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.
Results
Platform Natural Frequency
The natural frequency of the platform mass-spring system:
Where mtotal = mrotor + mplatform and ktotal is the combined stiffness of all springs (N/m).
Required Stiffness per Spring
Where n is the number of springs and ftarget = 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
Given: mrotor = 80 kg, mplatform = 15 kg, 1800 RPM, 4 springs, ratio 1/3
mtotal = 95 kg, fop = 30 Hz, ftarget = 10 Hz
ktotal = 95 × (2π×10)² = 375,055 N/m = 375.1 N/mm
kper spring = 375.1 / 4 = 93.8 N/mm
δstatic = 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.
A balancing platform (soft support) is a simple structure — typically a steel frame or plate — mounted on springs. It supports a rotor for field balancing by allowing free vibration response at operating speed. The platform’s natural frequency is tuned well below operating speed (typically ≤ 1/3).
The natural frequency must be well below operating speed to ensure the system operates in the isolation region — above the resonance peak. At a frequency ratio of 3, transmissibility drops to about 12.5%, meaning the rotor vibrates freely and the balancing instrument can accurately detect unbalance.
Common configurations:
- 4 springs — most common, one at each corner
- 2 springs — small, lightweight rotors
- 3 springs — triangular platforms
- 6–8 springs — large, heavy rotors
All springs must have equal stiffness and the load must be centered.
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. Ensure the platform is flat and all spring mounting points are at equal height.
Yes, but rubber mounts have higher damping (reducing measurement precision), and stiffness varies with temperature and load history. Coil springs are preferred for their consistent, well-defined stiffness and low damping. Dynamic rubber stiffness is typically 1.3–2× higher than static stiffness.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and software. Design your balancing platform and verify results with our portable balancers. Used in 50+ countries.
