See how an RV reducer, harmonic drive, planetary gearbox and cycloidal reducer get their ratio. Drag the tooth counts, enter your motor speed and torque, and read the output.
Pick a gearbox type and drag the sliders. The drawing is rebuilt from the tooth counts you choose, moves at the speeds they produce, and shows the output speed and torque for your motor.
How an RV reducer gets its ratio. Change the sun, crank gear and pin counts. The spur stage and the cycloid stage multiply: ratio = 1 + (crank gear teeth ÷ sun teeth) × pin count, so 14, 30 and 20 give about 44:1.
Turn on JavaScript to change tooth counts and see the ratio, output speed and torque update live.
The same formulas drive the drawings above. Each example uses the default tooth counts in the simulator.
A spur planetary first stage drives crankshafts that orbit two cycloid discs inside a pin ring, for very high stiffness.
i = 1 + (Zcrank gear ÷ Zsun) × Zpins
Example: 1 + (30 ÷ 14) × 20 = 1 + 42.86 = 43.86, about 44:1.
An elliptical wave generator deforms a thin flexspline so its teeth engage a rigid circular spline two teeth at a time.
i = Zflexspline ÷ (Zcircular spline − Zflexspline)
Example: 60 ÷ (62 − 60) = 30:1, output turns opposite to the input.
A central sun gear drives planets that roll inside a fixed ring gear; the planet carrier is the output.
i = 1 + Zring ÷ Zsun
Example: 1 + 48 ÷ 12 = 5:1 for one stage; two stages multiply, 5 × 10 = 50:1.
An eccentric cam wobbles a lobed disc around a ring of pins; the disc turns one lobe per input revolution.
i = Zlobes = Zpins − 1
Example: 12 pins → 11 lobes → 11:1, output turns opposite to the input.
Output torque = motor torque × ratio × efficiency. The simulator uses typical efficiencies of 85% for RV reducers, 78% for harmonic drives, 96% for single-stage planetary gearboxes and 90% for cycloidal reducers. These are general catalogue values; use the datasheet of the model you choose for sizing.
In a harmonic drive the flexspline has two teeth fewer than the fixed circular spline, so each input turn moves it back by two teeth. In a cycloidal reducer the disc rolls backwards one lobe per input turn. Both reverse the direction. Planetary and RV reducers keep the motor direction.
Three planets spaced 120° apart only mesh with the sun and ring at the same time when the sun and ring tooth counts add up to a multiple of three. The simulator snaps the planet count to the nearest value that fits.
Standard ratios are listed on each gearbox page. If you need a ratio or mounting that is not listed, send us the requirement and we will check whether the tooth counts and housing can be made for it.
Every gearbox can be joined to any motor, robot joint or housing: we machine a custom coupling bored to both shafts, plus an adapter flange if the mounting faces differ. Send both shaft sizes, a drawing or just the motor model number.
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