Harmonic Drive HP8 and CP8 Miniature Planetary Gearheads Review: Specs, Price and Applications
Updated: 4 days ago
HP8 and CP8 are miniature planetary gearheads in a 25 mm square package for small servo-driven mechanisms. HP uses a standalone input pinion with a precision through bore, while CP includes a removable input hub-pinion assembly. They are low-backlash planetary transmissions, with a documented backlash limit of 30 arcmin; they should not be described as zero-backlash strain-wave gear units.
Quick Verdict
Consider HP/CP when a compact motor connection and modest planetary reduction fit a small positioning or instrument axis. Compare input attachment, backlash tolerance, torque duty and load support against the complete mechanism. The 25 mm package and small-motor positioning do not establish a complete actuator, a sterilizable medical assembly or a universal positioning accuracy.
Harmonic Drive HP8 and CP8 Miniature Planetary Gearheads at a Glance
Specification | Details |
Package | 25 mm square miniature planetary gearhead |
Ratios | 5:1 / 16:1 / 25:1 |
HP input | Standalone input pinion with precision through bore |
CP input | Removable input hub-pinion assembly |
HP-8F ratio 5 | 0.40 Nm rated; 2.26 Nm repeated; 5.88 Nm momentary; 0.12 kg |
HP-8F ratio 16 | 1.07 Nm rated; 2.55 Nm repeated; 5.88 Nm momentary; 0.15 kg |
HP-8F ratio 25 | 1.57 Nm rated; 2.26 Nm repeated in July 2026 catalog; 5.88 Nm momentary; 0.15 kg |
Maximum-speed entry | 5000 rpm input in rating table; operating duty qualifications apply |
Output radial/axial entries | Ratio 5: 52/47 N; ratio 16: 76/47 N; ratio 25: 89/47 N |
Backlash | ≤30 arcmin measured at ±5% rated torque |
Life entry | L10 20000 hours at rated torque; not unconditional machine life |
Price | Request a quote for HP or CP, ratio and exact motor interface |
Design and Engineering Assessment
The three ratios change torque and mass together. Ratio 5 lists 0.40 Nm rated torque at 0.12 kg, while ratios 16 and 25 list 1.07 and 1.57 Nm at 0.15 kg. These are separate operating configurations; do not present 1.57 Nm alongside the ratio-5 mass or a ratio-5 output speed.
The current manufacturer-linked July 2026 catalog lists ratio-25 repeated torque as 2.26 Nm, while the web table shows 2.56 Nm. This review uses the catalog figure for that entry. Resolve the exact supplied unit’s approved duty data before designing a recurring load near either value, rather than treating the discrepancy as spare capacity.
A limit of 30 arcmin is half a degree, so the allowable backlash can matter in a small precision mechanism. It is measured at ±5% rated torque, not established as a guarantee of loaded tool-point accuracy. Transmission error, compliance, feedback location and the downstream mechanism contribute additional effects.
The manufacturer positions HP/CP for small servomotors and semiconductor or medical mechanisms. Those are application directions, not product-level guarantees of cleanroom class, medical-device approval or sterilization resistance. The OEM remains responsible for the finished machine’s environment, safety and regulatory requirements.
HP Versus CP Motor Attachment
Select the input configuration from the motor shaft and assembly concept. A standalone pinion with precision bore and a removable hub-pinion assembly have different installation and service implications. Confirm pinion location, shaft fit, retention and alignment from the actual drawing.
The HP/CP ordering distinction concerns the input connection, not an electrical protocol. Match the motor, feedback and drive separately. A suitably sized motor still needs a verified mechanical interface and a torque-speed curve compatible with the selected reduction and duty.
Sizing a Small Axis
Calculate input speed from required output speed and ratio, then check the motor’s available torque at that speed. Include friction, efficiency and the inertia of the motor and transmission. A higher reduction can increase available output torque while lowering output speed and changing the dynamic response.
The 5000 rpm table entry is an allowable maximum input-speed limit. Establish the applicable continuous or average operating duty with the manufacturer. Small assemblies can have limited heat-rejection paths, particularly when installed inside an instrument or enclosed mechanism.
Bearing Loads and Tooling
Radial load entries rise from 52 N at ratio 5 to 76 N at ratio 16 and 89 N at ratio 25, while the listed axial entry is 47 N. These are separate rating conditions, not an invitation to combine every maximum simultaneously. Confirm how the load application point and combined forces are evaluated.
A pulley can impose radial force from preload as well as transmitted torque. A cantilevered tool can impose overturning demand and shaft deflection. Keep the load close to its support where possible and review whether an external support arrangement is needed for the actual mechanism.
Backlash, Feedback and Acceptance
If direction reversal matters, evaluate output motion under a representative reversing load. Motor encoder counts divided by ratio describe an ideal kinematic scale, not a measurement of every downstream movement. A mechanism with finite backlash can produce different behavior on approach from opposite directions.
Consider consistent approach direction or load-side feedback where appropriate, while recognizing the limits of each strategy. Software compensation does not remove mechanical compliance, impact or wear. Define the acceptance test at the output and include load, temperature, direction and settling conditions.
Life and Purchase Scope
The catalog’s L10 20000-hour entry is tied to rated torque conditions. It is a statistical design rating, not an unconditional warranty or a promise that an assembled machine will need no service for that duration. Apply the manufacturer’s speed, duty, load and lubrication guidance.
A useful quotation identifies HP or CP, reduction ratio, motor shaft and mounting dimensions, load geometry, operating cycle and environment. Confirm current delivery and commercial terms directly; an older quick-delivery statement is not evidence of present stock.
Applications and Selection
Small servo axes, precision instruments and compact semiconductor or medical-machine mechanisms
For Harmonic Drive HP8 and CP8 Miniature Planetary Gearheads, define the actual machine duty before selecting an ordering configuration. Include the required operating point, available installation space, environment and control interfaces. The specification table describes the product or family; the surrounding machine determines which of those features matters for the intended job.
Price and Value
Price: Request a quote for the exact configuration. Compare the product, compatible control equipment, required mechanical parts, cabling and commissioning as one installed system. A component price alone does not represent the cost of a working automation axis.
Evaluate an alternative against the same duty and acceptance criteria. Match the continuous operating requirement first, then compare transient capability, feedback, mechanical fit and support. This avoids choosing between superficially similar products whose ratings describe different operating conditions.
Pros and Cons
Advantages
Compact 25 mm square package supports small mechanical axes
HP and CP provide distinct input attachment options
Three documented ratios allow a clear torque-speed comparison
Limitations
Finite backlash can affect reversing precision
Ratio-25 repeated-torque conflict needs configuration-specific confirmation
External motor, drive and environmental qualification remain necessary
Who Should Consider Harmonic Drive HP8 and CP8 Miniature Planetary Gearheads?
OEM designers selecting a configured motor-driven mechanical axis
Harmonic Drive HP8 and CP8 Miniature Planetary Gearheads FAQ
Are HP8 and CP8 zero-backlash strain-wave reducers?
No. They are miniature planetary gearheads with a specified backlash limit of 30 arcmin under the stated measurement condition.
How do HP and CP differ?
HP includes a standalone input pinion with a precision through bore. CP includes a removable input hub-pinion assembly. Confirm the selected motor connection and installation drawing.
Which ratios are offered?
The manufacturer lists 5:1, 16:1 and 25:1 for the size-8 F design. Each has its own torque and mass entries.
What is the rated output torque at ratio 25?
The catalog lists 1.57 Nm rated torque at ratio 25 and 0.15 kg mass. Repeated and momentary torque are separate limits.
Which ratio-25 repeated torque is used here?
This review uses the July 2026 catalog value of 2.26 Nm. The web table lists 2.56 Nm, so confirm the approved data for the exact supplied configuration before sizing close to that boundary.
What does the backlash measurement mean?
The limit is ≤30 arcmin at ±5% rated torque. It describes lost motion under that condition and is separate from complete-axis accuracy or encoder resolution.
Does the 20000-hour life entry guarantee machine life?
No. It is an L10 rating at stated load conditions. The actual duty, speed, installation, lubrication and environment must be included in the application review.
What should be requested before ordering?
Request the complete HP or CP code, ratio, motor-interface drawing, torque-speed duty approval, combined bearing-load limits, installation guidance and current commercial terms.
Prices are indicative and may change. Confirm the final configuration, commercial terms and delivery schedule before ordering.
