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Re: Rear wheel steering

To: Jon Hobden <Jon.Hobden@rdel.co.uk>
Subject: Re: Rear wheel steering
From: john robinson <john@engr.wisc.edu>
Date: Wed, 07 Jun 2000 11:07:32 -0500
Howdy,
          I think the main difference in a Rear Wheel Steer vehicle while 
doing course corrections, is the lack of perceived motion in the desired 
direction; because the rear of the vehicle is going in the opposite 
direction (vehicle tail goes left while the driver wants the direction of 
the vehicle to be going right), which is opposite to the "normal" driving 
feel. The comment of driving to a correction indicator is not bad, a long 
painted line on the hood in conjunction with a pressure probe attached to 
the nose which would effectively lengthen the nose of the vehicle, giving 
the driver a long pointer to view the actual direction of the vehicle, 
especially if the driver is as far back in the vehicle as possible. I 
believe a RWS vehicle comes down to driver adaptability/skill, more than 
the dynamics of FWS vs. RWS..

(the rear wheels skid to the outside of the turn in a "normal" Front Wheel 
Steer) while in a RWS

At 09:55 AM 6/7/00 , you wrote:

>A picture is worth a thousand.......
>
>Having thought about this some more, Jon, you're right about kid's toys and
>what you are brought up on, as I said a few days ago, boats (and for that
>matter most aeroplanes) manage by steering from the wrong end.
>
>The problem with rear steer is that it requires anticipation (and a blind
>faith in the future) on the part of the driver.   Consider a car off the
>desired centre line, within the limitations of the character set (you'll
>need to select a monospaced font for this like Courier or Lucida):
>
>(For the example we'll assume a simple reverse tricycle for the rear steer,
>I can't cope with trying to get offset rears to look right)
>You start a fair way offline, and turn towards the line:
>
>                 |                     |
>                 |                     |
>  +-------+      |       +-------+     |
>  | /   / |      |       | |   | |     |
>  |       |      |       |       |     |
>  |       |      |       |       |     |
>  |       |      |       |       |     |
>  |       |      |       |       |     |
>  |       |      |       |       |     |
>  | |   | |      |       |   \   |     |
>  +-------+      |       +-------+     |
>                 |                     |
>                 |                     |
>
>
>Once heading back towards the line you straighten up
>
>          /           |         /           |
>         / /          |        / /          |
>        /      / /    |       /      / /    |
>       /        /     |      /        /     |
>      /        /      |     /        /      |
>     /        /       |    /        /       |
>    /        /        |   /        /        |
>   /  /     /         |  /    /   /         |
>         / /          |          /          |
>          /           |         /           |
>
>
>This is where it gets to be different.
>With a front steer you basically get to the line and point the wheels down
>it (obviously there's a progression, but you get the idea).
>With rear steer, you need to correct BEFORE you are aligned (like turning
>the back of a boat in against the dock).
>
>             |                         |
>             |                         |
>          /  |                  /      |
>         / |                   / /     |
>        /      | /            /      / /
>       /        /            /        /|
>      /        /            /        / |
>     /        /            /        /  |
>    /        /            /        /   |
>   /  /     /|           /    -   /    |
>         / / |                   /     |
>          /  |                  /      |
>             |                         |
>             |                         |
>(sorry about the "-" for the rear wheel, but there's nothing between that
>and "/" in the character set - I'm sure you get the idea)
>
>
>Once you're back online, everything's hunky dory:
>
>      |                      |
>      |                      |
>  +-------+              +-------+
>  | |   | |              | |   | |
>  |       |              |       |
>  |       |              |       |
>  |       |              |       |
>  |       |              |       |
>  |       |              |       |
>  | |   | |              |   |   |
>  +-------+              +-------+
>      |                      |
>      |                      |
>
>
>Except that you have to effectively anticipate the correction to each minor
>deviation in the same way.   I'm sure you could condition yourself to it,
>but at the end of the day is it worth learning a whole new driving style?
>   It's also worth noting that neither boats or planes are so concerned
>about accurately following a line;  they concern themselves only with the
>next waypoint, so maybe in today's non-SA GPS era the solution is in
>driving to a correction indicator rather than what you see out of the
>window.
>
>It's all very well my saying all this - the likelihood of ever having to
>prove it is zero.   Good luck to any of you guys who have the ability,
>money and commitment to actually try any of this out.
>
>
>Jon Hobden
>Horley, England


              John Robinson, Mechanician
   Mechanical Engineering University of Wisconsin
                 1513 University Ave.
                  Madison, Wi. 53706
                     608-262-3606
                   FAX 608-265-2316
        Current World Land Speed Record Holder
                 Bonneville Salt Flats
            H/GCC 92 cu.in. 1980 Dodge Colt
                   131.333 MPH set 1995
                   136.666 MPH set 1996



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