Strain-wave (harmonic) gear
Harmonic Drive SHD-2SH gear units
A short, flat hollow-shaft strain wave gear unit with an output bearing. It is about half the length of SHG/HFUS units, for slim rotary axes.
Key specifications
| Bore (max) | 40 mm |
|---|---|
| Rated torque (max) | 185 Nm |
| Peak torque (max) | 700 Nm |
| Ratio | 50–160:1 |
| Backlash (max) | 0 arcmin |
| Sizes | 14, 17, 20, 25, 32, 40 |
Summarised in our own words from Harmonic Drive SE / Harmonic Drive LLC's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1 · Source 2
Notes on this data
Harmonic Drive LLC lists ratios 50/80/100 with maxima at SHD-40-100: rated 185 Nm, repeated peak 398 Nm and momentary peak 700 Nm. Harmonic Drive SE lists ratios 50–160, repeatable peak torque of 12–453 Nm, a hollow shaft of 11–40 mm and a tilting moment of 37–424 Nm. SHD-2UH-LW is also listed by LLC. Accuracy is 1–1.5 arcmin.
Specify Motion is not affiliated with Harmonic Drive SE / Harmonic Drive LLC. Harmonic Drive and SHD-2SH gear units are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Harmonic Drive part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
Cup-type strain-wave gear component sets for building your own joint; the LCSG high-torque version lifts capacity by around 30% over the standard LCS.
| Published maximum | SHD-2SH gear units | LCS / LCSG |
|---|---|---|
| Rated torque | 185 Nm | — |
| Peak torque | 700 Nm | — |
| Ratio (max) | 160:1 | 500:1 meets or exceeds |
| Backlash (lower is better) | 0 arcmin | — |
Hollow-shaft strain-wave gear units with a large central bore for routing cables and services; LHSG is the high-torque version (over 30% more torque).
| Published maximum | SHD-2SH gear units | LHS / LHSG |
|---|---|---|
| Rated torque | 185 Nm | — |
| Peak torque | 700 Nm | — |
| Ratio (max) | 160:1 | 500:1 meets or exceeds |
| Backlash (lower is better) | 0 arcmin | — |
Ultra-flat cup-type strain-wave gear with a very short axial length, light weight and high stiffness for its size.
| Published maximum | SHD-2SH gear units | LCD |
|---|---|---|
| Rated torque | 185 Nm | — |
| Peak torque | 700 Nm | — |
| Ratio (max) | 160:1 | 500:1 meets or exceeds |
| Backlash (lower is better) | 0 arcmin | — |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What a strain-wave (harmonic) gear is
A strain-wave gear, often called a harmonic gear, reduces speed using three parts: an elliptical wave generator, a thin flexible toothed cup or hat called the flexspline, and a rigid circular spline with internal teeth. The wave generator deforms the flexspline so its teeth engage the circular spline at two points. Because the flexspline has typically two fewer teeth, each input turn advances it slightly, giving ratios of about 30:1 to 160:1 in one stage, with near-zero backlash.
When engineers choose a strain-wave (harmonic) gear
Choose a strain-wave gear for compact, lightweight, high-ratio reduction with near-zero backlash, such as robot joints, cobots, medical robots, aerospace and optics. Hollow versions allow cables through the centre. The trade-offs are torsional stiffness at low load, which is lower than some alternatives, limited input speed and the risk of tooth ratcheting under overload. For shock loads and heavy base joints, cycloidal reducers are often preferred.
How to specify the Harmonic Drive SHD-2SH gear units
Send these with your enquiry and an engineer can confirm the right SHD-2SH gear units variant or an equivalent:
- Ratio (:1)
- Rated, peak and momentary torque (Nm)
- Input speed limits (rpm)
- Torsional stiffness (Nm/arcmin)
- Hysteresis and accuracy (arcmin)
- Component set or housed unit
- Hollow shaft diameter and output bearing loads
Common mistakes to avoid
- Exceeding momentary torque and ratcheting the teeth
- Ignoring low-load stiffness in precision control
- Poor housing tolerances for component sets
- Using the wrong lubricant or quantity
Harmonic Drive SHD-2SH gear units: frequently asked questions
What is the Harmonic Drive SHD-2SH gear units?
A short, flat hollow-shaft strain wave gear unit with an output bearing. It is about half the length of SHG/HFUS units, for slim rotary axes. Published series figures include bore 40 mm, rated torque 185 Nm, peak torque 700 Nm, ratio 50:1. It is made by Harmonic Drive SE / Harmonic Drive LLC; Specify Motion can help source it or propose an equivalent.
Who makes the Harmonic Drive SHD-2SH gear units?
The Harmonic Drive SHD-2SH gear units is made by Harmonic Drive (Harmonic Drive SE / Harmonic Drive LLC) and is listed here for engineers comparing options. Specify Motion is not affiliated with Harmonic Drive SE / Harmonic Drive LLC; brand names are used only to identify the product.
What is the bore of the Harmonic Drive SHD-2SH gear units?
The published series maximum bore is 40 mm. Individual models and sizes in the SHD-2SH gear units range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Harmonic Drive SHD-2SH gear units?
Yes. On published figures, LeaderDrive LCS / LCSG and LeaderDrive LHS / LHSG are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
Why do strain-wave gears have near-zero backlash?
The flexspline teeth are preloaded into the circular spline teeth by the elliptical wave generator, and many teeth engage at once. There is no clearance between teeth at the engagement zones, so backlash is close to zero. Lost motion comes mainly from elastic deflection.
What is the difference between a strain-wave component set and a housed unit?
A component set is the wave generator, flexspline and circular spline, which the machine builder mounts in its own housing with bearings. A housed unit adds a housing, output bearing and seals. Component sets save weight and space; housed units are easier to integrate.
Further reading: Harmonic vs planetary vs cycloidal · How to select a gearbox · Gearboxes and harmonic drives
Other strain-wave (harmonic) gear series
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