Gradall Discovery Series: Niche-Market Appeal

By Walt Moore, Editor | January 26, 2016

Gradall identifies its new Discovery Series models as highway-speed, wheeled-excavator crossovers, setting them apart from the company’s XL Series highway-speed models—those machines with a Gradall-built chassis that can travel on-road at speeds approaching 60 mph. The chassis under the freshly designed excavator upper of the Discovery Series, however, is a new departure for Gradall—basically a standard Freightliner medium-duty truck, modified only to accommodate the dynamic forces of the working excavator.

Gradall says that the new Discovery Series models, the two-wheel-drive D152 and four-wheel-drive D154, will have most appeal to market segments that might always have wanted a Gradall, but thought they couldn’t afford one. Small, budget-conscious municipalities and specialty contractors, those placing curb and sidewalk, for instance, come to mind. In some operations, says Gradall, the Discovery Series might be a viable replacement for a large backhoe loader.

But then again, says the company, the new machines will fit any fleet looking to expand its capability to perform a variety of moderate-duty excavating and utility chores (drainage, curb removal, roadside mowing, for example) at a modest price.

Compared with the smallest of Gradall’s highway-speed excavators, the XL 3100 IV, the new Discovery models have price tags some $80,000 less, and because they have gross vehicle weights less than 33,000 pounds, the new models are exempt from federal excise taxes, which must be paid on the 40,000-pound XL 3100.

“Avoiding those taxes is a big deal for people buying machines,” says Gradall’s Mike Popovich, vice president-excavator products. “It results in substantial savings.”

According to Gradall, the new Series (“D” for Discovery, “15” for its metric-ton weight class, and “2” or “4” for drive configuration) offers a more-compact, more-maneuverable design than its conventional highway-speed counterparts and has the least tail swing of any Gradall model.

Gradall specs show a tail swing (the distance from the center of rotation to the back of the counterweight) of 6 feet 8 inches. Tail overhang (the distance from the rear-tire sidewall to the back of the counterweight when the upper is 90 degrees to the chassis) is only 29 inches. But on the flip side, says the company, the new models have less lifting capacity than the XL 3100. On average, considering lift capacities at various radii over the side at ground level, the Discovery has about 20 percent less capacity, primarily a consequence of using a smaller counterweight to conserve space in the interest of minimal tail swing.

Initial operator impressions

“I had to initially remind myself how this machine is designed and marketed,” says Sean Poyner, who, along with fellow operator/instructor Chris Tomblin, at the Operating Engineers Local 150 training center in Wilmington Ill., has spent many hours in Gradall excavators.

“After running the D152,” said Poyner, “it’s apparent that it’s not going to be a high-production machine like the XL Series—but I don’t think that’s Gradall’s intent. I see it as a good machine for the contractor or municipality using it periodically, not as an every-day production machine. For this purpose, I think it’s great.”

Tomblin’s initial reaction to the machine was similar: “The stability is excellent—it’s a Gradall—and there isn’t much difference in that regard, compared with the XL. But I don’t think it’s an excavator in the ‘construction’ sense of the word; it has adequate breakout force for digging, but I’d like to see more down force. You have to work at digging a hole, but it does the job.”

Poyner and Tomblin, who ran Gradalls for contractors and now are lead instructors for a Gradall-specific class they developed for apprentices at the training center, spent the better part of a mid-October day last fall running the D152, on loan from local Gradall dealer Finkbiner Equipment. Poyner drove the machine from Finkbiner’s yard to the training center and was impressed with its on-road performance.

“The Freightliner’s comfortable and has all the amenities—heat, AC, cruise control—and it does get from a stoplight to 55 [mph] right now,” said Poyner. “I don’t see the D152 being an off-road machine like the 4100 we have here [the Gradall XL 4100 II in the Local’s fleet], but that said, Chris and I had it in soft dirt most of day, and there was no problem.”

Discovery design overview

Popovich, along with Finkbiner president, Marty Ahrendt, and Finkbiner technician, John Bazan, first gave the Local 150 operators a walk-around of the new 31,000-pound machine, pointing out its notable features.

“Gradall’s overall design goal with the Discovery Series,” said Popovich, “was to make the machine small, light and inexpensive, with as little tail swing as possible.”

That goal, however, was developed around Gradall’s hallmark feature, the rotating telescopic boom, which remains at the center of the new excavator’s design. The Discovery’s boom is a bit shorter and lighter than those of the XL Series, said Popovich, but retains all the operational characteristics, including 220-degree rotation and 60-degree hoist-down capability. Reach at ground level for the D152 is 25 feet 6 inches.

Although the Discovery excavator itself is newly designed, not a carry over from the XL 3100, it does use the XL cab—but with a few significant interior tweaks, such as a new monitor that integrates more switches and controls into its touch screen, compared with its counterparts.

The implement hydraulic system is new, plumbed by the Parker Hydraulics Group and incorporating a new Rexroth variable-displacement pump and main valve. And, in line with Gradall’s design goals, available buckets are a bit lighter and hydraulic cylinders a bit smaller.

The carrier chassis, however, represents a notable new direction in design for Gradall excavators.

“The Discovery uses a Freightliner M2 chassis with a very specific Gradall spec,” said Popovich. “It has a heavy-duty frame and liners end-to-end, as well as heavy-duty reinforcing braces. We consulted with Freightliner about exactly what forces would be placed in the chassis, especially when working off the corners.”

Popovich further explained that Gradall bolts a full-length torque box to the Freightliner’s heavily reinforced frame to dissipate the excavator’s working forces, rear to front, effectively isolating the truck frame from abrupt shock loads.

At the front of the torque box is the boom cradle, within which is integrated the machine’s hydraulic reservoir and oil cooler. A Freightliner-supplied PTO drives the Gradall-installed Rexroth load-sensing piston pump, which supplies hydraulic flow to the excavator via a newly developed swivel.

The chassis for the D152 and D154 uses standard Freightliner components, including a Cummins ISB 6.7 engine—rated at 220 horsepower and 520 lb.-ft. of torque in the D152 and 250 horsepower and 660 lb.-ft. of torque in the D154 at 1,500 rpm. The Cummins is coupled to a five-speed Allison 3500 RDS automatic transmission.

The only modifications Gradall makes to the chassis are the removal of the stock rear suspension in order to mount the axle directly to the frame and torque box, installation of a steering cylinder to allow driving the machine remotely from the upper cab, and the addition of lock-out valves to stabilize the truck’s front axle when the excavator is in operation. The rear axle does have a Gradall-spec ratio that limits highway speeds to 55 mph, but the chosen ratio, said Popovich, allows more comfortable maneuvering when the machine is driven from the upper cab.

Asked if the use of a non-Gradall-built chassis might have a negative connation for  buyers, given that the company has built its own carriers for so long, Poyner thought not: “Because it’s a new concept, I think the machine will be more accepted,” he said. “The company didn’t get rid of an accepted design in the process—just added more of a specialty item.”

Gradall's remote-drive system

Although Gradall had significantly redesigned the remote-drive system for its recently announced XL Series IV models, the system used in the Discovery is completely new—and is responsible for much of the cost savings, compared with conventional XL models.

Series IV models employ a separate hydraulic drive system for upper-cab operation, using a hydraulic motor that drives into a transfer case. Depressing an accelerator in the cab allows instant on-site travel, and the system provides two speed ranges, 2.5 and 5 mph, selected via a switch.

“It’s a complex system,” said Popovich, “but it works really well on Series IV machines.  It’s smooth and the operator doesn’t have to do a lot. But with the Discovery, the two separate drive systems are no longer required—the drive system for both cabs is now essentially the same.”

When the Discovery’s remote-drive system is engaged (which won’t occur until the engine is below 1,100 rpm), an electronic control shifts the Allison into first gear and the machine is ready to drive. Programming in the machine’s processor ensures that the engine will not stall at the lower speed, said Popovich, and the new remote-drive system provides speeds to 7 mph.

“The new design eliminates the transfer case, hydraulic motor and counter-balance valve,” said Popovich, “and
allows the use of a smaller pump, smaller swivel and fewer lines and related porting. We significantly reduced the number of components, and that helps keep costs down. From a system-design perspective, it’s simpler; from the operator’s point of view, it’s a little more involved.”

With the new system, the operator must first step on the brake pedal, and when the monitor indicates that the remote-drive system is ready, the operator then uses the forward/reverse pedal to drive the machine.

“From an operator’s perspective, the Discovery’s remote-drive system is more complicated to use than the XL system,” said Tomblin. “You have to be patient [while the system readies itself], but most construction people tend to be impatient if machine response isn’t instantaneous. We’re all creatures of habit, we’re used to what we’ve learned, so anything that’s different requires a learning curve. The performance of the system, though, is very good.”

Poyner said the new system has a different feel than that of the XL’s hydraulic system, but he also liked the performance of the new system.

“Once you get used to it, it’s fine,” he said. “You just have to remember to first engage the brake. As Chris said, it’s a learning curve. If you’d never operated a Gradall before, then you’d not have some of the comments we have, because you wouldn’t know any different. But with the increased speed—7 mph—I’ll go with the new system.”

Commenting about the operators’ observations that the system is not as fast to react as the hydraulic system, Popovich said that the built-in delay was a studied decision.

“The engine deceleration required to activate the system can occur so quickly in an electronically controlled engine, that the drive system could virtually engage instantaneously. We didn’t want to do anything too aggressive right out of the chute, so the time lag is built in. We can tweak the system once we know how users react to it.”

Other notable comments

Another observation the operators had was also speed-related; both thought that the boom-lower speed could be faster.

“If I have to come down with enough force to snap some curb,” said Poyner, “given the boom’s short stroke and its speed, I’m not sure I could do it.”

The bucket-shake feature, however, met with universal approval.

“The bucket-shake is worth its weigh in gold when you’re spreading stone,” said Tomblin. “Saves a lot of time, versus having to deal with material dumped in a pile.”

On the potential wish list for the machine was a hydraulic coupler.

“A quick-connect would be a useful feature,” said Poyner, “but that’s not to say that perhaps it will be available in the future. But on the other hand, most people who buy this machine probably will use it for a specific purpose and won’t be changing attachments that often.”

Poyner’s comment, though, might prompt some prospective buyers to ask about the Discovery’s versatility. According to Popovich, the machines are designed for pin-on attachments, which initially will include an excavating bucket, 36- and 60-inch ditching buckets, curb-removal bucket, grapple, and tree shear. Future auxiliary hydraulics to the end of the boom will allow powering either a 50-inch rotary mower or 40-inch flail mower.

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