In reply to MrChaos :
That would be one way of doing it, but for the physics and modeling inclined people, you can make a pretty basic model to do the work, too. I'm sure someone can find a light car to start with, and then get some good drag data for it (I'd suggest using the certified drag data that OEM's submit to the EPA), and you can make a pretty decent physics model to determine that.
If you can find a car that someone took speed data for an entire lap, just replicate that at stock weights and drag just to get an idea of the energy used. One can even incorporate regen braking into that.
Start with a very ideal model to get the scale of the effort.
Well, I agree Alfa, but maybe an even easier way to do it is to use the gasoline equivalency. Figure out how much gas people burn at the track in an hour in a similar weight car. A gallon of gasoline in a standard 4 stroke engine converts to energy easily.
Sure, you might be able to get some back for regeneration and stuff, but it would like you said get you in the ballpark quickly.
To be clear, I don't think going for the 50k is realistic right now, but I think racing in the ev class would be a hoot as you all work toward the 50k.
MrChaos said:
alfadriver said:
Before getting too far, the #1 calculation is to estimate how much energy will be used over an entire race. Once you know then you can figure out how many batteries you will need. THEN you can come up with a package to change those batteries.
The good thing about doing that calculation is that you can target what track uses the least amount of energy to race on, and focus 100% on that venue.
You'll also know how many battery sets you need based on charging rates given the infrastructure.
so what you are saying is somebody needs to take a fully charged $5k leaf to each track and see how many laps you get before you run out of juice.
Sonds like a good GRM article.
If only someone at GRM had one...
In reply to Robbie :
The issue with the gas equivalency is the estimate of equivalency. What is used for a normal road car doesn't work for a race car- unless there's a good estimate of BSFC at WOT. I guess the over estimate would be in favor of a safety factor for batteries. Then all you need is the number of gallons of fuel someone uses for a stint and an entire race.
None the less- that's where one needs to start. Even if it's just for fun, that has to be done- so that you know how many times you will need to swap and change batteries.
Since there's no budget for the stuff that matters, the best bet would be to get your hands on a FE motor (they're so close to 100% efficient that you need high-end equipment to prove that they don't violate the laws of physics) and build a swappable battery pack with some exotic battery tech. At least li-po, ideally dual-carbon (they're being used in non-military satellites so it should be possible to get some...somehow). Keeping the powertrain costs under 6 digits would be an achievement, but it would work.
In reply to Tom Suddard :
Sounds almost like a concept I've had in my head for a couple of years - relay racing of electric cars, have a team of cars and drivers one car at a time on track with a transponder passed as a baton.
I mean i still have aspirations of rallycrossing a 1st/2nd gen leaf in SF.
This 1800lb Tesla powered Cobra Replica gets a 20 minute stint (about 22 miles) out of a 27KWh Kia pack with the power limited to 200KW. Multiply that pack by 6 and you should get more than a 2 hour stint. They are running into heat problems with the Tesla motor/inverter combo so it is likely not operating at peak efficiency.
One lap in an electric golf cart. Split 49k among the whole field for bribery purposes. Everyone parties for the rest of the time. Everyone wins. Jcamper
Jcamper said:
One lap in an electric golf cart. Split 49k among the whole field for bribery purposes. Everyone parties for the rest of the time. Everyone wins. Jcamper
This is genius and just might work once!
You would still have to deal with 5.5 tons of nickels however.
Leaf drivetrain in a 1st Gen Honda Insight seems like a good starting point.
MrJoshua said:
This 1800lb Tesla powered Cobra Replica gets a 20 minute stint (about 22 miles) out of a 27KWh Kia pack with the power limited to 200KW. Multiply that pack by 6 and you should get more than a 2 hour stint. They are running into heat problems with the Tesla motor/inverter combo so it is likely not operating at peak efficiency.
I was doing some maths.. I'll keep it short since I loathe typing on a phone. This is a great data point!
.75 kw = 1 hp. So that battery is good for 36 hp constantly. Figure you want 150 hp constant for an hour, so you need a 110 kwh battery. Ideally you'd get 3 hour stints.. I need to do a little reading to see if the total battery capacity is simply 110 kw-hr * 3 hr = 330 kw.
My hp requirements are conservative..
If 27KWh lasts 20 min, need 81 KWh for an HR run time which is 108 hp average. So, take my estimate above and knock it down 1/3.
Jcamper said:
One lap in an electric golf cart. Split 49k among the whole field for bribery purposes. Everyone parties for the rest of the time. Everyone wins. Jcamper
The maths don’t work with a hundred car field that each has $1500 into the race. However if your electric is close to the top of class A I can see a full field bribe to sand bag the end of the race a little. Realistically you would only have to bribe the teams ahead of you. Bribes are budget exempt correct?
Using the Telsa Cobra #s above, 14 hours of running @ speed** would be approx 1134 KWhr of total battery. You probably wont fit more than 50-75kwhr in a race-sized vehicle, so you aren't going get a 2 hr stint.
You can't put it all on the pass. side as suggested above. A Tesla pack weighs around 1000lb, so that would murder your CG and also your L/R balance.
IMO you need to do the floorpan like Tesla does, but you need to find a way to do a quick swap, which is going to be very very difficult, especially trackside. The other option is to move the driver to the center of the car and do batteries on either side, but that's got a number of issues that come with it.
It will be very interesting to see some teams attempt this.
** the question is, do you need 200kw average (250hp) in a Miata sized car to run at the front of the pack? I would imagine you do not. I would think you could get near the front on a lot less power.
This would be a interesting PR move for a OEM. They already have the R&D budget. Buy a clapped out car, cage it, install the drivetrain of their choice. A couple of dozen batteries and a hot swap kit. They could probably pull it off.
In reply to ProDarwin :
You do not need 250hp to run in the front. Look at the winners. Lots of high one hundreds of hp cars there. But you do need consistency and reliability.
sergio
Reader
3/3/19 2:06 p.m.
How are all the electrical components going to handle the heat of running mostly flat out for hours? In real world driving all cars run around at part throttle most of the time, even EV’s.
sergio said:
How are all the electrical components going to handle the heat of running mostly flat out for hours? In real world driving all cars run around at part throttle most of the time, even EV’s.
A testing agency found that leaf motor seems to be able to put out 80Kw (roughly 107hp) continuously so if you kept it at or below that on average it should be OK. At the range needed the batteries would be only putting out a small portion of their power capability so they should be pretty easy to keep cool. I think the inverter would be the issue as it might get hot trying to run at full throttle so often.
dculberson said:
In reply to ProDarwin :
You do not need 250hp to run in the front. Look at the winners. Lots of high one hundreds of hp cars there. But you do need consistency and reliability.
Absolutely. And on top of that, a 180hp car does not put out a constant 180 hp. That's peak. So the average power load may be more like 150hp or 112kw.
kb58
SuperDork
3/3/19 6:52 p.m.
Don't forget to zoom out periodically to consider the resulting EV as a whole. If it ends up at 3000 lbs and 150hp, it isn't going to be competitive regardless of the drivetrain (I don't think). To be fair, I have no idea what the major parts weigh, but then we're back to knowing how much energy is necessary, plus the number of stops for swaps, plus the time of each swap, etc., etc. A pretty cool engineering challenge, that's for sure.
I'm actually considering building around an electric drivetrain, and will be watching this with interest.
sergio said:
How are all the electrical components going to handle the heat of running mostly flat out for hours? In real world driving all cars run around at part throttle most of the time, even EV’s.
Most inverters and motor controllers nowadays actually have preprogrammed limp modes for this problem- they come with little temp monitors for the battery pack that are like, hair thin that you can set to lower battery discharge at specific temps.
I think you would need a water-cooled setup to dissipate that kind of energy. Probably easy for battery & inverter, I'm not sure how many of the motors in EVs are water cooled?
