Thanks for the welcome, sorry if this reply is too long, but here goes;.
The Multidrive ejector truck grew out of a number of different requirements. If I recall correctly, David J Brown designed (perhaps before his Multidrive days) huge off-road land trains for a sugar cane operation in Africa. These had to cope with soggy ground conditions, carry a large volume of material, but still remain reasonably maneuverable; hence the development of a self-steering rear bogie wheels. I'm trying to rack my brains to remember how this worked, the best I can do is as follows;
There was a telescoping articulated bar that connected the rear bogie to the truck tractor unit (the trailer was mounted to the tractor by a conventional 5th wheel). As the tractor unit turned to the left, this would force the rear bogie to steer right. Or to put it another way, as the tractor unit turned to the left, the upperstructure of the trailer followed it, leaving the bogie wheels pointing straight ahead in the original line. As the tractor unit straightened-up this would force the bogie back in line. I appreciate that this all sounds a little child-like, and my explanation is inadequate in this forum, but it worked in practice. One unforeseen consequence of the design was that it was very difficult to jack-knife the combination.
I'm not sure if the sugar-cane trailers were powered, but before the next reincarnation of the design, the rear four wheels on the bogie were driven by an articulated drive shaft (driven by the tractor unit) running the length of the trailer, just below the steering bar.
Then the UK Army came along with an urgent operational requirement for Eastern Europe (some place like Bosnia I think). Many would say that the UK MoD didn't really want to deal with Mr Brown, after his days at Bedford/AWD. Apparently, he went a little over the top with his criticisms of the UK Government, after they took the military contract away from Bedford and essentially sounded the beginnings of the end of the British heavy truck industry (more about this latter).
Anyway, by this time he had made another fortune by selling his ADT factory and designs to Caterpillar. Incidentally, he held a position within Caterpillar's global design committee for many years and at one point Cat was sniffing around his ejector-truck design. However, his critics suggested that Multidrive was, in effect, the world's biggest garden shed for a retired vehicle designer.
But, getting back on track, despite the UK MoDs reluctance to deal with a past critic, Multidrive could solve an urgent problem for them; the bulk transport of fuel and water across high mountains in the snow. The army's fleet of (cold war) bulk tankers were basically built around road-going trailers, and couldn't hack the terrain.
Multidrive's driven, self-steering trailer was hooked-up to the Army's existing truck tractor units, a military-spec tanker body fitted and within a short period of time a small fleet was on front-line duties. The vehicles worked reasonably well, but tended not to be that solider-proof, and were only ever designed as a short-term measure to meet an urgent operational requirement. The follow-on contract matched the trailers to a more suitable tractor unit and the contract included training military drivers at Multidrive's Thirsk HQ. DJB owned a couple of thousand acres of moorland nearby, which was handy for that realistic off-road experience.
By now you must be wondering what has this all got to do with his ejector truck? UK MoD procurement has got a dreadful reputation for trying to fight the last war, not equip for future battles. One contract that was still being banded about was airfield damage repair vehicles. During the Cold War, millions were spent of a fleet of construction equipment to get the runways at RAF bases in the UK and Germany up and running in a matter of hours after being bombed. Although many had very little hours on the clock, the fleet was old and replacements were sought.
One requirement was for a 30+ tonne dump truck, but there was an usual proviso; it had to be able to be transportable by air. The military wanted fewer vehicles to do the same job, so it would be handy if such a truck could also spread a load, not simply dump it in a pile for a dozer and another driver to level out. Anyway, Multidrive designed their own tractor unit for this application, which ended-up with a 450hp Cat C15 engine, driving a fully automatic Allison 6-speed transmission, mated to a 2-speed drop box.
An ejector body was the way forward, but the designs of the time had a serious flaw for this application; they were far too heavy. The theory was that an ejector version of an ADT body had to withstand high bulging forces, as the heavy duty hydraulics forced the headboard to force the load out of the back. All this extra steel and larger hydraulics just added weight.
Multidrive's design was to shift the load by a heavy duty conveyor belt. A small hydraulic motor at the rear of the body spooled-in the belt, moving the load rearwards and out without any bulging forces, therefore the body could be made lighter. The Headboard plays no part in the ejection process, apart from being pulled along by the end of the belt, to clean the sides of the body. There was very little carry-back. Of course, there was nothing to stop this ejection being carried out as the vehicle was moving, hence spreading the load. A lightweight body and a huge engine delivered wonderful fuel economy and performance.
The MoD contract came to nothing (it was realised that there was no longer a requirement), but what DJB had designed was a true alternative to conventional ADTs (who many people say he had invented in the first place). Of course it had a problem in the really awful conditions that conventional ADTs can operate in, but for a lot of applications this is not necessary and (unloaded) it could easily reach 50mph on the road (as I found out once along the A19).
A few were sold around the world, the South African's use them to spread coal (the above images taken at a Kier site in Scotland), and there was even a high-sided version working in a waste application in the UK. However, the loss of a substantial contract to re-equip the UK Army with trucks knocked the stuffing out of Multidrive. The plan was to open a production line at a well-known light van manufacturer's existing premises and restart manufacturing heavy trucks in volume in the UK. Mr David J Brown unfortunately died shortly afterwards.
There is very little of this stuff in the public domain, so I though that I would share an historic photograph with this forum. The last project that Mr David J Brown worked on was a range of armoured truck/transporters that could tackle some serious terrain, even fully loaded. Of course, at the time (2004), the UK MoD couldn't foresee a time when such a vehicle may come in useful....
Now, did someone ask about Multidrive agricultural tractors...?
multidrive.JPG
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