About the Model:

This is a model of an Oshkosh PLS Vehicle. PLS stands for Palletised Load System. This refers to the system used to quickly load and unload pallets of materials at the front line of battle.

The vehicle has 10 wheel drive, driven through a 5 speed epicyclic gearbox and a two speed torque splitting transfer case. The drive from the transfer case splits the drive to 5 axles through 3 inter-axle differentials. All axle differentials are lockable, as are the inter-axle differentials. There is an epicyclic hub reduction to each wheel. The front tandem axle steers, as does the rear most axle, to reduce the turning circle of the vehicle.

There is a small materials handling crane situated behind the engine and gearbox. This has two outrigger feet and revolves 180 degrees on its turntable. Two rams raise the crane into the air. The crane arm has an outer section with a further 3 extending sections inside it. The load is carried by a hook and rope.

The rear of the chassis has the loading and unloading system operated in two sections using hydraulic rams.

All of these features have been reproduced on the model. Hydraulics have been simulated using either cord and wire systems or rotating screwed rods. The motive power for the transmission is a Marx Hectoperm motor. The epicyclic gearbox uses 2.5" gear rings with 19t pinions as sun and planet wheels.

The material handling crane is operated via 7 switches located on the side of the model. There is also a remote switch which can be plugged into the model which will operate the crane and the rear demountable pallet. The cab houses switches for operating two sets of diff locks and a 2nd set of controls for the rear platform.

The transmission, including both gearboxes, steering and rear platform are all radio controlled. The epicyclic gearbox is electrically operated via electromagnetic clutches which are used to brake each annulus to select the gear. A 5 position rotary switch operated by a servo connects each clutch in turn to a power supply.

The power for the model comes from onboard batteries. There is also a facility to plug in an external power source.

The model has taken about 3 years to build. Over 100 nineteen tooth pinions have been used in the transmission and there are 13 motors in all.

DETAILS

1. Steering. The original vehicle has hydraulic power assisted steering, with the steering drive to the rear axle being a shaft drive down the side of the vehicle, with a gear reduction/reversal gearbox part way down. In the model, all the steering boxes are operated by worm and pinion, as this looked very much like the real machine. It was then possible to have the drive to the rear steering axle as per the prototype. To overcome the limitations of the worm drives, thrust races were used for each one. They were formed from small bevel gears trapping 7 small ball bearings against a washer (these were also used in the helical drives to the axles).

2. Cab. The cab is removable like the real vehicle. Power connections plug in for the switches which control the diff lock servo motors and the demountable load system. The steering drive is taken to the vehicle via a dog clutch. The seats can recline and they are also sprung.

3. Diff locks. The axle differential cases have a bossless 57 tooth gear bolted to one side (this part was included in the Action Packs with the sprint motor in 1981). Immediately beside this, a 57t gear is locked to the half shaft. A 19 tooth pinion on a sliding shaft below can be brought into mesh with both gears to lock the diff. This is operated by a Bowden cable actuated by a lever which is moved using a single eccentric. The eccentric is driven by a small motor with suitable gear reduction.

4. Crane and transmission. This whole unit can be removed from the chassis be undoing two bolts. The crane can then be removed from the gearbox structure by removing a further four bolts, together with the slewing pinion. When the whole unit is replaced on the chassis, a pair of drifts at the cab end aid location into to journals formed by the chassis members with cranks bolted below. The vertical drive to the slewing action of the crane is picked up by a worm gear on a shaft running at right angles to the chassis.

5. Power Supply. The model is driven by onboard batteries. One battery powers the transmission and all of the radio control gear. Two more 12 volt units power the crane, unloading system and the diff lock servos. There is the facility to plug in an external supply to take over from the 12 volt units. A pair of 9 volt cells are used for the power supply to the gearbox selector unit.

The non standard parts used in the model are as follows

1 2.5" gear rings
2 5.75" rubber tyres
3 30/45 and 22/55 gear pairs from Exacto
4 Mini Single pole, double throw, centre off switches
5 Motors
6 Nylon coated fishing wire
7 Narrow face 19t pinions
8 MW long sleeve pieces
9 Small ball bearings used in thrust races.