Tiny drones, no bigger than your palm, were the big stars of an Army experiment in Hawaii, participants told Breaking Defense. Larger ground robots, however, struggled in the jungle.

Staff Sergeant James Roe told me he was “blown away” by the PD-100 Black Hornet, a commercially available mini-drone used in PACMAN-I (Pacific Manned-Unmanned Initiative, part of the Pacific Pathways exercises). “That was a system that we could actually take right now…on the battlefield,” Roe said. “Some of these other systems, as with any electronics and robotics, there are some things that have to be worked out.”

Ground robots got particularly mixed reviews. They helped haul equipment for the chronically overloaded infantry, and some could even fire a remote-controlled machinegun, but the tracked ‘bots couldn’t keep up with foot troops over rough terrain.

“There are numerous places, at least on this island, where that SMET (Squad Multipurpose Equipment Transport) cannot go,” said Broc Garner, like Roe a staff sergeant in Bravo Company, 2/27 Infantry. In a mission over rough ground, said Garner, “at a certain point, we’re going to have to either abandon this machine …. or leave two people with it” on guard.

That’s manpower a platoon can’t spare. Indeed, just dedicating troops to operate the remote-controlled machines was a big burden on the small units, Garner said.

The Army’s tactical radio network also needed boosting. One senior Army scientist involved, Lonnie Freiburger, explained the robots didn’t use regular Army radios “as they do not provide the necessary bandwidth.” Instead, he said, they used a 4G LTE cellular phone network. [Clarification: The network used commercial technology but was set up and run by the Army.] That’s a reasonable expedient for an experiment, but not something to rely on in combat, when the enemy can listen in or simply blow up cell towers.

The experiment also tested relays to boost signals so they could penetrate the thick foliage, said Freiburger, who works for Tank-Automotive Research & Development Command (TARDEC). One approach was a mini-drone hovering in place. Another was a “canopy buoy” dropped from a helicopter into the jungle canopy.

Ad hoc as it was, the experiment’s network workarounds worked. Neither Garner nor Roe complained about communications. Instead, they exulted in the ability to see video feeds of what awaited their troops in the next village or down the trail, and in the ability to share that video with their superiors.

“The situational awareness tools that we had up there are the ones we’re definitely looking forward to obtaining” as regular issue, Garner said. In current operations, he explained, “the hardest thing to do (is) get that positive identification of a weapon or of hostile intent” so you are cleared to fire. The ability to share video makes that process much faster and easier — without having to put soldiers in harm’s way to check out the target.

American commanders have enjoyed drone video for years, but unmanned aircraft are in high demand and rarely available to frontline soldiers. Besides, an infantry squad can hardly carry around a one-ton Predator or even a 460-lb Shadow. But then again, just needs to see over the next hill.

Enter the PD-100, with a maximum range of a mile-and-a-half and a weight of less than an ounce. “It’s a little smaller…than your palm, it’s 18.25 grams,” said Roe. “It’s very easy for me to set it up, it takes probably three to five minutes for me to have it up in the air.”

The PD-100’s small size also makes it hard for the enemy to see or hear, so it can scout ahead of a surprise attack without giving the game away. Unlike the quad-copters you can buy at Wal-Mart, “there’s no sound. You wouldn’t even know it’s flying over you,” Roe said. “It looks like a bird….The enemy’s not going to know.”

One shortfall is the mini-drone’s tiny body doesn’t have much room for batteries: It can only fly for 25 minutes without needing to recharge. So each squad was issued two PD-100s with a backpack charger, as well as the remote controls. You fly one drone while the other’s charging, then switch them, for what Army science advisor Drew Downing called “almost constant eyes on target.”

How long does the charger last? “We ran it up to three-and-a-half hours, literally leapfrogging birds the entire time,” Garner said. It’ll drain faster if you turn the handheld display to full brightness or if you fly in bad weather — the drone can manage winds up to 40 knots (46 mph).

Once the charging station runs dry, you can recharge it from the ground robots, which had hybrid engines (like a Prius) which could act as mobile generators. For modern soldiers as likely to be overburdened by spare batteries as by ammunition, that’s a big plus.

Garner and Roe also appreciated the robots’ ability to mount sensors and haul equipment, particularly a .50 caliber heavy machinegun, the kind of firepower foot troops simply can’t carry. Some of the larger robots were even rigged with a remote-controlled gun mount. Operators are safely hidden in cover, send them towards the enemy and then open fire.

Until the remote broke, which happened to Garner’s unit twice. The fallback was to have a soldier fire the machinegun manually. But then the gunner’s only cover was the robot’s chassis, leaving him largely exposed while making a lot of noise, the kind of target the enemy is bound to notice.

The remote control “worked at the beginning, but by the end, yes, we did just have to place a guy behind that 50 cal,” said Garner. “He definitely gets left out in the open.”

A more reliable remote shouldn’t be too hard a fix but the mobility limitations are much harder to resolve. A vehicle simply can’t climb, jump, or wade like a human soldier. Tanks overcome this problem by brute force, crushing obstacles or smashing them aside. A smaller tracked robot lacks the height and mass.

Garner suggested the ground robots would prove most useful in cities, where they can drive on flat surfaces. “I do think it’s a good system,” he said. “It’ll be an asset in an urban environment.”

“We had, obviously, mobility challenges, more mobility challenges than we would ever expect in other terrain,” Freiburger acknowledged. Robots that can travel over the ground — amidst obstacles and clutter — are simply less mature than ones that can travel through the empty air. “Little money’s been invested into that area,” he said, but the experiment will inform the requirements process that unlocks more funding.

The experiment didn’t necessarily show the ground robots to best advantage, added Downing, who’s the Army Research & Development Command (RDECOM) advisor to US Army Pacific. The limited land area available didn’t allow for long route marches, on which foot soldiers would have been much more grateful for robotic mules to haul their gear. “A lot of these technologies would have shown a lot better and been more impressive if the soldiers actually had to traverse 20 miles of terrain and then conduct their mission,” Downing said.

That said, the Army is listening intently to what soldiers like Roe and Garner said. “Everything they said is captured,” said Downing. “We collected literally hundreds of surveys.”

Besides the foot troops with mini-drones and tracked ground robots, he and Freiburg said, there were also convoys of self-driving Humvees, with scout drones and mine-sweeping robots clearing the way. There were defensive perimeters watched by automated sensors, and drones rigged to detect poison gas or radiation.

“We have all this technology, and we’re trying to figure out how to integrate it,” said Downing. “We don’t want to inundate the soldier…. This is kind of our crawl-walk-run strategy.”