Morgan Pope is a Ph.D student investigating robots that live at the boundary of airborne and surface locomotion at Stanford’s Biomimetics and Dextrous Manipulation Lab. He’s the lead author on a paper about SCAMP that is in review for IEEE Transactions on Robotics, and enjoys reading, Star Wars, and trying to keep up with his three small children.
What goes up must come down—unless it can perch on something first. Quadrotors have limited endurance because of restrictions on battery capacity and the physics of small-scale flight, but perching can allow them to operate for hours or even days, gathering data or performing communication tasks while stationary. Perching can be tricky, because the odds of your drone landing in just the right place are low. Adding the ability to climb allows your drone to reposition itself more accurately, with the added bonus that it works if it’s too windy for flight.
At Stanford’s Biomimetics and Dexterous Manipulation Lab, we saw a chance to combine our experience in perching and climbing with a new robot capable of multi-modal operation in unstructured outdoor environments. The result was the Stanford Climbing and Aerial Maneuvering Platform, a collection of words that gives us an excuse to call our robot SCAMP.
SCAMP is the first robot to combine flying, perching with passive attachment technology, and climbing. It can also recover from climbing failures, as well as take off when it’s ready to fly again. It does all of this outdoors, using only onboard sensing and computation, leveraging lessons from all our previous climbing robots, our recent work in perching, and mother nature.
Over the last decade, we have developed a series of climbing robots that use directional adhesives to create smooth, reliable climbing gaits. Microspines (hardened steel barbs mounted on compliant suspensions) are our original directional adhesive, and they enabled Spinybot and RiSE to climb rough surfaces. We then developed gecko adhesive, which enabled directional adhesion on glass and led to the creation of Stickybot I, II, and III. As we refined our understanding of directional adhesion and climbing, we were able to miniaturize Stickybot into a 9-gram robot capable of pulling 100x its body weight up a wall. This was made possible by using a compact, powerful servo and alternating loads between two feet which move on simple, one-dimensional trajectories.
We took these lessons and re-applied them in the context of microspines to create SCAMP’s climbing mechanism. We used the same compact, powerful servo, and the same strategy of transferring loads between two feet, but since we were looking for maneuverability instead of carrying capacity, we designed it to have a longer stroke length (9 cm/step instead of 1.2 cm/step). We also learned that it helped to add motion towards and away from the wall because concrete and stucco are not as flat and predictable as a glass window. The end result is a climbing mechanism that uses one high torque-density servo to drive long steps up the wall, and one even smaller servo to actuate motion towards and away from the wall. These two servos, combined with the carbon fiber frame and spiny feet, weigh only 11 grams. In effect, we’ve taken our 9-gram micro glass climber, modified it for speed instead of load capability, given it an extra servo to handle two-dimensional surface profiles, outfitted it with microspines, and strapped it to a tiny quadrotor.
The leg design of SCAMP is reminiscent of many climbing insects, from daddy longlegs to the praying mantis, and that’s no accident. Animals want long, efficient steps, but are limited by the weight of their limbs. As we descend into the realm of insects, allometric scaling laws mean long, thin, almost weightless legs become the preferred solution. SCAMP isn’t quite insect-sized, but the robot is small enough that modern engineered materials like carbon fiber and Spectra let us create legs that are as long and weight-efficient as a those of a climbing insect.
Flying and Perching
A good climbing mechanism is not the optimal perching mechanism, and that means we had to reconsider our approach to attaching to the wall. Previously, we’ve perched outdoors using a fixed-wing robot, and indoors using quadrotors and a motion-capture system. In both cases, the vehicles lost control authority as the maneuver neared completion, meaning that we had to engineer a suspension to absorb the impact and, in the quadrotor case, an opposed-grip attachment system that could resist loads in any direction. In the natural world, animals use aerodynamic forces throughout the perching process, and that’s the approach we took for SCAMP.