Introduction

When the power transmitted between two shafts is relatively small, motion can be transferred using plain cylinders or discs, commonly referred to as friction wheels. These rely on surface contact and friction to transmit torque.

However, as the transmitted power increases, slippage between the discs becomes significant, leading to loss of synchronization and unreliable motion transfer.

Why Gears?

To overcome the limitations of friction wheels, gears are employed. Gears transmit motion from one shaft to another through the successive engagement of teeth, ensuring precise and slip-free transmission.

This method does not require any intermediate link or connector. Instead, the gear teeth mesh directly, allowing for controlled and continuous motion transfer.

Contact Mechanics

In gear systems, the surfaces of the two gears make tangential contact and roll along the tangent at the point of contact. This rolling action ensures smooth transmission.

Importantly, no motion occurs along the common normal at the point of contact. Any such motion would either break the contact or cause one gear to penetrate the other, violating the physical constraints of gear engagement.

Key Takeaways

• Friction wheels are suitable only for low-power transmission.
• Gears eliminate slip and ensure definite motion transfer.
• Gear teeth engage tangentially, enabling rolling contact.
• Motion along the common normal is physically impossible and undesirable.