking function on the rear wheels is quite a large compromise, that I think sensible people would consider unacceptable. Weight transfer may leave the rear axle with perhaps under 40% of the weight for taller vehicles, but the hub motor is never going to be able to apply enough torque to lock the wheels even in that case. Losing even 20% of braking capacity is huge. And on RWD cars (I know I know, most people here think RWD is stupid or something), you absolutely cannot replace the brake because the front does more braking.

Many cars aren't coming with drum brakes anyhow, because they suck. The secondary drum brakes used for the handbrake are not going to suffice either. Heck, the Honda Accord (current one at least) has rear disk brakes.

Even if braking performance weren't an issue, is embedding the motor armature into a new "brake" hub really easier than just bolting a motor to the spindle and using gears?

[freebeard]

A cross-section drawing of this invention would answer a lot of questions.

If there is that much room between the drum and the rim, your brakes are too small.

[cfg83]

freebeard -

Originally Posted by freebeard

A cross-section drawing of this invention would answer a lot of questions.

If there is that much room between the drum and the rim, your brakes are too small.

Until I see more I will be cautiously optimistic.

CarloSW2

[dremd]

Very cool, I owned an Accord Wagon like that before, great car, fantastic idea. When someone complains about unsprung weight I direct them to the nearest body on frame SUV / truck with the live axle.