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Four-wheel maneuverability (Read 1170 times)
Apr 29th, 2009 at 11:53am

chornedsnorkack   Offline
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Cars usually have wheels that can roll forward or back, and turn only a limited angle from there. They are controlled by steering wheel for turning and by gear lever for reversing.

What kind of compromises in steering and transmission might make a four-wheeled contraption capable of being driven directly crabwise? And what input devices could a driver use to drive such a car?
 
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Reply #1 - Apr 29th, 2009 at 1:44pm

ShaneG   Offline
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If I'm not mistaken,(which I may be), I think the Early Mitsubishi 3000gt vr4's used a four wheel steering for higher performace driving as an assist because it was such a heavy pig.

Also, I think a few Skylines have had a similar feature.

But the point is, at some point during a highspeed turn, the car would indeed be driving in a 'crablike' manner.
 
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Reply #2 - Apr 30th, 2009 at 9:48am

beaky   Offline
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IMHO, only thing that would really be good for is parking. Grin  You could vastly reduce the turn radius, but how fast could one really take a corner with a car like that?
 

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Reply #3 - May 1st, 2009 at 3:14pm

chornedsnorkack   Offline
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beaky wrote on Apr 30th, 2009 at 9:48am:
IMHO, only thing that would really be good for is parking. Grin  You could vastly reduce the turn radius,

Precisely.
beaky wrote on Apr 30th, 2009 at 9:48am:
but how fast could one really take a corner with a car like that?


Trying to take fast corners would mean high accelerations anyway.
 
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Reply #4 - May 1st, 2009 at 3:31pm

scalper_old   Offline
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beaky wrote on Apr 30th, 2009 at 9:48am:
IMHO, only thing that would really be good for is parking. Grin  You could vastly reduce the turn radius, but how fast could one really take a corner with a car like that?


You are on the button. I had a 93 nissan 240 with the Hicus steering. = 4 wheel steering. parking was just a pure joy. the trying to park a honda accord the same way forget about it.

I miss me old yellow and black roof 240
 
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Reply #5 - May 13th, 2009 at 3:01am
U4EA   Ex Member

 
I wish I had a dollar for everytime I got caught "high-speed" crabbing around the bomb dump in a Coleman Tug! Grin

The Colemans were able to do a 180 within their own length. Cheesy

A time or two a month there'd come a call over the radio from the head-shed tower,  "Echo 10!  Your shop chief would like to speak to you in his office." Shocked

 
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Reply #6 - May 14th, 2009 at 4:55am

chornedsnorkack   Offline
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U4EA wrote on May 13th, 2009 at 3:01am:
I wish I had a dollar for everytime I got caught "high-speed" crabbing around the bomb dump in a Coleman Tug! Grin

The Colemans were able to do a 180 within their own length. Cheesy


Does it have rounded front and back end then?
 
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Reply #7 - May 15th, 2009 at 2:42am
U4EA   Ex Member

 
Nope!  Just 4-wheel steering!

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Coleman Tug, a.k.a Aircraft Tow Tractor.  100,000lb tow capacity.  When I was in the USAF we used them for towing munitions trailers.  They were painted a decorative OD.
 
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Reply #8 - May 15th, 2009 at 4:11am

chornedsnorkack   Offline
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U4EA wrote on May 15th, 2009 at 2:42am:
Nope!  Just 4-wheel steering!

[img]

But then its diagonal is longer than its length. How can it possibly turn around in its length?
 
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Reply #9 - May 16th, 2009 at 12:17am
U4EA   Ex Member

 
Uhhhhhhh, could be cause its turn radius, when both the front and rear steer is at full limit, is a foot or so shy of it's length.

Full steer puts the tires at about a 60 angle from centered.....when the fronts are one way and the rears are another, the tug will crab just a tad shy of dead-a$$ sideways!

I'm no geometry expert so I can't logically discuss the specifics.  All I can say is we never actually got out a tape measure and chalkline.....but I almost squished my boss one time by quick-turnin' as he stood next to the driver side door....with the rear bumper!
 
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Reply #10 - May 20th, 2009 at 3:35am

chornedsnorkack   Offline
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On usual cars, turning steering wheel turns both axles, right?

How are the two axles separately controlled on a Coleman tug?
 
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Reply #11 - May 20th, 2009 at 4:39am

expat   Offline
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chornedsnorkack wrote on May 20th, 2009 at 3:35am:
On usual cars, turning steering wheel turns both axles, right?

How are the two axles separately controlled on a Coleman tug?


Same as any tug, Coleman, Schopff, Fresia, clever hydraulics and a computer or two if it is not older than 10 years or so.

Matt
 

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Reply #12 - May 21st, 2009 at 4:41am

chornedsnorkack   Offline
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expat wrote on May 20th, 2009 at 4:39am:
chornedsnorkack wrote on May 20th, 2009 at 3:35am:
On usual cars, turning steering wheel turns both axles, right?

How are the two axles separately controlled on a Coleman tug?


Same as any tug, Coleman, Schopff, Fresia, clever hydraulics and a computer or two if it is not older than 10 years or so.

Matt

I have only seen outside pictures of Coleman tugs. What is the inside like, what kind of driver controls allow 4 wheel steering to be separately controlled?
 
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Reply #13 - May 21st, 2009 at 4:48am

expat   Offline
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chornedsnorkack wrote on May 21st, 2009 at 4:41am:
expat wrote on May 20th, 2009 at 4:39am:
chornedsnorkack wrote on May 20th, 2009 at 3:35am:
On usual cars, turning steering wheel turns both axles, right?

How are the two axles separately controlled on a Coleman tug?


Same as any tug, Coleman, Schopff, Fresia, clever hydraulics and a computer or two if it is not older than 10 years or so.

Matt

I have only seen outside pictures of Coleman tugs. What is the inside like, what kind of driver controls allow 4 wheel steering to be separately controlled?


In all the tugs I have driven, it is push button control. And not quite sure what you mean by separately controlled? The options are generally, forward wheel steering, rear wheel steering, four wheel steering and the ability to crab, i.e all wheels pointing in the same direction, so you can go forward/backwards diagonally.

Matt
 

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Reply #14 - May 22nd, 2009 at 3:16am

chornedsnorkack   Offline
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expat wrote on May 21st, 2009 at 4:48am:
chornedsnorkack wrote on May 21st, 2009 at 4:41am:
expat wrote on May 20th, 2009 at 4:39am:
chornedsnorkack wrote on May 20th, 2009 at 3:35am:
On usual cars, turning steering wheel turns both axles, right?

How are the two axles separately controlled on a Coleman tug?


Same as any tug, Coleman, Schopff, Fresia, clever hydraulics and a computer or two if it is not older than 10 years or so.

Matt

I have only seen outside pictures of Coleman tugs. What is the inside like, what kind of driver controls allow 4 wheel steering to be separately controlled?


In all the tugs I have driven, it is push button control. And not quite sure what you mean by separately controlled? The options are generally, forward wheel steering, rear wheel steering, four wheel steering and the ability to crab, i.e all wheels pointing in the same direction, so you can go forward/backwards diagonally.


I mean, a steering wheel is a continuous input control. You could turn your front wheels 60 degrees from centered, or 30 degrees, or 53 degrees - and angle.

But I understand then that there is no separate continuous input control? You cannot turn your front wheels 50 degrees to the right and rear wheels 23 degrees to the right - you only have 3 options by push button, namely 50 degrees to the right if crabbing, 50 degrees to the left if 4 wheel steering, or 0 degrees if front wheel steering.

Correct?
 
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