I would think that you could create a "magnetic" braking system.

your rotors would be strong magnets and you would put multiple coils around the rotor.

Then you put a large variable resistance load somewhere to turn the energy to heat. By doing so you can place the heat load in more optimum spots for cooling.

It's to simple, so I am sure I am missing something.

 

In theory its fine. The execution just takes some work.

At present, Honda uses regenerative braking in the Insight (and probably the new Hybrid Civic). However, this involves using the electric "flywheel" motor to slow the car and generate current.

No reason you couldn't do something similar with the actual brakes, except size and abuse concerns might be a problem.

UL

 

It was the insight/electric cars that got me thinking. No plans to build any.

You would think more race cars (like F1) would use something like it.

 

If i'm not mistaken the amount of brake torque is proportional to the induced current flow. And everyone knows that current flow is very good at toasting bread ;-) The point being that, tho you may be able to do away with wear surfaces and the heat they generate you'll still have to dump that energy somewhere and that will likely produce just as much heat. Not to mention that you cant transmit that energy through wires etc without loss and induced heat. It also seems to me that all that current implies a sh!tload of copper or someother similarly heavy and conductive metal.

 

dave,

While what you say is true, remember what krazik mentioned: "...you can place the heat load in more optimum spots for cooling."

While I agree there would be a lot of heat involved, the heat coils could be placed directly under the car, or in front, or in the rear...anyplace directly in the airflow and still be better than where brake pads are.

I'm wondering if I shouldn't try and calculate how much power it would actually take to stop a 3000 lb car using reverse magnetism in the same distance as standard brakes...

 

I would imagine that if the power needed to accelerate a car at .25Gs at 25mph was say 100hp then aproximatley the same power would be needed to decelerate it at that rate. I say aproximately because you have various other forces working to help decelerate the car.

Though i've never seen the calculation i would imagine that for a given standard conductive metal there is an ideal minimum mass required to produce a given HP. I wonder how the weight of current electric motor tech compares to that ideal.

 

True, but I like to think I can stop a car one heck of a lot faster than getting it moving. I'd like to do 60-0 in MUCH less than 6 seconds.

 

Sounds like a drag-chute (retractable, of course) might be a better idea;-)

 

Magnetic retarders that do this to the driveshaft are required on all schoolbuses in Colorado, and can put some impressive hp figures out, but they weigh about 500 lbs, pull 1500 amps at full load, and make a lot of heat! But they don't make contact, and can't burn up like shoes or pads.

 

It is an interesting concept. I've read a feq speculations that Honda has the next NSX with a hybrid powerplant.

As far as power required:

energy = force * distance
power = energy / time
power = force * distance / time = force * velocity

S2k weighs 2800 lbs = 1270kg
lets say we can decel @ 1g = 9.8 m/sec^2
force = 1270kg * 9.8m/s^2 = 12446 N

power = 12446 N * velocity
~150 mph top speed = 67 m /s
power @ 150 mph = 12446N * 67m/s = 834 kW (ouch!) (all 4 wheels combined)
this will linearly taper off until you have 0 power dissapated at 0mph.

I have a 5kW pretty high tech motor sitting in my office that weighs about 40 lbs to give some reference.
ABS under with electric motors would be a different world. No pulsing. You could control your wheel speed to your hearts content (ignoring serious engineering issues to get to this point).

Since I am in blue sky mode right now, if you could do this, (and store the energy) then there isn't any reason why you couldn't accelerate at the same rate.