The 8443 Log Loader is a great example of how to pack a lot of really innovative features into a smallish set. There's never been another log loader before or since except as an alternate mode. This set features a pneumatic system for the main boom operation, and a marvelous 6 wheel steering system which combines an articulated chassis with rack and pinion steering. Although it has a seat for a Technic figure, a figure does not fit nor would it be anywhere near the right scale. The model appears mechanically quite simple with hardly any gears, but the two stage motion of the boom and multiple axle steering angles are anything but obvious.
Despite the small size, this is one of my favorite models because it is so unique and accomplishes all its goals with so little effort and so much flair.
This model contains a double acting pneumatic system. The components of this system are connected with rubber tubing routed through and around the holes in the beams as well as through some rigid tubes from the flex system.
A single pump is located on the rear of the vehicle. Depression of the piston produces pressure. The pressure is split and fed to the inlets of two selector valves (switches) with two outputs each. Selection of the switches in either direction allows pressure to flow to either chamber of the actuators.
Finally, there are two pneumatic actuators which have ports at the head and rod ends to accept input from the switches. Head end pressure extends the piston, while rod end pressure retracts it.
This model has one large actuator and one small actuator.
The steering of this model is completely unique in the Technic line, and that makes it very special. Virtually every Technic model with more than 100 parts has steering, and virtually all of them are simple rack and pinion using a 4 bar linkage. A few loaders use an articulated chassis instead. But this 6 wheel model uses both.
A "hand of god" control on the top turns a vertical axle with two 8 tooth pinion outputs. One output goes forward to a traditional rack and pinion system, but the other goes back and drives the ring gear of a turntable. The turntable is fixed to the aft chassis. The gear ratio is set such that the middle axle turns to a smaller angle than the turntable resulting is a nice flowing curvature of the 3 axles. Although the front axle technically doesn't turn, it still forms part of the curve.
The rear axle features a pendular suspension with limited travel, allowing it to traverse small obstacles and still keep all 6 tires on the ground. The red axle in the computer image is the pivot point. Although you can see that the axles are mounted to steering arms, they do not steer but are fixed to the aft chassis.
The boom can be lifted pneumatically. An actuator pushes to pivot the boom up and retracts to pull it down. Because the actuator rod end is not mounted to the boom itself but to a link attached to the jib, a 2 stage motion results. As the actuator extends, the jib first rotates outward because it requires less force. Once it bottoms out, the entire boom lifts. This motion is repeated in reverse on retraction. This system results in a system which mimics the motion of a system with two independent actuation circuits, but achieves it with a single actuator. Genius.
make sure to watch the animation to understand the motion.
The log grapple opens and closes with a small pneumatic actuator. To prevent all the motion from happening on one side or the other, the two halves of the claw are geared together with spur gears. Despite being similar in appearance, this claw operates totally differently (and much better) than that on 8868.
This set uses six of the rubber 20x30 balloon tires and wheels.
By Technicopedia