Physicists pull off the gecko's feat

For years scientists have tried — and failed — to engineer materials that would enable robots to mimic the gecko’s ability to scale walls, windows and seemingly any other surface. Now, a team from the US has developed a nanotube material that is not just a match for gecko feet but 10 times more adhesive.

Look close enough at a gecko foot and you will see an ordered, forest-like structure — roughly half a million fine hairs that each sprout into hundreds of even thinner, spatula-shaped tips. When these tips come into close contact with a surface they induce strong van der Waals forces that keep the foot anchored — that is, until the gecko decides to peel it off.

In the past scientists have attempted to copy this hair structure by fabricating arrays of polymer pillars, but these can sustain little more than a third of the gecko’s adhesive force. Although nanotubes have proved better, it is difficult to replicate the delicate tip structure of gecko hairs that would enable the nanotubes to reach their theoretical limit.

Stuck on you

The US team, led by Zhong Lin Wang of Georgia Institute of Technology, has made a structure that looks at least similar to gecko feet through chemical vapour deposition of an ethyne–hydrogen–argon gas over a silicon substrate. By introducing an iron catalyst on the substrate and controlling the temperature and duration of deposition, the team end up with an array of vertical nanotubes with spiralled, fuzzy tips.

In tests on glass, sandpaper and plastic, Wang and colleagues found that their nanotube material exhibited adhesive forces of about 100 Ncm^–2, almost an order of magnitude greater than a gecko foot (Science 322 238). That is strong enough for a 4 × 4 mm pad of the material to suspend a 1.5 kg hardback textbook. “In future work modifying the surface of the nanotubes with polymers, proteins, etc, we should be able to make the adhesive nanotubes stick to a wide variety of surfaces,” Liming Dai, one of the team members, told physicsworld.com.

Mark Geoghegan, a physicist from the University of Sheffield, UK, thinks an advantage of the US team’s fabrication technique is that it does not use expensive lithography — although it is still not cheap. “A pack of 20 super-strong carbon-nanotube post-it notes would probably cost well over $1000 per note,” he jokes.

Pulls off normally

A more fundamental advantage of Wang and colleagues’ material is that it is not stoutly adhesive in all directions. If the material is stuck to a wall it will resist a strong downwards tug, but if it is pulled directly away (that is, along the normal) the nanotubes can peel off one by one. It is this property that allows geckos to hang from walls while being able to prize off their feet to scurry around.

Dai says he and the team are now planning to optimize the structure and scale it up so that they can make “spiderman” gloves.

Physicists pull off the gecko's feat

For years scientists have tried — and failed — to engineer materials that would enable robots to mimic the gecko’s ability to scale walls, windows and seemingly any other surface. Now, a team from the US has developed a nanotube material that is not just a match for gecko feet but 10 times more adhesive.

Look close enough at a gecko foot and you will see an ordered, forest-like structure — roughly half a million fine hairs that each sprout into hundreds of even thinner, spatula-shaped tips. When these tips come into close contact with a surface they induce strong van der Waals forces that keep the foot anchored — that is, until the gecko decides to peel it off.

In the past scientists have attempted to copy this hair structure by fabricating arrays of polymer pillars, but these can sustain little more than a third of the gecko’s adhesive force. Although nanotubes have proved better, it is difficult to replicate the delicate tip structure of gecko hairs that would enable the nanotubes to reach their theoretical limit.

Stuck on you

The US team, led by Zhong Lin Wang of Georgia Institute of Technology, has made a structure that looks at least similar to gecko feet through chemical vapour deposition of an ethyne–hydrogen–argon gas over a silicon substrate. By introducing an iron catalyst on the substrate and controlling the temperature and duration of deposition, the team end up with an array of vertical nanotubes with spiralled, fuzzy tips.

In tests on glass, sandpaper and plastic, Wang and colleagues found that their nanotube material exhibited adhesive forces of about 100 Ncm^–2, almost an order of magnitude greater than a gecko foot (Science 322 238). That is strong enough for a 4 × 4 mm pad of the material to suspend a 1.5 kg hardback textbook. “In future work modifying the surface of the nanotubes with polymers, proteins, etc, we should be able to make the adhesive nanotubes stick to a wide variety of surfaces,” Liming Dai, one of the team members, told physicsworld.com.

Mark Geoghegan, a physicist from the University of Sheffield, UK, thinks an advantage of the US team’s fabrication technique is that it does not use expensive lithography — although it is still not cheap. “A pack of 20 super-strong carbon-nanotube post-it notes would probably cost well over $1000 per note,” he jokes.

Pulls off normally

A more fundamental advantage of Wang and colleagues’ material is that it is not stoutly adhesive in all directions. If the material is stuck to a wall it will resist a strong downwards tug, but if it is pulled directly away (that is, along the normal) the nanotubes can peel off one by one. It is this property that allows geckos to hang from walls while being able to prize off their feet to scurry around.

Dai says he and the team are now planning to optimize the structure and scale it up so that they can make “spiderman” gloves.

Zuumer Electric Scooter: Hands-On, First Drive

Zuumer inventor Tom Boyd with his baby.

It’s official - I’m buying one. After just a single ride on Zuumcraft’s new Zuumer Electric Scooter, I’ve just put my $250 down payment for my very own unit. Why? Because the Zuumer is the single most innovative, most useful, and most fun VLEV (Very Light Electric Vehicle) that I’ve ever ridden, and I’ve tried a few. And I don’t impress easily.

The Zuumer Electric scooter is a new kind of VLEV invented by Tom Boyd of Zuumcraft, Inc., of San Diego, CA - it’s a three-wheel electric stand-up scooter that uses an innovative new suspension system on the rear wheels of the unit. This suspension system allows both rear wheels to independently lean into the angle of a turn similarly to how a motorcycle would do. The combination of the two rear wheels and the independent suspension system allows you to ride this scooter very similarly to how you might a skateboard or snowboard. In fact, the closest feeling that I can describe to how riding a Zuumer feels is that it is like snowboarding a road. Except, you can snowboard up hill.

Hands-on With the Zuumer

I live in San Diego and had the opportunity to meet Tom Boyd, the inventor of the Zuumer, and ride one of his scooters. Tom calls himself an evangelist of electric vehicles and the Zuumer, and it shows; his passion for his product and the EV industry was evident as soon as he got out of his truck at the bike trailhead where we met. And true to the Zuumer’s appeal, I barely had time to shake his hand before someone walked up to check one out and proceeded to ask a ton of interested questions.

Tom spent some time showing me some of the unique and innovative features of the Zuumer. The Zuumer features:

The front wheel of the Zuumer - the 1000 watt motor is integrated into the wheel hub.		The rear wheel assembly. Notice how the rear wheels stay perpendicular to the plane of the floorboard - this is what makes the Zuumer so stable and responsive.

That awesome independent rear suspension: this is the heart of this device, and once you get on and you ride it, you’ll understand why it’s such a big deal. You can carve and cut very sharp and quick corners on this vehicle, and it remains stable at top speed - unlike many other stand-up scooters I’ve tried. Once you learn how to shift your body weight and turn by changing your center of gravity, you’re not driving anymore - you’re surfing, and it is exhilarating. For those that have always wanted to feel what it’s like to surf, or snowboard, or skateboard, get on a Zuumer - you’ll get to a similar feeling with a much quicker learning curve.

A 1000 watt brushless front hub motor: This thing’s got power - 20mph top speeds are for real, not just a claim. And the unit didn’t slow down all that much going uphill. The fact that it’s integrated into the front hub makes this motor more efficient, less prone to wear, quieter, and easier to maintain than a motor with a chain or belt drive.

Another shot of the independent rear suspension system.		The modular battery pack under the scooter’s floorboard. Tom is sliding one out to illustrate how they are removed from the unit.

Two Modular Lithium Polymer batteries: Each battery is modular, and features a unique digital display that tells you how much charge and riding time is left on the battery. You can take the batteries out of the unit, and recharge them at home - there’s no need to wheel the whole scooter into your house to recharge. Together both batteries provide you with 20 miles of range. This is nothing short of amazing for a stand-up scooter, and is by far the longest claimed range I’ve ever seen for a scooter of this size.

An intelligent motor and battery controller: If the battery charge gets low, a ‘limp home’ mode kicks in that will slow down the motor to ensure you have enough charge to get home without completely discharging the batteries. This is useful when you get caught off guard with a low battery charge. You’ll get home slower, but you’ll get home.

A key less alarm system: This feature is the pinnacle of cool and useful. Basically, you get a key fob just like your car alarm. Press a button, and the unit turns itself on and is ready for action. Press another button, and the power is killed, and the alarm turns on. A mercury switch in the vehicle will activate a loud alarm if anyone tries to walk off with your scooter (the scooter will not operate with the alarm on). Another button activates a ‘panic’ mode, setting off the alarm. I have to say, this feature alone adds tremendous value to this product, as you can confidently step away from your prized scooter without worrying about it getting stealthily wheeled off while you’re getting your coffee. A definite real-life concern with my current unit, and a concern for anyone living in an urban environment.

The left handlebar. Notice the buttons for lights and the horn.		The right handlebar. Notice the electronic key dangling from the handlebar, and above it the cruise control button.

Cruise control: Yeah, you read that right. Cruise control. Crank up the throttle to the desired speed, press a button, and the scooter will remain at that speed until you hit the brakes. Now you’re riding! Now grab on to the middle of the handlebar with your leading hand, turn sideways, and you’ve got yourself a motorized snowboard, able to carve uphill or downhill. What a feeling - I know, I tried it. Seriously however, this feature will appeal to anyone who has ever ridden a stand-up scooter and knows what a pain it is to maintain a desired speed. The cruise control leaves you free to enjoy what the Zuumer is all about - that awesome feeling of surfing the concrete, at 20 mph.

Headlight, brake/taillight, and horn: You can ride the Zuumer at night if you need to, as the Zuumer includes a very light LED headlight and tailight system. A brake light also illuminates when you activate the brakes. A loud horn is also provided on the unit for when you need to get those slowpokes out of your way.

Three disk brakes: The Zuumer can safely stop from 20mph in less than 15 feet, and can do it without you flying off the unit. That’s impressive.

Adjustable handlebars: Short or tall, the Zuumer takes them all. The handlebars are adjustable, so you can set them to whatever height is comfortable for you.

Solid construction throughout: The Zuumer I rode was a pre-production model and made from high-quality machined aluminum and steel - it felt rock-solid to drive and was a thing of beauty to behold. The production models will be just as well-constructed, Tom said.

The Zuumer in all its glory.

How much does it cost for all this goodness? The retail price is currently set at $2,195, and Zuumcraft is taking deposits now for its first batch of Zuumers, due out in January 2009. I have to tell you, it’s great to already know what I’m getting for Christmas!

Tom calls the Zuumer “Cool, Green, Fun” and I have to agree with him on that point. All in all, I got to spend about an hour riding on the Zuumer with Tom, and it was exhilarating. I was able to ride the unit standing forward, like on a traditional stand-up. I was also able to ride it sideways, like a skateboard or snowboard. The unit was responsive to my every shift and turn, and I was quickly carving lazy S’es on the road. When we came to turns, I was able to lean into them and take them steeply at speeds which would have had me flying off of my regular stand-up. All in all, it was amazingly fun. At the end of my ride, I found myself stalling for more time, just to get a few more minutes with the device. What sucks now is that I have to wait for three months to get my hands on my own unit.

Tom and Zuumcraft are planning to sell the Zuumer directly online through their website, http://www.zuumcraft.com and have identified several target markets to sell the device to. I think that anyone who is interested in getting an alternative transportation device of any kind should take a good look at the Zuumer - in my mind, the target market is anyone who is interested in a fun, fast, and useful personal electric transportation device.