Harmonic Drive FBS-2UH Hollow-Shaft Gear Units Review: Specs, Price and Applications
Updated: 4 days ago
Harmonic Drive FBS-2UH is a flat hollow-shaft gear-unit family with an integrated output bearing. Its central opening allows a machine designer to route services through a rotary axis, while sizes 25 and 32 and ratios of 30:1, 50:1 and 100:1 provide distinct torque and stiffness choices.
Quick Verdict
FBS-2UH is worth considering where through-axis routing and axial packaging are important. Select the complete size-and-ratio combination against the load cycle, external bearing loads and required stiffness. A large bore and a high peak-torque figure do not establish the continuous operating capacity of the finished axis.
Harmonic Drive FBS-2UH Hollow-Shaft Gear Units at a Glance
Specification | Details |
Architecture | FBS-2UH flat hollow-shaft gear unit with output bearing |
Sizes and ratios | 25 and 32; 30:1, 50:1 and 100:1 |
FBS-25-30 / 50 / 100 rated torque L10 | 15 / 22 / 37 Nm, respectively |
FBS-25-30 / 50 / 100 repeated peak limit | 25 / 47 / 70 Nm, respectively |
FBS-32-30 / 50 / 100 rated torque L10 | 30 / 43 / 56 Nm, respectively |
FBS-32-30 / 50 / 100 repeated peak limit | 48 / 92 / 106 Nm, respectively |
Momentary peak limits | Size 25: 50 / 93 / 100 Nm; size 32: 96 / 151 / 151 Nm, ordered by ratio |
Published mass | 1.3 kg for size 25; 2.2 kg for size 32 |
Design and Engineering Assessment
A hollow-shaft layout is valuable when routing around the outside of a joint would increase the machine envelope or expose cables to repeated snagging. The bore remains a mechanical passage, not an electrical rotary connection. Continuous rotation still needs a suitable slip ring or another engineered arrangement for services that cannot tolerate accumulated twist.
The six catalog combinations are not interchangeable torque ratings for one product. FBS-25-100-2UH has a published rated torque L10 of 37 Nm, while FBS-25-30-2UH is listed at 15 Nm. The size and reduction ratio change the operating envelope and must remain attached to every quoted specification.
Current manufacturer data lists a 106 Nm repeated-peak limit for FBS-32-100-2UH. An older source headline of 25–92 Nm therefore does not describe the complete current set. More importantly, the same size-32 ratio-100 row has a 56 Nm rated torque L10 and a 151 Nm momentary limit; these represent different constraints, not three alternative continuous ratings.
Reduction can improve the torque available at the output, but it also changes reflected inertia, required motor speed and axis behavior. A compact gear unit must be evaluated with the intended motor, coupling and control loop. The gear-unit mass alone is not the total rotating-axis mass or the complete installation envelope.
Torque Duty and Input Speed
Separate sustained running, repeated accelerations and exceptional events when constructing the load cycle. Compare each with the relevant manufacturer rating and its stated life and speed conditions. A momentary peak allowance should not be used as a normal recurring production target.
Output speed requires input speed multiplied by the reduction ratio. Confirm the exact input-speed and lubrication limits for the selected unit before combining a high output-speed target with a high ratio. A ratio chosen for torque can become unsuitable when the motor-speed requirement is considered.
Output Bearing Loads and Mounting
The incorporated bearing supports the output, but radial, axial and overturning loads still need checking against the exact unit data. Account for the lever arm from the bearing to the actual payload. Moving the same load farther away can change bearing moment demands without changing the drive torque in the same proportion.
Use the specified mounting faces, fasteners and fit tolerances. Support deflection in the surrounding machine can dominate an otherwise stiff gear unit. Evaluate the assembled load path rather than treating the gearbox as an isolated rigid component.
Accuracy, Stiffness and Control
The current table distinguishes standard accuracy from several torsional-stiffness values. Accuracy describes a different property from load-dependent angular deflection. A positioning requirement under changing torque needs both the transmission characteristics and the structural compliance of the complete axis.
Where the axis must settle quickly, test the actual payload inertia and fastening arrangement with the selected control loop. Mechanical resonance and friction influence tuning. Increasing controller gain is not a substitute for correcting a flexible mount or choosing an appropriate motor-and-gear combination.
Alternatives and Service Routing
Compare a hollow-shaft unit with a conventional solid-shaft gearhead using the same routing requirement. A smaller external package can lose its advantage when separate cable loops or additional bearings are added. Conversely, a large bore provides little benefit where no service needs to cross the axis.
A direct-drive motor avoids the same reduction architecture but requires its own torque, thermal and bearing assessment. Compare the complete installed system at the same output duty, including motor, controller, bearings and cable management. Do not infer an accuracy or cost advantage from the drive architecture alone.
Applications and Selection
Compact rotary axes requiring a central passage for cables, tubing or another routed service, with an independently selected motor and servo system.
For Harmonic Drive FBS-2UH Hollow-Shaft Gear Units, 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
Central passage supports compact through-axis service routing
Two sizes and three ratios provide clearly separate selection options
Integrated output bearing reduces the need to assemble an equivalent bearing arrangement separately
Current manufacturer table distinguishes rated and peak torque limits
Limitations
Gear unit requires a separately selected motor and control system
Peak limits cannot replace a sustained-duty assessment
Routing through a bore does not eliminate cable-twist limits
Payload moments and surrounding structural compliance remain important
Who Should Consider Harmonic Drive FBS-2UH Hollow-Shaft Gear Units?
Consider Harmonic Drive FBS-2UH Hollow-Shaft Gear Units for compact rotary axes requiring a central passage for cables, tubing or another routed service, with an independently selected motor and servo system. Establish the required operating point and installation interfaces before choosing the configuration, and use a representative loaded cycle as the acceptance basis.
Harmonic Drive FBS-2UH Hollow-Shaft Gear Units FAQ
What is an FBS-2UH gear unit?
It is a flat hollow-shaft precision gear unit with an integrated output bearing. It provides reduction and a central routing passage; it is not a complete motor-and-servo-drive actuator.
Which sizes and ratios are listed?
The current manufacturer range includes sizes 25 and 32 with reduction ratios of 30:1, 50:1 and 100:1. Ratings must be read for the exact size-and-ratio ordering code rather than combined into one hypothetical configuration.
Is 106 Nm the continuous torque of every FBS unit?
No. That value is the repeated-peak limit listed for FBS-32-100-2UH. The same row lists 56 Nm rated torque L10 and 151 Nm momentary peak. Each limit has a different selection role and must be applied within the manufacturer's operating conditions.
Can the hollow shaft carry cables through continuous rotation?
The bore provides physical space for routing. Ordinary cables can still twist during repeated rotation. Unlimited rotation requires a suitable electrical or fluid rotary connection, or another routing design compatible with the actual service.
Does the integrated bearing remove external load calculations?
No. The selected bearing must support the actual radial, axial and overturning loads, including the payload offset. Verify these loads and the mounting structure against the exact unit documentation.
Does a higher ratio always improve the machine?
A higher ratio changes motor speed, reflected inertia and the available torque relationship. It can help one requirement while making another harder to satisfy. Compare the intended output cycle and motor operating range before selecting it.
What does FBS-2UH cost?
Request a quote for the exact ordering code, quantity and required accessories. A working axis also needs the chosen motor, drive, mounting parts and service-routing arrangement; no universal installed price is claimed.
How should the completed axis be tested?
Test representative load cycles and output positions, monitor thermal behavior and inspect cable motion. Include settling, reversal and the relevant payload moments. Assess normal production duty separately from exceptional peak events.
Prices are indicative and may change. Confirm the final configuration, commercial terms and delivery schedule before ordering.
