Fantasy engine

[mech5496]

Z,

As mentioned, I would go with twin 'final drive' clutches, one for each rear wheel for vectoring, so the transmission would spin all the time. The E-CVT control unit could let the engine rev up to a certain limit (lets say 500rpm above the max power RPM) when the driver pulls a clutch paddle, while at the same time would disengage both clutches. Full throttle, engine revs up, let go the paddle, ECU slips the clutches (to avoid belt slip, otherwise just dump them), car starts accelerating, ECU reads front wheel speed so it starts to shift the CVT to keep the engine on the max power RPM, off you go. Not a very common CVT launch...

[Homemade WRX]

Originally posted by Bus_Lengths:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">

If going CVT, I'd just make it a narrow RPM torque monster. Small bore, large stroke, short rod ratio...

I imagine this is what you were implying, but I believe you mean 'narrow RPM power monster'.
</div></BLOCKQUOTE>

No, I meant torque but failed to mention 'relative' to FSAE engines.

If I wanted power, I'd go with my turbo CBR250RR engine again.

[MCoach]

Fantasy engine for FSAE?

Simple, stupid, simple.

Single cylinder, 250cc, 4 valve, Crank masses kept low in weight and radius to enable lower CG.
Two speed transmission, integrated.
Salisbury differential, also integrated.
Supercharger mounted on the back of the engine between cylinder jug and diff.
Aluminum or magnesium block.
Carb that thing, let's go racing.



Just to add more fuel to this:
Wheels and tires: 8" in-house customs.
Shifter: on steering column (a la shifter kart)
Chassis: Minimum template fit
Electronics: Spark only (no driver signals, extraneous sensors). Coil/points run off flywheel, single wire ignition.
Driver: 85lb sickly horse jockey
Miscellaneous: Reduction of part count focused on the entire car. Lots of aluminum and lightweight.


In a game of no minimum weight, I don't care how much power is available. If anything can be smaller, lighter, more efficient, do it. It's a race to the bottom, anything otherwise is wasting time. This I would only put secondary to driver development in the game of FSAE. Want to pull 1-2 seconds faster in the same car without changing anything? Let the driver play around with the car, learn it, anticipate it.

[Will M]

Well if we expand the idea to include set ups for a formula car that we would want to own rather than a set up that we think would be best for winning a formula competition I would go electric.
I confess that I have never work on an electric team and don’t know too much about them but this is the design I see in my head.
--------------------------------------------
I would have one motor driving each rear wheel with a single gear reduction (if a reduction is needed).
And as I would have the car set up for real autocrosses instead of FSAE events the battery would be much smaller (roughly 10% the size of a typical formula battery pack).
The battery would be set up for quick swaps; i.e. a fresh battery for every run.

The current electric cars can match the pace of many ICE cars and if you remove 90% of their battery weight I think you’d have a killer combination.
Lower cooling requirements would help with aero designs.
A smaller drive train would help with packaging.
Independent electric motors lead to traction control and torque vectoring.

Of course it wouldn’t have the energy to finish the endurance event but the ‘weekend autocrosser’ goes to autocrosses not to endurance races.

Just my 2 cents.

-William

[JulianH]

Will, electric is a nice choice (Both the Delft and the AMZ car of 2012 weighted around 110kg without batteries (and without aero on our side) and had about 85kW).

Take enough energy for 2 AutoX laps and you are still in the "lightest FSAE car ever" region.

But, electric cars are sooo expensive, I think therefore the "weekend autocrosser" would still choose a combustion car.

[mech5496]

I thought this was an IC-only thread. IMO endurance is an integral part of the comp and cannot be ignored, but since this is a fantasy thead...

Given the 85kw limit, take a look at Delfts' DUT12; 85kw, 145kg, 4WD. Now cut about 15kg from batteries (their battery pack was already really small) and add aero. What you have is what I expect DUT 13 to be, but lighter.

If you forget about the 85kw limit, take a look at our car. Ditch 75% of battery capacity (and about 30kg) and move what is left on both sides of the cockpit for less MoI and less rearward weight distribution Add a second motor, and of course, lots and efficient aero. In direct drive configuration and 10", the car has a top speed of 172kph, just right for autox, aint it? Boom, 220kg, 200kw (272hp), 1500Nm torque at the rear axle.

Wanna get completely nuts? Ditch the voltage limit and substitute the above motors with two Yasa 400... Two one-stage gearboxes (one per motor) with a reduction of 3,75:1 to get the same top speed as above. Being 3kg/motor lighter would keep the weight about the same, while placing the motors lower and a bit forward would account for better GC/MoI. OK, numbers! 220kg, 330kw (449hp!) and 3000Nm torque on the rear axle... thats more than 2000hp/tonne! Plus the massive torque! I know, it is a complete overkill, but definitely impressive, aint it?

[Jon Burford]

But, electric cars are sooo expensive, I think therefore the "weekend autocrosser" would still choose a combustion car.

I thought that was the whole point of Formula Student?

[MCoach]

Having worked on robots that come to a halt without warning nor signs of what's wrong, electric is definitely not something for a weekend autocross project. Things just stop and everything looks ok. Could it be a loose wire? A cracked solder joint? A misplaced connection? Maybe that NPN transistor we never tested before installation decided to short itself. With so many things to go wrong, it can become very tricky and time consuming to track down the problem. Ask GFRe about that.

When was the last time you took apart your computer because it wouldn't start properly? Did you fix it? You'll find that it comes down to something stupid like corrupted code or a blown capacitor on something else obscure like the graphics card. What typically happens? The part or system is diagnosed on a bench top and then replaced. Fine. That's easy, swap out audio card, swap in new one.

...But what if it's your car?

If these cars were meant to race in a series where the focus was on pure winning in an autocross setting and the project was able to be supported by professionals, then sure, I'll concede the advantage electric has on being able to point the car exactly where you want it.

[Jon Burford]

@M
I don't really mind the complexity and as I have said previously, I have a complete love of the AMZ car from 2012 and I am massively impressed by the tech and effort that it takes to make them work.
Despite that I would never buy an electric car to go racing in, I just don't see it for myself, the cost being one and the experience another.

The IC engine is an ancient mechanised wonder, an almost laughable method of turning a shaft. Why is it then that not even modern tech can drag me away from it?? It's the sense of drama, the vibration, the noise, the smell. There is something about that. This isn't just me going on, being a potential costumer for a weekend race car myself, that's what I want, not an electric powered anything and I'm sure I'm not alone. That has to count for something.

[Owen Thomas]

I can agree with the sentiments posted by MCoach and Jon. It's fair to expect that your typical weekend warrior can check suspension bolts and change the oil, and generally troubleshoot regular automotive problems with the (vast) resources available for IC engines. Is it equally fair to expect that they can check for electromagnetic interference in a sensor wire? Or stare down miles of C++ to fix a problem with one of the control systems? Probably not.

At the same time, I do not think these opinions are particularily valid for this competition. Sure, the idea of making a weekend autocross car for retail promotes making a robust, well rounded design, but the reality is that the majority of competitive FSAE vehicles are not this way. A car made to be sold in bulk (>1) would be far more driven by the marketing needs, and take multiple years and iterations. We have inexperienced students making a prototype in (typically) a year or less. We also have the unique advantage that the designer of any given system is usually around to troubleshoot it when something goes wrong - something not available to the consumer.

This argument comes up all the time around here, but I think it's important to remember that the "weekend autocrosser" statement in the rules is outlying a premise for the competition. It is not the goal. That said, some very competitive teams build the car to clean house at normal autocross events (eg Jayhawks, Maryland), but the difference is still that these are 1-off cars, and would be fundamentally different if they were made to be sold.

Anyways, this topic was about fantasy "engines", but I also agree that the potential advantages of electric drive are pretty tempting. Additionally, I think it's interesting that this thread has evolved more into "what is your fantasy engine package", instead of just "engine". You can make almost any size and power work (as shown by the many ideas posted), but in the end it really just comes down to packaging.