Suspension Design

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Hello "Z",

You miss a point there... engineering is not solely based on the idea to have the best concept ever... Engineering is to MAKE THINGS WORK ! And one of the aspect of making something work is risk management. Your ideas are perhaps great but they are a HUGE gamble. With the numbers of years we put in every FSAE years it's a huge gamble.

You also miss another point : gain.

What is the gain Z? We want laptimes comparaison, we want compliances study and weight study, we want drag and downforce figures, we want inertia and CG comparaison...

Give us figures! Science is based on facts. Be an engineer. The day you prove your point, well all FSAE will be rocking those beam axled side-engined mutli-steered cars on whatever tire you used with the frame type you used. And there is no problem with that.

You might have the best ever concept but a concept is just a concept. History is written on what is done not what is thought.

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You should explain WHY you think it's such a gamble to try one of many Z's suggestions. Earlier I explained that sure, there is very little out there on FSAE cars that isn't double wishbone suspension, but there have been cars that use 'other' suspensions that are very competitive. Single cylinders, v-twins, and four cylinders have all managed to win at different points and times, why not different types of suspension as well?

As far as facts and figures go, there's a lot you can figure out without building anything. In face, a LOT of money is spent on engineers who say they can figure stuff out before they build it, bc it costs a lot less money to do it that way.

Car companies release concepts that usually are better than the final product. What's wrong with Z's concepts? After all, that may be his strategy: hoping some of us will pull the wool from our eyes and try something new and potentially more competitive.
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4WS should be totally allowed in the current rules:
Steering
T6.5.1
The steering wheel must be mechanically connected to the wheels, i.e. “steer-by-wire” is prohibited or
electrically actuated steering, is prohibited.
T6.5.2
The steering system must have positive steering stops that prevent the steering linkages from locking
up (the inversion of a four-bar linkage at one of the pivots). The stops may be placed on the uprights
or on the rack and must prevent the tires from contacting suspension, body, or frame members during
the track events.
T6.5.3
Allowable steering system free play is limited to seven degrees (7°) total measured at the steering
wheel.
T6.5.4
The steering wheel must be attached to the column with a quick disconnect. The driver must be able
to operate the quick disconnect while in the normal driving position with gloves on.
T6.5.5
The steering wheel must have a continuous perimeter that is near circular or near oval, i.e. the outer
perimeter profile can have some straight sections, but no concave sections. “H”, “Figure 8”, or cutout
wheels are not allowed.
T6.5.6
In any angular position, the top of the steering wheel must be no higher than the top-most surface of
the Front Hoop. See Figure 3.
T6.5.7
Steering systems using cables for actuation are not prohibited by T6.5.1 but additional documentation
must be submitted. The team must submit a failure modes and effects analysis report with design
details of the proposed system as part of the structural equivalency spreadsheet (SES) or structural
requirements certification form (SRCF). The report must outline the analysis that was done to show
the steering system will function properly, potential failure modes and the effects of each failure mode
and finally failure mitigation strategies used by the team. The organizing committee will review the
submission and advise the team if the design is approved. If not approved, a non-cable based steering system must be used.

I wonder how much extra development time and driver training having 4WS would take. I think it's most definitely a try before you buy idea on an old car. Lots of testing, lots of decisions to make.

Ian, if the steering is all mechanically attached, but you have electronics that say 'switch gears' in the rear steering to change the steer direction (turn left wheels left to turn left wheels right) then I believe you would be in the clear. You aren't electronically controlling the steering, just what will happen when you steer.

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You should explain WHY you think it's such a gamble to try one of many Z's suggestions. Earlier I explained that sure, there is very little out there on FSAE cars that isn't double wishbone suspension, but there have been cars that use 'other' suspensions that are very competitive. Single cylinders, v-twins, and four cylinders have all managed to win at different points and times, why not different types of suspension as well?

As far as facts and figures go, there's a lot you can figure out without building anything. In face, a LOT of money is spent on engineers who say they can figure stuff out before they build it, bc it costs a lot less money to do it that way.

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Max, you got it right entirely! My point isn't making a whole car. My point is using simulation to prove your point. It's like in design event, explain WITH NUMBERS what is backing your choices! Laptime simulation and FEA are a very good arguments when done right.

And there is no wool to pull from any eye... just some time to spent analysing on a system that nobody in FSAE has real experience on.

Xavier,

As I understand it Z’s complaint is not that you aren’t using his ‘killer-app’ design, but rather that you/we are not doing preforming the full analysis you just described.
Z’s concept is sound and has been well explained, and critiqued.
That is to say it could be used to design and build a car that meets FSAE rules and has certain positives and negatives.
Ultimately everything important about the design will come from the individual team’s implementation.

There are many concepts that can win FSAE.
If you want to know the real gains (or losses) that Z’s design will realize you will have to do that work yourself.

-William

Well with the new cable steering rule, it would make rear steer a lot easier to accomplish. You wouldn't be able to select your steering option, however. And without steer-by-wire, the entire topic is pretty much moot.

Am I wrong in thinking there was a rule limiting the amount of rear toe compliance (steer) allowed in the car? I can't find it in the rules.

Didn't TU Graz run rear steer a couple years ago?

I am not so sure about this whole rear steer idea.

While it might be possible to come up with some numbers with a suspension simulator that imply some advantage under certain conditions, that may not be the entire story.

The idea of crabbing around a slalom turn may feel decidedly strange and unnatural to the driver in such a way that it detracts from the drivers intuitive feel of what the car is doing.

It is possible to crab an aircraft by applying rudder while keeping the wings level, and it is a most peculiar and unsettling feeling.

Don't underestimate the importance of being able to see, feel, and sense what the car is doing within the traction circle, and have all the drivers senses agree.

Really odd effects such as banking the opposite way, or crossed over steering direction, or opposite yaw to real directional change can really confuse the human brain.

If the car does not feel a natural extension of the human body, there is very likely to be a much longer learning curve which some drivers may never be able to come to terms with, of feel truly at ease with.

It would be fun to try though, especially after a few beers.
But will it make the car consistently faster ?

AxelRipper

There is a rule about 'slop' in the steering system.
I think it is about 5 degrees at the wheel, or something like that.

-William

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Originally posted by rjwoods77:
Look at what UWA is up to...

http://sphotos-a.xx.fbcdn.net/...8445_214229793_n.jpg

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Rob,

Hmmm..., I'm seeing a beam-axle-ish Lotus 88?

I think front is at bottom-right. Are those "E" shaped steel pieces the lateral-location-links-cum-heave/pitch-springs? Hope they did enough testing...

Should be interesting!
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Ian,

"I think a 4WS electronic interface might prove difficult or impossible to get declared legal."

My "red and green steering wheel buttons" would simply move a linkage at the back of the car to one of three fixed positions (eg. changing the length of a "Pitman" arm there). If electronics not allowed, then do it all pneumatically (ie. via pneumatic push buttons on wheel). If this not allowed, then two "bicycle handbrake type levers" (or "paddles") on the wheel, and all mechanical back to the rear Pitman arm (cables or whatever). This last one is ergonomically very similar to your "pull/pushing" of the steering-wheel rim.

As also suggested by others (Max, Tony), this would be best done as a parallel research project by modifying a previous year's car. I think it would be VERY educational from a VD perspective. So much so that following years' cars might be better even with conventional front-only steer (ie. from better understanding of ackermann, rear roll-steer, compliance-steer, etc.).

In fact, IMO, all bigger than average teams should spend half their resources modifying old cars, and combining "blue-sky" research with driver training. Cut-and-butt Monday to Friday, burn rubber every Saturday and Sunday...

Also note that good ergonomics is a tricky problem. Very often the "most obvious way" turns out to be awkward and clumsy, while the "most comfortable way" is not at all obvious at the start. Computer gaming software writers figured this out ages ago. Engineering software writers still haven't got a clue how this works! http://fsae.com/groupee_common/emoti...n_rolleyes.gif It takes an open mind, and a lot of trail and error... http://fsae.com/groupee_common/emoticons/icon_smile.gif
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Xavier,

"Your ideas are perhaps great but they are a HUGE gamble."

As I have argued before, the reason FSAEers keep copying the same-old-same-old is that they have nothing to lose by losing. THERE IS NO GAMBLE! (Ie. no necks on chopping blocks.)

If your school implements a policy something like,
"As positive inspiration to future FSAE teams, all current team members who fail to win their events outright ... will have their rotting carcasses nailed to the workshop wall!!!",
then I am quite sure you would consider at least some of the alternative suspension types on this thread. After all, you can't get in front of the others, by following them... http://fsae.com/groupee_common/emoticons/icon_smile.gif
~o0o~

"Give us figures! ..."

Read my posts. I give plenty of figures. I like figures!

Or, better yet, (as Max asks) give us your figures. Come on, "Be an engineer!". http://fsae.com/groupee_common/emoticons/icon_smile.gif
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William,

"Z’s concept ..."

So far I have pushed the Twin Beam-Axle concept because I reckon it gives the most benefits, for the least effort, in FSAE. The "radicalness" of it may work against it. (Why? They are common in Speedway, Nascar++, US Autocross, many types of production car racing, Off-road, etc., etc...)

Anyway, coming soon, the "very close second" from that list of alternative suspension types (hint: it is structurally very simple, is perhaps an easier step for FSAEers used to double-wishbones, but has minor kinematic disadvantages, which don't matter much, because "Any suspension will work, if...").

Z

^^ What Tony said

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Originally posted by Warpspeed:
I am not so sure about this whole rear steer idea.

While it might be possible to come up with some numbers with a suspension simulator that imply some advantage under certain conditions, that may not be the entire story.

The idea of crabbing around a slalom turn may feel decidedly strange and unnatural to the driver in such a way that it detracts from the drivers intuitive feel of what the car is doing.

It is possible to crab an aircraft by applying rudder while keeping the wings level, and it is a most peculiar and unsettling feeling.

But will it make the car consistently faster ?

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As I've mentioned very recently, these type of actions are unfamiliar to cars, but common in my background. They key is practice.
Assuming a car is set up properly for a course...going a bit out on a limb here:



What three makes a fast driver fast?

Talent, Practice, Practice.


Practice, as everyone should know, makes perfect. But, the second practice is different than the first. The second practice I list to illustrate a point that there is more that comes with it. A driver must be able to anticipate the movements and actions to be taken in the near future or react on instinct to adjust for errors. I would say that after driving something with a mecanum style drive system, even at only a top speed of 20mph, that you get used to it. You are already turning your head before you hit that button to strafe a vehicle (feels weird to say that on these forums without quotes. HA!) completely sideways around obstacles. Practice the controls and you get past that sick feeling that the vehicle is doing something that it shouldn't be, you just anticipate it.



On a note of rear steer (bump steer):

Rear steer can be considered to come into play in two different ways, either it steers in phase or out of phase with the vehicles steered direction. In the OEMs such as Mazda or Nissan with the RX-7 or Skyline, they either use compliance bushings or hydraulics, respectively. In our application I've seen geometry used to achieve this (bump steer aligned toe link). When used in phase, the car tends to push itself out of the corner, creating less of a yaw moment from the rear, and leading to a stable understeer condition. The other direction leads to out of phase steering that rotates the car more quickly around a corner and can lead to an unstable oversteer condition.

This can be all fine and dandy depending on what design theory you are following about cornering, but it must also be noted that a straight line is the most awkward path to follow. Bumps cause the car to dart around like a Chihuahua shitting razor blades and transience plays hell on the system. It's widely documented that cars that incorporate these design features into the OEM vehicles are typically overridden by whatever means it takes for track use because it causes the car to become unpredictable and unstable as the driver doesn't know when or how much the system is active at higher speeds. Things like that become dangerous. But again, it's about anticipation, and a system that you can anticipate is useless.



Z,


My thoughts going through suspension design this year:

With double wishbones basically mimicking a swing axle, why not use one? We did end up using double wishbone this year (with some relatively big changes from previous), but a swing axle doesn't seem to be all that negative for these uses. Travel is +1/-1 inch of travel which leaves little camber gain, and design steps are nearly the same as wishbones. It is a little inferior to double wishbone kinematicly, but could potentially save weight and give a mounting link to attach a direct actuating damper.