how to calculate gear ratio for gear motor?
Core Methods for Calculating the Speed Ratio of Gear Reducers
The speed ratio of a reducer, the matching motor power,
and the output torque are interrelated and mutually influential.
Different automated equipment requires different speeds,
making the selection of different reducer speed ratios crucial for different operating conditions.
Today, Huxing will discuss how to calculate and select the transmission ratio of a reducer.
The speed ratio (gear ratio) is the ratio of the motor's input speed to its output speed,
and it is also the torque amplification factor.
Correct calculation directly determines the equipment's performance and lifespan.
I. Tooth Count Calculation Method (Most Accurate)
Speed ratio i = Number of teeth on the driven gear ÷ Number of teeth on the driving gear.
For example, if the driving gear has 10 teeth and the driven gear has 50 teeth, then i = 5:1,
the output speed is reduced to 1/5, and the torque is amplified by 5 times (ideal operating condition).
II. Speed Measurement Method (Applicable to Existing Equipment)
i = Motor input speed ÷ Output shaft speed. Measured with a tachometer,
it can take into account actual factors such as gear wear.
III. Overall Speed Ratio of Multi-Stage Gearboxes
Overall speed ratio = First stage speed ratio × Second stage speed ratio × … For example,
three speed ratios are 2:1, 3:1, and 2.5:1, with a total speed ratio of 15:1.
IV. If it is a planetary gear reducer,
then the planetary reducer speed ratio = number of teeth on the internal ring gear divided by the number of teeth on the sun gear + 1.
Key Correction—Efficiency Loss: Actual output torque = motor torque × speed ratio × transmission efficiency (η).
Worm gear efficiency may only be 50-90%, and helical gear efficiency is approximately 98% per stage.
It is essential to reduce efficiency accordingly; otherwise, the motor is prone to overload.
Advanced Consideration—Inertia Matching (Required for Servo Systems): For frequent start-stop or
high-speed dynamic response applications, the optimal speed ratio N = √(load inertia ÷ motor rotor inertia).
This value optimizes acceleration performance; ignoring it will lead to sluggish system response or oscillations.
Common Mistakes:
1. Confusing the driving and driven gears, resulting in the reciprocal ratio.
2. Including the idler gear (only changes the direction of rotation, does not affect the speed ratio).
3. For single-stage speed ratios exceeding 10:1, multi-stage reduction gears should be selected.
4. Self-locking characteristics not considered:
Worm gear reducers with speed ratios >20:1 may not be able to drive in reverse;
requirements must be confirmed.
Before selecting a speed ratio, it is essential to clearly define the load torque, speed,
duty cycle (continuous/intermittent), and starting impact. Only through a combination
of our selection tools and verification by our engineers can long-term reliable operation be ensured.
