Steering Arm Question

[erau_paul]

Hey Guys,

I have a question about the tie rod location. In the RCVD book it says that the tie rod should be roughly located in the front view geometry but you should reference Ch. 19 for the tie rod outer point. I only see a short section on page 713 on the location of the tie rod. I understand the general "quadrant" that it says it should be located in (Figure 19.1 and 17.17) but I guess I don't see any further details about its placement.

My other question is that it isn't immediately obvious to me why the tie rod should intersect the instant center.

Thanks,

Paul

[Cristiano]

A good approach is to position it inline with the upper or lower A arm.

http://fsae.com/groupee_common/emoticons/icon_wink.gif

[erau_paul]

Thanks.

1 more question. On page 628 in FCVD there is a equation for calculating the FVSA in regards to the track, wheel camber, and chassis roll angle. When I try to do some calculations I get answers that are clearly incorrect and there are no examples. Can someone explain to my how to apply this equation?

Thanks,

Paul

[woodsy96]

The reason you want the tie rod to intersect or be close to intersecting the IC is to control bump/roll steer, though actual analysis should be done to see where it should sit, maybe with some consideration for compliance.

As for the FVSA length,
eg.

Half track = 500mm
Camber compensation in roll = 0.5 deg/deg
FVSA = 1000mm

So, if you want 100% camber compensation in roll (1.0 deg/deg), then FVSA = half track. If you want 0%, then your FVSA = infinite.

[erau_paul]

Thanks for the help!

[ADNAN @ MHSSC]

[I have a question about the tie rod location. In the RCVD book it says that the tie rod should be roughly located in the front view geometry but you should reference Ch. 19 for the tie rod outer point. I only see a short section on page 713 on the location of the tie rod. I understand the general "quadrant" that it says it should be located in (Figure 19.1 and 17.17) but I guess I don't see any further details about its placement.]



I believe the reason for this placement has to do with compliance in your suspension bushings.......

i.e you might get an undesirable steer effect due to suspension compliance while braking or accelerating.


However I am not completely clear regarding this.......
I would like to know what the more experienced members think regarding this.


I hope this is satisfactory and All the BEST with your build!

[EPMPaul]

Basically, when your bushings are compliant, you want the deformation to make the car stable.

It doesn't apply so much in an FSAE context though. Most teams use either rod ends or spherical bearings in their assemblies, so those won't really move so much. So, even if there is compliance(which will be minimal in this case), how much will it really change handling considering the alignment on your car isn't going to be perfect in the first place. That's up to you to figure out.

[Zac]

While I agree that compliance shouldn't be an issue for FSAE cars in theory, in practice it turns out to be a significant source of toe and camber change, even for the better performing cars.

I would wager that rear toe compliance would correlate pretty well with lap times.

I also see a lot of cars with very poor alignments.

[erau_paul]

Originally posted by woodsy96:
The reason you want the tie rod to intersect or be close to intersecting the IC is to control bump/roll steer, though actual analysis should be done to see where it should sit, maybe with some consideration for compliance.

As for the FVSA length,
eg.

Half track = 500mm
Camber compensation in roll = 0.5 deg/deg
FVSA = 1000mm

So, if you want 100% camber compensation in roll (1.0 deg/deg), then FVSA = half track. If you want 0%, then your FVSA = infinite.

Thanks. When I try to apply your example to the equation it does not work.

Roll Camber = Wheel Camber / Chassis Roll
Roll Camber = 1 / 1

FVSA = (t/2)(1-Roll Camber)
FVSA = (500mm)(1-1)
FSVA = 0

Could you please explain this.

[woodsy96]

I should have been more clear: by roll camber I meant camber gained per degree of roll.

i.e. for a camber compensation of 1 deg/deg of roll (therefore camber gain in roll = 0, but lots of camber gain in bump)

FVSA = (t/2)/(1-0) = t/2

for a camber compensation of 0.3 deg/G (i.e. camber gain for 1 deg body roll = 0.7 deg),

FVSA = (t/2)/(1-0.7) = ~1.67.t