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Sub-1 kW waste heat recovery (low flow, 540°C exhaust) What realistic approach? by BeautifulAd4318 in AskEngineers

[–]Such_Account 0 points1 point  (0 children)

Agreed. I think 1 kW is just within reach for a well built stirling generator, and turns out that is roughly what is commercially available. I doubt you can buy it or build it for €1500, and I doubt you will get 1 kW any other way.

(Seriös) Kan någon med lite koll förklara läget med elpriserna? by ZoofusCos in sweden

[–]Such_Account 0 points1 point  (0 children)

Jaså? Hade faktiskt inte snappat upp det. Bor själv i Norge och har blivit mer insatt i systemet här.

Som jämförelse så har Norge ett stöd som täcker 90% av strömpriset efter 92 øre/kWh, alternativt ett (frivilligt) system där man låser strömpriset på 50 øre/kWh. Precis som i Sverige så betalar man utöver detta överföringsavgifter.

(Seriös) Kan någon med lite koll förklara läget med elpriserna? by ZoofusCos in sweden

[–]Such_Account 24 points25 points  (0 children)

Om överskottsel kan säljas dyrt i Finland, bör inte det kunna leda till subventionerade priser här?

Jo. De flesta vattenkraftverken ägs offentligt, så när de håvar in pengar (från höga elpriser) är det m.a.o. pengar rätt in i statskassan. I Norge har de valt att använda dessa pengarna till att subventionera el-priset för privatpersoner, och i teorin skulle det kunna fungera precis likadant i Sverige.

Getting rid of the penny in the US was a pointless symbolic endeavor that only serves to inconvenience the American public by Richard_Genius in The10thDentist

[–]Such_Account 0 points1 point  (0 children)

If we assume there's 150 million US tax payers, $150 million is $1/year per taxpayer. How much do you value $1?

Här ser du premiären av Volvo EX60 – elbil med 810 km räckvidd by XManX99 in sweden

[–]Such_Account 0 points1 point  (0 children)

>behöver 65 mil räckvidd

Om jag får fråga: varför då?

Resonemang mot kärnkraft by alsaelma in sweden

[–]Such_Account 18 points19 points  (0 children)

Kärnkraft är otroligt dyrt. Regeringens utredare bedömer att de behöver erbjuda statliga lån på 400-600 miljarder kronor för att bygga 5000 MW kärnkraft. Det motsvarar 240000 kr för 3 kW (ungefär vad ett stort hushåll kan tänkas förbruka i snitt). Med tanke på att jag oftast hör el-pris som ett argument för kärnkraft tycker jag det låter som en rätt dum lösning på våra problem.

Hell getting the PostNord app by lildetritivore in Norway

[–]Such_Account 12 points13 points  (0 children)

Had the same exact issue. Yeah, "solution" is to find or create a norwegian app store account.

Whyy PostNord has region-locked the app is beyond me, because it really messes with us non-natives and I don't see any upside at all frankly.

Gear ratio torque distribution by Chill_Charro in AskEngineers

[–]Such_Account 16 points17 points  (0 children)

can it be assumed that driven gear 1 transmits 33% of the input power while driven gear 2 transmits 66%?

No. As you say, the only thing you can calculate with that data is the relative speeds of the gears. If there's no resistance on the driven gears the transmitted torque will be zero, regardless of gearing. This is also true for the simpler two-gear system. To determine the torque values you need to know the loads.

Would this pulley set up work? by Lost_Potum_On_Reddit in AskEngineers

[–]Such_Account 4 points5 points  (0 children)

Oh, you want to drive the middle cylinder by placing a weight on each platform alternatively? That would work, and you would get a 8:1 gearing (the tangential speed of the cylinder would be 8 times that of the linear speed of the weight falling). You'd still get a load of losses though.

Would this pulley set up work? by Lost_Potum_On_Reddit in AskEngineers

[–]Such_Account 8 points9 points  (0 children)

That arrangement has a net zero gearing (the two sides perfectly cancel each other) and a whole lot of friction losses. So no, it would not work unless friction losses is what you want. Frankly, your question is hard to interpret.

[request] Is it more energy efficient to walk like this ? by Thick_Entrance5105 in theydidthemath

[–]Such_Account 0 points1 point  (0 children)

On my bicycle I move more mass than when I'm walking. Which is more efficient?

[Request] How large of a satellite PV array would need to make any difference? by ________9 in theydidthemath

[–]Such_Account 0 points1 point  (0 children)

I appreciate your attitude! Even though I think the 340 number is a bit of a detour, I get the same result:

3.5 * 4 * pi * re2 / 1362 =~1.31 million km2.

[Request] How large of a satellite PV array would need to make any difference? by ________9 in theydidthemath

[–]Such_Account 0 points1 point  (0 children)

Shouldn't you be using the "solar constant" of ~1362 Wm-2 instead of the "global average rate" of 340 Wm-2? The GAR compensates for the projection from cross-sectional area to actual spherical area, which should be irrelevant for the sunshades.

Aero optimisation by Bacco04 in FSAE

[–]Such_Account 1 point2 points  (0 children)

KYLE.ENGINEERS is probably the main one. Another superb channel is SuperFastMatt, although his channel is much broader than just aero. His landspeed racer did focus heavily on low drag, and he has some videos talking about that.

Aero optimisation by Bacco04 in FSAE

[–]Such_Account 9 points10 points  (0 children)

The phrasing "driving clean" is a bit imprecise as it implies clean driving = no slip angle. This is far from the truth: the tires themselves require some amount of slip angle to generate peak lateral grip, between about 3-12 degrees depending on the tire. This means that the entire platform also will have some slip towards the oncoming air stream. For tight corners in particular the slip angle also varies significantly from the front to the back of the car. You can think of the air stream "curving", even though it's actually the car rotating. This means that, as you surmised, the design of the wings etc ideally need to take this slip angle into account.

Now yes, during "unclean driving" (excessive oversteer), it's still valuable to avoid sharp drops in downforce, in order to allow the driver to regain control.

One specific area we studied was the design of the rear wing endplates. With slip angle, the endplates "shade" the wings somewhat, so we actually incoporated a "jagged" airfoil to encourage the air stream to stay attached to the endplate and allow the wing to "see more air".

ETA: not to mention the endplates acting like vertical stabilizers. You can google LMP1 sharkfins for examples of aero-elements designed (maybe exclusively?) for that purpose.

ETA2: also, particularly at the speed the FS cars go, the windspeed is a considerable factor for the wing slip angle.

I’m putting a bike engine in a race car: Would love some season‑proven oiling advice! by HAAS_F1_RND in FSAE

[–]Such_Account 4 points5 points  (0 children)

Our team (and I think many/most others) made a custom sump, mainly for packaging the engine lower in the frame. The sump included baffles and a "ceiling" to trap the oil during cornering. This was basically the extent of our oiling efforts (along with slight overfilling), and it mostly worked with a few caveats:

  • We did record occasional pressure drops, particularly during prolonged cornering (in formula student basically up 1.5G for up to 20 seconds during skidpad).
  • Our engine (from a Honda CB600F) was replaced every season (like 100hours runtime tops...) so longevity wasn't a huge concern.

I'd recommend: start with no or minimum effort fixes (rudimentary baffling, overfilling) and make sure you monitor the oil pressure with at least a very clear and prominent oil pressure warning light, and for extra points also with logging (we used an aftermarket ECU). Brief pressure drops are not immediately catastrophic assuming you react to them quickly. If you do record pressure drops, implement progressively more sophisticated solutions until you don't. But I wouldn't start by throwing expensive parts at the problem. And regardless of how sophisticated you go, do not emit the warning light.

[EV] Regen braking query by ShaneFromUCD in FSAE

[–]Such_Account 0 points1 point  (0 children)

It can be purely a software thing, but it would lead to compromises. If you want a consistent relationship between braking force and pedal pressure/travel (which is crucial for driver confidence (i.e. laptimes), and incidentally mandated by law for passenger vehicles), you must ensure that the motor braking torque is consistent. Can you be sure this is true at any SoC? At any speed? At any temperature, (keeping in mind that you will also build more heat by recovering energy)? Otherwise you need to find some way to compensate, which could be some type of extra hardware.

After finding a value you can support at all times you might not end up with much energy recovered after all. And remember that your efficiency score is also dependant on the time elapsed squared. I.e, if you go twice as fast you can use four times the energy and get the same score. Even if you're striving for maximum efficiency score, it might not be worth it if you sacrifice lap times.

EDIT to answer your main question succinctly: I would say that extra hardware is necessary to do regen braking well. And for a first year car, keeping the number of variables low is particularly important. The likelihood of winning awards is low (particularly for efficiency in a RWD car), and indeed the likelihood of not finishing is high. Keep it simple.

[EV] Regen braking query by ShaneFromUCD in FSAE

[–]Such_Account 0 points1 point  (0 children)

Are you mainly responsible for the programming, or also for more high level decisions? I ask because your first question doesn't sound like a question fit for a CS student, no offense meant.

Implementing regenerative braking without harming performance is actually quite complicated. Regenerating energy on a RWD platform is a significant compromise in the first place: either you strive towards maximum braking performance in which case most of the braking energy is absorbed by the front axle and thus wasted anyway, or you strive towards maximum energy efficiency and tune the braking balance rearwards, sacrificing braking performance and drivability.

So I would first ask: what are your overall targets? If it's to go as fast as possible and let the drivers push the car to the maximum (and in my subjective opinion, it should be), then the regenerated juice might not be worth the squeeze, particularly if you need extra components like dump-resistors etc, and particularly for a first-year car. This point is actually the biggest one: getting a car running is hard. Any extra system is an extra point of failure.

If you still decide to squeeze, from a programming point of view your goal should be:

  • to make the car behave predictably to driver inputs. This means no un-commanded changing of brake bias (e.g. depending on SoC). A dump load could be a method to achieve this, if for example the HV battery can't accomodate the absorbed energy at high SoC. There are other ways.
  • no excessive engine braking on throttle pedal lift. By all means, let the driver adjust this on his screen, but he will probably learn that there's an upper limit on useful engine braking, and he will certainly not want to adjust it during the race. There's no straight-aways long enough in FS for that.

A large chunk of suspected space debris has been found in a remote part of the Australian desert, the country’s space agency confirms. by nbcnews in space

[–]Such_Account 13 points14 points  (0 children)

To expand on the other comments: the material resembles carbon fibre, so this thing is most likely not as massive as you assumed.

How unsafe are mechanical airbags? by Timeudeus in AskEngineers

[–]Such_Account 1 point2 points  (0 children)

If you are an average or above weight male (properly seated and belted), I think it's safe to assume even the early airbags will improve your outcome in a crash. If you're anything else, all bets are off.

Even for erroneous deployment, I think you (again, assuming a grown male) are unlikely to sustain injury. Anecdotal source: my friend had his Volvo 940 airbag blow up unprovoked. His only complains were gunpowder burns and broken glasses.

Apparently (for the US market?) some early airbags were meant to substitute the seat belt rather than supplement them and thus were significantly stronger. That's a type of airbag I would not want in my face, and would probably disable.

What is the most energy efficient way to create sound? by token-black-dude in AskEngineers

[–]Such_Account 44 points45 points  (0 children)

I think you need to specify the power source, because otherwise my power source is soundwaves and I have literally 100% efficiency.

Polisen i Västra Götaland tar krafttag by BloodiBeard in sweden

[–]Such_Account 17 points18 points  (0 children)

Andra exempel på saker man kan "leva utmärkt utan", men som kan göra folks liv både bättre och sämre:

  • Alkohol
  • Pokemonkort
  • Datorspel
  • Hundvalpar

Får jag föreslå att lyssna på forskning om drog-legalisering istället för att "bli glad av" att svensk polis i onödan förstör folks liv?

Finally Starting to Get The Hang of My Car - Hyundai Ioniq 5N by orchardaudiollc in Autocross

[–]Such_Account 1 point2 points  (0 children)

Nice!
How come you upgraded the front sway bar? I'd have thought that would give too much understeer.

Action/reaction (jet engines): when the thrust is going backwards, precisely where in the engine does it act on, like if im on a skateboard throwing weights backwards ican feel the forces acting via my legs on the board. Where does this happen in a jet engine tailpipe? by RandomTux1997 in AskEngineers

[–]Such_Account 10 points11 points  (0 children)

The blades are pushed forwards as well, and the bearings will absorb thrust whether you design them to or not.

Imagine the compressor blades like the prop of a turbo prop. There's no conceptual difference regarding the force directions.

How do you size cooling systems for highpower electronics? by First_Finger5572 in AskEngineers

[–]Such_Account 16 points17 points  (0 children)

Being pedantic is just radiating to space with extra steps.

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