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Original Year
 1986
# of pieces
 380
Categories
 Other: Arctic Action
Dimensions
 26(L)x12(W)x20(H)
Features
 4 wheel steering, rear ramp,
plow
Other Views

8660 Arctic Rescue Unit
iso revolve
Click the image to download the LDraw file of this model.
Model by Widetent

Set 8660 was released in 1986 as one of 4 sets in the new Arctic Action theme.  This set features four wheel rack and pinion steering, an opening rear ramp, and two of the new Technic figures with a helmet, skis, and poles.  There is also a tracked snow plow which is stowed in the back of the vehicle.

This is the first set to have more than 4 wheels and the first to feature 4 wheel steering which, in this case, is on the front and rear axles.  The plow is only the second time the wide chain links were used for a tracked vehicle.  This is also the first set to feature the worm gear which is what allows the rear ramp to work without backdriving.  There are a lot of white beams here, and this remains one of only a few sets to ever contain them.

Features
Steering
The front and rear wheels can be steered using an overhead control or a steering wheel in the cabin. 

The overhead "hand of god" control drives an axle connected to a pair of 14 tooth bevel gears.  The bevel gear axle runs forward through a quartet of 8 tooth pinion gears to turn the driver's wheel.   There is also a 24 tooth gear on the main axle from the overhead crank which mates with a 24 tooth crown gear.  This final axle runs to both the forward and rear gear racks which drives them in opposite directions at the same ratio.

The steering mechanism itself uses the new control arms and toothed links as shown in the computer image.

This model has an excellent turning radius with the four wheel steering, allowing this vehicle to pick its way across the glaciers avoiding crevasses.  Although it would be cool even if it had no useful purpose.
 steering    steering
Click for an animation of the steering in motion.
Ramp
A rear ramp/gate can be opened via a crank on the left side of the vehicle.  The crank drives a worm screw which mates with a 24 tooth spur gear. This first stage results in 24:1 gear reduction and cannot be backdriven (because the axial friction is higher than the backdriving torque due to the screw pitch angle) which allows the ramp to be supported so that it does not fall under its own weight.  The axle then passes through a set of 14 tooth bevel gears.  The final axle is mated to the ramp through toothed connectors and links which force the ramp to rotate at the same rate as the final axle.

This ramp is very steep making it somewhat difficult for the plow to enter.
 ramp    ramp
Click for an animation of the ramp in motion.
Plow
There is a small snow plow stowed in the rear of the vehicle which has a seat for the driver.  It rides on a pair of tracks.  The front plow folds up over the top for stowage.
 plow
Wheels and Tires
This set has 6 of the 13x24 Model Team wheels and tires, and is the first Technic model to use them.
 wheels
 

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