HH-31ZY Worm Gear Motor Speed Ratios: How to Pick the Right RPM
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The HH-31ZY worm gear motor is sold in 12 gear ratios, from 26.8:1 to 710:1. The ratio you choose decides two things at once: how fast the output shaft turns, and how much torque it delivers. Get the ratio right and the motor disappears into your mechanism. Get it wrong and you get a turntable that crawls when it should spin, or a motor that stalls under a load it should have handled easily. This guide gives you the full table and a three-step method for picking from it.
How Ratio, Speed, and Torque Trade Off
A gear ratio of 26.8:1 means the motor shaft turns 26.8 times for one turn of the output shaft. Higher ratio means:
- Slower output. Output speed falls as ratio rises.
- More torque. Output torque rises as ratio rises — up to the gearbox's rated maximum.
- More gear stages. The highest ratios use 4 gear stages instead of 3, which is part of why they cost the same motor more effort to build but deliver more torque.
The 31ZY's motor runs at 5000 RPM and 3.5 W. The gearbox trades that speed for torque, and the table below shows exactly what each trade buys you.
The Full Ratio Table (Rated Values)
These are the datasheet's rated figures under load. The 12V and 24V versions share the same values.
| Gear ratio | No-load speed (RPM) | Rated speed under load (RPM) | Rated torque under load (kgf·cm) | Gear stages |
|---|---|---|---|---|
| 26.8:1 | 187 | 149.3 | 1.6 | 3 |
| 50:1 | 100 | 80.0 | 3.0 | 3 |
| 78.9:1 | 63 | 50.7 | 4.8 | 3 |
| 93.1:1 | 54 | 43.0 | 5.7 | 3 |
| 122:1 | 41 | 32.8 | 7.4 | 3 |
| 166.7:1 | 30 | 24.0 | 10.2 | 3 |
| 213:1 | 23 | 18.8 | 13.0 | 3 |
| 263.2:1 | 19 | 15.2 | 14.4 | 4 |
| 310.5:1 | 16 | 12.9 | 17.0 | 4 |
| 406.7:1 | 12 | 9.8 | 22.3 | 4 |
| 556:1 | 9 | 7.2 | 25.0 | 4 |
| 710:1 | 7 | 5.6 | 25.0 | 4 |
Two things to notice. First, torque stops rising at 25.0 kgf·cm — the 556:1 and 710:1 ratios both deliver the maximum, and the extra ratio only buys slower speed. Second, always size from the rated speed under load column, not the no-load column: a mechanism that needs 15 RPM wants the 263.2:1 ratio (15.2 RPM loaded), not the 310.5:1 ratio, whose 16 RPM no-load figure drops to 12.9 RPM once loaded.
Pick Your Ratio in Three Steps
Step 1: Fix the output speed you need. How fast should the shaft actually turn in use — a turntable at 15 RPM, a curtain drive at 40 RPM, a slow rotisserie at 6 RPM? Find the row whose rated speed under load is closest to that number, erring toward slightly faster rather than slower: you can always slow a mechanism down, but a motor that is too slow cannot be sped up.
Step 2: Check the torque in that row covers your load. The rated torque column is the torque available at that speed. If your load needs more torque than the row offers, move to a higher ratio (slower, stronger) until torque covers it — and accept the slower speed that comes with it. If no row covers both your speed and your torque, the 31ZY is the wrong motor for that job: step up to a larger drive rather than overloading this one.
Step 3: Check the shaft loads. The 31ZY's output shaft is rated for up to 3 kgf radial load, 5 kgf axial load, and 15 kgf maximum press-in force. A heavy plate hung off the shaft, or a mechanism that pushes along the shaft, must stay within these figures. Torque alone does not clear a design.
Rotation Direction Varies by Ratio
One detail that catches people out: the output rotation direction (clockwise vs counter-clockwise for a given input) changes across ratio segments in the datasheet. If your mechanism depends on a specific direction, confirm the direction for the exact ratio you order before you build around it — do not assume it matches a different ratio of the same motor.
Holding Position and Backlash
Like all worm drives, the 31ZY holds its output position when power is off, within its rated load — no brake needed for a turntable that must stay put. Backlash is rated at 2° or less, so reversing direction introduces only a small dead zone. If your mechanism reverses often and positions precisely, that 2° figure is the number to design around.
Worked Examples
A display turntable at about 15 RPM. The 263.2:1 row gives 15.2 RPM under load with 14.4 kgf·cm — a good match for a moderately loaded display, with torque to spare.
A curtain drive at about 40 RPM. The 93.1:1 row gives 43.0 RPM under load with 5.7 kgf·cm. If the curtain is heavy, step to 122:1 (32.8 RPM, 7.4 kgf·cm) and accept the slower travel.
A slow rotisserie at about 6 RPM. The 710:1 row gives 5.6 RPM with the full 25.0 kgf·cm — the slowest, strongest option in the range.
FAQ
Does 24V give more speed or torque than 12V?
No. Per the datasheet, the rated speeds and torques are identical for the 12V and 24V versions. Pick the voltage that matches your system.
Why do the two slowest ratios have the same torque?
Because 25.0 kgf·cm is the gearbox's rated maximum. Beyond 556:1, a higher ratio only reduces speed further; it cannot raise torque past the rating.
Can I run the motor faster than the rated speed by raising voltage?
Do not. Over-voltage over-drives the motor and risks overheating and shortened life. If you need more speed, pick a lower ratio instead.
What if my exact speed is not in the table?
Pick the nearest ratio that is slightly faster than you need, then slow the mechanism mechanically (a belt, a larger driven wheel) or with timing if your control allows it. Never pick a ratio that is too slow and hope to speed it up.
For the other motor in the range, or for choosing between the two, see our HH-370 vs HH-31ZY comparison. For wiring basics, see our guide to wiring a linear actuator.
The Short Version
Decide the speed you need, read across to the torque in that row, and check the shaft loads. Ratio is the whole selection problem for this motor — the table above is the answer key.