Anti-ackerman steering

[siskue2005]

the only car not sporting anti ackerman is the Lotus AFAIK

Could that be their secret for their great race pace?

[marcush.]

haha ..that lotus is now a Caterham --you quoted me from 2010...
I´m not sure what Lotus is doing these days..in terms of Ackerman.

Sure Ackerman is something altering dynamic toe settings ( as does bump steer) so there is a change in slip angle for the inside wheel .Assuming you adjust the slip angle of the outside wheel with the steering wheel a more suitable slip angle on the inside wheel should improve your front end grip capacity as the effect will be more pronounced with more steering lock
the effects would be more obvious in tighter corners and more after initial turn in ..
But even this is oversimplifying things as other factors come into play that may influence grip by a much greater magnitude.
So if you cannot calculate it would make sense to evaluate =test the ackerman sensivity of your car driver tyre track combo and decide if its worthwhile pursuing any adjustment to gain speed or improve balance.
If your stopwatch does not tell and the driver cannot tell a difference it ´s time to look elsewhere ...maybe in tyre understanding( )

[Greg Locock]

sorry it is really really easy -as tom said :
You could for examble fix outer joint of the toelink to the upright by using a bracket .This bracket could be bolted to a corresponding surface of the upright .By adding and removing shims you can alter the position of the svivelpoint towards more or less ackerman.

If I were an FSAE design judge or scrutineer on that car (clue I have been both) then that system would receive a very thorough investigation. Bolted joints on spindles in the steering system are inherently unsafe, you would have to overdesign and incorporate redundancy. By all means build a development spindle that you can adjust, but for contests you should commit to a fixed steering arm on the spindle. Quite why you are adjusting ackerman at the outboard end is something only you know.

[Jersey Tom]

sorry it is really really easy -as tom said :
You could for examble fix outer joint of the toelink to the upright by using a bracket .This bracket could be bolted to a corresponding surface of the upright .By adding and removing shims you can alter the position of the svivelpoint towards more or less ackerman.

If I were an FSAE design judge or scrutineer on that car (clue I have been both) then that system would receive a very thorough investigation. Bolted joints on spindles in the steering system are inherently unsafe, you would have to overdesign and incorporate redundancy. By all means build a development spindle that you can adjust, but for contests you should commit to a fixed steering arm on the spindle. Quite why you are adjusting ackerman at the outboard end is something only you know.

Even on pro racecars there can be an immense amount of adjustment built into... just about anything. Steering system, control arm pickups, what have you. Various means of doing it, practical and safe.

I'd argue that in a FSAE environment, once you've fabricated a part for the car, the likelihood of building a second iteration "optimized" version is minimal to non-existent. Extremely unlikely IMO to be able to do your test and tune sessions, find which spindle configuration you like the best, go back and design a one-piece item, fabricate it, do whatever surface finish, and install it for comp.

Admittedly I may be a bit biased as the last set of FSAE uprights I designed were totally modular. LCA pickup, UCA pickup, caliper mount, and steering pickup all bolted on. Does it take some thought to do properly? Sure. But the extra advantages included something like an order of magnitude improvement in manufacturing time with a substantial reduction in raw material as well.

In any event there are a variety of ways of doing adjustable Ackermann that are easy, practical with high serviceability, lightweight, and safe. Just comes down to tie rod and steer arm orientation, however you want to do it. Don't be afraid of moving the steering rack around either.

[Lycoming]

just curious, why did you have a bolted on caliper mount? was it a CNC milled upright, or welded sheet metal? and did you have adjustable roll center height? how many of those adjustments did you actually use that season?

[Jersey Tom]

CNC milled. Easier to design, faster to produce with more accuracy on tolerance. The design had high emphasis on DFM, taking advantage of conventional workholding without special fixtures.

Anyway, the main reason for everything (caliper mount included) being bolt-on was so that the main piece - the spindle body - could be used at all corners of the car. Easy to produce a bunch of them and have spares to boot, that could fit any corner. At the time the calipers were outboard on the front and inboard on the rear. Likewise with the control arm pickups, with different control arm geometry front to rear you could accommodate it easily with different UCA/LCA pickup brackets.

In theory, in subsequent years they could try a different caliper on the previous year's vehicle by just slapping on a different caliper mount and away you go.

Did we take advantage of all the modularity and adjustment range during that year? No. Too pressed for time, money, and people.

I'm still a big fan of modularity and built in adjustment. At the FSAE level it saved immense amount of time and money. At the pro level, the adjustment lets you do what you need to and gives you the extra bit of control in your setup. I've seen it on open and closed-wheel race cars.

[marcush.]

I have built a few cars in my life and never ever something broke off not in paddock not in competition -i´have seen a lot of FSAE things fail to complete their runs though...I don´t see your problem with bolted joints.the motorsport and automotive world does do without redundant systems since day one so two nice bolts and a nice flat parallel flange will do
the trick for me -even though i´m a big fan of nicely cast or machined bits...why would you want to have a spindle anyways? FSAE is about saving weight,no?

I would prefer to campaign one of Toms bolted creations all day long....

[Greg Locock]

I didn't say i wouldn't let it pass, I implied I would want to see a lot of proof it was a safe design and well made. In my day job a bolt on steering arm would not allowed to be driven on public roads, and even on the proving ground tracks the car would have to be tagged.

[Jersey Tom]

In my day job a bolt on steering arm would not allowed to be driven on public roads, and even on the proving ground tracks the car would have to be tagged.

Race tires aren't allowed on public roads either. Nor many things. OEM world is just completely different.

[marcush.]

I didn't say i wouldn't let it pass, I implied I would want to see a lot of proof it was a safe design and well made. In my day job a bolt on steering arm would not allowed to be driven on public roads, and even on the proving ground tracks the car would have to be tagged.

i´m a bit curious now...how would YOU attach the steering rod to the hub -a flexure ? At some point you just need a bolt or something to keep the assy serviceable.
It´s not uncommon to see bolts on mass produced cars to attach the swiveljoints to the upright.

[Billzilla]

Just give the car about 75% Ackerman, it will be as close to as good as it's going to ever get.

[marcush.]

Just give the car about 75% Ackerman, it will be as close to as good as it's going to ever get.

to drive around the block ,participate at Indy 500 or in a autcross? it can´t be the same for all? Or would you say it´s just not worth it?
I have the feeling this is more important on light low powered cars negotiating tight twisty tracks with corners over 90° on a high speed track with only fast corners at the same radius the effect will tend to zero...
but just how much could you expect to gain?
My 2 cents : if your car does not have balance or grip and a soft chassis to begin with the effect might be not even nticeable on the watch or for the driver to feel .Maybe your tyre wants exactly what the designer has specified .but given the wide range of possible ackerman settings this is unlikely .But I would not expect miracles coming from this ...It´s a finishing touch to a well sorted machine.Priority C or D and something a small team never ever will have time or recources to untap.
It´s a bit like Marrussia or HRT thinking about kers...you are 3or 4 seconds behind and KERS might buy you 3 tenths ...but you have to BUY it as you don´t have any inhouse expertise .So this is something to make others more wealthy and will not add much to your knowledge base...so leave it alone till you see it is the last bit that stops you from scoring ...

[olefud]

Just give the car about 75% Ackerman, it will be as close to as good as it's going to ever get.

to drive around the block ,participate at Indy 500 or in a autcross? it can´t be the same for all? Or would you say it´s just not worth it?
I have the feeling this is more important on light low powered cars negotiating tight twisty tracks with corners over 90° on a high speed track with only fast corners at the same radius the effect will tend to zero...
but just how much could you expect to gain?
My 2 cents : if your car does not have balance or grip and a soft chassis to begin with the effect might be not even nticeable on the watch or for the driver to feel .Maybe your tyre wants exactly what the designer has specified .but given the wide range of possible ackerman settings this is unlikely .But I would not expect miracles coming from this ...It´s a finishing touch to a well sorted machine.Priority C or D and something a small team never ever will have time or recources to untap.
It´s a bit like Marrussia or HRT thinking about kers...you are 3or 4 seconds behind and KERS might buy you 3 tenths ...but you have to BUY it as you don´t have any inhouse expertise .So this is something to make others more wealthy and will not add much to your knowledge base...so leave it alone till you see it is the last bit that stops you from scoring ...

I agree that Ackerman is more of a dial-in than a setup tool. However, my idea of leaving it alone would be a nominal 100% as baseline. Ackerman is accentuated on short wheelbase cars.

[Greg Locock]

Ackerman only needs to be 100% if you are driving steel tired carriage wheels on gravel driveways.

Ackerman varies with steering wheel angle, so you need to decide what shape the curve is. if you plot wheel 'fight' vs ackerman angle for real tires you'll find that 100% ackerman is not a particularly good target for anything.

On prototype built up spindles I'd weld the steering arm and strength test the resulting assy if it was to be used for handling as opposed to steering work. Adjustment for ack could be via eccentirc taper inserts for the ball joint, or by moving the rack. However in practice for our production cars Ackerman is set to minimise parking efforts at full lock, not by handling.

On centre Ackerman is strongly affected by the static toe settings, and that is how several real racing series other than F1 investigate it.

As I keep saying, a bolted steering arm could pass scrutineering if it were properly designed. The loads are fairly simple to estimate, and the Factor of Safety in the steering system should be rather high anyway (what would you use and why?). Of course for FSAE you would gain a lot of extra design points if you actually measured your tie rod loads in some typical events (what event should be used to qualify the strength of a tie rod?) and used those to assess your design.

[olefud]

Ackerman only needs to be 100% if you are driving steel tired carriage wheels on gravel driveways.

Ackerman varies with steering wheel angle, so you need to decide what shape the curve is. if you plot wheel 'fight' vs ackerman angle for real tires you'll find that 100% ackerman is not a particularly good target for anything.

I’m missing your point. It would seem that Ackerman would be required by steel wheels on a rubber surface (high friction) rather than gravel (low friction)

In general, proper Ackerman is a function of the center of turn which differs from that of steel wheels as a result of slip angle that, in turn, is determined by over/understeer as a result of a bunch of other factors including roll moment/stiffness,.

With low slip angle tires and a short wheelbase, 100% Ackerman is a pretty good default baseline, though still requiring dial in to complement/correct other handling inputs.