A hay tedder is an agricultural machine that lifts, spreads, and fluffs cut hay so it dries more quickly and evenly. Drying matters because hay must reach a safe moisture level before baling to prevent spoilage, mold growth, and overheating in storage. The machine uses spinning rotors with spring tines to throw hay into a loose, airy layer.
This simple action combines ideas from rotational motion, friction, airflow, and energy transfer.
Key Facts
- Tangential speed of a tine tip is v = 2πrf, where r is rotor radius and f is rotation frequency.
- Angular speed is ω = 2πf, measured in radians per second.
- Power required by the tedder is P = τω, where τ is torque and ω is angular speed.
- Drying rate increases when hay surface area and airflow increase, but excessive speed can cause leaf loss.
- Ground speed affects overlap and spreading pattern, with typical tedding speeds around 6 to 12 km/h depending on crop and field conditions.
- Centripetal acceleration at the tine tip is a = v^2/r = ω^2r.
Vocabulary
- Hay tedder
- A hay tedder is a machine that spreads and aerates cut hay using rotating tines to speed drying.
- Rotor
- A rotor is a spinning hub or wheel that carries tine arms around a circular path.
- Tine
- A tine is a flexible metal finger that lifts and throws hay as the rotor turns.
- Power take-off
- A power take-off is the rotating shaft on a tractor that transfers engine power to an attached machine.
- Moisture content
- Moisture content is the fraction or percentage of water in hay compared with its total mass or dry matter mass.
Common Mistakes to Avoid
- Using rotor speed without converting units, which is wrong because equations for angular speed usually require revolutions per second or radians per second, not revolutions per minute.
- Assuming faster tedding is always better, which is wrong because excessive tine speed can shatter dry leaves and reduce hay quality.
- Ignoring ground speed, which is wrong because the spread pattern depends on both rotor motion and how far the tractor moves during each rotation.
- Treating all hay as drying at the same rate, which is wrong because crop type, thickness of the swath, humidity, sunlight, and wind strongly affect evaporation.
Practice Questions
- 1 A tedder rotor has a radius of 0.75 m and spins at 180 rpm. What is the tangential speed of the tine tips in m/s?
- 2 A tractor supplies 4.0 kW of power to a tedder rotor spinning at 20 rad/s. What torque is being delivered to the rotor?
- 3 A farmer notices that hay is drying slowly in thick clumps after mowing. Explain why using a hay tedder can speed drying, and describe one condition where tedding too aggressively could reduce hay quality.