This tractor/trailer combination, released in 1993, was one of the physically largest Technic sets to date. It is effectively 3 sets in one box. Individually, none of the models would stand out from the pack. Taken as a whole, however, they make a rather unique addition to the Technic line. This method of combining multiple models in one was much more common in the Model Team theme.
The tractor features rack and pinion steering, a locking 5th wheel coupling, and even has proper dual rear tires! The trailer features locking landing gear and a worm driven loading ramp. The forklift could have easily been a set in its own right and features rear steering, fork lifting, and fork tilting.
With 18 wheels, this set forges new territory in Technic. It also contains a pair of the rubber bumpers used as fuel tanks and a whole lot of red beams.
The tractor is a single rear axle unit with dual wheels and tires. It's a bit boxy but does a great job of integrating with the set of while using minimal parts.
The front wheels can be steered using an overhead "hand of god" control. The overhead control drives an axle connected to a pair of 14 tooth bevel gears. The second axle drives a flexible rack via an 8 tooth pinion gear. The steering mechanism itself uses the steering arms and toothed links as shown in the computer image.
Note that, in this case, the steering arms actually point forward instead of back. This works OK with these control arms because there is no caster (the wheel axle is centered under the rotation point). If there were caster, this would be an unstable arrangement since the reverse caster will cause the wheels to diverge from center when moving forward rather than return.
The 5th wheel coupler works very much like a real tractor. The coupling hitch on the trailer slides in between the side rails as the tractor backs up to it. After the pin contacts the forward stop, the unit is locked.
This coupler is locked via a crank on the left side. The pole reverser handle turns an axle attached to a pair of crankshaft elements. These pull a link which is attached to a pair of triangles. When these triangles are pulled forward, they engage the trailer pin. Since the crankshaft elements go over center, this locks the pin in position so that towing force cannot pull it open. This effect can be seen in the animation.
This low frame multi-axle trailer is obviously designed for hauling heavy equipment. It has an open frame and a sturdy loading ramp.
The "landing gear" is the pair of feet which deploy to support the front of the trailer when not attached to a tractor. They raise and lower on a 4-bar linkage, keeping them perpendicular to the ground. A pole reverser handle turns an axle attached to a pair of crankshaft elements. These drive a link which moves the 4-bar linkage. Since the crankshaft elements go over center, this locks the feet in the down position so they do not collapse under weight. In the photograph you can see that these parts are stopped against a pair of 1x1 round plates which prevent further rotation.
The large rear loading ramp is driven by a crank on the front side. This crank turns a worm gear which mates with a 24 tooth crown. An axle runs the whole length of the trailer and then drives a perpendicular axle through a set of 14 tooth bevel gears. This final axle drives a pair of liftarms which raise and lower the ramp.
Because the mechanism uses a worm gear, it cannot be backdriven (because the axial friction is higher than the backdriving torque due to the screw pitch angle). This helps keep the ramp up when in transit.
If we are to assume that the forklift is to scale with the rest of the set, then this is a huge forklift indeed. It would be perhaps 30 feet long. There are forklifts this big which would typically be used for heavy loading of things like shipping containers. The double front tires suggest that this is designed for very heavy lifting.
The train roof used as an engine cover is a nice touch.
The rear wheels can be steered using an overhead "hand of god" control behind the cabin. The wheel control drives an axle connected to a pair of 14 tooth bevel gears. The second axle drives a rack via an 8 tooth pinion gear. The steering mechanism itself uses the steering arms and toothed links as shown in the computer image.
The forks are lifted via a fairly complex gear train. A crank on the right side turns a worm gear. The presence of the worm gear ensures that no weight on the forks will backdrive the system. Next is a 24 tooth crown followed by a pair of 14 tooth bevel gears. Then there's another gear pair with a 24 tooth crown and a 16 tooth spur. This drives yet another 16 tooth spur. It is important to note that this second spur gear is on the same axle about which the whole fork assembly tilts. This allows torque to be passed through this joint no matter what position the tilt is in.
A final pair of 16 tooth spur gears are located at the top and bottom of the fork boom. They are connected by a long chain loop. A single chain link is the wide (tread) variety. This connects to the fork assembly and forces it to follow the chain movement.
The fork assembly is one of the least binding of the Technic forklifts. A series of tiles along the front of the boom keep the forks from tipping into the boom, and the flanges on a pair of liftarms keep the forks from tipping away. The semi-round nature of the liftarms keep everything moving smoothly as it slides along the boom.
The forks can be tilted via a pole reverser handle on the left side. This handle drives a crankshaft element connected to a link. The link tips the whole boom assembly about the lower pivot axle.
Since the crankshaft element goes over center, this locks the boom in the transport position so the lift weight will not cause the boom to tip forward.
This set is a gold mine of wheels and tires.
The tractor and the forklift each have 6 of the Model Team wheels and tires, for a total of 12.
The trailer has 6 of the old style small wheels with the medium size tires.
By Technicopedia