self steering trailer

Saw this one in NZ, and like the lads in the photo, I could not figure how it worked.
www.flickr.com/photos/46046969@N03/5117374314/in/photostream/
Anyone out there familiar with them ?

AtkiPete
GuddayM8

Gr8 Pix
Keep m Cummin

Bit hard to say Lookn @ the pic
But a Wild Ass Guess

<1> the rear steer is Hyd controlled by remote wirless doodadd
<2> the lead axle on RSend is on caster steering like front axle of truck, n if set up right will follow the truck in a reaction slightly slower than the truck
but haven said th@ it could wander on the rd if U hit a pot hole or bad camber on rd
<3> Linkage from the kingpin area to the RSend when turning can B effective , But me no C any linkage in pix

Also
Ifn I'm alowd an Also
the rear 5th wheel may have 2 B locked to reverse the beast

Az Alwayz
EyeDoSt&2BCorrected

Jist Ask WHV
He'd kno or find out 4 U

Cya
[ch9787]

We had a couple of these at a refrigerated haulage company I worked for in the mid '70's,they were the latest thing.They were near max length (60ft back then),and pulled by a cab over Kenworth with a lazy axle fitted,the Cummins uprated to 330hp with a turbo...big power back then.I think they were just caster selfsteering,didn't seem to be anything fancy back there.Scary to drive (I only drove one in the yard) - looking in the mirror it looked like you'd lost the trailer coming out of a turn,as it swung so wide.You don't see them anymore - I think they were banned as they really get out of shape in a jack-knife,taking up the whole road.I don't remember anything technical as I was just a young fella,and they were just trucks I worked on.

I dint see no linkage, hydraulics or wireless do dad, so I think it all just castors. Saw it going forward and it followed the truck nicely but reverse would be something else.

atkipete - These things were popular on logging trailers, as I understand, but went out of favour, because of stability and tracking problems when worn.

The 3 axles are mounted on a separate chassis, like a dolly, with a turntable. There are rods and linkages connecting the leading axle and the turntable.
This setup turns the front axle, when the truck rounds a curve, allowing the trailer to swing wide and follow the truck. I can't find a diagram or details of the actual setup .. maybe VicHung can help out here.

One track is quite right in his description as to how they work.
I used to tow a spread 3 axle dog with the same setup back in the 70s in NZ for trailways transport. That trailer was absolutely brilliant to tow in tight winding roads and would actually track wider than the truck on tight bends. The only real failing with it was the tare weight, just too heavy.

If I remember correctly, didn't some of the oil companies try them out some years ago around Melbourne. I'm certain I saw them getting around with the last axle on the tri steering around corners and as I recall they used a caster type steering arrangement.

Sorry for the late reply, but I've just got back from a 4-day trip so haven't seen the internet for a while. I'm afraid that I'm not going to be much help anyway although I have driven such things many years ago.

We had a couple of similar type self-steering arrangements on a couple of semi-trailers, which only appeared to be connected to the chassis by a turntable (fifth wheel); they had no rods or linkages to keep the wheels in line and I don't really know how they worked. They used to track pretty well, in fact they were inclined to swing wide on the corners rather than cutting in. There were quite a few different systems but our ones just had an air-operated locking pin in the turntable for reversing. If I manage to find out anything more I'll post it up.

Could this be an explanation?

"Pivotal bogie systems have been used for some time in the heavy haulage industry as a means of steering
extremely long semi-trailers. It is only recently however that this principle has been applied to normal length
semi-trailers.
In a pivotal bogie system a ballrace-mounted tri-axle bogie assembly replaces the fixed-axle trailer group. The
ballrace allows this assembly to yaw freely relative to the trailer chassis. The bogie consists of a fixed front axle
and two steered rear axles, which steer in relation to the angle between the bogie and the trailer chassis. Thus the
axles progressively steer as the angle between the bogie and the trailer increases, bringing the bogie back inline
with the trailer chassis."

From this presentation to the 7th International Symposium on Heavy Vehicle Weights & Dimensions in 2002:

www.cvdc.org/recent_papers/JujnovichCebon_7ISHVWD.pdf

If the two front axles of the tri were fixed and the rear axle castoring I could almost get my head around it. But the front axle is on a turntable, then the whole tri axle group is on another turntable.