Ackerman or parallel steer?

[Mechanicaldan]

Just a quick survey.

Do you run Ackerman or parallel steer?

Last year we ran parallel steer, but I think we should have Ackerman because of the small radius of the turns at competition.

Cyclone Racing
www.cyclone-racing.com/fhome.htm (http://www.cyclone-racing.com/fhome.htm)
Iowa State University
Project Director

[PatClarke]

Dan,
Put some Ackermann in the new car. On second thoughts, put lots of Ackermann in the new car http://fsae.com/groupee_common/emoticons/icon_wink.gif
PDR

Rudeness is a weak mans imitation of strength

[Eddie Martin]

Show me your tyre curves. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Eddie
UOW Racing

[PatClarke]

AAAaaahhhh, Eddie was paying attention at the Claude seminar http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Rudeness is a weak mans imitation of strength

[Mick_P]

If only i could get $1 for every time Claude said that line at MOTEC... hahaha http://fsae.com/groupee_common/emoticons/icon_wink.gif

Mick Partridge
Swinburne University of Technology

[Schumi_Jr]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Eddie Martin:
Show me your tyre curves. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Eddie
UOW Racing<HR></BLOCKQUOTE>

Sure, any stab data will give you a general idea about what loads/slip angles your tyres are happiest at, but there are inherent limitations to the data the tyre manufacturers give you. All tire data is from taken from steady state conditions and the temperature is a controlled variable.

The best way to determine your ideal ackerman settings (in my opinion) is through vehicle testing. The data you get from an MTS is useful, but there's no denying that you have a WAY better machine for tyre testing in your garage...

I remember in the 2002 design finals one of the teams mentioned that ackerman is better for steady-state conditions and parallel/anti is better for transients. Can anyone offer some insight into this?

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae (http://www.eng.uwaterloo.ca/~fsae)

[Gareth]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Schumi_Jr:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Eddie Martin:
Show me your tyre curves. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Eddie
UOW Racing<HR></BLOCKQUOTE>

Sure, any stab data will give you a general idea about what loads/slip angles your tyres are happiest at, but there are inherent limitations to the data the tyre manufacturers give you. All tire data is from taken from steady state conditions and the temperature is a controlled variable.

The best way to determine your ideal ackerman settings (in my opinion) is through vehicle testing. The data you get from an MTS is useful, but there's no denying that you have a WAY better machine for tyre testing in your garage...

I remember in the 2002 design finals one of the teams mentioned that ackerman is better for steady-state conditions and parallel/anti is better for transients. Can anyone offer some insight into this?

Aaron Johnston
University of Waterloo FSAE

http://www.eng.uwaterloo.ca/~fsae<HR></BLOCKQUOTE>

Show me your test data. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Charlie]

I couldn't agree more with Aaron's 1st point, we see too many high steer angles and transients for steady state tire data to determine your ackerman. I know that's what Claude said, and of course he is at least partially right, but our event is a lot different than, say a road course.

As far as ackerman being better in steady state and vice versa, I would expect the opposite-at least on our courses.

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Frank]

A problem with Ackerman steering.

It seems to me that if you implement Ackerman steering, the dynamic steering arm lever, ie the moment arm that the tie rod acts about the kingpin, is changing through steering angles. This is how you effectively obtain Ackerman geometry.

What I've noticed is that for high steering angles, the ratio of the lever arms (inner and outer) becomes drastic. The effect is that the "feedback"� through the inner wheel becomes dominant at high steering angles.

For example, if you are in a tight corner, and touched the brake, you have to fight (through the steering wheel) the braking force from the inside front wheel.

It seems that changing the length of the steering arms does nothing, as it is simply a ratio between inner and outer steering arms during cornering.

I am starting to think that if you implement Ackerman, you have to sacrifice the total available steering angle, to avoid this situation. For example our car had 100% Ackerman and was limited to 28 deg outer wheel, 45 deg inner wheel angles.

I've had to change the limit on steering to 25 deg / 35 deg , inner and outer steering angles respectively.

Regardless, I think that even with this limitation, the vehicle will turn a tighter corner with the Ackerman (at 25/35) than parallel steer with say 30/30 deg.

Has anyone else encountered this problem?

Regards all

Frank