Drive geometry & loading
mm
Pitch diameter (datum)
mm
Pitch diameter (datum)
mm
Recom.: 0.7(d1+d2) … 2(d1+d2)
rpm
kW
—
V-belt typical: 0.45–0.65
—
Results
| Parameter | Value | Unit | Formula / note |
|---|
Diagram
Formulas & V-belt profiles
Geometry
i = d₂/d₁ = n₁/n₂v = π·d₁·n₁/60 000 [m/s]
L = 2a + π(d₁+d₂)/2 + (d₂−d₁)²/(4a)
α₁ = 180° − 60°·(d₂−d₁)/a
Belt tensions (Euler)
F₁ − F₂ = P·1000/v [N]F₁/F₂ = e^(μ'·α₁_rad)
F₀ = (F₁+F₂)/2
F_shaft ≈ 2·F₀·sin(α₁/2)
μ' = effective friction (incl. wedge effect of V-groove). Typical: 0.45–0.65 for rubber on cast iron.
Belt sag
e = √(a² − ((d₂−d₁)/2)²)f_rec = 0.016 · e [mm]
Recommended sag (free span): ~1.5–2% of span length. Check by pressing belt at midspan. Too tight → bearing overload; too loose → slip.
V-Belt profiles (ISO 4184)
| Profile | d₁_min | v_max | P range |
|---|---|---|---|
| SPZ | 63 mm | 50 m/s | 0.2–3 kW |
| SPA | 90 mm | 50 m/s | 0.7–10 kW |
| SPB | 140 mm | 50 m/s | 2–25 kW |
| SPC | 224 mm | 50 m/s | 7–90 kW |
Design tips
- Minimum wrap angle: α₁ ≥ 120° for reliable power transmission
- Belt speed: 5–30 m/s ideal; v_max = 50 m/s for narrow V-belts
- Centre distance: 0.7(d₁+d₂) … 2(d₁+d₂)
- Standard belt lengths per DIN 7753 — round calculated L to nearest standard
- Use multiple belts for high power — minimise z to reduce shaft load
Notes on μ'
The effective friction coefficient μ' accounts for the wedge action of the V-groove: μ' = μ / sin(β/2) where β ≈ 40° groove angle, μ ≈ 0.35 rubber/cast iron.
This gives μ' ≈ 0.35 / sin(20°) ≈ 1.02 — but in practice slip losses reduce effective μ' to 0.45–0.65. Use 0.51 as default.