Small is Big
When it comes to robot components, small is big. If you’ve followed the robotics news lately, you know that academic and military R&D communities are busy at work developing robots that mimic – in form and function – small crawling and flying insects. Need to locate survivors in the rubble of a collapsed building? Simply release a swarm of heat-seeking crawling robots that can squeeze through cracks without disrupting the rubble and endangering trapped victims. Need an up-close view of a hostage situation? A swarm of flying microbots with photosensors could provide police with a composite, real-time image of the victims and their captors.
Despite ongoing advances in research laboratories, there are numerous challenges that must be overcome before practical autonomous insect swarms can become a reality. There are issues of how to provide communications between each insect-sized robot and their human masters, local computation, sensors, power, and of course, powerful, lightweight, controllable micromotors. And there’s the underlying issue of cost.
A recent advance in the area of micromotors has been the commercial availability of linear micromotors from New Scale Technologies (http://www.newscaletech.com). Their series of Squiggle motors fills the void between the microscopic nanomotors and the miniature servos and electronic/pneumatic linear actuators popular among robotics enthusiasts.
I had the opportunity to evaluate New Scale’s mid-sized offering — the Squiggle SQL-1.8-6 linear motor — shown in the photo. As the name suggests, the motor is a mere 1.8 mm in width. The rectangular motor body is 6 mm long, with a 12 mm axial screw running through its center. The 160 milligram SQL 1.8 is capable of handling a 30 g load when driven by a 400 mW, 40V, 171 kHz pulse. The even smaller SQL 1.5 linear motor can work with a 20 g load. As illustrated in the photo, the electrical connection to the Squiggle motor is via a flex printed circuit strip.
With a PC-based control application and USB-to-Squiggle interface, I was able to vary the travel rate from micrometers per second to millimeters per second, with an impressive 0.5 micrometer resolution. Although the relatively fragile motor was glued to a polycarbonate mount for evaluation purposes, I could easily envision a spider-sized eight-legged walker, powered by 16 skeleton-mounted Squiggles.
The size of the peripherals that accompanied the motor — a wall wart power supply, a USB driver card, and a three-foot USB cable — not to mention the desktop PC and software — explains why the robotics shops aren’t offering autonomous robots sporting Squiggle-based grippers and actuators. Even a six-pin DIP dwarfs the Squiggle, much less a PIC or BASIC Stamp. However, the control issue should be partially solved by the time you read this. New Scale has a miniature ASIC driver under development that could form the heart of a Squiggle spider robot.
Power issue is another matter. The smallest battery packs that I’ve used are thin-film lithium-polymer cells designed for miniature indoor R/C aircraft. The thin, dime-sized cells power a single-motor aircraft for about five minutes. As such, an autonomous eight-legged Squiggle spider would likely have a lifespan measured in seconds with current battery technology. Even so, in some applications, 20-30 seconds of operationcould be worth the cost of a swarm of insect-sized microbots.
On the topic of microsensors, with the exception of Hall-effect devices, I haven’t seen any commercial sensor offerings that come close to the level of miniaturization required for an insect-sized microbot. I’d like to have an affordable ultrasonic or IR rangefinder comparable in relative size to the Squiggle. However, consider the challenge in creating a suitable IR rangefinder with standard components. A typical IR LED alone is about the size of an insect’s head. And the available ultrasound rangefinders require even more volume. Clearly, when it comes to microsensors for autonomous microbots, it’s time for a new generation of SMT devices.
Although autonomous microbots made completely of commodity — read affordable and readily available — components may be a few years away, there are myriad applications of micromotors in other areas of robotics. The most obvious applications range from the manipulation of camera optics and R/C mini helicopter control surfaces, to control of microvalves in implantable drug delivery devices to surgical robots. Although I expect to see the first large-scale applications of micromotors in the consumer electronics industry, the medical applications will likely have the most profound effect on quality of life.
Consider that current surgical robotics rely on standard-sized motors connected to scalpels and other instruments through cables. Although these robotic systems enable surgeons to operate with greater efficiency and effectiveness than traditional methods, because of the physical arrangement of cables and instruments, the working area is constrained to only a few inches across. The use of micromotors connected directly to instruments would allow for a much larger work area for tele-surgeons, as well as lighter, mechanically simpler surgical robots. Size and weight can be critical factors if the remote patient happens to be an astronaut on Mars, or a critically injured US soldier in a remote area of the world. SV