Which module should a new legged-robot project start with?

Whatever your reference codebase used — matching the published platform (often AK- or GO-class) saves weeks of controller retuning. Innovate on the robot, not the joint, first.

Why is a harmonic joint so much more expensive than a QDD module of similar torque?

The strain-wave reducer, the dual encoder and the tighter machining are the cost. QDD gets its price from a simple low-ratio planetary set and a single encoder — you trade zero-backlash precision for backdrivability and a lower bill.

Rated or peak torque — which do I size to?

Rated. Peak is a burst that lasts seconds; your duty cycle lives at rated torque, and thermal limits are what actually cap continuous output. Ask for the derating curve.

CAN, EtherCAT or RS-485 for a new build?

CAN/CAN FD if you're research-driven (cheap tooling, big ecosystem); EtherCAT if the arm must slot into industrial automation; watch for RS-485 on specific modules like the Unitree GO-M8010-6. Decide once — it's the least reversible choice here.

Do these prices include tax and shipping?

No — they're indicative single-unit EXW China. Add freight, your import duty/VAT, and for US buyers current tariffs. Verify duties with your customs broker, and send models + quantity + destination via the RFQ form for a landed quote.

Can I get custom windings or gear ratios?

Yes — Chinese vendors quote customs at surprisingly low MOQs (tens of units†), typically adding a few weeks of lead time. Bring a spec sheet, not a wish list.

Robot Actuator & Joint Module Price Guide 2026

What actually sets the price

An actuator is a motor, a reducer, an encoder, a driver board and a housing in one package. Six levers move the invoice:

Gear architecture — the single biggest lever (see the tradeoff table below). Harmonic and cycloidal reducers cost multiples of the low-ratio planetary set inside a QDD module.
Rated vs. peak torque — you pay for continuous torque and the thermal design that sustains it. Peak is a seconds-long burst; motion happens at rated.
Encoder — a single output-side encoder is fine for legs; a dual encoder (motor-side + output-side, 17-bit+) is what makes a precision arm joint hold position under load, and it adds cost.
Backlash — harmonic ≈ zero backlash; planetary QDD lists arcminutes. Precision buyers pay for the low number.
Ingress protection (IP) — an IP-rated sealed joint for outdoor or washdown duty costs more than an open lab module.
Bus + documentation — CAN/CAN FD modules are cheaper than EtherCAT industrial joints; and a complete English protocol doc plus a working SDK is worth real money in saved integration weeks.

Gear architectures: the tradeoff

Buying the wrong family is the classic integrator error — a harmonic joint on a leg shatters its wave generator; a QDD on a precision wrist wanders. Decide the family before you compare brands.

Family	Architecture	Strengths	Weaknesses	Native use case	Relative cost
QDD (quasi-direct-drive)	Torque motor + low-ratio planetary (~6–10:1)	Backdrivable, high bandwidth, impact-tolerant, honest torque control	Lower torque density, heat at stall	Legged robots, force-interactive arms, humanoid limbs	Lowest
Planetary (high-ratio)	Robust multi-stage planetary gearing	High torque, shock-tolerant, cheap to build	Backlash grows with ratio; not zero-backlash	Bases, heavy joints, AGVs	Low
Cycloidal / RV	Cycloidal disc, high reduction	Very high torque density, shock-tolerant, stiff	Weight, complexity, cost	Heavy industrial joints, robot bases	High
Harmonic (strain-wave)	Frameless motor + harmonic reducer (50–160:1) + dual encoder	Zero backlash, compact, high ratio	Not backdrivable, fragile under shock, pricier	Cobot/precision arms, humanoid wrists	Highest

The short version: QDD trades torque density for backdrivability and price and is why legged robots and force-controlled arms are cheap to actuate; harmonic trades backdrivability and shock tolerance for zero-backlash precision and is why cobot wrists cost more. Cycloidal/RV sits between planetary and harmonic — bought when you need both high torque and reasonable precision in a heavy joint.

Price tiers (indicative EXW China, 2026)

All the individually catalogued modules below fall inside the site's <$1k band — that is the story of the QDD segment China owns. Harmonic and cycloidal integrated joints step up into higher bands (and are frequently POA), because the reducer alone is the expensive part.

Tier	$/joint	What you get
Micro / student QDD	~$50–150	CAN bus, single encoder, community-grade docs, low continuous torque
Research QDD	~$150–600	Better thermal design, real support, published controller baselines
Integrated harmonic joint	Higher band, often POA	Dual encoder, zero backlash, brake options; priced well above QDD
Industrial / sealed / certified	Higher band / POA	IP rating, EtherCAT, MTBF data, traceability

We are not quoting a hard figure for harmonic integrated joints here because the catalogued actuators are QDD modules; a costed harmonic option comes back with your RFQ. Directionally, an integrated harmonic joint carries the reducer premium on top of the motor and electronics, so it prices several times a comparable QDD module.

Catalog comparison: QDD modules

Figures below are from the Sourcebotics catalog. Torque and price figures are manufacturer-reported; confirm the exact variant against current maker pricing before you commit a PO.

Model	Class / gearing	Rated / peak torque	Bus	Indicative single-unit (EXW)	Lead
Robstride RS00 / CyberGear class	Micro QDD (CyberGear lineage)	~12 Nm peak class	CAN	~$50–120/joint	1–2 wks
Damiao DM-J4310	QDD	~3 Nm rated / ~7 Nm peak	CAN	from ~$70	1–2 wks
Unitree GO-M8010-6	QDD, 6.33:1 planetary	~23.7 Nm peak	RS-485	~$150–300	1–3 wks
MyActuator RMD-X8	Planetary QDD (RMD-X series)	by size across series	CAN	~$200–500/joint	1–3 wks
T-MOTOR AK80-9	QDD, 9:1 planetary	9 Nm rated / 18 Nm peak	CAN	~$400–600	1–3 wks

Reading the table: Robstride/CyberGear is the ultra-budget tier — verify QC batch to batch. Damiao is the budget disruptor beloved by student teams. Unitree GO-M8010-6 is battle-proven in Go-series volume with good docs, but note it runs RS-485, not CAN — a bus decision to make deliberately. MyActuator RMD-X offers a wide, well-stocked catalog across sizes. T-MOTOR AK80-9 is the published-paper default (MIT-Cheetah lineage), which is why matching it saves controller-retuning weeks.

How to read a spec sheet (the traps that cost money)

Design to rated torque, celebrate peak. A module advertised on its peak number may be rated at a fraction of it continuously. Ask for the derating curve (torque vs. temperature).
Check the encoder story. Single output-side encoder = fine for a leg. Dual encoder with 17-bit+ output resolution = what a precision arm needs. Don't overpay for a leg; don't underspec a wrist.
Ask for backdrive torque on QDD modules — the force-control spec vendors quietly omit when it's bad.
Confirm the bus before you buy twelve. CAN/CAN FD dominates research modules; EtherCAT dominates industrial arms; RS-485 shows up on some Unitree parts. Mixing buses costs you a gateway and a week.
Run the documentation test. Buy one, read the CAN protocol doc and SDK examples. If they're complete, the other eleven integrate in days. This predicts project success better than any torque figure.

Buying notes for integrators

MOQ is 1 almost everywhere in this segment; volume breaks typically start around 10–20 units, and volume pricing runs 15–30% below single-unit. Sample-first is the norm — use it.
Spares logic: encoders and drive boards fail before gears — put 5–10% spare boards in the PO for fleet builds.
Counterfeit watch: popular models attract marketplace clones; buy from the maker's authorized channel and verify serials.
Customs: actuators are generally low-friction goods — no batteries, modest tariffs outside the US — which is why components are often the easiest first import from China. Confirm your HS classification and duty with your customs broker; see the import playbook.

For the full catalog and filters, see actuators & joint modules.