4 wheel steer?

[C Z]

Has anyone ever trie a 4 wheel steering setup? Any thoughts on the subject?

[C Z]

Has anyone ever trie a 4 wheel steering setup? Any thoughts on the subject?

[Denny Trimble]

Here are some research papers from the SAE store:

Lateral Response of a Formula Sae Race Car (UW, 1994 4WS project)

Four Wheel Steering--Maneuverability and High Speed Stabilization (U-California)

Investigation of Four-wheel Steering Algorithms for a Formula SAE Car (Univ. College Dublin)

University of Washington Formula SAE ('98, '99, '03, '04)

[jack]

WWU has an old FSAE car with 4 wheel steer (1980's). i guess it worked. they mention it as the first FSAE car with 4 wheel steer in that history of FSAE article on the SAE website. food for thought: for one reason or another, it was the first and last WWU car with 4WS

jack @ WWU
http://www.etec.wwu.edu

[gug]

Uni of Newcastle's 4ws:

http://www.we-todd-did-racing.com/wetoddimage.wtdr/i=wMjE4Njk0NnM0MTNkZmQzMXk1NDE%3D.jpg

thats a steering rack (i assume, couldnt see inside) down low. from what i could see the cable moves that small wheel facing us, then that wheel allows for adjustment in the steering angle.

they also have done 4wd. car didnt get running at the event though. if someone from Newcastle wants to explain exactly how the system works, i would be very interested. it appears to give pure countersteer with about 50% of the angle of the front wheels.

i wouldnt have expected cables to be strong enough to hold the forces though.

oh yeah, there is a great article on the 4ws that a f1 team tried in a racecar engineering mag. i think it must have been about no.1 or 2 in volume 13, i dont have it.

- the problem with the world is stupidity. i'm not saying there should be a capital punishment for stupidity, but why don't we just take the safety lables off of everything and let the problem solve itself?

[This message was edited by gug on December 08, 2003 at 08:09 PM.]

[James Waltman]

Viking 22 had the 4 wheel steering (1992). It was a big car and I think that the team wanted more maneuverability. It was also a spool rear end with monster tires (11+ inches contact patch – 280mm).

These pictures may help show how the system was set up.

The red line is the steering column. Green lines are the cable. Blue circle is the bobbin/spool that the cable wraps around. Orange circles are pulleys that direct the cable out to the sides were it runs in the side pods to the back of the car. The yellow circle at the rear is the pivot point.
http://dot.etec.wwu.edu/fsae/SharedPictures/Viking%2022/Pedal%20view.JPG

http://dot.etec.wwu.edu/fsae/SharedPictures/Viking%2022/Pulley.JPG

http://dot.etec.wwu.edu/fsae/SharedPictures/Viking%2022/Rear.JPG


The rear wheels turn the opposite direction of the fronts. They don't turn as much but I won't guess at the ratio.

The cable was aircraft cable. It is used to control scores of airplanes and the FAA thinks that they are strong enough for that. The front wheels are on the same system and also use cables. I have heard that the judges didn't like the cable steer idea (safety concerns) but I don't know if that would still be true today. I don't think that the "drive by wire"� ban counts this form of wire (cable).

There is a short video here of the rear end steering. (http://dot.etec.wwu.edu/fsae/SharedPictures/Viking%2022/) This is from lock to lock with the steering wheel. The 10"� rims give perspective to the tire width.

James Waltman
http://dot.etec.wwu.edu/fsae/
Vehicle Research Institute at
Western Washington University

[Denny Trimble]

Wow... I've gotta stop by some day and check that out in person http://fsae.com/groupee_common/emoticons/icon_smile.gif

I'm designing a 7-axis cable-driven mechanism for my thesis, maybe I'll pick up some pointers from that design.

University of Washington Formula SAE ('98, '99, '03, '04)

[jack]

for the record, that car was 560lbs... (255kg)

C Z,
another idea, if your looking for more yaw, is "fiddle brakes". they are discussed in Formula One Technology (peter wright). here is a quote:

"McLaren [1997] provides its drivers with a switch to select either rear brake, acording to the direction of the corner, which they were then able to either turn car in under power (by braking the inner wheel) or prevent inner wheel spin when accelerating out of a corner."

i think this is a pretty cool idea--assuming your drivers can drive...i know what your thinking-how could this be legal if the brake pedal had to activate all four wheels? F1 had the same rule. you just need a third brake pedal (assume the clutch is taken care of else where)

i probably should have post this under a different topic, but if you want a car with greater yaw control, i'd pick this over 4WS.

jack @ WWU
http://www.etec.wwu.edu

[All Wheeler]

The little wheel that is cable fed is a cam mechanism which allows full adjustability from -1/3 to + 1 steering ratio. In the rack was a disc with two pushpull rods connecting to a slider block in the aluminium 'rack'. By offsetting the connection points of the push/pull rods, an implied ackerman effect was acieved. We did some slalom testing of the vehicle without driving power, and from what we could tell, the system was an absolute cracker at around 0.3:1 +steering ratio. It was remarkably agile and had a small turning circle for such a monster of a car. The mechanism gave a trailing steering ratio designed to avert king pin offset torque steer at higher steering angles on the drive wheels. The idea behind the cables is to preload them such that they effectively don't see any fluctuating loads. The steering was very heavy whilst trying to steer on the spot, but once moving became significantly lighter. We never managed to test for driving torque steer effects, but with any luck we might have some data soon. What brought the steering unstuck was that the interface between the pushpull rods weren't forked yoke connections, which resulted in the stripping of a thread in the front 'rack'. As a consequence, we had to retro-fit the University of Adelaide's spare steering rack (A smart 4 Hr operation). Thanks to those guys for their help, but unfortunately we suffered other problems that prevented us from competing in the dynamic events

[clausen]

My advice regarding 4ws is to be absolutely sure you understand the problem before you try to solve it.

I'm quite sure that when you do, you'll come to the conclusion that a simple mechanically connected constantly countersteering system will be of no help.

One of the last 6 or 8 racecar engineering mags has a good story about Benetton (i think) 4ws

Regards

Paul Clausen
Uni of Adelaide

[gug]

i think that article was in about #1 or 2 in volume 13 racecar engineering, good reading. thought i had it scanned into my computer somewhere but cant seem to find it.

- the problem with the world is stupidity. i'm not saying there should be a capital punishment for stupidity, but why don't we just take the safety lables off of everything and let the problem solve itself?