logo
Original Year
1998
# of pieces
774
Categories
Cars and Trucks: Tow Trucks
Cars and Trucks: Big Rigs
Dimensions
49(L)x24(W)x29(H)
Features
Steering, winch, wheel lift,
Rotating hoist, pneumatics
Other Views

8462 Tow Truck

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


The 8462 Tow Truck, released in 1998, was new or unusual in many ways.  Apart from the uncommon blue and turquoise color scheme, this flagship model used pneumatics including the new air tanks.  The body is a somewhat futuristic "swoopy" shape built from Technic bricks and flexible tubing.  Most conspicuously, the new deep dish silver wheels were used.  The wheel lift also employed some new bent liftarms which quickly disappeared from the parts catalog.

This is a somewhat divisive set among fans.  Many feel that it is a not a very accurate representation of a real tow truck.  With its long list of technical functions, it represents the utility of a tow truck rather well, but the body and wheels are more stylistic than accurate.  In the end then, whether or not this set is great is a matter of taste.  I like it.

This truck is very sturdy with its traditional studded chassis and angled body.  Although it does not have a drive train with differentials or an engine, the multitude of pneumatic parts make up for its absence.  It also uses stickers sparingly for head lights, tail lights, and a license plate.

Features

Functions
The features of this tow truck are dominated by the pneumatic system as can be seen in the cutaway render at right.  There are very few gears in the model, but there are still 6 technical functions.
guts
Pneumatics
The model features a robust pneumatic system with three large actuators, three switches, one pump, and two air tanks.  As shown in the computer image, the air tank are in series with the supply which then splits to go to the switches.  The air tanks are disguised as fuel tanks on either side of the vehicle.  They store a large amount of pressure: enough to supply the actuators several times.

There are two switches on the left of the vehicle which control the wheel lift and one on the right which controls the hoist.  The actuators are quite powerful and can lift a heavy vehicle.

The plentiful pneumatic tubes are color coded:  gray is supply, black is extend, and blue is retract pressure.  The tubes are mostly hidden within the structure such that they are not conspicuous when the model is finished.
pneumatics    pneumatics
Steering
The front wheels can be steered using an overhead "hand of god" control.  The overhead control drives an axle connected to a pair of 12 tooth bevel gears.  The second axle drives a rack via an 8 tooth pinion gear.

The steering rack geometry is unusual in that it is not a simple 4-bar linkage.  The central rack is connected to tie rods which can rotate providing Ackerman correction.

Because the wheels are so deep, the kingpin axis is actually inside of the wheel.  This is one of the only Technic models with such geometry which allows minimal tire longitudinal motion when at full steering lock.
steering   steering
Click for an animation of the steering in motion.
Wheel Lift
The wheel lift is raised and lowered on an arm driven by a pneumatic actuator.  This actuator is oriented nearly vertically between the chassis rails and therefore has excellent mechanical advantage.  It can life a heavy vehicle, but the pressure gradually bleeds down over time.

The total angle of the arm is exaggerated in this model.  It lifts far higher than a vehicle would ever be towed.

The blue diagonal brace seen in the picture makes the arm very strong and rigid.
wheel lift    lift
Click for an animation of the wheel lift in motion.
Tow Bar
At the rear of the wheel lift arm is the tow bar which physically supports the towed vehicle.  This bar must lock down at about 90 and must also be able to rotate up and stow when no vehicle is being towed.  The rotation is powered by a pneumatic actuator within the wheel lift arm.

In order to be able to turn corners, the tow bar must be able to pivot on a vertical axis, but this also means that the bar might not be straight when it is time to stow it.  This model solves that problem with a clever use of sloped Technic bricks.  The animation shows how the tow bar centers itself automatically when stowing.
tow bar     lift
Click for an animation of the tow bar rotating.
Boom Hoist
A boom hoist in the center of the truck can pull a vehicle from a ditch using a cable and hook.  The boom arm can be stowed and deployed with a pneumatic actuator by extending a 4-bar linkage.  The actuator does not actually support any cable weight when the boom is deployed.  Rather, the thin 7L liftarms which rotate to deploy the boom jam against each other and act as an end stop in either direction.
boom    boom
Click for an animation of the boom hoist in motion.
Winch
The boom hoist utilized a winch with a ratcheting cable drum.  The corner of a #6 angle connector mates with a 16 tooth gear to act as a ratchet pawl.  When this is lifted, the cable can be extended.  Otherwise the pawl's own weight locks the drum and cable in position.  The sheave uses a heavy metal hook to keep the cable taut as the line is payed out.
winch    winch
Click for an animation of the winch in motion.
Rotation
This is a rotator tow truck which means that the boom can rotate to recover vehicles from either side of the vehicle.  The rotation is powered by a rubber crank on the right side of the vehicle which drives the ring gear of a turntable via a set of bevel gears.  The overall ratio is 56:8 = 7:1.
slew    slew
Click for an animation of the boom slewing.
Wheels and Tires
This set uses 6 of the new deep dish futuristic silver wheels with hard rubber tires.  While they might not very accurate for a tow truck, they fit this model pretty well.
Wheels



Other Views

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

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