Multi-material RC pushrod buckling calculator with metric/imperial unit toggle, adjustable servo torque, and intermediate guide supports.

Units
Servo torque 1.8 kg·cm
Horn arm 10 mm
Stall force: 17.6 N
CF round rod
Diameter 2.0 mm
— N · — g/dm
CF tube
OD 3.0 mm
ID 1.5 mm
— N · — g/dm
Balsa + M2.5 steel
Balsa Ø 6.5 mm
Steel ends (each) 40 mm
— N · — g/dm
Fibreglass rod
Diameter 2.0 mm
— N · — g/dm
Piano wire (steel)
Diameter 1.6 mm
— N · — g/dm
Total length 300 mm
Guide supports: P_cr boost: 1×
P_cr drops with the inverse square of length.
Pinned ends. Pultruded CF: E=130 GPa, ρ=1.55 g/cm³. Pultruded fibreglass: E=40 GPa, ρ=2.0 g/cm³. Hard balsa: E=4 GPa, ρ=0.18 g/cm³. Music wire / steel: E=200 GPa, ρ=7.85 g/cm³. M2.5 thread: 2.05 mm minor for I, 2.27 mm equivalent for mass. Stepped balsa+steel column solved by Rayleigh approximation. Supports as ideal pin nodes at equal spacing; P_cr scales as (n+1)². Each support adds 1 g. Servo stall force = torque ÷ horn arm. Conversions: 1 in = 25.4 mm, 1 N = 3.5969 oz-f, 1 g/dm = 0.0269 oz/in, 1 kg·cm = 13.887 oz·in. Y-axis caps at 200 N / 720 oz — actual values in panels.