Official Baja SAE Forums Homepage
Forum Home Forum Home > General > Design Discussion
  New Posts New Posts RSS Feed - 4 Wheel Steering
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

4 Wheel Steering

 Post Reply Post Reply
Author
Message
Birdman View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Sep/14/2009
Location: Fargo, ND
Status: Offline
Points: 10
Post Options Post Options   Thanks (0) Thanks(0)   Quote Birdman Quote  Post ReplyReply Direct Link To This Post Topic: 4 Wheel Steering
    Posted: Jun/17/2010 at 12:18pm
Would teams that have done 4 wheel steering in their cars be willing to share any tips or advice?  We are considering 4 wheel steer for next year, especially if the course is anything like the Western Washington course this year.
Lee- NDSU Mini Baja
Back to Top
GT Steve View Drop Down
Milling Master
Milling Master


Joined: Apr/02/2009
Location: NN, VA
Status: Offline
Points: 69
Post Options Post Options   Thanks (0) Thanks(0)   Quote GT Steve Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 9:24am
We (Georgia Tech) experimented with 4 wheel steer for a number of years, first with an active (hydraulic) system that was slaved off the front end, and then with passive (roll-induced) and found the active to be too much extra complexity to really be worth the hassle, however the passive rear-steer was useful, but is really only works at relativly high speed with a fair amount of body roll.
 
I know Auburn has also incorporated a passive rear-steer for a number of years, I don't know if the still do.
 
Cornell university also built and ran a working hydraulic rear-steer system in 2009, which was part of what earned them a design win at Auburn (not just for the flashy carbon drive shafts).
 
I don't know that the extra complexity and weight is worthwhile for a typical Baja competition.  It would pay off in the rock crawl, but isn't worth the weight in any endurance course i've ever seen.
 
Anyone old enough to remember the "monster truck" from SD back in 2007 knows that a car can be built to dominate one event (the rock crawl, which it did dominate), but it was not competitive in the endurance race or other events.
GT Off-Road Alumni
Georgia Tech ME'07

Bigger Hammer Engineering
Back to Top
ehunt View Drop Down
Milling Master
Milling Master
Avatar

Joined: Nov/17/2008
Location: Cornell
Status: Offline
Points: 54
Post Options Post Options   Thanks (0) Thanks(0)   Quote ehunt Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 10:50pm
We ran 4 different iterations of rear steer, 2 passive and 2 active. The 2009 active rear steer we ran definitely helped the cars maneuverability, though eventually this year we decided the complexity wasn't worth it. Also the packaging of the new vehicle didn't leave room for the the cylinders. The active systems generally proved better than passive systems. Since the passive systems are basically bump steer in the rear different rides heights played havoc with toe.

So this year we abandoned rear steer in the name of durability and we were pretty happy with that choice getting second in endurance in Carolina and 5th in endurance in Rochester. The extra design points are nice but not nearly as nice as the 400 points you can have in the endurance race.  As for the maneuverability of the 2010 car we changed some suspension designs and that seemed to do the trick. One such thing is rear track, the South Dakota car has run an active rear steer with a steering rack for many years, but they also run a rear track that is as far as I can tell identical to their front track, not the same for our car.

Conclusion: rear steer is a neat and most of the time helps out, though with a better suspension design we've felt that it doesn't warrant the extra complexity.

Eric Hunt
Cornell Baja
08-09 Team Captain


Its not your aptitude but you attitude that determines your altitude.
Back to Top
Red_Beard View Drop Down
Organizer
Organizer


Joined: May/14/2009
Location: Bellingham, WA
Status: Offline
Points: 269
Post Options Post Options   Thanks (0) Thanks(0)   Quote Red_Beard Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2010 at 2:49pm
Originally posted by ehunt ehunt wrote:



Conclusion: rear steer is a neat and most of the time helps out, though with a better suspension design we've felt that it doesn't warrant the extra complexity. 


Works well for us... We haven't designed a 2-wheel steer car in over 5 years now.
SDSM&T 09-10 Team Lead
2nd & 9th Baja West

Project Engineer
Matrix Service - Bellingham, WA
Back to Top
Birdman View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Sep/14/2009
Location: Fargo, ND
Status: Offline
Points: 10
Post Options Post Options   Thanks (0) Thanks(0)   Quote Birdman Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2010 at 1:06pm
Are you able to lock the rear steer out for the endurance race, or is it always active?  Also, what kind of ratio between front and rear steer do you typically run?

Edited by Birdman - Jun/21/2010 at 1:09pm
Lee- NDSU Mini Baja
Back to Top
ehunt View Drop Down
Milling Master
Milling Master
Avatar

Joined: Nov/17/2008
Location: Cornell
Status: Offline
Points: 54
Post Options Post Options   Thanks (0) Thanks(0)   Quote ehunt Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2010 at 3:41pm
we could lock ours out, just had some static tabs that we could switch the tie rods into
Eric Hunt
Cornell Baja
08-09 Team Captain


Its not your aptitude but you attitude that determines your altitude.
Back to Top
SDTech View Drop Down
Milling Master
Milling Master
Avatar

Joined: May/13/2009
Location: Rapid City, SD
Status: Offline
Points: 68
Post Options Post Options   Thanks (0) Thanks(0)   Quote SDTech Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2010 at 7:08pm
Originally posted by Birdman Birdman wrote:

Are you able to lock the rear steer out for the endurance race, or is it always active?  Also, what kind of ratio between front and rear steer do you typically run?


No, we don't lock it out for endurance.  As far as the ratio, that's a well kept trade secret...we've spent quite a few years finding one that worked well at low and high speeds...
SDSMT Baja SAE
Car #'s 4 & 6 - Oregon
Car # 14 - Wisconsin

#4 & #79 - Western Washington

2010-2011 SDSM&T Team Lead
Back to Top
kruegdr View Drop Down
Milling Master
Milling Master

Train Master

Joined: Oct/22/2008
Location: Lawrence, KS
Status: Offline
Points: 52
Post Options Post Options   Thanks (0) Thanks(0)   Quote kruegdr Quote  Post ReplyReply Direct Link To This Post Posted: Jun/24/2010 at 1:33pm
The 2005 AU rear steer was passive, and had different mounting points for "land maneuverability mode" and "endurance mode". It was quite successful, and the only weight penalty was a few ounces for the second mounts. Granted, a system like this must be paired with a well-tuned sway bar, but even without rear-steer, a sway bar significantly helps maneuverability.
"Where all them baja cars at??"
Back to Top
ffriolet View Drop Down
Bolt Sorter
Bolt Sorter


Joined: Feb/20/2010
Location: Qu├ębec
Status: Offline
Points: 37
Post Options Post Options   Thanks (0) Thanks(0)   Quote ffriolet Quote  Post ReplyReply Direct Link To This Post Posted: Jun/24/2010 at 2:40pm
Originally posted by kruegdr kruegdr wrote:

The 2005 AU rear steer was passive, and had different mounting points for "land maneuverability mode" and "endurance mode". It was quite successful, and the only weight penalty was a few ounces for the second mounts. Granted, a system like this must be paired with a well-tuned sway bar, but even without rear-steer, a sway bar significantly helps manoeuvrability.


I wouldn't say that a swaybar will help significantly in manoeuvrability. It may help if your car suspension is not design properly to run without one. We and Laval didn't use saybar and have quite good result in manoeuvrability on all three competition.
Back to Top
Red_Beard View Drop Down
Organizer
Organizer


Joined: May/14/2009
Location: Bellingham, WA
Status: Offline
Points: 269
Post Options Post Options   Thanks (0) Thanks(0)   Quote Red_Beard Quote  Post ReplyReply Direct Link To This Post Posted: Jun/25/2010 at 10:36am
Originally posted by kruegdr kruegdr wrote:

The 2005 AU rear steer was passive, and had different mounting points for "land maneuverability mode" and "endurance mode". It was quite successful, and the only weight penalty was a few ounces for the second mounts. Granted, a system like this must be paired with a well-tuned sway bar, but even without rear-steer, a sway bar significantly helps maneuverability.

We have never used a sway bar.
SDSM&T 09-10 Team Lead
2nd & 9th Baja West

Project Engineer
Matrix Service - Bellingham, WA
Back to Top
kenneth.mandeville View Drop Down
Welding Master
Welding Master
Avatar

Joined: Apr/24/2009
Location: Raleigh, NC
Status: Offline
Points: 98
Post Options Post Options   Thanks (0) Thanks(0)   Quote kenneth.mandeville Quote  Post ReplyReply Direct Link To This Post Posted: Jun/25/2010 at 11:03am
Quote I wouldn't say that a swaybar will help significantly in manoeuvrability. It may help if your car suspension is not design properly to run without one. We and Laval didn't use saybar and have quite good result in manoeuvrability on all three competition.


If your roll stiffness is good rear to front then you probably won't need a sway bar, this is usually from a good roll axis and ride frequencies.  But it is very easy to throw a sway bar (especially for trailing arms) on to do that.

We have never done a 4 wheel steer car but the only thing I would think of is that the center of rotation for a turn will change, and this will depend on your ratios.  So there will be a different akerman angle in the front compared to a front steer car.


Edited by kenneth.mandeville - Jun/25/2010 at 11:04am
Back to Top
kruegdr View Drop Down
Milling Master
Milling Master

Train Master

Joined: Oct/22/2008
Location: Lawrence, KS
Status: Offline
Points: 52
Post Options Post Options   Thanks (0) Thanks(0)   Quote kruegdr Quote  Post ReplyReply Direct Link To This Post Posted: Jun/25/2010 at 11:18am
You're right, but there's always compromises, and there's several ways to achieve a well-behaved suspension. A swaybar can be a "patch fix" after the fact, or it can be designed into the suspension from the beginning. Our choice was to have an integrated swaybar in our suspension so that other suspension goals could be met. That car took 1st, 2nd, and 6th in land maneuverability for its competition year.
 
"Where all them baja cars at??"
Back to Top
Waffles View Drop Down
Welding Master
Welding Master
Avatar

Joined: Jun/02/2009
Status: Offline
Points: 110
Post Options Post Options   Thanks (0) Thanks(0)   Quote Waffles Quote  Post ReplyReply Direct Link To This Post Posted: Jun/25/2010 at 11:26am
Sway bars add an independent degree of freedom to suspension design.  It allows you to adjust roll stiffness independent of pitch (or jumping) stiffness.  At some point you may not be able to get the setup right because your traditional shocks couple pitch and roll stiffness.  If you ran a front to rear "sway bar" you could further decouple pitch stiffness.
Back to Top
Birdman View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Sep/14/2009
Location: Fargo, ND
Status: Offline
Points: 10
Post Options Post Options   Thanks (0) Thanks(0)   Quote Birdman Quote  Post ReplyReply Direct Link To This Post Posted: Jun/25/2010 at 1:05pm
Those of you who have designed 4-wheel steer systems, what resources did you use?
Lee- NDSU Mini Baja
Back to Top
Unproductive View Drop Down
Milling Master
Milling Master
Avatar

Joined: Jul/11/2009
Location: Rochester NY
Status: Offline
Points: 66
Post Options Post Options   Thanks (0) Thanks(0)   Quote Unproductive Quote  Post ReplyReply Direct Link To This Post Posted: Jun/25/2010 at 6:21pm
Originally posted by Waffles Waffles wrote:

Sway bars add an independent degree of freedom to suspension design.  It allows you to adjust roll stiffness independent of pitch (or jumping) stiffness.  At some point you may not be able to get the setup right because your traditional shocks couple pitch and roll stiffness.  If you ran a front to rear "sway bar" you could further decouple pitch stiffness.


Google "UWA kinetic suspension", some interesting stuff if you dig deep enough.
-Bob
Back to Top
abhishek View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jul/29/2012
Location: india
Status: Offline
Points: 2
Post Options Post Options   Thanks (0) Thanks(0)   Quote abhishek Quote  Post ReplyReply Direct Link To This Post Posted: Jul/29/2012 at 12:20pm
Hello,our college team has entered into SAEINDIA BAJA this year, and we are plaaning to have a four wheel steering in our vehicle.

so could anyone please specify how much rear wheel steer angle we have to take for 36 degree front  wheel  steer angle. (we have decide  a 36 degree front wheel steering, but still advices are welcomed :) )

please reply.


thanks in advance
Back to Top
Soccerdan7 View Drop Down
Organizer
Organizer
Avatar

Joined: Sep/22/2010
Location: CA
Status: Offline
Points: 780
Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/29/2012 at 2:47pm
That depends on what you want out of the 4 wheel steering and how you plan to package it. Our 2008 and 2009 cars had around 8 degrees of rear steering which seemed pretty nice and was easily packaged with our old dual a arm rear suspension, but we had more front steering angle and massive camber gain in steer. More angle would actually slow you down considerably in endurance but is nice for maneuverability, so adjustable would be ideal. If you have a 3 link or trailing link rear suspension, you have much more packaging constraints, so it is difficult to get more than 5 degrees.
Danny

Cornell

(fall'07 - spring'12)
Former Captain / MEng / that guy with all the carbon
10 races, 7 top ten's, 2 overall wins
Back to Top
nihal View Drop Down
Bolt Sorter
Bolt Sorter


Joined: Jun/09/2012
Location: patna
Status: Offline
Points: 16
Post Options Post Options   Thanks (0) Thanks(0)   Quote nihal Quote  Post ReplyReply Direct Link To This Post Posted: May/23/2013 at 10:30am
hey danny
We are planning to install 4ws in our car.
But we are not quiet sure about caster trail, scrub radius caster and kingpin angle for the rear wheel as we have no experience with 4ws. 

Can u refer me some specific link or book to go through. I will be great if you provide some help to us
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.062 seconds.