What is a balancing platform?

A balancing platform is a simple structure mounted on springs that supports a rotor for field balancing by allowing free vibration response at operating speed. Its natural frequency is tuned well below the rotor's operating speed.

Why must the platform natural frequency be below operating speed?

The platform natural frequency must be well below operating speed to ensure the system operates in the isolation region, above resonance. At a frequency ratio of 3, transmissibility drops to about 12.5%.

How to choose the number of springs for a balancing platform?

Common configurations: 4 springs for rectangular platforms, 2 for small rotors, 3 for triangular platforms, 6-8 for large heavy rotors. All springs must have equal stiffness.

What materials are best for building a balancing platform?

Welded steel frame or plate (10-20 mm thick) is most common. Aluminum for smaller rotors. Platform mass is typically 10-25% of rotor mass.

Can I use rubber mounts instead of springs?

Yes, but rubber mounts have higher damping and variable stiffness. Coil springs are preferred for their consistent, well-defined stiffness and low damping.

Free Engineering Tool

Balancing Platform Design Calculator

Design a balancing platform (soft support) for field rotor balancing. Calculate the required spring stiffness, natural frequency, static deflection, and transmissibility.

Soft Support Design Transmissibility 2–8 Springs

Rotor Mass (kg)

Platform Mass (kg) — ~20% of rotor

Operating Speed (RPM)

Number of Springs

Frequency Ratio Target

Quick presets

Results

Required Stiffness per Spring

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Total Stiffness (k_total)

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Platform Natural Frequency (f_n)

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Static Deflection (δ_static)

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Transmissibility

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Frequency Ratio (f_op / f_n)

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Total Mass

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Platform Natural Frequency

The natural frequency of the platform mass-spring system:

Where m_total = m_rotor + m_platform and k_total is the combined stiffness of all springs (N/m).

Required Stiffness per Spring

Where n is the number of springs and f_target = RPM/60 × ratio (e.g. ×1/3).

Transmissibility

Undamped transmissibility at operating speed:

For good balancing conditions, T should be less than 15%. A frequency ratio of 3 gives T ≈ 12.5%.

Static Deflection

Practical Example

Example — 80 kg Rotor at 1800 RPM

Given: m_rotor = 80 kg, m_platform = 15 kg, 1800 RPM, 4 springs, ratio 1/3

m_total = 95 kg, f_op = 30 Hz, f_target = 10 Hz

k_total = 95 × (2π×10)² = 375,055 N/m = 375.1 N/mm

k_{per spring} = 375.1 / 4 = 93.8 N/mm

δ_static = 95×9.81 / 375,055 × 1000 = 2.49 mm

T = 1/(3²−1) = 12.5%

⚠️ Note: Ensure all springs have equal stiffness and the load is centered. Unequal deflection causes tilting, which distorts vibration readings during balancing.