July 19, 2000 12:00 am

CORVALLIS (AP) A toy inventors crazy bet ended with his idea taking flight for da Vinci Days, a local festival showcasing art, science and technology.

Michael Marks, co-owner of Heartfelt Toys, built a working helicopter after a friend bet him $25 two years ago that he couldnt do it. Now, his creation is in the towns Central Park, providing rides for children at the festival, which runs through Sunday.

I guess you could say I did it because it was there in my head, said Marks. It became a challenge, and an inventor loves challenges.

Marks first built a helicopter prototype out of an electric blender turned upside down, with a shaft and rotor where the beater usually is. He attached the contraption to a boom, which pivoted on a pedestal with counter weights to help provide lift.

The final product, about 20 times the size, works much the same way. On one side of the boom is a plastic lawn chair. Above the chair sits an electric motor taken from a treadmill. The motor drives a handmade wooden rotor.

On the other end of the boom is a series of barbell weights, levers and garage door springs. Because the weights and springs provide most of the lift, the small engine only has to provide 10 to 15 pounds of lift, Marks said.

The child who sits in the chair controls the speed and tilt of the motor. The motors speed dictates the height of the chair. The tilt drives the ride forward or backward in a circle.

For now, only children older than 8 years old and lighter than 100 pounds can ride in the people copter.