Belt Drive Theory - Vocabulary (Open/Cross Belt, Velocities, Tensions, Power)

Vocabulary flashcards covering key concepts from the belt drive lecture notes, including velocities, tensions, lengths, friction, centrifugal effects, and power.

Linear velocity

The speed of the belt along its length; also called peripheral velocity; equal to the belt’s circumferential speed.

Peripheral velocity

Another name for linear velocity of the belt; the speed at the belt’s circumference.

Velocity ratio (VR)

The speed ratio between driven and driving pulleys; for no slip in belt drives, VR = n1/n2 = d2/d1 (open belt).

VR with belt thickness

Adjustment of VR to account for belt thickness t: VR = n2(d1 + t) / [n1(d2 + t)].

Slip (S1/S2)

Relative motion between belt and pulleys; S1 is slip between driver and belt, S2 is slip between belt and follower.

Tension on the tight side (F1 or Ft1)

Tension in the belt on the tight (driving) side that transmits power.

Tension on the slack side (F2 or Ft2)

Tension in the belt on the slack side, lower than the tight-side tension.

Angle of contact

Wrap angle of the belt around a pulley, in radians; larger wrap increases friction capacity.

Coefficient of friction (μ)

The friction coefficient between belt and pulley surface; used with angle of contact to determine tension ratio.

Belt speed (v)

The linear speed of the belt as it moves over the pulleys.

Radius of pulley (r)

Radius of a pulley (driving or driven) around which the belt runs.

Power transmitted by a belt

Power is the product of belt speed and the net driving tension: P ≈ v (Ft1 − Ft2) (adjusted if centrifugal tension is included).

Torque on driving pulley

T1 = r1 × (Ft1 − Ft2); torque produced on the driving pulley by the belt tensions.

Torque on driven pulley

T2 = r2 × (Ft1 − Ft2); torque transmitted to the driven pulley by the belt tensions.

Open belt drive

Belt arrangement where pulleys rotate in the same sense and belt has a specific wrap geometry; length and tension relations depend on center distance and pulley sizes.

Cross belt drive

Belt arrangement where the belt crosses itself, causing pulleys to rotate in opposite directions and altering wrap geometry.

Length of open belt drive

The belt length in an open belt configuration, determined by center distance and pulley diameters with a standard correction term.

Length of cross belt drive

The belt length in a crossed belt configuration, determined by center distance and pulley diameters with geometry changes due to crossing.

Center distance (C)

The straight-line distance between the centers of the two pulleys.

Centrifugal tension (Fc)

Tension in the belt due to belt mass and speed; Fc = m v^2, acts along the belt tangent to motion.

Tensions with centrifugal tension (Ft1, Ft2)

Effective tight- and slack-side tensions when Fc is included: Ft1 = F1 + Fc and Ft2 = F2 + Fc.

Maximum tension in the belt

The maximum allowable belt tension, typically Fmax = σmax × A, where σmax is the material’s safe stress and A is cross-sectional area.

Initial tension

The belt tension when the system is at rest; used to ensure proper belt grip and service life.

Maximum power condition

A design condition in which the belt transmits maximum power, often when F1 = 3 Fc (tight-side tension equals three times centrifugal tension).