Innovative Concept the Wheel Deal

29 February 2012
The Northern Territory Police, Fire and Emergency Service’s Mechanical Workshop team waved goodbye to one of their fondest babies today – a trial fire fighting tanker which left for Jabiru.
Both sides fully extended
Click to View Images

The Isuzu NPS300 light tanker/grass fire unit is travelling to major centres to allow NTFRS members the opportunity to see the unit, which is being looked upon as a possible way to future proof the service as it struggles to overcome the long-used but weight-restricted Landcruiser tray backs.

While the tank itself is super sexy, onboard is another eye-catching feature – a locally designed, engineered, developed and installed tyre carrier.

NTPFES fleet manager Peter Hill said the tyre carrier was developed to allow members to safely manage the trial unit’s heavier spare tyre, which now weighed in at around 90 kilograms.

“The design and development of the carrier was necessary to accommodate a heavier tyre, following the service’s decision to trial a light truck as a possible replacement for the Landcruiser tray back and the new truck’s conversion from dual rear wheels to super single wheels,” Peter said.

The electrically driven, spare tyre cradles, fitted to the tyre carrier, were designed to allow for safe storage, removal and replacement of spare tyres.

“It will allow all NTFRS members to safely remove and stow the spare tyres,” Peter said.

The spare tyre carrier is conveniently positioned on the tray between the cab and the fire fighting platform. Originally a single spare tyre was stowed under the tray’s passenger side, however our fleet crew deemed it impractical not only to hold the heavier spare tyres, but because the nature of the bush work made the tyres susceptible to damage from logs.

“Placing the spare tyres in this location allowed a doubling of the spare-tyre carrying capacity. This new location also freed up space underneath the tray for a long tool box,” Peter said.

It took two days for workshop manager George Theodorou and workshop fabricator Grant Mitchell to develop the concept for the spare tyre cradle, then a further two months to design and fabricate the carrier and the fire fighting platform.

The spare tyre carrier consists of two steel wheel cradles which are triangular in shape. A steel-framed arm supports each cradle which holds the spare tyre. The tyre is held in place by a threaded steel clamp.

A single winch, powered by the truck’s battery and located between the spare tyres, is used to operate both cradles. Each cradle operates independently of the other by using a single, three position winch controller, which can be plugged into either one of two winch plugs, located on either side of the front of the tray.

The cradle is locked into the arm by a spring latch (spring-loaded latch) which is released by the operator when the tyre is ready to be lowered. It also has a safety cut out switch on the tyre release lever, making it super safe.

Attached to the arm is a secondary locking device. That device is a lever-operated spring latch which positively locks the arm into the tray. The arm has a secondary function as an electrical cut-out to the winch. This prevents the winch being operated inadvertently. The tyre carrier cannot be lowered unless the lever is pulled and the spring latch is released.

The tyre cradle is lowered by the aid of a spring in a slide track and the cradle descent is then controlled by the winch cable. As the arm travels from its stowed position it allows the cradle to rotate on its pivot shaft, keeping it upright until the cradle makes contact with the ground.

To stow, the operator reverses the winch operation allowing the main arm to be lifted by the winch until it is secured back into the stowed position. As this happens, the cradle pivots allowing it to rotate back into its lock up position.

The two spring latches automatically secure themselves cutting all power to the winch.

The design team also fitted a microswitch to the tyre carrier frame and a buzzer in the cab to alert the driver if either of the tyre cradles is not fully stowed.

Finally, a long electric winch controller lead allows the operator to stand well back for safety.

“All in all we feel this is an excellent design, extremely safe and very practical for NTFRS requirements,” Peter said.

“We really hope our members find the carrier useful and we’re extremely proud of the team for coming up with the unique design.”