Suspension Conclusions

[Lemon Lime]

Hello mates , My name is Marwan Alabassiry , I'm 18 years old and I'm from Cairo , Egypt ( Helwan Uni. ) . Warm greetings and afterward ; After one month of studying kinematics and suspension ; I came up with more than an idea .. I thought to share them and to check whether this is the right route I'm on ... Ok , * Dampers ; They are probably the most important thing one should care of and study their effect and also their adjustability should play a major role ... In my humble opinion ; They're like the tip of the rope . ** Camber change ; Alright I think one should compensate the camber change due to roll and take car of more than the camber change due to heave / squat .. Google " Lancaster links " and you'll find out that these guys built a suspension to compensate camber change due to roll and neglecting the camber change due to heave / squat ... *** Friction ; Don't waste what you've done by leaving great friction areas around the rockers mounting points or the damper strut mounting point in the rocker . **** ARBs . For a car that it's net weight including the driver and the fuel = 300 KG .. One might not need ARBs .. Just the stiff springs would do enough , But an adjustable ARB will be better for adjustability issues , I say this because many FSAE cars are very narrow to install a conversion ARB or one should think outside the box to fit an ARB in a tiny space . ***** Tyre TTC , Well I see that a 300 KG Race car with speed limit to MAX 100 Km/h won't push it beyond the limits .. Just some basic info on tyres and tyres temp. and one should handle it properly ( AGAIN THIS IS MY HUMBLE OPINION .. TTC MIGHT BE EXPENSIVE OR A MONEY TO WASTE IF YOU ARE LIKE ME " A FIRST YEAR " and in a team who is just beginning and not playing hard yet ). Ofcourse all of these beside studying from RCVD and general web browsing and to mention ; I've used a nice free software " Wishbone.exe " to design a kinematics assembly for a FSAE racer car .. And it went well .. Sort of ! ; I mean apart that the roll centre lateral migration was to be 8 inches .. But I managed that later ... Thanks a lot for your valuable time and thanks again for your well perceive .

[Claude Rouelle]

Lemon Lime,

Please contact me via engineering@optimumg.com

Thanks

[Lemon Lime]

Mr.Rouelle ,
Thanks for caring and reading Sir Claude , I sent an email per your request Sir on the mentioned email address , Once again thanks .

[Karam Atteia]

Marwan, my team mate(HELWAN UNI.)

here some few extra conclusions http://fsae.com/groupee_common/emoticons/icon_smile.gif .. wish this would help

1-TIRES.. Read about tires even you wouldn't use the TTC in your design, but it will make you see things from another point of view. Tires are the most single important aspect in this whole system, it is the only contact between your vehicle and the road without it you can't transfer forces to the road to acc. or brake or even turn, keeping it in contact to the ground along all road conditions and circumstances is the big deal. all you have to do is to keep the tire working in the best range of camber angles under different loads. Tires are load sensitive where the load transfer is a very bad effect in our trim which affects the overall grip. if it is your first year don't waste time and money on TTC and be satisfied only to know why people use TTC, that would help!

2-SUSPENSION GEOMETRY (kinematics).. Before starting your geometry, you have to know your tires and wheels dimensions (Rim diameter, width, offset)then you have to pack every thing in it (brake disc if outboard, calipers, wheel bearings). now you can start your design from the outside and then move towards the inside from there as you said. starting from your front view geometry with decisions on RC height, front view swing arm length(rate of camber change & roll center lateral migration)and the length of the upper arm relative to the lower arm(amount of camber change with bump).Regarding the KPI angle as small as possible achieving a scrub radius near zero.
then now you can move to your side view knowing the positions of your UBJ and LBJ on the upright. take the decisions on your amount of anti-dive/squat/rise and your side view swing arm length(rate of caster change).
Now you have two 2-D planes(front & side), all what you need to do is to join these points in the 3-D world on your CAD to get your wishbones planes. then get your chassis pivots. don't miss the toe link or your steering geometry.
Then use a kinematic analysis program to check what you have done and know if you need to change any thing ( i used SusProg-3D ). [Read RCVD chapter 17 sus geometry & Chassis Engineering (Herb Adams)]

3-RIDE&ROLL RATES.. they have significant effect on cornering performance as they directly affect the tires normal forces distribution, and these rates also depends on your wheel loads. before starting these iterations you have to know your springs&ARB motion ratios, vehicle weight and static weight distribution , RC height, max. lateral acceleration, front and rear track width and wheel base. then you have to start with choosing your ride spring rates depending on your decisions on your front and rear Ride frequencies, then calculate the amount of roll resistance from these springs and compare it with your target on the Roll Gradient to size an appropriate front and rear ARB. put in consideration your TLLTD (total lateral load transfer distribution) to balance your front and rear ends. start with an initial understeer and make you ARBs adjustable.(take care from your units)
[Read RCVD chapter 16 (ride and roll rates)and chapter21(suspension springs) and OPTIMUM G technical tips]

4-DAMPERS.. as a first year team you have to know dampers and their adjustability and how to use them on the track to tune up your vehicle. don't waste time on designing them, just select a damper with numbers of damping forces near what you need for your case and then you can design your rocker mechanism to use the full damper stroke(from here we get our MR). choosing your damping ratios with a compromise between response time and overshoot(compromise between vehicle control and ride comfort which we don't care about in our trim) start with ride and single wheel bump damping then try to know your Pitch and Roll frequencies and Inertia of your sprung masses, for your pitch and roll damping understand.
[Read OPTIMUM G techtips and RCVD and RCVD chapter 22 (Dampers) and Learn&Compete chapter 7 (Dampers)]

5-DESIGN YOUR SYSTEM .. before designing any part of your suspension you should know the material you are going to use on manufacturing it (never design an upright without knowing its material). you have to eliminate any friction in your system specially at your revolute joints ( the rockers), take in consideration your wheel impact as all your upright and hub and ball-joints and bearings will be packed inside it. make every thing adjustable , but as your first year be satisfied of your camber and toe adj. and your antiroll bars and your pushrods(for ride height).

GLORY GLORY EGYPT
Karam

[Lemon Lime]

Mr.Karam http://fsae.com/groupee_common/emoticons/icon_smile.gif .. Thanks a lot for your valuable reply .. I really appreciated it ... And I hope one day to be like you Mr.Karam ... Again Be assured that your valuable notes are appreciated and considered as a no.1 priority when I continue studying again after the final exams . Many thanks http://fsae.com/groupee_common/emoticons/icon_smile.gif


Note : Mr.Karam is my best team mate and we do discuss topics as these whenever we meet .. I mean ; When Mr.Karam replies here doesn't mean that we don't meet as a team ! Just to clarify .
Thanks for you well perceive .