Treadmill Dyno

[taylorp035]

Over the last few weeks, I have been hard at work on my new supermileage car.  We have finished a new FUEL INJECTED Briggs and Stratton 3.5hp engine.  The problem is that our old dyno that is used to test these engines is really hard to use (it's a water brake, but controlling the resistance is super touchy).  So, the new plan is to use my treadmill motor and a large array of light bulbs to make a variable load.   This way we can effectively test the engine and fine tune it to be more efficient.  It should put out  about 120v, so we should be able to run light bulbs with no problem + keep the current down.

The motor is rated for 3960 rpm @ 150v and 16 amps continuous.  The engine red line is ~4,000 rpm.

The car we are building should weigh ~80-90 lbs empty and get 1500+ mpg on a stock engine.

In the end, this means that I may have to dismantle my windmill.

[taylorp035]

Here are a few pictures of the car and the engine so far.  Improvements include a brushless starter motor, throwing out the lead acid batteries, full ceramic bearings on all three wheels, a drag coefficient of ~0.11, a plate clutch that allows the rear wheel to spin freely, a higher gear ratio of 12:1, wheel skirts, a speedometer good for 0.1 mph increments, and a very ambitious computer that will automatically control the plate clutch using a 5th scale airplane servo, the starter motor, the fuel pump motor, calculate the grade of the road and figure out instantaneous acceleration, mpg, and efficiency, and it will control when the engine shuts off.

[taylorp035]

I can't wait until I get some wheels on it.  The rear one should be on by this Friday.  The fronts are waiting for their hubs, which have drum brakes made in England.

[SparWeb]

In the end, this means that I may have to dismantle my windmill.

Whatever it takes, man!
Ceramic bearings are bloody expensive aren't they!
You can't start with a rip-cord?  Contest rules?
If this is a college team project for you, these can be very memorable.

I remember those engine/dynamometer tests in college, too.  LOTS of fun. 

I look forward to seeing the evolution.

[taylorp035]

Well, you could use a pull start, but we only run the engine for ~2 seconds and then coast for a minute.  Doing that 20-30 times would be annoying.  There was ONE team that had a pull start last year (out of 25 ) and they modified a cordless drill to start their engine before the 2 days were up.

As for the ceramic bearing, yes they are very expensive.  The ones we have ran $60 a piece x 6 .....  and we are not exactly sure what the advantages are.  A big difference will come from the fact that last year's bearings had seals and the ceramics don't.  I did some very rough calculations and came they to a 2-10% increase in mileage.

Right now I am looking into exhaust and intake tuning, which could prove beneficial.  I am also looking into heating the engine up with resistors since the engine is almost always cold and engines don't like to run when they are cold.  I am looking at about 30,000 J, which should be enough to heat a small briggs block by 50-80 F.

[SparWeb]

As for the ceramic bearing, yes they are very expensive.  The ones we have ran $60 a piece x 6 .....  and we are not exactly sure what the advantages are.  A big difference will come from the fact that last year's bearings had seals and the ceramics don't.  I did some very rough calculations and came they to a 2-10% increase in mileage.

Once was looking into ceramic bearings as a replacement for steel ones.  As I remember it wasn't the seals that robbed as much energy as pre-loading forces...  The problem at the time was heat build-up not auto mileage so nothing I can remember related to that.

Right now I am looking into exhaust and intake tuning, which could prove beneficial.  I am also looking into heating the engine up with resistors since the engine is almost always cold and engines don't like to run when they are cold.  I am looking at about 30,000 J, which should be enough to heat a small briggs block by 50-80 F.

Maybe you could direct the exhaust gas back directly over the head's cooling fins?  Suicidal for an engine that runs continuously, of course, but if your bursts of engine use are short enough...  Box up the engine so that the vehicle's airflow doesn't also cool it...  Hmm Can't do the first suggestion and the second at the same time.

A good source of ideas, at least as far as the chassis is concerned, could be the international solar car race websites and blogs etc.

Google "North American solar Challenge".  Hints about how to handle the "panic" and "mad scrambles" on race-day may also help.

[taylorp035]

We were thinking of routing the exhaust so it would go through the fins and then out the exhaust pipe.  As for airflow, there is none.  The engine bay is pretty well protected.  There might be a little air going through the rear wheel, but I doubt very much.

As for the chassis, we don't have a frame made of metal.  It is really just the body with some carbon fiber ribs inside.  All we did was wrap pink house foam with carbon fiber and it is super strong.


Today I just spray painted a test piece of carbon fiber with white Krylon paint meant for plastic.  I will then spray it with clear coat and then wet sand it with some 1000 grit sandpaper.

I also saw for the first time our rear hub, made out of a solid chunk of aluminum.  It is extra special since it is narrower than a standard bike hub, it will accept the new ceramic bearings, the one side will have the interrupter disk for the speedometer (120 tooth), and the other side will accept one half of a hydraulically operated plate clutch.  The rear wheel should spin for ever.  I saw a video on line where a guy spun a wheel with almost no effort and it spun for 8 minutes with the ceramic bearings, compared to 1 minute for the hybrid ceramic and 30 seconds for the steel bearings. 

[SparWeb]

We were thinking of routing the exhaust so it would go through the fins and then out the exhaust pipe.  As for airflow, there is none.  The engine bay is pretty well protected.  There might be a little air going through the rear wheel, but I doubt very much.

Then watch out that exhaust can't accumulate in the cabin, if it gets out of the many joints and bends in the tubes.  You will need a firewall of course, so maybe sealing that up is not going to be difficult.

[taylorp035]

We will have a firewall, as it is a requirement in the rules.  I'm not sure that it will be 100% air tight, but it should be pretty close.  It will not matter anyways, as the exhaust pipe must stick out side of the car.

Google "North American solar Challenge".  Hints about how to handle the "panic" and "mad scrambles" on race-day may also help.

I did this competition last year too, and it was a blast.  Our car worked for the most part last year, minus the brakes and the starter motor wanting to fall off.  Luckily, you rarely need brakes and the starter came unbolted at the very end of a run (9.6 miles), so it didn't hurt our mpg.  One of the difficult requirements to meet is the braking test, which we must show a 0.25g's worth of deceleration, which is really hard to do on super thin tires and a weird weight distribution.  Last year it took me 7 attempts to pass the test, mainly b/c only one front brake was working.  The year before, they had the brake on the rear wheel, which made it almost impossible to stop the car.  If you lock up the tire, it instantly blows, so there is no room for error.  This year, we are using dual drum brakes up front.   These brakes are only found in trikes and wheel chairs and they are only sold by a shop in England.

A major issue that we haven't solved yet is whether or not we can actually put all of the power on the ground.  The reason I say this is that we will probably have about ~60 ft*lbs of torque on the rear wheel, which is way too much.  Last year's car accelerated at about 2 m/s^2 and this year's car will be a minimum of 3 m/s^2, which is like a rocket.  Most of the car's there probably accelerated at about 0.5 m/s^2 or less.

Last night, we got our new budget passed, so we now have another $900 to spend.  The car will probably end up costing in the ball park of $7-8k, which is a lot of money.  Some teams spent $40k + last year.

[ghurd]

Goofy thought...
Add another wheel?
One with brakes that would drop down to the ground when the brakes are applied?
8" plastic kids scooter wheel with tube tires kind of wheel?

Maybe even use it as the drive wheel, retractable drive wheel, since the vast majority of the time the car will be coasting (?).
G-

[SparWeb]

A major issue that we haven't solved yet is whether or not we can actually put all of the power on the ground.  The reason I say this is that we will probably have about ~60 ft*lbs of torque on the rear wheel, which is way too much.  Last year's car accelerated at about 2 m/s^2 and this year's car will be a minimum of 3 m/s^2, which is like a rocket.  Most of the car's there probably accelerated at about 0.5 m/s^2 or less.

Ah, engines aren't they grand?  80% of the time you only need 20% of their power and the other 20% time you need at least 80% power.  And yet you have to carry around the full weight of the thing 100% of the time!

Okay you obviously don't need me distracting you with jealous vicarious commentary so get back to work!

[taylorp035]

Goofy thought...
Add another wheel?
One with brakes that would drop down to the ground when the brakes are applied?
8" plastic kids scooter wheel with tube tires kind of wheel?

The thought had crossed my mind and several of my teammate's minds before.  We were seriously thinking of going Fred Flintstones style with the brakes, maybe having a handle that would drag on the ground.  I think this year's design is much better when it comes to stopping, so we shouldn't have any issues.

Okay you obviously don't need me distracting you with jealous vicarious commentary so get back to work!

  We usually have our meetings every Friday night, from 6:30 til midnight or later.  Last time we stayed until 1:30.  I am almost done with my second paint test, where I sanded a test piece of carbon fiber (6x8") and I painted it with white and blue Krylon spray paint.  Today I put on 4 layers of clear coat and tomorrow I will wet sand it with some 1000 grit sandpaper.  I think I put too much paint on it because some of it is crackling.  The first layer was good, but I think I put too much of the second layer on (roughly 24 hr's later). 

[dnix71]

Are pneumatic tyres a requirement? If not then why not use a solid wheel with a rubber tread. If not that, the fancy cars have had wheel speed sensors that make it impossible to "spin ze tires" on your BMW or Mercedes unless you mod chip them first. Maybe a throttle feedback control with optical sensors aimed at the ground and the back tire. If the slip exceeds a certain level, have a solenoid pull back on the throttle.

[taylorp035]

Maybe a throttle feedback control with optical sensors aimed at the ground and the back tire. If the slip exceeds a certain level, have a solenoid pull back on the throttle.

We should have enough sensors on this car to determine that  

For this project, I have spent ~100 hours on an Excel based MPG calculator.  I can enter all of the variables known to man (engine efficiency, rolling drag coefficient, max engine rpm, air density, ....)  There are 16 variables that you can change.  On the output side, it gives you a mpg number based on your max and min velocities, and a mpg number that is the maximum possible + the speeds that you can achieve that number.  More or less, the excel spreadsheet helps me get around some really nasty integrals and thinking that I don't want to do.  It takes 45 seconds for the new answer to come up after you enter in the number.  My last change to it was adding the kinetic energy of the flywheel into the equation.

The results says that we should go from 10 to 21 mpg and start the engine 16 times.  It comes out to 4200 Joules per coast, so about 5.6 hp * seconds.  

Are pneumatic tyres a requirement?

No, but the improvements would be only better if the road was perfectly smooth.   The track that we race on is meant for dump trucks, so there are some decent cracks in the pavement.  Putting solid tires on a car with no suspension would be crazy.  You are right that it could be better, but it would make for a very heavy tire and the tires that we use are already really good.  Rolling resistance of a steel wheel would be ~0.001.  Our tires are about 0.002.  We own a tire that can go as low as 0.0008, but it's $200 a tire.

[taylorp035]

The windmill is officially no more.  I pulled the motor like I said I would.  I then neatly stacked the wood components and all of the corresponding bolts in my basement, right next to an older windmill and my pile of VAWT blades.

I then took the motor to school, which I hope in 2-3 months we will have a running electrical dyno. 

[taylorp035]

Last night I put together our new back wheel for the supermileage car and balanced it.  It has some new ceramic bearings in the hub which are amazing.  I spun it up with my hand and it went for 12 minutes!

[taylorp035]

Here is the 12 min spin down test for those who don't believe or just have nothing better to do  

http://www.youtube.com/watch?v=edxSy2QDm5g


My new record is 16 min and 55 seconds and I hope to increase that to 20 minutes.  Air drag seems to be the major contributor to it slowing down.

[taylorp035]

UPDATES 

Almost finished the body work last week.  The fuel injected engine with brushless starter motor is done (never seen anyone else do this before).  We should do some dyno testing with in a month hopefully.

Shooting for 1544 mpg (double our record) with a stock engine.  Hopefully we can break 2000 mpg and get 1st place.

We did do an accidental crash test over Christmas break.  We pushed the car at 6-8 mph into a ~1000 lb shipping pallet.  We did a lot of damage upfront, but the 4 point safety harness kept the driver safe.





And here is a video of the starter motor.

http://www.youtube.com/watch?v=GivPYe3fvc0

[SparWeb]

Thanks for the update.
Is this for the Eco-Marathon in April, or the SAE supermileage in June?

[taylorp035]

Sorry for the slow reply, been really busy.

This is for SAE Supermileage in June.

We just  submitted our last request for parts to build the dyno.  We ordered v-belt pulleys, a 40" belt, (10) 300 watts light bulbs, 10 light socket bases, and a 30 A analog ammeter. 

This way we can see how efficient the engine is.  The light bulbs should allow for different loads.  I think 3000 watts should be enough... 20A * 150volts roughly.  We will test a stock engine, the electronic fuel injected engine, and we are making progress on an overhead valve engine with a higher compression ratio.  We plan on testing them all with pump gas and the iso-octane. 

[taylorp035]

Our budget was officially passed, so I will order the parts on Friday. 

I took a video of the test runs, but the one would get stuck processing every time when I upload it.

I hope to have a really good update in 2 weeks, 3 weeks if we are slow.

[taylorp035]

This week we hooked up the engine to the treadmill motor with a chain.  We then hooked up 3 150w flood lights.  At about 60-70 volts, the chain would start to get jumpy.  Top speed came at 85v with almost no appreciable load on the engine.  The v-belt should be here next week.

[Madscientist267]

So if you don't need so much power from the engine, why do they give everyone one with so much power?

Or did I miss something... ? (Did a lot of reading in the last couple hours between this, the 'deep-cycle' thread, and the rules)... 

Steve

[taylorp035]

Well,  Briggs and Stratton sponsors the event, which they have given every team a free engine every year for the last 30 years... hence we use the same old engine design that needs to be modified to get good performance.  Hence our team fuel injected one of our 10 engines that we currently own.  The best thing to do is to raise the compression ratio from the 7-9:1 up to 14:1 or even as high as 18:1, in which you can gain 50-100% in thermodynamic efficiency.  Obviously this idea is easier said than done, especially since we are doing this as a club, not a senior design project.

With only ~75 lbs on the rear tire and a static coefficient of ~0.8 and a 10:1 gear ratio, we can only put down 5 ft-lbs from the engine, which the stock one is 4.9 ft-lbs.  With the E.F.I. engine, that torque number could be higher.  Our car last year was the fastest accelerating car there, at about 2 m/s^2, which takes you from 10 - 25 mph in a jiffy (like 2-3 seconds), which is rather uncontrollable, especially when your target speeds is so critical.  This year's car is going to have a speedometer accurate to 0.1 mph ( home made) and hopefully a G -meter and a GPS unit.  We have about 5 E.E's who are making a computer for the car, in which it will control the plate clutch with the servo and the power to the fuel injection system, as well as the brushless starter motor.  This year's car should accelerate at about 3 m/s^2, which will seem like a rocket ship.  The computer will automatically kill the engine when the time is right so we waste less fuel.

As you can see by the previous posts, we are working on an electric dyno with my treadmill motor.  We plan on hooking up 3000 w of light bulbs for a consistent load on the engines, so we can test the efficiency (relative efficiency only since we don't know the efficiency of the treadmill motor).

Since everything is made of carbon fiber, the whole car with the engine and everything will only weigh ~ 105 lbs.  The EFI engine + wires = 27.6 lbs alone.  The frame rails are only about 3 layers thick, but they are unbelievably strong.  Most of the outside is 5 layers thick, but since there are no sharp edges, it is relatively floppy.  Our drag coefficient was calculated to be about 0.11 and area is 0.444 m^2, which is fairly good.  The winning team's car last year had a drag coefficient of only ~.10 but an area of only 0.28 m^2.  They got 2300 mpg, but their clutch was sticking, so they should of had a higher number.  The record in our competition is about 3000 mpg.

You could do an all wheel electric drive and be able to put down ~ 10 hp, so you could do a 18:1 compression ratio with the stock 148cc engine.  You would probably blow the head off the engine, which would be bad since it is so close to your head (like less than 1"). 

I will keep updating this thread probably every week with the updates, especially on the dyno.  Since I am the president of the club, I know just about everything, so you can ask me just about any question.  A lot of the information is on the website.  As you can see, there are 32 teams signed up already from ~ 5 different countries (truly international).

[Madscientist267]

Sheesh... 3000 mpg?

That's virtually incomprehensible. Although apparently possible.

I guess we 'pay' a lot for the thrill, comfort, and safety features that the average passenger car provides.

On the other hand, I've always thought that running an engine full time seemed kind of unnecessary. But as you mentioned, pulse and glide does not lend to 'comfortable' very well. Every time I've used it as a tactic to just get me to the next gas station, anyone riding with me perks up as if ready to ask what is wrong... LOL But it does work.

One of my recurring solutions in my head has been an even higher gear (or even set of gears) that can allow the engine to run at just above idle speeds (say, 1200 RPM), so that it is running at the bottom of the torque curve for each 10 MPH or so.

In other words, 1st - 3rd, acceleration, just as they are now.  

Then:

4th, 1200RPM @ 45MPH
5th, 1200RPM @ 55MPH
6th, 1200RPM @ 65MPH

and with freeway speeds trending toward what they are... 7th, 1200RPM @ 75MPH.

Running the engine at higher RPM (even though not using the torque) still requires more fuel than a lower RPM does, and if the engine/tranny/weight/dynamics are all matched, there's no reason that an average everyday car cannot be designed this way.

Then again, I'm a control freak, and whatever I own must be a stick shift. Could be done with an automatic too obviously, but many people are more concerned with 'git' than 'got', and would rather feel the power than save the gas. Stupid IMHO, but a reality. Just look at any car commercial.

Sure, acceleration is great, but I'd rather save at the pump. Kept driving a 50cc scooter around for quite a while @ 90MPG for that reason. Granted, it wasn't the initial reason, but that's another thread (likely for another forum too).

And so the difference shows there too - 90MPG vs 3000MPG - there's more than just the aerodynamics in that. LOL Not sure, call me crazy, but the engine having to zip along @ 9000RPM continuously to keep 27MPH may have had something to do with it...  

One other question about your car I can't quite make out - the O2 sensor. Don't they have to be up to temperature to provide useful information to the computer? It would seem that 2 or 3 seconds wouldn't be enough to get it hot enough to give good data... ?

Steve
  

[Bruce S]

taylorp035;
Could I ask a small but important favor?
For the building of the frame and body using the carbon fibre , could you post some of the pics over in the transportation area too
Please
I have a great amount of interest in this, partly because I used to teach small engine repair for the local public school system way back in '79 ( was a fill in for the regular teach while he recovered from back surgery) and i never lost the thrill for building with these engines.
I am also curious about the compression ratio. I know "we" used to shave then polish the head all the while checking to make sure the spark plus didn't put a whole in the piston.
14:1 sure, but 18:1 WOW! what is the fuel type? if only using petrol how do you keep it from auto-igniting? or is it because it's run so short of a time the engine stays cool enough to not be too much of a problem.

Many Thanks for some great info in these posts.
Bruce S
 

[Bruce S]

Sure, acceleration is great, but I'd rather save at the pump. Kept driving a 50cc scooter around for quite a while @ 90MPG for that reason. Granted, it wasn't the initial reason, but that's another thread (likely for another forum too).

And so the difference shows there too - 90MPG vs 3000MPG - there's more than just the aerodynamics in that. LOL Not sure, call me crazy, but the engine having to zip along @ 9000RPM continuously to keep 27MPH may have had something to do with it...  

Steve
  

Steve;
One of the cool little things "we" would do with the 49cc scooters, once the warranty had expired  , was to get into the CV area , there's fly-weights in there and using different weights you could "tune" the bottom end and top end.
The weights I believe started out at 150grams ( don't quote me on that).
For heavier people who had problems with getting going, we would adjust for more torque on take off for people who wanted a better "zip" to top end we would adjust the weights accordingly as well.
One quick way to have better over all performance was to go get a drill and small bit 5/16" remove the chrome cover off the back of the muffler and drill 3 equally spaced holes. This would allow the engine to exhale a little better, so zip was noticed without major  surgery.

best we could get was 105 mpg consistently, 3000 would be astounding!!
Cheers;
Bruce S


 

[ghurd]

"3000 would be astounding!! "
I agree.  A lot.
Hope I did it right...

3000MPG is (in US measurements) -
4 miles per teaspoon.
12 miles per tablespoon.
308 miles per (ghurd's) coffee mug.
and
NY, NY to LA, CA... with 61 teaspoons left in a 1 gallon tank.

Wow!
G-

[Bruce S]

I'm still working out the dynamics of the 18:1 compression ratio 
My MB 300TD is sitting nicely at 20:1 , I know it is supposed to be closer to 21:1, but with 177K on it and taxes coming due 

Even ethanol auto-ignites around 15:1? not sure of that , never had the testicular fortitude to find out  .

Having too much fun working with these numbers 
Bruce S
 

[taylorp035]

Yay, you guys bit the bait 

And so the difference shows there too - 90MPG vs 3000MPG - there's more than just the aerodynamics in that. LOL Not sure, call me crazy, but the engine having to zip along @ 9000RPM continuously to keep 27MPH may have had something to do with it...  Huh

One other question about your car I can't quite make out - the O2 sensor. Don't they have to be up to temperature to provide useful information to the computer? It would seem that 2 or 3 seconds wouldn't be enough to get it hot enough to give good data... ?

The best mpg would be at a constant speed, since air drag is exponential ( squared ) in terms of mpg.  Also, for the difference in mpg, look at these numbers:  10-15 x less weight, a CD * A of only 0.04 instead of 20-30 times higher (wikipedia has lots of info on this).  Transmission is about 95-98% efficient, also there is no alternator.  The Rolling resistance coefficient is also much lower, which 0.0008-0.0024 instead of 0.006-0.008 for a car.


As for the O2 sensor, we program the computer to have a start up mode pretty much, in which the software can learn the "fuel map".  Apparently the O2 sensor works pretty quickly, but I didn't build the engine.

Sheesh... 3000 mpg?

The record is about 3,000, but if last year's 1st place car actually ran well, they could of had 4000+ mpg.  The record for any type of ICE engine is significantly higher but I don't know the number... the record for a hydrogen fuel cell with the equivalent amount of energy is 12,000 mpg, but their rules were a little looser than ours.

For the building of the frame and body using the carbon fibre , could you post some of the pics over in the transportation area too Grin

Umm... I wish my school's website would be accessible to you guys.  It has about 130 pictures and 20 videos...   Maybe if I have more time this week end.

As for the carbon fiber, the stuff is best stuff in the world.  It's easy to make and requires no skills.  Basically you mix the 2 part epoxy to the directions and add glue to your carbon fiber fabric.  The hard part is not to get anything stuck the to carbon fiber, so for this problem you use lots of ceran (plastic) wrap.  Anything made of the same plastic will not stick to the glue (like bubble wrap).  Lexan is good for making shiny smooth surfaces.
For the cost, 1 yd of 60" wide is $20-50, so it's worth it for small projects.  I'm not sure how much we have in the car right now, but it is probably 30yd^2 at least.

If you want to make a beam, basically wrap C.F. around some foam (we use the pink house insulation).


As for the compression ratio, you are right.  Regular gas would ignite.  Hence we are provided with iso-octane, which will not pre-ignite.  Hence an 18:1 ratio is possible.  We don't actually have an engine that is 18:1, but there are some older engines that run at 14:1.  The downside is that 100- octane gas is $200 per gallon.  You could run 93 pump gas in the engines with the lower compression ratios with no loss in power.  At $200/ gallon, the cost benefit doesn't exist anymore.  The competition usualy gives away the extra fuel, which usually amounts to a gallon per year.  We probably have ~8 gallons in storage.  I hope the stuff doesn't go bad   

"3000 would be astounding!! "
I agree.  A lot.
Hope I did it right...

3000MPG is (in US measurements) -
4 miles per teaspoon.
12 miles per tablespoon.
308 miles per (ghurd's) coffee mug.
and
NY, NY to LA, CA... with 61 teaspoons left in a 1 gallon tank.

We used about 30 grams of fuel last year I believe.  If you go to the sae website, the 2007 year has data on the fuel used for each car to 5 significant figures.  Last year we used about a film canister for 9.6 miles.  I think my calculations were about 33 grams at 777 mpg, but that may be off by 10-20%.

best we could get was 105 mpg consistently, 3000 would be astounding!!
Cheers;

You have a drag coefficient of 0.7+, a bad engine, and bad tires.

I'm still working out the dynamics of the 18:1 compression ratio  Grin
My MB 300TD is sitting nicely at 20:1 , I know it is supposed to be closer to 21:1, but with 177K on it and taxes coming due  Undecided

Even ethanol auto-ignites around 15:1? not sure of that , never had the testicular fortitude to find out  Shocked .

Having too much fun working with these numbers  Cool

I'm not an expert in this field, but there are a lot of issue with the higher compression.  A smaller bore diameter would definitely be required ( we have a block with a 50cc cylinder ).




I can't wait til we get the transmission in the car and we build the cooled seat.  The transmission will be a single friction plate clutch.  We may not have enough force on the plates, so we may have to add teeth to the plates.  This would require some timing challenges between the clutch engagement, the tire rpm, the engine rpm, and the tire rpm.


If anyone was wondering about the bearings, we have 6 full ceramic bearings in the three tires.  Using full ceramic bearings instead of steel bearings with seals helps a lot.  We spun our tires by hand, and they rotated for 16 minutes!  The steel bearings only rotate for about 30 seconds.  The bearing resistance is only about 1% of the rolling resistance.  Hence our car should roll for about 2 minutes while coasting from 20 mph to 10 mph on flat ground.  In reality, most of the course is at about a -0.1% grade, so I have coasted for 0.8 miles while going from 34 mph to 4 mph     The back curve on the track is about a 1% grade, which is very noticeable in these cars.  We would have to fire the engine twice to get up the hill.

[Madscientist267]

Damn... haha Talk about thinking WAY outside the box...

All of what you're saying makes perfect sense to me, but there's little to no (closer to no) chance in hell I would have ever thought of all of this if I were designing something like what you all are doing with these things.

While it's true, every little tiny detail adds up, I'm surprised nobody mentioned something like the driver not eating for 3 days before the run, and taking diuretics to reduce the weight by that much more!

Ok, well, now I have... LOL so hmmm... has it been done?

I'd be willing to bet that regardless, the shortest, twiggiest guy on the team ultimately ends up becoming the driver.

While I'm on the subject, how much does driver skill play into this? Like percentage wise? Or is that a well known 'constant'?

Steve

[ghurd]

I keep coming back to something from the other post-
"for our cooled seat, which may require a good 200 watts while running".
Put an ice cube in his mouth when he starts, and let him sweat?

Wondering, since it is almost an antique engine, are the antique efficiency boosters done?
(port & polish the head, intake, and exhaust, plus make sure the gaskets are not goofing up the works)
G-

[Bruce S]

For the building of the frame and body using the carbon fibre , could you post some of the pics over in the transportation area too Grin

Umm... I wish my school's website would be accessible to you guys.  It has about 130 pictures and 20 videos...   Maybe if I have more time this week end.

As for the carbon fiber, the stuff is best stuff in the world.  It's easy to make and requires no skills.  Basically you mix the 2 part epoxy to the directions and add glue to your carbon fiber fabric.  The hard part is not to get anything stuck the to carbon fiber, so for this problem you use lots of ceran (plastic) wrap.  Anything made of the same plastic will not stick to the glue (like bubble wrap).  Lexan is good for making shiny smooth surfaces.
For the cost, 1 yd of 60" wide is $20-50, so it's worth it for small projects.  I'm not sure how much we have in the car right now, but it is probably 30yd^2 at least.

If you want to make a beam, basically wrap C.F. around some foam (we use the pink house insulation).


As for the compression ratio, you are right.  Regular gas would ignite.  Hence we are provided with iso-octane, which will not pre-ignite.  Hence an 18:1 ratio is possible.  We don't actually have an engine that is 18:1, but there are some older engines that run at 14:1.  The downside is that 100- octane gas is $200 per gallon.  You could run 93 pump gas in the engines with the lower compression ratios with no loss in power.  At $200/ gallon, the cost benefit doesn't exist anymore.  The competition usualy gives away the extra fuel, which usually amounts to a gallon per year.  We probably have ~8 gallons in storage.  I hope the stuff doesn't go bad   


You have a drag coefficient of 0.7+, a bad engine, and bad tires.

I'm still working out the dynamics of the 18:1 compression ratio  Grin
My MB 300TD is sitting nicely at 20:1 , I know it is supposed to be closer to 21:1, but with 177K on it and taxes coming due  Undecided

Even ethanol auto-ignites around 15:1? not sure of that , never had the testicular fortitude to find out  Shocked .

Having too much fun working with these numbers  Cool

I'm not an expert in this field, but there are a lot of issue with the higher compression.  A smaller bore diameter would definitely be required ( we have a block with a 50cc cylinder ).

I can't wait til we get the transmission in the car and we build the cooled seat.  The transmission will be a single friction plate clutch.  We may not have enough force on the plates, so we may have to add teeth to the plates.  This would require some timing challenges between the clutch engagement, the tire rpm, the engine rpm, and the tire rpm.


If anyone was wondering about the bearings, we have 6 full ceramic bearings in the three tires.  Using full ceramic bearings instead of steel bearings with seals helps a lot.  We spun our tires by hand, and they rotated for 16 minutes!  The steel bearings only rotate for about 30 seconds.  The bearing resistance is only about 1% of the rolling resistance.  Hence our car should roll for about 2 minutes while coasting from 20 mph to 10 mph on flat ground.  In reality, most of the course is at about a -0.1% grade, so I have coasted for 0.8 miles while going from 34 mph to 4 mph     The back curve on the track is about a 1% grade, which is very noticeable in these cars.  We would have to fire the engine twice to get up the hill.

Thanks for the info on building this with CF!!
Iso-Octane will absorb moisture if it is not kept in a closed container, yep it'll go bad. BUT good thing is it'll still be good for standard road type engines.

For a better engine, a bore that increases flame spread would be your best bet. Shorter stroke to reduce possibility of the pressure increase , which is not linear with regards to compression ratios. a more squat based cylinder with a piston head that could cause vortex mixing and shorter stroke would be the way I would go, but my thinking is that you cannot fidget with the internals of the engine to that degree.

See what you did , now I gotta go get my old M.E. books out and work that design out.
Bummer that I'm poor .
Again thanks for all the updates and answering these Qs  really is appreciated !
Bruce S