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

[oil pan 4]

Originally Posted by Otto

4. How hard to rig it for regenerative braking?

I say screw regenerative braking.
Lose the regen braking and you can knock off a nice portion of the cost.

[cfg83]

Hello -

My friend had a good question :

Since the two rear wheels have independant motors when going around a curve or corner the outside wheel has to turn slightly faster - no? Like what the differential does mechanically this would have to be done electronically with the motor drive software.

CarloSW2

[Weather Spotter]

The regen breaking is whats attractive about this idea. I coast to most stops but in the cases where I need to break suddenly or find I am gaining to much speed down a hill, I want to recover that energy. It would also help when I take a new route and fined a stop sign when i did not expect them. it would also be nice for my city driving (idiot lights).

[oil pan 4]

It may not cost that much more to add regen to an AC system.
My thinking is usually based on serries wound DC, because that is what I would use.

If there is a sizeable price difference they may want to sell 2 versions, one with regen and one with out.
I think the more of these they sell the better.

And there is a wiki for "adding a hybrid system". Guess I should add this.

[Otto]

After viewing the MTSU and ABC television videos, I think this thing is an excellent idea, but could be significantly optimized:

1. Put the permanent magnets on the wheel itself, further from the axis of rotation (the axle centerline), for more torque per pulse of electricity. This means you can dump the brake drums, using lighter, better, and thinner brake disks instead. With regenerative braking taking much of the braking load, this means the disks could be even smaller/lighter than normal, further reducing unsprung wheel weight. Since the stress path which applies torque to the wheel travels between permanent and electromagnets, putting the permanent magnets on the wheel itself means less stress going circuitously down through wheel center section, meaning the wheel center section could be made thinner and lighter, i.e., less unsprung wheel weight than conventional.

2. Put the stator electromagnets on a fixed pizza-pan disk, adjacent to the permanent magnets on the inner surface of the wheel. This structure not only holds the electromagnets, but streamlines the inner surface of the wheel, as it acts as a fairing, reducing aerodynamic drag in that area. Think: Wheel shape is effectively pizza pan covers on both sides of the wheel. Porsche Design 90 or sewer lid aluminum wheels would be ideal, as they are already among the lightest wheels made and have nearly the same outer surface shape as pizza pans. A composite wheel would save further weight, albeit at significant co$t.

3. Dump the entire engine, transmission, drivetrain, exhaust, fuel, cooling, etc. assembly, reducing vehicle weight accordingly, and go with purely battery powered electric drive. Maybe a small onboard diesel auxiliary power unit running at optimum constant rpm to drive an alternator to keep the batteries topped off only as needed. Run the apu on used cooking oil. This presumes some light, cheap diesel can be found. (I know that lightweight, diesel, and cheap are mutually exclusive terms, but hope springs eternal.)

Trains and ships run on this method--diesel driven generators make electricity to power electric motors that then drive the wheels or propeller shafts.

Later, as better/cheaper/lighter lithium batteries such as lithium-air become available, or lenr heat source for a stirling engine generator come online, remove the diesel and its weight.

[Frank Lee]

Torque forces especially acceleration through the wheel are minute compared to braking, bump impact, and cornering forces. Don't look for lighter wheel potential with that idea.

Wheels, being on the "front line" with regard to impacts and other ugly events are oftentimes not perfectly true, even though they started out that way. If the rim itself is to also function as a motor, I think it will need a robust design such that it doesn't lose lots of efficiency if running tolerances get huge i.e. the thing gets knocked wobbly.

I like the idea of having wheels be the "fuse" between the expensive bits and all the hazards of the road.

[Otto]

Originally Posted by Frank Lee

Torque forces especially acceleration through the wheel are minute compared to braking, bump impact, and cornering forces. Don't look for lighter wheel potential with that idea.

Wheels, being on the "front line" with regard to impacts and other ugly events are oftentimes not perfectly true, even though they started out that way. If the rim itself is to also function as a motor, I think it will need a robust design such that it doesn't lose lots of efficiency if running tolerances get huge i.e. the thing gets knocked wobbly.

I like the idea of having wheels be the "fuse" between the expensive bits and all the hazards of the road.

Those are very good points, Frank, and thanks for sharing that perspective.

As for lighter wheels, didn't the Corvette crew try out composites some years back? If so, how'd that turn out?

As for the wobbly wheel problem after curb rash or big potholes, I'm wondering how much battle damage happens to the inner arc surface of the wheel. Not the bead rim, but that concentric curved surface where the wheel rim/sidewall turns inward (and where stick-on weights go), which is where I'd want to put the permanent magnets. I've bent a rim or two on an old BMW, saved them, so will look to see how much deformation (if any) happened there.

Again, my reason for wanting to put the permanent magnets as far out on the wheel as practical, is to get as much torque as possible from a given shot of electromagnetism: The farther out, the more torque. Compare to the MTSU app. on the brake drum: The effective lever arm on those magnets could be improved substantially.

[rmay635703]

Originally Posted by cfg83

rmay635703 -

I know what you mean, but I can understand that it's "saveiotic" in the sense that no wiring = lower cost in exchange for higher risk, aka you only have to concentrate on the wheel-well of the car for now and the interweb of bad guys later.

CarloSW2

Signal Wires don't need to be much more than 32 guage or so and they don't even need to be true copper, these can be had for pennies and opticouplers can go to the moving bits if you are afraid of fatigue.

Having dealt with industrial equip & bluetooth & wifi, in a factory setting I can say anything wireless is NOT something I would want on an OTR vehicle. There are a lot of things in the environment that will make the blasted thing inop for seconds at a time or take it out completely until you get away from the problem.

If you were driving in the middle of nowhere, fine; in a city, no way.

[rmay635703]

Originally Posted by oil pan 4

I say screw regenerative braking.
Lose the regen braking and you can knock off a nice portion of the cost.

Actually regen isn't that expensive ($100 of real added cost or less), its controller manufacturers that make it so because of the novelty.

AKA a series wound motor and a shunt wound motor really aren't any more expensive to produce in terms of cost to produce.

The controllers aren't that far apart in cost of materials either.

Now retail, sadly it has little to do with cost of materials in the specialty market.

Also remember overseas there are regen series wound controller available (and its mainly programming to get the feature) although less effective they would be very cost effective.

[Otto]

Seems like a few cents of wire would replace vastly more expensive wifi, be more reliable, and less prone to interference.

Regen means less onboard battery storage needed, since you're getting "free" juice back at every slowdown and stop. So, regen is effectively cheaper and lighter, and pays for itself. With less battery storage needed, less structure and weight to support it is also needed, making for secondary savings in weight and cost.

I looked at inner surfaces of two bent aluminum BMW wheels, no sign of deformation much inboard of the lip, so am sticking to my view that said inner surface would be good as a mounting place for magnets on the wheel.