Hybrid Racecar?
 

Howdy all,
I have built a few racecars over the years and now have two chassis without drivetrains that I was thinking about converting to some form of a hybrid racer. One is a Lotus 7 style chassis with IRS that would make for an easy conversion if I can find a drive system that would do it justice. Any ideas?

I'm a fan of hybrids, and they're great at lots of things. Honda's IMA system is the lightest and least powerful one out there, but it still adds around 150lbs to the car.

The electric motor will make the car quick off the line, and add lots of torque at low RPM's, but after a lap or two the batteries will be flat. You'll get approximately nil regenerative braking to recharge with, because that is a SLOW process. Fine for around town, but nowhere near fast enough for a race track.

I say keep it lightweight and simple, and skip the hybrid drive.

The hot setup seems to be use lots of regenerative braking, and use the stored power sparingly, for lower speed acceleration and for passing boosts. In a race, any time the engine has power to spare, the brakes have more. A well-cooled ni-cad battery sized to run your motor/generators for ten minutes either way will be able to handle the amperage and give you a bit of reserve to play with. Some new lithium cells promise very fast charging rates, too, with great efficiency (and cool-running) Capacitors, of course, are instant, but expensive and heavy. Given that you may have to throw away some heat as well during braking, you can run the generator and battery past maximum efficiency for their weight, and come out ahead, if you are careful about cooling. Of course, the electric system can implement all the traction tricks a silicon brain can think of too, even with a "dumb" disk brake setup in parallel.

I think it depends on what type of race you are considering entering. If it's one where gas mileage might make a difference (i.e., you could skip a pit stop and thereby gain track position by getting better fuel economy, or you're only allowed a certain amount of fuel for the race), then you might have an advantage with a hybrid. If the race is not gas-mileage limited, then I think there would be no advantage to having a hybrid and it might be a hindrance due to added weight.

If you decide to go ahead with it, I would consider a 2nd Generation Toyota Prius drivetrain. You might be able to get one for a reasonable price from a wreck. It has decent power and good regenerative braking.

Most of our races are 30-40 min sprints and on road courses (Road Atlanta, Carolina Motorsports Park, etc) and they involve heavy braking as well as short sprints. My Lotus 7 chassis was oversized for a V8 so I have plenty of room for batteries, etc. - I just wondered if it was even feasible to consider it.

What about using a KERS (flywheel) type storage system like they do in F1 racing.

I was leaning more towards a constant speed diesel attached to a generator that powers an electric motor (ie. locomotive). My thoughts were to have batteries simply as temporary storage.