Driving a Different Path
March 9, 2006 — Among rough-terrain cranes, there are many individually unique features but few cranes that stand out as a whole. One exception is Link-Belt's RTC-80100 Series II rough-terrain crane (Image 1), introduced in 2002. The RTC-80100 was conceived from the desire to build an RT crane in the 90- to 100-ton class that was more transportable than other products on the market. Link-Belt Construction Equipment Co.,
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Image 1. One of MARCO Crane Rental's Link-Belt RTC-80100s works at the Mesa Gilbert Municipal wastewater treatment plant in
The key to achieving these attributes lies in one single deviation from all other RT cranes: the use of a hydrostatic drive system. Conventional cranes utilize the tried-and-true differential drive train, usually with powershift transmission. But the drive system (Image 2) on the RTC-80100 is like no other RT crane.
Hydrostatic drive
Hydrostatic drive is being used with more frequency in the off-road mobile equipment market. In place of drive lines and axle hosing, you will find the extensive housing required to supply six individual wheel motors. The size of this system dictated that Link-Belt turn to alternative sources to assemble a system with these massive requirements. Its search for a supplier led Link-Belt to Linde Hydraulics Corp., Canfield,
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Image 2. A close-up look at the RTC-80100's drive train.
The demand for hydraulic flow in the RTC-80100 is massive. Two large, main-drive variable displacement pumps, also provided by Linde, supply the demand. Each displaces a maximum 88 gpm and operates at 6,000 psi. One pump provides dedicated hydraulic supply to the left wheel motors, while the other powers the right motors. Motors are supplied by SAMPO Hydraulics, based in
A Linde model DVC 10 microprocessor manages this system and works in conjunction with the engine throttle and the engine control management system. Three drive range modes are available: two-wheel high speed, which produces a maximum 18.5 mph drive speed; two-wheel low speed; and six-wheel drive. The dual drive ranges are achieved by utilizing two two-speed drive motors that displace 384.4 cubic inches per revolution in high speed and 192.2 cubic inches in low speed. Another four single-speed motors displace 192.2 cubic inches, which shift into neutral when in high speed drive. These motors are independently mounted on a suspension with hydraulic dampening.
Precise control
The hydrostatic drive system delivers precise drive control to the operator. For example, a key selling point of the RTC-80100 is its impressive pick-and-carry load chart. When operating over the tandem axles (technically the rear axles), the chart allows a maximum 45-ton capacity. The crane's low profile and center of gravity also contribute to this capability.
Because of the hydrostatic system, the engine can be mounted just about anywhere an engineer desires to place it. In this case, it is mounted in the superstructure, opposite the operator's cab. By placing the engine in the upper, Link-Belt could build a box frame carrier, which according to the company, improves torsional resistance and strengthens the carrier. The result is less flex in the frame, providing improved stability and added operator confidence. Other benefits include reduced height of the carrier. This, combined with using smaller 23.5x25 diameter radial tires, lowers the overall stowed height to 12'2.5".
The innovative 6x6x6 hydrostatic drive/steer system on each wheel delivers a remarkable turning radius • just 21 feet • for a crane with a 26-foot-long carrier. The RTC-80100 offers four steering modes • front only, coordinated six-wheel, six-wheel “crab,” and rear only. Combine these key features with the unit's super smooth hydrostatic drive system, and you have a crane that offers very impressive jobsite maneuverability.
Full-powered boom
A U-shaped, five-section boom uses strategically placed wear pads (Image 3) to disperse the load in order to maximize the overall boom strength and stability. These pads encompass the entire circumference of the formed boom.
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Image 3. Wears pads are uniformly distributed around the circumference of the formed boom.
The 150-foot main boom operates in three modes. For maximum strength, the A-max (1) system allows for the inner and center sections to be extended to a maximum 95 feet. For maximum stability, the A-max (2) allows the tip, outer, and center sections to be extended to a maximum of 122'6". In standard mode, all sections are telescoped equally.
An optional 31-foot lattice extension allows for an additional second bi-fold section for a total of 51 feet. Deployment of the bi-fold is a one-person operation. There are also optional 15-foot extensions that can take you all the way to 85 feet. All combined, the maximum total tip height is 243 feet and jib offsets are at 2°, 25°, and 45°; there are no deductions for stowed attachments.
The main winch, supplied by Braden, has up to 21,000 pounds of available line pull and maximum 430 fpm line speed. It is equipped with a two-speed drive motor with automatic brake. Asynchronous, parallel double cross-over grooved drums minimize rope harmonic motion, improve spooling, and rope service life. In addition, deflector rollers are intended to prevent premature rope wear when operating the boom at lower angles. A removable two-speed auxiliary winch is an option.
Next issue, I will share my first-hand impressions of this crane, after a visit to the facility where it is produced and to a jobsite where one owned by MARCO Crane Rental,
