Harmonic Drive RSA-8A Integrated Servo Actuators Review: Specs, Price and Applications
Updated: 4 days ago
Harmonic Drive RSA-8A combines a miniature strain-wave actuator, brushless motor, motor feedback and CANopen servo drive in one assembly. Ratios 30, 50 and 100 provide different torque and output-speed limits. Its four-conductor power-and-network connection simplifies one part of the installation, while the host motion control, machine safety and load-support design remain external responsibilities.
Quick Verdict
Consider RSA-8A for a compact OEM rotary mechanism that fits its torque-speed duty and CANopen control architecture. The useful distinction is its integrated amplifier and small package. Select from the continuous as well as maximum ratings, and distinguish motor-derived output counts from an independent output encoder or a guaranteed positioning accuracy.
Harmonic Drive RSA-8A Integrated Servo Actuators at a Glance
Specification | Details |
Integrated functions | Actuator, brushless motor, 14-bit motor-input absolute encoder and servo drive |
Ratios 30 / 50 / 100 | Allowable continuous torque 0.7 / 1.2 / 2.0 Nm; maximum torque 1.8 / 3.3 / 4.8 Nm in the cited brochure |
Output speed by ratio 30 / 50 / 100 | Allowable continuous 116.7 / 70 / 35 rpm; maximum 283.3 / 170 / 85 rpm |
Power supply | 24 VDC nominal; +7 to +30 VDC listed range |
Communication | CANopen; manufacturer lists DS301/DS402 and torque, velocity, position, CSP, CSV and CST modes |
Four-conductor connection | CANH, CANL, +24 VDC and 0 VDC; use the specified wiring and mating arrangement |
Feedback | 14-bit, 16384 counts per motor revolution; brochure/order tables identify motor-input sensing |
Output-equivalent count scale | 491520 / 819200 / 1638400 counts per output revolution for ratios 30 / 50 / 100; calculated through reduction |
One-way positioning accuracy | 2 arcmin in the brochure; distinct from the count scale |
Motor current, ratios 30 / 50 / 100 | Maximum 4.0 / 4.0 / 3.5 A RMS; allowable continuous 2.05 / 2.0 / 1.7 A RMS; these are motor currents |
Output and mass | Shaft or optional F flange output;200 g standard, 190 g with F option |
Moment-load entry | 3.46 Nm allowable moment load; validate actual combined load and duty |
Environment | Brochure operation 0 to 40°C; enclosed, self-cooled; specified clean indoor environment |
Price | Request a quote for exact ratio, output, cable exit, cables and control scope |
Design and Engineering Assessment
The integrated drive removes the need for a separate cabinet amplifier for this axis, but does not remove the host controller, network, supply or fault-handling design. The four-conductor connection carries both DC power and CAN signals. Cable routing, connectors, grounding and network termination must still support a reliable machine installation.
The continuous-versus-maximum distinction is central to sizing. At ratio 100, the brochure lists 2.0 Nm allowable continuous torque and 4.8 Nm maximum, with 35 rpm allowable continuous output speed and 85 rpm maximum. These are separate limits rather than one guaranteed operating point. Evaluate the actual torque-speed cycle and thermal conditions before selecting the ratio.
The encoder ordering and specification tables identify 14-bit feedback on the motor input. Multiplying 16384 counts by ratio 100 produces 1638400 output-equivalent counts per revolution. That count scale does not independently measure output compliance and does not override the separate 2 arcmin positioning-accuracy entry.
A single-turn motor encoder also does not by itself establish an unambiguous full output revolution after power loss. One motor revolution spans only a fraction of an output turn through the gearbox. Define the required homing, retained position and restart behavior for the mechanism instead of treating the absolute label as a complete load-coordinate strategy.
Choose ratio from the actual duty
Ratios 30, 50 and 100 increase allowable continuous torque from 0.7 through 1.2 to 2.0 Nm, while continuous output speed decreases from 116.7 through 70 to 35 rpm. Maximum torque and speed have their own entries. Do not combine the fastest speed of ratio 30 with the torque of ratio 100.
The brochure identifies the output values as typical. Include acceleration, process torque, external forcing and energized holding in the selection, then qualify the real loaded cycle and ambient conditions. A compact integrated actuator can still accumulate heat in both motor and electronics.
CANopen modes and host responsibilities
The manufacturer lists torque, velocity and position modes as well as CSP, CSV and CST. Confirm the exact controller profile, synchronization and supported firmware when specifying the host. A protocol name alone does not establish compatible motion behavior or a working application program.
HDL software supports setup, tuning and diagnostics without requiring the final CANopen master for every commissioning step. The production machine still needs defined enable, referencing, command-timeout, error and restart sequences. Preserve the parameter set with the actuator’s complete ordering code.
Motor feedback is not load feedback
The motor encoder provides 16384 counts per motor revolution. At ratio 30, 50 or 100, the published output-equivalent scale is 491520, 819200 or 1638400 counts. These are ratio-derived motor counts, rather than measurements from a separate output encoder.
The 2 arcmin one-way accuracy specification and gearbox compliance remain relevant even though the digital scale is much finer. If the mechanism needs direct load-position assurance, specify the measurement and control architecture that can establish it. Test the process location through reversals and external load changes.
Shaft, flange and cable exit
The blank output code denotes a shaft and F denotes a flange. PT1, PT2, PT3 and PT5 identify rear, right, left and front cable exits respectively. Choose from the actual drawing, allowing connector clearance, cable bends and access to install or replace the unit.
The brochure mass is 200 g for the standard assembly or 190 g with F output. Do not confuse grams with kilograms in a reused table. Check output moment, radial and axial loading for the attached mechanism rather than assuming that torque capability alone qualifies an overhung load.
Supply, current and environment
The nominal 24 VDC supply has a listed 7–30 VDC range. The motor-current columns use RMS phase values, which are different from DC input-supply current. Size wiring, power supply, protection and any regenerative-energy handling from the exact installation requirements.
The brochure specifies 0–40°C operation in a clean environment free of the listed contaminants. Enclosed and self-cooled does not establish an IP65 wash-down rating. Respect the actual environmental and thermal scope when placing the compact actuator near a process.
Commissioning, holding and alternatives
Start with controlled current and speed, verify direction and feedback interpretation, then test the intended homing method and the loaded trajectory. Include warm operation, communication loss and power interruption. The four-wire architecture does not by itself provide an independent safety function.
If the mechanism must hold a gravity or spring load with power removed, provide the required machine holding arrangement. Compare RSA-8A with the smaller RSF-5B IDT or another integrated actuator at the same continuous duty, feedback requirement and control scope. A bare reducer plus motor and external drive is a different installed architecture.
Applications and Selection
Consider RSA-8A for compact robotic or OEM rotary mechanisms where its torque-speed duty, CANopen interface and environmental limits fit the machine. The component does not establish a complete certified robot joint or a machine-level safety architecture.
For Harmonic Drive RSA-8A Integrated Servo Actuators, 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
Combines motor, reducer, feedback and servo drive in a compact assembly
Three ratios provide different continuous torque-speed selections
Four-conductor power and CANopen connection supports distributed control
Shaft/flange and cable-exit options support a defined mechanical layout
Limitations
Continuous torque and speed are lower than maximum entries
Motor-derived counts are not independent output-position measurement
Absolute motor feedback does not alone define full output-coordinate recovery
Supply, host control, thermal integration and required holding/safety functions remain external
Who Should Consider Harmonic Drive RSA-8A Integrated Servo Actuators?
Consider RSA-8A when local drive integration and a compact rotary actuator are useful and the machine can supply a compatible CANopen host, DC power, load support and defined reference/fault behavior. Qualify the continuous duty and actual process-position result.
Harmonic Drive RSA-8A Integrated Servo Actuators FAQ
Does RSA-8A include the servo drive?
Yes. It integrates the motor drive with the miniature actuator and motor feedback. The machine still needs a suitable DC supply, CANopen host and defined mechanical and fault-handling architecture.
Can ratio 100 deliver 4.8 Nm continuously?
No. The brochure separates 2.0 Nm allowable continuous torque from 4.8 Nm maximum. It also separates 35 rpm continuous output speed from 85 rpm maximum for that ratio.
Is the 14-bit encoder on the motor or output?
The manufacturer’s ordering and specification tables identify motor-input sensing. The output-equivalent count scale is calculated using gear ratio; it is not evidence of a separate output encoder.
Does 1638400 output-equivalent counts establish that angular accuracy?
No. That is the ratio 100 motor-count scale. The brochure separately lists 2 arcmin one-way positioning accuracy, and the assembled mechanism adds its own compliance and load effects.
Does a single-turn absolute motor encoder eliminate all homing?
Not automatically. Define how the machine establishes the full output coordinate and recovers after power loss. One motor revolution covers only a fraction of an output revolution through the reducer.
What is carried by the four conductors?
CANH, CANL, positive DC supply and 0 VDC. Follow the specified connectors, network and power wiring; four conductors do not by themselves establish a machine safety circuit.
Does enclosed construction mean it is suitable for wash-down?
No IP65 rating is established by the enclosed/self-cooled description. The brochure specifies a clean environment and 0–40°C operation. Match the exact installation requirements.
What is the price?
Request a quote for ratio, shaft or F flange output, cable exit and extension cables. Include the supply, CANopen host, mounting and any required load sensing or holding arrangement for the complete machine.
Prices are indicative and may change. Confirm the final configuration, commercial terms and delivery schedule before ordering.
