Lemons launches EV class - and $50k prize for overall race win in an EV!

akylekoz said:

sergio said:

Bump drafting will get you a black flag. Too many BFs and the team could be kicked out. Or put in time out for a few hours 

No real bumping just a lot of consistent drafting.  With cheaty class A cars that have really big fuel cells.  If you can figure out an E Lemons car how hard would adaptive draft control be to rig up,  set the cruise and required following distance.

It actually really helps for the whole autonomous thing. Just follow me! Then you need to figure out how to make it pass you and win on the last lap. 

EDIT - wait. The lead car has penalty laps so it wouldn't win anyway. Holy crap. 

GameboyRMH said:

GIRTHQUAKE said:

codrus said:

Teslas get about a lap and a half around Laguna Seca before the the batteries hit the max temperature and you lose most of the power to prevent them from overheating.

I don't doubt it. The only battery I know of that has active water cooling for operation is the Volt.

Actually the Tesla battery is water-cooled (or at least liquid cooled, IIRC it uses a silicone-based coolant similar to computer coolant), the problem is that the motor overheats. Check this out:

https://www.quora.com/How-does-the-cooling-system-in-electric-motor-work-on-Tesla

Thanks for the link! Shows what I "know" but hard data on some parts of the Teslas are still being uncovered.

Right now, if a lemons team were to attempt this idea it seems like the internal battery packs would have to be configured to be swappable using something like upgraded quick disconnects watercoolers use for computers. Regen braking would be a given so you'd have to use an AC motor, and your controller would have to be a beefy unit to handle the constant discharging. For charging those batteries not in use, a far slower and more controlled method to maintain them and keep temps down would be good not TOO dissimilar to the team that was using those RC chargers.

But there's another problem to charging- recharging a battery is not like filling a tank, it's more akin to picking books off your table to clean it off. Batteries are stored potential energy, which is why we have chargers now that advertise things like "Charges to 50% within 4/6 hours!". They can do this because it's easier to charge a battery from 0-50% than 50-100%. No matter what, that team will have to test and find their "sweet spot" for where to charge a battery to AND how far to discharge it, relative to how long it will take to recharge.

In reply to GIRTHQUAKE :

From what I recall working on EV batteries, it's something like 20% minimum charge for Lithium - type chemistries, and "Full" charge is pretty much anything over 90%.  But yes, the charge rate isn't linear.  

The Plymford could be a good lead vehicle, it could be fitted with the air diffuser dealie like the cyclists use.  It's actually a deceptively fast car, despite being classed in 'C'.  My fastest lap around CMP is about 2:05.  The Class 'A' winner did about a 1:50 IIRC.  Me and another guy are pretty much the fastest drivers on our team, but I'm no where near a hot shoe.  Plus we had terrible tires.  With decent drivers, $$$$ tires, and a healthy shot of cheatonium, it could easily run down in the sub-2 minute range.  The 460 chows down on distilled dead dinosaur, which would make it an even more comical choice as the pace vehicle for an EV.  

Question.  I haven't followed lemons/chump/whatever in a while.  What are the top placing cars running for power & weight?  Specifically Miata sized cars.

C Class is pretty much where it’s at in Champcar.  Lexus SC300, 3 series BMW’s, etc.

ProDarwin said:

Question.  I haven't followed lemons/chump/whatever in a while.  What are the top placing cars running for power & weight?  Specifically Miata sized cars.

You mean power: weight ratio?  I think around 12 to 15 lbs/ hp is pretty typical for a top-running car.  

At the wheels?  Whats a LeMons spec Miata weigh in at ~1900 w/o driver?

Im thinking they use manufacturers rated HP. 

So I didn't quote the post but on the power required I also got around 50kWh per hour.  I used the calculation below

So I have been giving this some thought and I think that it is possible.  Don't be shy there will be some math.

1. How much energy does a gas car use?

My car(mid-pack at best) at ~#2700 and not a lot of HP uses around 4 gallons per hour.  Call it 5 gallons per hour to a front runner.
One gallon of gas contains 33.7 kWh of energy in it and I will assume that the efficiency(gas to wheels) is around 20%.

5[gal/hour] * 33.7 [kWh] * 0.20[%] = 33.7[kWh/hour][kW]

This means that I need to supply ~34 kW to the car continuously to run at race pace. This is not the same a the battery requirement.

2. How much storage do I need?

Motor and drive line efficiency ~90% 
Battery charge usage capacity ~ 80% (can't drain the batteries all the way, Tesla batteries are good to around 80% depletion)

33.7[kWh/hour]/ 0.90 [%] / 0.80 [%] = 46.8 [kWh/hour]

Call it 50 [kWh/hour] of energy consumption continuous.

3. What does this mean for racing?

From looking at race data, front running cars spend ~30-45 min in the pits fueling and changing drivers.  Lets call it 35min total off track to be competitive. 

I am going to allocate 15min of that 35min to driver changes. Leaving 20min for all of the battery changing. 

If I swap batteries every hour I would have to do 14 pit-stops maximum (the brake in the race would reduce this by one), every two hours would be 8 pit-stops. 

20 [min] / 14 = 1:25 [m:s]
20 [min] / 8 = 2:30 [m:s]

Conclusion

From looking at this simple calculation I think that it might be possible to be competitive.  I think that the battery swap times could be achieved with smart pack design, quick release fasteners and a well design removal/install fixture or rig.  I also think that 100 kWh is not an unreasonable amount of batteries, Tesla's already come with 100kWh packs. (you would need like 5x this to have enough sets).  It would definitely not be easy but I think it is doable.  For less than $50k probably not, and it would require 20x the thought and engineering that goes into a regular Lemons car.

As for the battery and motor heat discussion, they would have to be water cooled.  Both the batteries and motors are water cooled on Teslas and I think that this system would have to be modified to increase the cooling capacity.  I would need to do a bit more calculation but I would suspect that it is not an unreasonable amount of heat to dissipate.  

50kw is not going to put you out front.  Thats 67 hp (average).  You'd be a backmarker at best.  Here's how a VVT Miata (1900lb, 151whp, capable of running at the front) stacks up against a 2800lb EV Miata.  As you can see, it takes a little more than 125kw to achieve similar performance.  Then you have to account for pitting a lot more often.

In reply to ProDarwin :

Big difference between peak and average power in use, especially with a high enough power-to-weight ratio to win the race! 

chaparral said:

In reply to ProDarwin :

Big difference between peak and average power in use, especially with a high enough power-to-weight ratio to win the race! 

Indeed, but WOT usage is more like 80 or 90%, not 30%

In reply to ProDarwin :

It's 80-90% of the time if you only have 140 horsepower. I picture this thing doing traction-limited acceleration for the first quarter of every straight and then just cruising to the next corner. That way we're dumping as little energy as possible into the brakes and the airflow behind us. 

Yeah, but that's pitting a stock 4-pot against the bevy of AC and DC engines whom can easily produce hundreds of pound feet of torque on top of that "67 HP". EV West's engine page has several motors like the Remy AC that are 160Kw peak but 440Nm of torque. I'm not a racer- yet- but that torque coupled with regenerative braking has to mean something, especially after seeing the results of the Lotus Evora EV's from Speed Academy.

In reply to volvoclearinghouse :

Yup, and that charge/discharge rate will be crucial also for heat control, even when the batteries are resting and waiting for another go on the track.

Having a roaring land barge like the Plymford being the lead vehicle for a junkyard Tesla would just be laughably wacky. As for our EV "racecar", I think we gotta fuse future with lemons racing and make it look cyberpunk as all hell. Mismatched LED lights, exposed tubes, angular lines... I nominate a Subaru XT as our EV vehicle, those things are aerodynamic as hell already.

chaparral said:

In reply to ProDarwin :

It's 80-90% of the time if you only have 140 horsepower. I picture this thing doing traction-limited acceleration for the first quarter of every straight and then just cruising to the next corner. That way we're dumping as little energy as possible into the brakes and the airflow behind us. 

Ok.  My earlier point still stands.  80-90% of 140 hp is not 67 hp.

Also, when your car weighs an extra 1000lb, you need more hp.

ProDarwin said:

chaparral said:

In reply to ProDarwin :

It's 80-90% of the time if you only have 140 horsepower. I picture this thing doing traction-limited acceleration for the first quarter of every straight and then just cruising to the next corner. That way we're dumping as little energy as possible into the brakes and the airflow behind us. 

Ok.  My earlier point still stands.  80-90% of 140 hp is not 67 hp.

Also, when your car weighs an extra 1000lb, you need more hp.

A 100 kWh pack will provide as much power for acceleration as any of the reasonably priced motor controllers want. It should be capable of 300 hp pretty easily. The average power consumption calculated above is very much an average of the energy used and is a very useful calculation for determining pack size. I had a  100-120 kWh 1000-1200lb pack in mind from my back of the napkin calculations so I think he hit a decent start for estimating energy needs.

I think the base consumption is quite a bit off for a number of reasons:

1) its based on a slow car.  You need to be at the front of the pack which means more power and more fuel.

2) The 20% number is off (it isn't that low) and is in favor of lower power needed

3) power needs will be higher in an EV due to a significant difference in weight

4) look at a WOT estimation.  If you are at WOT 90% of the time in a 140hp car, its an easy estimate.  140 * .9 * .745 = 94.5kw avg. output.  Again, thats the average output of the gas engine which is in a much lighter car.  Also I don't see a 2800lb car with 140hp winning the race.

It would be interesting if someone had a datalog of TPS on a car with known power and weight.

GIRTHQUAKE said:

Yeah, but that's pitting a stock 4-pot against the bevy of AC and DC engines whom can easily produce hundreds of pound feet of torque on top of that "67 HP". EV West's engine page has several motors like the Remy AC that are 160Kw peak but 440Nm of torque. I'm not a racer- yet- but that torque coupled with regenerative braking has to mean something, especially after seeing the results of the Lotus Evora EV's from Speed Academy.

Power is the most important number.  Gears can be used to change the torque up or down, but all you can do with power is decrease it.  

It's all a power game and how you use it.

Torque just means you have to shift less.  

Ideas:

1. Long extension cord

2 Laser aimed at roof mounted solar panel

3 LS powered onboard generator

When EVwest brought their E36 car to autocross in San Diego it could not get the power down even in the dry it was like a lightswitch, making the car drivable and usable will be a challenge also

alfadriver said:

GIRTHQUAKE said:

Yeah, but that's pitting a stock 4-pot against the bevy of AC and DC engines whom can easily produce hundreds of pound feet of torque on top of that "67 HP". EV West's engine page has several motors like the Remy AC that are 160Kw peak but 440Nm of torque. I'm not a racer- yet- but that torque coupled with regenerative braking has to mean something, especially after seeing the results of the Lotus Evora EV's from Speed Academy.

Power is the most important number.  Gears can be used to change the torque up or down, but all you can do with power is decrease it.  

It's all a power game and how you use it.

But isn't that another feather in an EV's cap? When you can modify horsepower levels with inverters and negate shifting due to their innate torque it just feels like another leg up.

That's all accounted for in the graph I posted earlier.  Even without shifting and lots of torque, look at the power output required to run up front.

In reply to GIRTHQUAKE :

Power = volts x amps(*efficiency).  Can't play with it anymore than that.