Crab Walk: Sideways Moving Armored Fighting Vehicles?

shin_getter

shin_getter

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View: https://www.youtube.com/watch?v=A8wW-yF_UvQ


The potential of all-wheel steering to move vehicles diagonally seems like a useful feature. Tight space handling advantages aside, additional advantages includes being able to point the hull armor towards threats regardless of direction of travel and potentially removing the need for a turret. It seems like there hasn't been widespread success for this idea.

Can't find any AFV that explicitly have crab-walk as a feature, closest thing I can find is:
based on chassis described somewhat here:
www.motortrend.com

Four-Wheel-Steer Jeeps

The concept of combining four-wheel steering with four-wheel drive was a favorite idea in the early days of four-wheeling. Some of the more notable four-wheel-s
www.motortrend.com www.motortrend.com

Also:
www.motor1.com

Arquus Scarabee Is A Side-Winding Behemoth Made By Volvo

Volvo Group's Arquus presents its latest defense vehicle, the Scarabee, with a distinct four-wheel steering system.
www.motor1.com www.motor1.com

Still, I'd expect more prototype and experiments over the years, can anyone point me to them?

How bad is the suspension/handling problem for a vehicle moving all directions at speed?
 
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Why do they call it 'crab-walk' when simply 'all-steer' like those ubiquitous heavy-lift flatbed modules ?

Nearest thing I've seen to true crab-walk are a forestry design that could literally tip-toe between trunks, even on hill-side, and a scary surf-zone ROV for obstacle / mine clearance.

Can foresee several of the latter 'crabbing' out of the 3AM waves, nailing a so-bored beach-patrol with a volley of .50 cals prior to SEAL insertion...
 
The mech in question, I presume:

Walking Tractor Timberjack by John Deere - The Old Robot's Web Site

Walking Tractor designed by John Deere subsidiary Plustech in Finland. John Deere prototype walking tractor, loggers and canal dredgers have walking equiptment too. This is a fantastic piece of equipment that can go up and down rough mountain terrain in snow and mud. It is a great practical...
www.theoldrobots.com

https://bot-spotting.tumblr.com%2Fpost%2F164333318170
View: https://bot-spotting.tumblr.com/post/164333318170/john-deere-walking-harvester-walking-tractor
 
When I was in the Australian Army I used to drive a rough-terrain Forklift which had four wheel steering. One of the tricks I learnt was to steer the rear wheels one way and then steer the front wheels the same way so I could manoeuvre sideways alongside a truck to bring the pallet I was loading in line with the other ones onboard.
 
I seem to recall a Honda car from the 90s that had four-wheel steering. My Citroën ZX (and I think my Saab 9-3) had some form of 'passive' rear steering. Or am I thinking of something else or been listening to salesman's 'balleaux'.

Chris
 
You're remembering correctly Chris, Honda had active 4WS in the 1990s, on a few cars. It's been used occasionally since then on high-performance vehicles to increase cornering ability. Passive rear steering had a rear wheel geometry that would deform under cornering loads to give a small steering angle.
 
Tatra has trucks that can do crab steering:
View: https://www.youtube.com/watch?v=u1CctCBTj48


The Oerlikon GDF-D03 concept from the 1980s had it:

gdf-do3-image02-s.jpg
 
There was a mid-sized production car of that era, I cannot remember model, that would have suffered from an 'unfortunate' turning circle due to too-narrow front wheel arches due to transverse front engine being a tad too big. So, steering being power-assisted anyway, the rear wheels got a bit of 'turn'. Not a lot, certainly not 'crabbing', just optional semi-taxi-turn. IIRC, it was reduced / inhibited at speed unless, 'in extremis', you stamped brakes hard enough to invoke their 'anti-lock' facility.

The enhanced ability to weave around obstacles was offset by loss of trunk / tail-gate width, the 'mechanicals' weight and the additional plumbing. As I remember it, drivers either loved or hated it. Didn't catch on, partly because transverse engines became even more compact, the need for a work-around lost...

I only remember its existence because I wrote it into 'Weekend', short story about an anniversary that turned 'Grimdark Gothic'...

The hotel lights seemed a mirage, there and gone again. Dave wearily coaxed their car through the storm-lashed head-land lane.

"Nearly there, Mary," he muttered. "Somewhere along--"

A huge truck surged out of the night. Dave stamped and swung. ABS, ETC, 4-drive and power-steer clawed them up the soft verge to safety. The truck swept by. Its wake soused their windows. Its driver hooted derision. Its single side-light flickered into the dark.

"Nearly," Dave sighed, easing their car from muddy ruts. He signalled for the hotel's gates, now barely yards away. They halted under the narrow canopy. Dave shook his head. "Mary, that was the worst drive since..."

Mary let a hint of sadness show. She knew. That other night had scarred them: The frantic dash to the District Hospital's A&E when their called Ambulance ditched, the night of screams, the futile tears, the crushing sorrow. Dave's quiet, brave, weary, 'We can try again', had gone on hold too long.
 
CJGibson said:
I seem to recall a Honda car from the 90s that had four-wheel steering. My Citroën ZX (and I think my Saab 9-3) had some form of 'passive' rear steering. Or am I thinking of something else or been listening to salesman's 'balleaux'.

Chris
Click to expand...
Yes, the Prelude 4ws had it.
I tested it. It was horribly counterintuitive because at low angle all 4 wheels would go in the same direction (supposed to make highway lane-changing smoother), and then at greater angle the rear wheels would turn the other side to make the turning radius smaller (for tight-manôeuvering when parking, for ex). It worked decently well in each case if taken separately, but if you were not careful the transition from one mode to the other could really get hairy and send you where your never planned to go.

Would have needed an autopilot, it was too unexpectable for most normal humans.
 
dan_inbox said:
CJGibson said:
I seem to recall a Honda car from the 90s that had four-wheel steering. My Citroën ZX (and I think my Saab 9-3) had some form of 'passive' rear steering. Or am I thinking of something else or been listening to salesman's 'balleaux'.

Chris
Click to expand...
Yes, the Prelude 4ws had it.
I tested it. It was horribly counterintuitive because at low angle all 4 wheels would go in the same direction (supposed to make highway lane-changing smoother), and then at greater angle the rear wheels would turn the other side to make the turning radius smaller (for tight-manôeuvering when parking, for ex). It worked decently well in each case if taken separately, but if you were not careful the transition from one mode to the other could really get hairy and send you where your never planned to go.

Would have needed an autopilot, it was too unexpectable for most normal humans.
Click to expand...

Yikes. Seems like the logical solution would have been to have a neutral speed band between about 15 and 40 mph where it didn't do anything at all.
 
Yikes. Seems like the logical solution would have been to have a neutral speed band between about 15 and 40 mph where it didn't do anything at all.

A number of cars have 4ws now. The current solution is to have rear wheels turn counter (but at a lesser angle) to the front at low speeds to reduce the turning circle and at high speeds to have them turn with (also at a lesser angle) the front wheels, giving the effect of a longer wheelbase and enhancing stability.

I think Musk might have said something about a crabwise mode for the Cybertruck?

www.hagerty.com

New Bentley Continental GT Speed is built for bends - Hagerty Media

Rapid Bentleys have always lived up to their names when it comes to straight-line performance, but the new Continental GT Speed is crafted for corners.
www.hagerty.com www.hagerty.com
 
Crab walk is a specific steering mode, with all wheels in the same direction so you can translate laterally. The other mode is regular countersteering to reduce the turning circle.

SPMTs have one more mode, because each axle is on a turret that can rotate 360º: they can drive in a circle, centered on any point:

View: https://www.youtube.com/watch?v=EFu45SVSYdc
 

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