Original Year
# of pieces
Construction Equipment:  Loaders
Movable arm, claw, slewing,
4 wheel steering, opening canopy
Other Views

8446 Crane Truck

iso revolve
Click the image to download the LDraw file of this model.
Model by marco9999

What the #$@! is this supposed to be?  I'm not quite sure.  I remember staring at it in the catalog back in 1999 wondering what it was.  By that time had I decided to collect all the models though, so I had to get it.  The title "crane truck" seems somewhat inaccurate.  Although it has an arm and claw on the back, it is more of a loader than a crane.  The futuristic styling does not seem consistent with any real vehicle, but the general concept is somewhat similar to a log loader.  Despite the questions concerning the subject, the model is full of great features.  The rare green color is the first thing this model has in its favor.  Beyond that, there are more functions than you might expect.  The rear loader arm slews, deploys, and the claw opens and closes.  The chassis has 4 wheel steering, and the canopy opens to reveal the seats and allow a way for the drivers to enter.

The construction of this model is really a combination of many building styles.  The main structure of the chassis is traditional studded Technic, but it is heavily reinforced with newer studless parts.  In addition, it incorporates quite a few Bionicle (Slizer) parts.  The mirrors, the gear supports, the worm gearbox, the jaws of the claw, and several other parts are not traditional Technic.  The model also makes use of the new curved panels and a significant number of flexible axles and ribbed hoses.  As if that wasn't enough, it is green, one of the rarest Technic colors.  Despite the fact that this looks like a green model, there are actually only a handful of green parts.


The two front axles can be steered using an overhead "hand of god" control.  Each front axle has a steering rack, but the pinion gearing is not the same.  The second axle is driven directly by an 8 tooth pinion, but the front axle goes through a 1.5:1 increase first.  This results in the front axle steering more than the second axle which is exactly what you want for a common turning center.  Because the gear set reverses the direction of rotation, one steering rack is in front of the axle and the other is behind.

steering    steering
Click for an animation of the steering in motion.
Loading Arm
The loading arm uses a fairly complex kinematic setup.  As seem in the computer image, there are multiple pivot axes (shown in red).  The main body of the rear chassis pivots on the lower axis, and the arm itself pivots on the upper.  They are connected together on a long cantilevered arm.  When a knob on the right side is turned, torque is passed through a set of bevel gears (1:1), then a set of spur gears (1:1), another set of bevel gears (1:1) and up through the center of the turntable.  A worm gear housed inside a Bionicle assmebly turns a 24 tooth crown attached to a long crank to raise the arm.  Final reduction is therefore 24:1.

The motion is very interesting to watch.  The arm at first stays nearly parallel to the ground as it extends.  Once it clears the rear of the chassis, it pivots down until it just reaches the ground.  Someone worked out the geometry of this very carefully.
luff    luff
Click for an animation of the arm deploying.
The claw on the end of the arm has another interesting mechanism.  A single input knob pushes a shock absorber used as a tie rod.  The two claw jaws are linked together with a pair of 16 tooth spur gears to keep the claws  synchronized.  The knob attachment moves slightly over center when the claw is fully closed, which causes the shock absorber to hold it shut.

Another benefit of the shock absorber's variable length is that the claw can lock while holding something.  Even if the claw is still partially open, the spring will compress and the jaws will still lock.
claw    claw
Click for an animation of the claw.
The rotation of the superstructure is accomplished via a know on the left.  The knob goes through 2 sets of bevel gears before using an 8 tooth pinion to drive the ring gear of a large turntable.

The geometry of the superstructure is such that it can rotate a full 360 without contacting the canopy.

The knobs for the arm and the slewing are on the same axis on opposite sides of the vehicle.  Because the control for moving the arm goes through the center of the turntable, moving the arm tends to also rotate the superstructure.

slew    slew
Click for an animation of the arm slewing.
The canopy opens with one of the new damper elements.  The crank shown in tan in the computer image is used to bump the canopy open just far enough to allow the spring loaded damper to achieve a good mechanical advantage.  At that point, it raises slowly under its own power up to about 90 providing excellent access to the interior.
canopy    canopy
Click for an animation of the canopy opening.
Wheels and Tires
This set uses six of the new 56x30 balloon tires and the new metallic silver painted wheels.  It looks really good!

Other Views

Side View
side view
Top View
top view
Front View
Back View
back view
Computer Render

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