The Pentagon’s all-too-lifelike four-legged robot may be about to get a whole lot bigger, stronger, smarter and tougher to slow down.

Already, the BigDog quadruped machine can carry more than 300 pounds, walk around for nearly 13 miles on flat ground and keep its balance after getting kicked around. In other words, it’s a pretty decent prototype for a machine that could help carry soldiers’ gear when they’re out on a mission.

Now Darpa wants an upgraded bot that can lug 400 pounds on its back, trot for 20 miles in any terrain, and carry enough gas for an entire day’s operation. The agency is calling it a generic "Legged Squad Support System," or L3. But it’s pretty obvious that the machine Darpa has in mind is "BigDog on steroids," as one knowledgeable observer puts it. And unlike the typical Darpa project, this upgrade shouldn’t be too hard to pull off, our observer says.

But there will definitely be challenges. Throw in the added carrying capacity and the extra weight of gas, and the L3 is supposed to bulk up to 1250 pounds. All the extra weight will make it harder for the bot to get up, once it trips. Darpa also wants the machine to run quietly. Right now, the BigDog is one loud ol’ beast.

The machine will have to be able to sprint at a 10 mile-per-hour pace in 120-degree heat, climb stairs, slosh through water and squat on standby in the rain or snow for most of the day. The agency is looking for a smarter quadruped, too. No more joystick controls, Darpa says. The L3 should be able to follow a soldier around, navigate by GPS waypoints and respond to speech or gesture commands. Using laser sensors, the current BigDog did follow a human around for a 10-mile walk. But the path was basically clear. The new model will have to pick its way through all kinds of obstacles.

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