By Hiroko Sato

MediaNews

AYER -- Tim Leonard calls Whymcycle the "dancing bike."

The scooter-like bicycle with a single pedal has a rear wheel with an off-centered hub that causes the chain stay -- the bar that connects the hub to the pedal -- to jerk up and down as the wheel rolls forward. Leonard, an engineer from Groton, was pedaling this playful bike down the Nashua River Rail Trail with his teenage son four years ago when he ran into Duane Cromwell, a fellow town resident who was riding a trikke, a tricycle that one stands on and rocks back and forth to drive.

The chance encounter between Leonard and Cromwell, who serves as the chairman of Friends of Nashua River Rail Trail, resulted in the annual Human Powered Vehicle Festival that has brought together bike enthusiasts from around the region who handcraft or just enjoy riding unusual modes of transportation.

From unicycles to tricycles to "rat rod bikes," spectators are guaranteed to see -- and even get to try out -- unique, nonautomotive vehicles, Leonard said.

"I enjoy a party. It's just fun to get together," Leonard said.

It's even better when the party includes funky vehicles, he said.

The fourth annual Human Powered Vehicle Festival will take place in Ayer on Saturday, Sept. 21. Vehicle owners gather in the parking lot of the Nashua River Rail Trial near the MBTA train station in Ayer at 9 a.m., and enjoy a 15- to 20-mile-loop ride on the trail through Groton and Shirley. From noon to 4 p.m., the riders will parade up and down Main Street in downtown Ayer. If there is a steady rain that day, the event will be rescheduled for Oct. 5.

Organized by the Friends of Nashua River Rail Trail, the festival draws about 20 riders plus 200 spectators each year, according to Leonard. Many people visit downtown Ayer without knowing the event is taking place.

"Their jaws drop," Leonard said.

Leonard said a typical conversation with those who approach him starts like this:

"What is it?"

"It's a Whymcycle. Do you want to try?"

"Can I?"

They would ride it and exclaim, "This is cool!"

Leonard encourages them to come back the following year with their own bike. Some of them have, he said.

Leonard's love for human-powered vehicles started many years ago when someone he knew gave him a Whymcycle as a gift. A lifelong bicycle enthusiast who used to bike in Boston and in Cambridge, England, while studying at Boston University and the University of Cambridge respectively, he likes the idea of using his own muscles to move a vehicle. Just like many members of the Friends of the Nashua River Rail Trail, Leonard has enjoyed riding a bike on the local trail that boasts impressive waterfront views, forests and wildflowers in open fields.

Leonard heard from Cromwell after they first met that some Friends of Nashua River Rail Trail members had wanted to put together some sort of festival to bring community residents to the trail. The two men then came up with the idea for the carnival of unusual wheeled transport.

"So, the purpose of the festival is to get people to come out and celebrate the rail trail," Leonard said.

Human Powered Vehicle covers a whole gamut from bicycles to weta legs, which are leg extensions that look like bionic limbs. While some vehicles look amusing and primitive, there are also futuristic, fast-moving ones, like velomobile, a bicycle with an aerodynamic shell covering the vehicle and can travel at 40 mph.

"We are happy to include people who are into skateboarding, inline skating, roller skates and skis," Leonard said.

In fact, some participants in past festivals enjoyed showing off human-powered vehicles that look like a hybrid between inline blades and skis. Many participants ride readymade vehicles that they bought, but some even create ones from their own ideas, using scrap metals and other materials.

Participants come from all walks of life. Cromwell operates a business in the health-care industry. There are students, teachers, engineers and floor contractors among others. Leonard said many of the riders participating in the local festival live in Ayer, Groton and the surrounding towns with the rest coming from within a two-hour-drive range in New England.

The festival is free and open to the public. For more information, visit http://humanpoweredvehiclefestival.friendsofthenashuariverrailtrail.com/.

Follow Hiroko Sato on Twitter and Tout @satolowellsun.