Set 8843 was released in 1984 and was one of the first models to use the new pneumatics. This forklift features rear wheel steering as well as forks which raise, lower, and tilt. Raising and lowering is accomplished via the pneumatic cylinder and switch. Traditional studded construction and pinned construction are both used.
This model is a significant improvement over 850 in almost every way. The mechanics are better (the fork mechanism does not stick far above the vehicle when raised), it has pneumatics, and it looks much more realistic with an operator cabin.
This is one of only two models ever to come with the long stroke pneumatic actuator which was only available for 4 years. This actuator was never replaced by a similar unit when the new pneumatics came out, so this set remains rather unique to this day. The pump was available in 4 models, but was only yellow in two of them.
Main model |
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Features |
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Steering |
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The rear wheels can be steered using an overhead control or a steering wheel in the cabin. This is the first Technic model to combine both steering inputs. (The 8846 Tow Truck had a backdriving steering wheel but it could not actually be used to steer the vehicle because the belt would slip.) The path from the overhead control to the wheels is quite convoluted to hide the axles. The overhead control drives an axle connected to a pair of 14 tooth bevel gears. The second axle drives another set which runs vertically down the aft of the cabin. A third set of bevel gears drives a rack via a pair of 8 tooth pinion gears. The steering mechanism itself uses the new control arms and toothed links as shown in the computer image. On the other side of the steering rack, on the same axle as the pinion gears, another pair of 14 tooth bevel gears drive the steering wheel in the cabin. |
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Pneumatics |
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This model contains a single acting pneumatic system. The components of this system are connected with rubber tubing routed through the holes in the beams. A single pump provides air pressure. Depression of the piston produces positive pressure, and raising the piston produces negative pressure (suction), limited by atmospheric pressure. The pressure is fed to a distribution block with an input (pump) and two outputs (switch). One output has a check valve which flows out and the other a check valve which flows in. Each of these is routed to a different inlet of a selector valve (switch) with one output. Selection of the switch in one direction therefore allows pressure output, while selection in the other direction allows suction. Finally, there is a pneumatic actuator which has a port at the head end to accept input from the switch. Positive pressure extends the piston, while suction retracts it. This model has the long stroke (64mm) pneumatic actuator which is only found in two models. In the picture, the actuator is on the left, the selector valve is in the middle, and the pump is on the right. The distribution block is not visible. |
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Forks |
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The forks can be raised and lowered using a pneumatic actuator. The actuator does not drive the forks directly, but drives a pair of chains via two 16 tooth gears used as pulley wheels. One end of the chains is fixed to the vertical structure via a long chain link (track), while the other end is attached to the moving forks (see picture). Since the chain doubles back on itself, the chain has to move twice as far as the pulleys to which it is attached. The effect of this (a reverse pulley system) is that the forks can raise and lower twice the distance of the stroke of the actuator. When retracting, the actuator does not really pull the forks down, it only lowers the pulley, removing the force which holds the forks up. The forks must descend under their own weight, which works as long as there is no binding in the system. The moment created by the cantilevered weight is reacted by a force couple: the upper forward load is reacted by a set of tiles on the back of the vertical structural assembly, and the lower aft load is reacted by contact of the lower tiles against the vertical structural assembly. This use of tiles on both sides makes the motion of this forklift quite smooth, among the best of all the Technic forklifts. |
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Fork Tilting |
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The entire fork and lift assembly can also be tipped forward to aid in picking up a pallet from the ground (or dumping one on someone's head). A lever on the right side made of a toothed connector turns a 24 tooth gear used as a crank. A series of linear links attached to the crank connect to the vertical structural assembly which pivots about an axle on its base. |
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Wheels and Tires |
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This set contains 4 sets of wheels and tires of type:
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By Technicopedia