Useful · Servo drives and gearboxes
A servo motor with a planetary gearbox needs answers to three questions: what torque and speed the mechanism requires, which motor delivers them with a margin, and which gearbox withstands them — and can be mounted on that motor. The online sizing tool answers them at once for all Delta ECM-B3 servo motors and Li Ming planetary gearboxes in the catalogues and shows only the combinations that pass every check. The calculation step by step is in our article how to choose a planetary gearbox for a servo motor (in Bulgarian).
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What is included
| What | Scope |
|---|---|
| Servo motors | Delta ECM-B3 — 37 models from 0.1 to 15 kW, for 220 V and 400 V, with and without brake |
| Planetary gearboxes | Li Ming SERVOBOX / FABGEAR — 11 series (SN, SB, SE, SF, PB, FA, FB, FC, FE, FN, SD), ratios from 3 to 100 |
| Mechanisms | rotary load; lead screw — ball screw or trapezoidal; belt or drum; rack and pinion; hoisting — with a pulley block and a counterweight |
| Result | load on the output shaft, the combinations that pass, the checks of the selected one, other ratios and series for the same motor, inquiry |
How it works — four steps
- Mechanism. Choose one of the five types. The diagram below the buttons shows which quantities are needed — for example the pitch diameter D of the pinion for a rack, or the lead P and the diameter d for a screw.
- Load. Mass, speed, friction, inclination, external force and efficiency of the mechanism. For a trapezoidal screw the efficiency is calculated from the lead, the diameter, the number of starts and the thread friction; for a ball screw it is entered (catalogues give 90% and more). The inertia of the screw itself is added to the load. For hoisting, the ratio of the pulley block and the counterweight are entered.
- Duty cycle. The times for acceleration ta, motion at constant speed tc, deceleration td and dwell tp. If the load is also held during the dwell — vertical axis, hoisting, constant force — tick it: the motor then produces torque during the dwell as well, and this counts towards heating.
- Motor and gearbox. Supply 220 V or 400 V, gearbox series, permissible backlash, radial and axial force on the output shaft, motor with brake. In “Advanced settings” — what share of Tn and Tmax to use (90% by default), the permissible inertia ratio (4 : 1), the torque limit in the drive and how the maximum output torque is calculated.
What is checked
Every motor–gearbox pair goes through the checks below. A combination that fails any of them does not appear in the list.
| Check | Condition | Purpose |
|---|---|---|
| Motor RMS torque | Trms ≤ krms · Tn | heating — the root-mean-square torque over the whole cycle |
| Motor peak torque | Tpeak ≤ kpeak · Tmax | acceleration; with a torque limit in the drive — from the limited value |
| Peak speed | npeak ≤ nmax | the maximum speed of the motor |
| Inertia ratio | JL / i² ≤ limit · Jm | stable control; the load inertia falls with the square of i |
| Mean output torque | T2m ≤ T2N (Li Ming, Eq.2) | wear — the cubic mean over the cycle |
| Max. acceleration torque | T2max · Ks ≤ T2B (Eq.4), in cyclic operation S5 | acceleration and deceleration; Ks depends on the cycles per hour |
| Emergency stop torque | Tmax · i · η ≤ T2NOT = 3 · T2N | jamming and impact — with the full motor torque |
| Input speed | n1m ≤ n1N, peak ≤ n1B | bearings and heating of the gearbox |
| Output shaft forces | Fr ≤ F2rB, Fa ≤ F2aB | output bearings |
| Backlash | best class of the series ≤ permissible | positioning accuracy |
| Motor mounting | shaft Ø S among the input bores (C3), pilot LB (C5, H8), pitch circle LA (C1) | the motor fits the standard input of the gearbox |
How to read the result
Load on the output shaft — the force, torque, speed and inertia of the load, the operating mode (S5 and the duty cycle), the cycles per hour with the factor Ks and the mean torque T2m.
Combinations that pass — one row per motor, sorted by power: a single-stage gearbox if it is enough, with the ratio at which the motor has the largest margin. The columns show what share of Tn (heating) and of Tmax (acceleration) is used, the inertia ratio and the margin of the most loaded check. The smallest motor that passes is marked.
The selected combination — the motor torques in each phase of the cycle (already with the gearbox inertia), all checks with “OK” or “Warning”, and a table with the other ratios and series for the same motor: each cell shows the smallest gearbox size that passes.
Inquiry — the button opens an e-mail to sales@mechatronics.bg with the input data and the selected combination. “Copy result” and “Print / PDF” save the calculation, and the input is kept in the page address — the link leads to the same result.
What remains for the engineer
- The calculations are indicative and based on catalogue data. The final selection, the drive (amplifier) for the motor and the gearbox adapter are confirmed on inquiry.
- Above rated speed the torque of a servo motor drops. When the cycle reaches that range, the tool shows “Warning” and the values are checked against the T–N curve in the catalogue.
- The adapter and the shaft bushing are selected by Li Ming for the motor; the tool checks that the shaft, the pilot and the pitch circle are among the standard inputs of the gearbox.
- The ECM-B3M-L-221B and 221F motors (220 mm flange) have no standard input on Li Ming gearboxes and do not appear in the results — send an inquiry for them.
- If the cycles per hour are more than the Ks table in the catalogue covers, the check is marked “Warning”.
Questions and answers
Why is a larger gearbox suggested than the torque alone requires?
Besides the mean and the maximum output torque, the gearbox must withstand the full motor torque when the mechanism jams (T2NOT = 3 · T2N), the input speed and the shaft forces, and its input must accept the shaft and the flange of the motor. A smaller size often has no standard input for the larger motor.
What is the “Torque limit in the drive”?
The field limits the motor torque in % of Tmax; 100% means no limit. Below the checks the tool states what to set in parameters P1.012…P1.014 of the Delta ASDA drive (there the value is in % of Tn) for the cycle to pass, and up to what value the gearbox stays protected against jamming.
Is there sizing for other motors and gearboxes?
The online tool covers Delta ECM-B3 servo motors and Li Ming planetary gearboxes. For other motors and for worm, harmonic or cycloidal gearboxes, send an inquiry — we select them from the manufacturers’ catalogues.
How do I save or send the calculation?
The input is in the page address — copy the address and the link opens the same result. “Copy result” gives text for an e-mail, “Print / PDF” a sheet for your records, and “Inquiry for this combination” sends the data straight to us.
Need help with the selection?
Send us the motion — stroke, time, mass, accuracy — and we will propose a Delta servo motor and drive with a Li Ming planetary gearbox, checked for torque, inertia and mounting.
Open the sizing toolSend an inquiryDelta servo drivesPlanetary gearboxes
Sources of the tool: Delta ASDA-B3, catalogue EN 07.2024 (PDF) — data, shaft and flange of ECM-B3; Delta ASDA-A3, catalogue 10.2025 — ECM-B3M-L 221B/221F; Li Ming SERVOBOX / FABGEAR, catalogue 05.2026 — specifications, input dimensions and method (pp. 201–202); NEFF and ZIMM — trapezoidal screws; TBI — ball screws and screw inertia. Tool data: r2, 15.10.2026.