If you remember our Bots of War series from last year, than you’re familiar with iRobot’s hardcore military robot fleet. But just because they’re awesome doesn’t mean they’re done evolving.
The prototype arm you see in the video above doesn’t have an inner skeleton to give it rigidity — it uses air. Essentially, there are airtight plastic bags inside a skin made of a non-elastic constraining fabric. Air is pumped into the bags, which gives the arm volume and shape. Then, as the bags reach the fabric skin, they can’t expand any more, and that’s what gives the arm rigidity. Movement and manipulation are controlled by a series of cables that run through the inside and act as tendons. Servos at the arm’s joints take slack in and out of the cables, which create motion, or “tendon actuated articulation”.
So why do this when PackBots have arms that work very well already? We spoke to Chris Jones, Director for Research Advancement and Senior Principal Investigator at iRobot. He laid out several key advantages that an inflatable arm offers:
- It offers a significant reduction in weight. The arm you see in the video weighs only half a pound. In contrast, a typical PackBot arm weighs around 11kg. For a small, mobile robot, weight is hugely important. Dramatically cutting the weight means they are much easier to carry for soldiers, bomb squads, and rescue workers. It also puts less stress on the robot’s motors and increases battery life.
- It allows the bot to pack down much, much smaller. At the beginning of the video you see what the inflatable arm-bearing PackBot would like in its packed state. These robot could now be stackable. They would take up less space in a vehicle, which would allow for more room for other payloads. And because it can drive with the arm tucked inside its body, it can manoeuvre under obstacles that have a much lower clearance.
- It has much higher strength-to-weight ratio than a traditional arm. The inflatable arm can lift 1.8-2.2kg. That may not sound like much until you remember that it only weighs 227g, giving it a strength-to-weigh ration of almost 10:1. Traditional arms can lift more weight, but the strength-to-weight ratio is only about 2:1.
- You can customise the compliance of the arm, giving it the capability to give a little bit as it makes contact with the environment. If you accidentally drive your robot’s metal arm into a wall, it’s probably going to break the arm, or break the wall. The inflatable arm can bend, more or less, depending on how rigid you’ve inflated it to be. This also give is a soft touch, making the articulating fingers more supple and therefore more forgiving when you’re trying to pick something up.
- It’s much, much cheaper to make, which is good news for taxpayers.
The arm you see in the video is just one of several prototypes. Other concepts include an arm that might not be tendon actuated, but that might move by inflating and deflating different compartments in the arm, sort of like opposing muscles in a human arm. This is the same sort of concept iRobot used in the freaky and amazing Jambot ball.
Right now iRobot is at the research prototype stage, created under DARPA’s Maximum Mobility and Manipulation (DARPA M3) Advanced Inflatable Robot (AIR) project. iRobot just found out that it will be receiving another round of funding to continue development of these technologies. So, next time you give one of those big, Michelin Man inflatables a hug, watch out. He might cop a feel. [iRobot]