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Thread: Interesting old threads?

  1. #1

    Interesting old threads?

    Hi guys,
    I know there's been a great deal of interesting discussion on this forum over the last decade or two. Anyone know of any old threads worth reading?

    I submit the UTAS build thread as one: http://www.fsae.com/forums/showthrea...S-build-thread

    -Tim

  2. #2
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    Two funny ones.

    Quotes from the shop: http://www.fsae.com/forums/showthrea...-from-the-shop.
    Definition of engine displacement (...qwr): http://www.fsae.com/forums/showthread.php?5752-...

    It also would be nice to have a collection of Z's drawings.

    -William

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  4. #4
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    Tim,

    Similar to UTAS's build-thread is "Superfast" Matt McCoy's book. Here is his thread:

    http://www.fsae.com/forums/showthrea...-for-the-limit

    And last I looked his book was available here:

    http://www.superfastmatt.com/2012/01/free-racecars.html
    ~o0o~

    Superfast's story has a happy ending. Sadly, Christian's Aston-Uni build-thread doesn't end so well:

    http://www.fsae.com/forums/showthrea...design-process

    Nevertheless, there are valuable lessons to be learnt there. Beware stupid Supervisors!
    ~o0o~

    The "...objectively choose engine" thread is a good-un. Here is another in the same vein:

    http://www.fsae.com/forums/showthrea...Fantasy-engine

    And for full-car fantasizing:

    http://www.fsae.com/forums/showthrea...33-Fantasy-Car
    ~o0o~

    Of course, once you get serious about this whole FS/FSAE challenge, you should read Geoff's (Big Bird's) "Reasoning your way..." thread, which is stickied at top page 1 "Open Discussion" section. Compulsory reading, really, for anyone aiming high.

    On a more technical front you might look for the "Suspension Design" thread, and another called "Beam-Axles - Front, Rear, or Both". Well, I successfully hijacked those two, so I like them. But many other peoples' views there also. And for aero you can search for one called "WINGS". Sorry, but I don't have the urls for these right now.

    And many, many others, depending on what particular area you are interested in (eg. VD-simulation, brakes, electrics, ??). Also, some of the threads in the Competition section are very useful, giving close-ups of the comps themselves, plus post-comp de-briefings and analyses. Look for the longer ones.

    Happy reading!

    Z
    Last edited by Z; 05-29-2017 at 03:33 AM. Reason: Splenig!

  5. #5
    Thanks Z,
    Of course as part of an RMIT team (Electric) I've read Geoff's essay in full a couple of times. Sadly it seems to have disappeared from that thread though.
    At the moment we're all going through the "Can we beat AMZ, Delft etc at their own game or do something different" thing, but that's a topic on its own.
    Tim

  6. #6
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    Tim,

    RMIT(E) have done very well in recent years. With slightly better Static scores last year you would have won outright! You beat the 2nd place Spanish E-team in Dynamics.

    So,
    Can we beat AMZ, Delft etc at their own game or do something different...
    Why play follow the leader, when there is an opportunity to thrash them?

    Huh???

    Yep, my simulations are showing that a FRONT-WHEEL-DRIVE E-car would be a cracker!
    ~o0o~

    Here it is, if only to liven up the Forum for a day or two.

    BASIC SPECS:
    ============
    1. Similar overall size (LWH) to other cars, but lower power engine (<40 kW?) and smaller battery pack than typical E-car, so less mass. Definitely <200 kg.

    2. Mass-distribution with ~70% on front-axle, maybe more. Minimum possible CG height, say ~20 cm with driver.

    3. Fat tyres (say ~8" wide, 10" dia) on front, and skinny (6", OR LESS) on rear.

    4. Front-suspension VERY ROLL-SOFT, to keep both front-tyres planted at all times. Front also needs to be quite "axle-bounce"-stiff, because it carries most of the mass, which should run at low ride height.

    5. Rear-suspension VERY ROLL-STIFF, so inside-rear-wheel lifts off ground during hard cornering. This easiest done with a "twist-beam" (= all small cars these days). Rear-roll-rate adjustment can be done via tyre pressures, so "~infinitely"-stiff twist-beam is OK.

    6. If single motor (like your Emrax-228), then OPEN differential. Else twin motors (say, 2 x Emrax-208, or SMALLER) mounted either side of footbox with an "E-diff" acting as "open" (ie. same torque to each motor). Driveshafts and outer-CVs taken from front of a 4WD Quad-bike (eg. Yamaha Grizzly).

    7. Overall layout having very reclined driver with knees above front-axle-line. Batteries/controllers/motor(s) mounted under driver's legs, and/or alongside driver's legs/hips on either side of chassis. This gives minimum Yaw-MoI possible for these types of cars.

    8. IMPORTANT - Bodywork/aero aims for MINIMUM DRAG, via very streamlined overall shape. This reduces energy expenditure, hence smaller battery, less mass (-> virtuous circle!). Aero also aims for high downforce via efficient front-wing/undertray combination. But NO REAR-WING, aka "parachute" or "air-brake"!!!

    (Edit: 9. Also IMPORTANT - See Steer-Axis notes in next post.)
    ~o0o~

    ADVANTAGES:
    ============
    My sims suggest the above car can only expect an Accel time of around 4.3+ secs. It depends on details, but the 4WD AMZ and Delft cars, and also good RWD cars, will likely thrash it here.

    But (! ), it does have significant advantages in ALL other Dynamic events, including Fuel, which could be enough to make it the overall winner. These given here in reverse order of importance.
    ~o0o~

    3. A FWD-car can "regen" almost 100% of its braking energy (less electric losses, etc.). This is because with only 30% weight on rear-wheels, together with forward weight transfer, the rear-brakes do almost no work, ever! So they can be sourced from your little sister's scooter. However, the front-mechanical-brakes must be big enough to do ALL the braking. And electrical-regen-braking must be designed to cope with the big inrush-current into the batteries (maybe via super-capacitors?).

    The FWD-car has an advantage here over RWD E-cars in having better regen-braking, so potentially a smaller battery. However, it has no "regen" advantage over the 4WD cars (which are about equal), but it does beat them in having lower Yaw-MoI. It also has lower complexity than 4WD, so possibly also lower overall mass, and BETTER COST SCORE. Note that the rear-half of a FWD-car would be exceedingly simple, with just a twist-beam(-with-monoshock!) and some lightweight bodywork hanging off the MRH.
    ~o0o~

    2. The biggest theoretical gain comes from the potential for best possible aero-performance in FS/FSAE. The current aero-Rules, which allow large front-overhang but only small rear-overhang, favour a forward biased downforce distribution (eg. ~70%F, to match the Mass%). This forward bias also makes it easy to get very low drag, because a front-wing/undertray-with-tunnels combination can be extremely efficient (because "ground effect", etc.).

    By comparison, the other cars' rear-wings really are massive air-brakes/anchors/energy-guzzlers/battery-killers!

    Note that this advantage is purely a result of the current Rules (specifically, the allowable F/R overhangs). Different Rules = a different "question" = a different "best" answer.
    ~o0o~

    1. The biggest practical gain of such a FWD car is that it is VERY EASY TO DRIVE FAST, even by relatively inexperienced drivers (= students with ~1 year of occasional practice). Google FWD rally-driving techniques, but the basics are right-foot-flat-to-floor, then steer-front-wheels-in-direction-you-want-to-go. If, in higher speed corners, the car pushes out of the corner (ie. "understeers"), then a slight tap on the brakes with left-foot brings the tail around and tightens the radius. No need to lift! So less thinking required.

    Here is "Mini Cooper Slalom" on YouTube, courtesy of Claude from another thread, to give you the gist of it.

    https://www.youtube.com/watch?v=yAcmUmPch8U

    Watch closely at ~21 sec to see the inside-rear-wheel lift in mid-slalom (only visible for a split-second, so use pause).

    In short, FWD-racecars = GREAT FUN!

    Z
    Last edited by Z; 05-31-2017 at 11:49 PM.

  7. #7
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    Solar Flares

    Z. We likey !

    Count on some dream team to construct body panels and aero devices from photovoltaics. For front tires, I'd like to see a 'twin-tire' implementation with skinny low rolling resistance inboard tires carrying the load during straight and low cornering operations and outboard tires of slightly less rolling radius picking up the cornering loads.

    Big fat tires cost you a lot because Fx is always working against you. Turning on Fx and Fy only when you need them gets you mileage. And they can ride together on the same wheel.

    The only potential problem I imagine with this architecture is with Torque Induced Steer. Scrub radius needs to be locked in and not allowed to migrate with front suspension rebound otherwise somebody's wrists are gonna get busticated. Loss of traction on one side can generate large unbalanced steering forces.

  8. #8
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    Bill,

    For front tires, I'd like to see a 'twin-tire' implementation...
    I recall that perhaps the first ever Front-Drive racecar was built by American John Walter Christie, back around 1906. It had a ~45 litre V4 engine (yes, no typo!) with lateral crank and front-wheels bolted directly to the ends of the crankshaft, with the whole assembly steering like a cart-axle. Because the motor racing back then was already of the "go fast, turn left" style, same as the established horse racing, Christie fitted dual-wheels to the right-side of his engine/front-axle. So the idea of "dualies" certainly has a good pedigree. And it gives a good safety margin in case you get a flat.

    Christie went on to develop a very effective suspension for military tanks, which he offered to the US Army, but they declined. The Ruskies eventually bought Christie's prototypes, "for agricultural purposes only", developed them into the T-34 tank, and won the Second World War with them!
    ~o0o~

    The only potential problem I imagine with this architecture is with Torque Induced Steer.
    Yes, I forgot to put that important detail into the Specs list above. Here it is.

    SPECS (Continued...):
    ==============
    9. IMPORTANT! Steer-Axis-Geometry to be "centrepoint" or "centreplane". Namely, start with a VERTICAL Steer-Axis passing through centre of tyreprint, then maybe add a pinch of Caster (few degrees) and Trail (~1 cm) at most. Offset (aka "Scrub Radius") and Steer-Axis-Inclination (aka "KPI") to both be ZERO.

    And if motors mounted inboard, then driveshafts should be as close to PERPENDICULAR to the Steer-Axis as possible. So vertical SA => horizontal driveshafts.

    If Torque-Steer is still too much for driver, then try wider front rim widths (say, 8.5" rims for 7.5" wide tyres), and/or a bit more air in the tyres. In very worst case, fit the Electric-Power-Steering now common on most bigger Quad-Bikes.

    ~o0o~

    As a general comment, I should add that for "delightful-driving", rather than "draining-driving"", the whole steering linkage should have minimum friction (especially "stiction") and minimum slop (= backlash). So it must be MUCH better than the typical set-ups now seen in FSAE!

    Would love to hear from all the students thinking "You're MAD! A Front-Drive car will never work in FSAE!!!".

    Well-reasoned comments, criticisms, most welcome.

    Z
    Last edited by Z; 05-31-2017 at 11:50 PM.

  9. #9
    Quote Originally Posted by Z View Post
    Would love to hear from all the students thinking "You're MAD! A Front-Drive car will never work in FSAE!!!".

    Z
    Oh you already know my answer to that one .....

  10. #10
    Quote Originally Posted by tim_pattinson View Post
    Hi guys,
    I know there's been a great deal of interesting discussion on this forum over the last decade or two. Anyone know of any old threads worth reading?

    I submit the UTAS build thread as one: http://www.fsae.com/forums/showthrea...S-build-thread

    -Tim
    Thanks for bringing up the UTAS thread from 2014, I'm honored. (I also had a UTAS thread for 2015 which got a bit harsh as well, don't read that...)

    I'm still with the team. This years design is electric with 2 Emrax motors at the rear. I probably won't do a full explanation of UTAS in 2017 as I'm sort of at arms length to the reasoning and design process they are taking.
    University of Tasmania (UTAS)

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