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The Motorized Unicycle

Wed, 08/01/2012 - 2:15pm
Chris Fox, Associate Editor, Product Design & Development

Imagine a hybrid unicycle with the balancing elements and mobility of a Segway. Frightened yet? RYNO Motors has created a motorized unicycle, an all electric mobility product that’s been designed specifically to transport individual riders through, around, and in-between the obstacles that crowd dense urban landscapes.

The RYNO has the aggressive appearance of a motorcycle, but contains a unique balance system that allows a single wheel. As RYNO Motors CEO, Christopher Hoffman was driving to go fishing with his daughter, she asked "Hey daddy, I saw this one wheeled motorcycle in a video game, can you actually build that?" Hoffman, a 15-year veteran designing industrial machines for car parts, had never seen anything like it, so he went to work.

"My background has made me a good mechanical engineer when it comes to taking off-the-shelf components and figuring out how to build some robot out of them," explains Hoffman. As he approached the conceptual motorized unicycle, Hoffman was essentially trying to kill the project; searching for a technicality or expecting the system to be vastly expensive.

"I started with servo motors and conventional servo motors. I figured, if this is a gyro stabilized platform, I don’t need an encoder." Hoffman says, "I also realized that I didn’t even need all of the closed-loop motion control; it’s all open loop, so I was able to use a $35 scooter motor. I couldn't kill it on that." As he pieced together the initial build, Hoffman combined gyros from electric helicopters, a motor controller from a former BattleBots company, a motorcycle tire, and a processor for his first prototype.

"The [first] bike I made was a brick. In my head you could steer it, but when you actually got on the thing it was impossible. I got all the software working and got it to balance, but when a unicycle club came over to try it, only one guy could really ride it kind of well."

Balance and Turning

Using front to back gyro accelerometer technology, like the Segway, the RYNO has a simple pivot and balance system that has a slight learning curve, but quickly becomes easy. Steering is achieved like a motorcycle, "using a pair of handlebars, a throttle control, and a hand brake. The upper body of the RYNO pivots over the wheel on a steering joint, unlike the Segway, which uses a steering column that the rider has to control to steer around corners," explains Hoffman.

Turning is more in the hips and lower body as apposed to upper-shoulder strength. Hoffman says, "Turning is like falling into the turn with a very small amount of effort." The turning becomes natural after some time on the vehicle, but our natural tendencies have to be suspended in order to achieve fluid riding. New riders that fight the bike and brace against turns, like a car, take longer to learn than somebody who can feel their way into corners. Hoffman says, "All in all it takes about ten minutes to learn to ride in a straight line and it usually takes until the second day before turning becomes more natural."

When he started really delving into the apparent steering and balance issues Hoffman started playing around with flywheels and stabilizing. He based the flywheel ideas off of an MIT inverted pendulum robot that used spinning flywheels for balance. Hoffman quickly learned that this system was great in a lab, but you could never economically make something like it. "Then I started looking at motorcycles in a different way, and thought, 'what if we put steering on this thing?'" The idea was to use rake angle and a set back like the front fork on a motorcycle. "It didn’t completely make sense to have the wheel turn. I couldn’t mentally picture how it was going to work, but it was the only thing that we could think of that wasn’t going to be expensive," explains Hoffman.

As he was still looking for a way to kill the project, Hoffman thought, "If we can solve this steering thing great, if we can’t, it’s done."

Unicycles are a combo of pedaling and twisting for balance; doing three or four things in combination to balance. There is something about sitting on the RYNO with the handle bars and giving the rider something to crank on that makes it easier. Hoffman explains, "I welded together this piece of crap with a steering linkage in it, stuck a tire on, and loaded some software. I was riding the thing around the neighborhood in ten minutes."

Suspension

As the RYNO is intended to be a multi-terrain, urban vehicle, Hoffman wanted to allow the bike to handle pot-holes and off-the-curb riding. He thought they could use the tire as suspension, but with a one-wheel vehicle they needed a rock-hard wheel. Using a motorcycle racing tire, the RYNO is equipped with a 2.5" suspension with adjustable shocks. "This allows for riding off curbs at full speed and absorbing the shock of riding through pot-holes. It also allows the rider to adjust the ride height and dampening," says Hoffman.

Electromechanical Braking

According to Hoffman, the RYNO brings a new technology to the industry with its electromechanical disk brake system. He explains, "The problem with self-balancing vehicles is when you go to stop it actually leans it back, which dumps the energy from the battery. So, going 15 mph and stopping requires a huge amount of energy." After many smoking wires, toasted brushes, and killed batteries it was apparent that a new braking system was needed. "Essentially, it's a brake caliper with a servo motor in it, so you grab the brake lever and the bike sits back and starts grabbing this disc," explains Hoffman. The new braking system seems to open a avenue of opportunity for the one-wheeled market. Hoffman continues, "The physics with a motorcycle is that as you stop, at some point your body shifts over the handle bars. With one wheel, I just keep pulling back and back and back, until I’m burning rubber. I don’t know exactly what is going to happen when we ride with the new system, but I think with the suspension it could be really fun."

The Next Extreme?

"RYNO has been designed to resemble a conventional motorcycle in its controls, its riding position, and how it feels. What’s different is that it’s only half as long and, with their feet, riders can pivot 360 degrees on a vertical axis," explains Hoffman. This gives an interesting perspective to the uses of the RYNO. As an electric mobility product, the RYNO is safe to operate inside and out, so all these combined features allow riders to "enter an elevator, spin around, press the floor button, and then effortlessly back-up like any other person that is walking. "We have tested this use-case repeatedly in crowded elevators and sidewalks, and found that because the rider places their feet on the ground when stopped, other people find the product unobtrusive and very approachable," says Hoffman.

The RYNO is not street legal, per say, but rather in the same market for the same regulated usability case as the Segway scooter. "In the second year we may up the speed to 20 to 25 mph," explains Hoffman. Though the thought of traveling at highway speeds on a unicycle is exciting, the laws of physics come to bear after 25 mph, so there are no plans to expand beyond.

Looking to the new extreme, Hoffman digresses about aggressive stops, burning rubber, one-wheel drifting, and curb-hopping. Whether it's mudding, racing, or just changing up the gearing a bit, Hoffman says, "We encourage that and are looking forward to that kind of stuff."

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