SLA Suspension Model

Looks very nice. The best free software I know of for kinematics is wishbone.bas, one of the Locost websites has it. I have checked that against ADAMS and it seems OK.

Best way forward if you want it checked is to post a hardpoint list.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Thanks for prompt ad encouraging response, Greg. OK, for checking geometry, I've used this model (data is from test file I did in Lotus, but pls. ignore spring mounting points*):

STATIC VALUES
X Y Z
(mm) (mm) (mm)
1900.00 63.00 181.92 POINT:1 Lower wishbone front pivot
2150.00 63.00 181.92 POINT:2 Lower wishbone rear pivot
2000.00 688.00 181.92 POINT:3 Lower wishbone outer ball joint
1900.00 243.00 376.92 POINT:5 Upper wishbone front pivot
2150.00 243.00 376.92 POINT:6 Upper wishbone rear pivot
2005.00 665.61 421.88 POINT:7 Upper wishbone outer ball joint
4146.50 600.00 203.60 POINT:8 Damper wishbone end
4180.00 475.00 593.60 POINT:9 Damper body end
2030.00 665.61 421.88 POINT:11 Outer track rod ball joint
2030.00 243.00 376.92 POINT:12 Inner track rod ball joint
4180.00 486.00 690.00 POINT:16 Upper spring pivot point
4145.00 645.00 210.00 POINT:17 Lower spring pivot point
2000.00 688.83 286.92 POINT:18 Wheel spindle point
2000.00 737.83 287.00 POINT:19 Wheel centre point

Wheel travel is 77mm in bump and 77mm in rebound in 11mm increments, and steering travel is 12mm in 2mm increments. (As far as geometry goes, I don't recall encountering difference between my model and Lotus Suspension Analysis bigger than half a percent, but I checked only 'main' characteristics). Some of the results are shown in enclosed picture (less frequent characteristics are shown only in design position)- jounce, scrub, camber, steering/toe angle, roll centre height, mechanical trail, scrub radius, kingpin inclination, caster angle (plus brake force lever, spindle length, caster offset, vertical force lever, lateral force lever). Unfortunately, I've made this model forgetting I should be able to check svsa geometry calculations.

For given load at contact patch, model will also calculate ball-joint loads and loads at inboard bushings. It can also solve kinematics of pushrod/pullrod mechanism, calculate 'linearity' of springing, contact patch to damper motion ratio, &c. I've lost quite a while deriving the equations describing the model, so one can obtain velocities and accelerations of each individual component (should be useful when making dynamic model incorporating influence of unsprung masses, &c).

P.S. maybe it would be more convinient if anybody is willing to give me hard points of model they've already modelled so they can check it against existing data

That's a bit of an odd suspension.

Here it is translated into inches etc and run through wishbone.

the dos box shows the detailed results at 1 inch of rebound travel.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Sorry for the delay in replying. What do you mean odd suspension, Greg? (I'm guessing because the track rod is going *through* the upper wishbone)

Anyways, the reason for this delay is that I decided to make a full comparison with new LSA and added a new way of data input (most programs use hardpoint coordinates, and I guess it would be most convinient for you guys- so it woud make sense to add that) and suddenly I started getting nonsense results... After a bit of frustration and hand-wringing, today I found out that I merely forgot to move two equations after the redefinition of hardpoints. D'oh.

I expect to have this comparison done shortly and then sort out the flash program.

I'm back with comparison amost complete and would be very grateful if someone was to take a look. I'm enclosing the Excel table with head-to-head comparison with Lotus Suspension Analyzer 5.0c. The comparison was done on their template suspension, but so far only in bump/rebound.

My results are fairly good when comparing 'real' points- error is marginal, meaning below 0.00001, but what may be of relevance is that exception is the track rod outboard end with still relatively small discrepancy, but 10x greater than the rest. What I do not like are derived characteristics- e.g. camber, KPI and scrub radius are almost acceptable (discrepancy mostly around or below 0.1%), and the rest is not so. The main problem is toe angle, where I get big discrepancies (caster angle and mechanical trail are not that catastrophic).

I'd also be much obliged for assesment of roll center height and fvsa length comparison- even though error might be relatively acceptable, percentage wise- I'd say average is 0.5%, the absolute error may be too big. IMHO 900mm may be 1.6% of fvsa length, but it's still not much less than a meter- and that is big.

Thanks in advance.