An Ultra Light Urban Vehicle project at Bradley University shows how acetal gears — specifically gears made of DuPont Delrin POM — offer strength, toughness and low-friction attributes needed to take the load generated stress in drivetrain transmission systems while significantly damping noise and reducing weight inherent in metal gears.The Ultra Light Urban Vehicle project is the brainchild of Martin Morris, professor of mechanical engineering at Bradley University, Peoria, IL. The challenge to design and manufacture a zero-emissions vehicle began in 2006 and has evolved into a 3-wheeled vehicle licensed as a motorcycle that carries two people, baggage and weighs 430 lbs. It offers regenerative braking, a top speed of 45 mph and a range of 40 miles — Bradley Design Team claims it costs 0.6 cents per mile to operate.
Winzeler Gear, Harwood Heights, IL., provided design and manufacturing support, while DuPont Performance Polymers supplies Delrin acetal (POM).
“As the world changes, we need to challenge many of our preconceived notions. We also need more whole brain, especially right brain, thinking to innovate,” said John Winzeler, president — Winzeler Gears and a fervent supporter of student challenges and art programs. “Student design challenges and art programs are great ways to challenge our prejudices and stimulate new ideas.”
"Traditionalists would say harsh transmission applications preclude POM,” said Tim Brogla, program developer — DuPont Performance Polymers. “Clearly, this project challenges some of those ‘absolutes;’ it doesn’t require a leap of faith to see these gears in small engine transmissions, such us riding lawn mowers and golf carts.”
The drivetrain transmission uses several intricately machined gears that face conditions that traditional engineers may consider off limits for standard acetal material. “The high-performance nature of a homopolymer acetal can manage the torque and load while delivering low friction and reduced noise,” said Mike Cassata, design engineer — Winzeler Gear. “The planetary transmission gears of Delrin POM must withstand the torque produced by a 25 horsepower motor 6,000 RPM.”
The innovative gear transmission consists of a 14 teeth, 3 module, 42 mm pitch diameter sun gear mounted to the motor shaft. The sun gear drives 4 planet gears with 17 teeth and a 51 mm pitch diameter coupled to the output carrier shaft assembly. The planet gears rotate in a fixed internal gear with 50 teeth and a 150 mm pitch diameter. All gears are 25 mm facewidth.
"Gears can be machined from bar or plate stock of Delrin, significantly cutting cost and time while delivering mechanical properties comparable to the injection molded gears. “We can proceed from design to machined models in weeks, with a small tooling investment,” said Cassata.
And a bit of foreshadowing; the next generation of student design will challenge designers to take even more weight and noise from the vehicle by using more Delrin POM in the gears and housings. “The next generation will further show the viability of the product in harsh conditions, making it even easier to imagine using this often under-rated material in small engine transmissions like riding lawn mowers, golf carts — anywhere moving parts face the need to reduce weight and noise,” added Brogla.
