Writing an RFQ for robot actuators: what to include

By Tolerance Labs engineering team · Updated 18 October 2026

A supplier can only quote what you describe. A request for quote that states the application, the load cycle and the tests you will run gets answers you can compare, while one that asks for “a 40 N·m joint” gets a datasheet and a price that may not fit.

Start with the application

Open with a short paragraph about the machine: what it is, which joint the actuator drives, and what that joint does. A maker’s engineer often spots a problem, or suggests a better model, from two sentences about the use. Name the joint position, such as an arm shoulder or a quadruped knee, its orientation relative to gravity, and the life you expect, in years and hours a day. Say whether the joint must be backdrivable, hold its position with power off, or detect contact.

Then give the numbers. A requirement stated as a number with its conditions can be checked; adjectives such as “high torque” and “compact” cannot.

Separate needs from preferences. Mark each requirement as required or preferred, so that a maker can offer a near fit and state the gap, instead of declining to quote. Limits that the robot does not need, such as very low backlash or a high sealing rating, raise the price and shorten the list of makers who can quote.

The fields and why each matters

For the electrical and interface fields, name the controller you will use, not only the bus. “CAN FD at 1 Mbit/s arbitration and 5 Mbit/s data, 1 kHz updates for 6 joints on one bus” can be checked; “CAN” cannot. Reading a robot actuator datasheet lists the conditions behind each figure. Ask for them in the RFQ, so that the reply arrives with them.

Worked example: from application to a spec line

An arm’s shoulder joint lifts a 3 kg payload at 0.6 m from the joint axis. The upper arm and the parts beyond it, apart from the payload, weigh 2 kg with their center of mass at 0.3 m. The joint must move 90° in 1 s, then hold for 2 s, in a 3 s cycle, 16 hours a day.

• Gravity torque with the arm horizontal: 3 × 9.81 × 0.6 + 2 × 9.81 × 0.3 = 17.66 + 5.89 ≈ 23.5 N·m.
• Inertia about the joint, treating the masses as points: 3 × 0.6² + 2 × 0.3² = 1.08 + 0.18 = 1.26 kg·m².
• A move of 90°, or 1.57 rad, in 1 s with equal acceleration and deceleration needs a peak speed of 2 × 1.57 ÷ 1 = 3.14 rad/s and an acceleration of 4 × 1.57 ÷ 1² = 6.28 rad/s².
• Acceleration torque: 1.26 × 6.28 ≈ 7.9 N·m. Peak, with gravity at its worst: 23.5 + 7.9 = 31.4 N·m.
• RMS over the cycle, taking 31.4 N·m for 0.5 s, 23.5 − 7.9 = 15.6 N·m for 0.5 s and 23.5 N·m for the 2 s hold: √((31.4² × 0.5 + 15.6² × 0.5 + 23.5² × 2) ÷ 3) = √((493 + 122 + 1,105) ÷ 3) = √573 ≈ 23.9 N·m.

These numbers are a worst case, because gravity torque reaches 23.5 N·m only with the arm horizontal. A margin of about 25% on the continuous figure and 40% on the peak gives 23.9 × 1.25 ≈ 30 N·m and 31.4 × 1.4 ≈ 44 N·m, rounded up to 45. The spec line then reads:

Output torque 30 N·m continuous at 40 °C ambient, mounted on an aluminum plate; 45 N·m peak for 1 s. Speed 3.5 rad/s at 30 N·m with a 42 V bus. Duty: 1 s move, 2 s hold, 3 s cycle, 16 h a day, 5 years. Holds the arm with power off.

A maker can answer each part of that line with a curve or a test result. Sizing robot arm joints covers the sizing steps in more detail, and the joint torque calculator runs them for you.

Documents, samples and acceptance tests

• Datasheet with test conditions for every torque, speed and thermal figure, and a torque-speed curve at your bus voltage.
• 3D model in a neutral format such as STEP, and a 2D drawing of the interfaces with tolerances.
• Protocol manual for the bus, with every command, unit and fault code, and the setup tool.
• Test reports: what the maker tests at the end of the line, and whether a report comes with each serial number.
• Samples: how many, at what price, how soon, and whether they are built on the production line.
• Compliance documents that your market or customer requires, named one by one, so that the maker can say which exist and which do not.

State the acceptance tests you will run on arrival, so that the maker can run them first. For example: idle current, direction and encoder zero, a Kt check at one current within an agreed tolerance, and backlash at a stated test torque. Incoming inspection of robot joints and dynamometer testing a robot joint describe tests you can name.

Quantity tiers and commercial questions

Ask for prices at several quantities that match your plan, for example samples, a pilot lot and two production volumes. For each tier, ask for:

• The unit price, and any one-time engineering or tooling charge, stated separately.
• The minimum order quantity and the lead time.
• Warranty terms, and how a failed unit is handled.
• How long the model will stay in production, and how much notice the maker gives before it ends.
• Which options change the price, so that you can see what a relaxed specification saves.

Steps between tiers often reflect tooling and setup cost; robot actuator cost drivers explains why. Send the same RFQ to every maker, so that the replies compare line by line. When it is ready, you can send it to us through request a quote.

Checklist

• The application described in a short paragraph, with the joint position and orientation.
• Load cycle, continuous torque, peak torque with its duration, speed at torque, and duty.
• Bus voltage range, interface, update rate and feedback needs.
• Mechanical interface, envelope, mass limit and environment.
• Documents, samples and test reports requested.
• Acceptance tests stated.
• Quantity tiers with dates, and tooling and engineering charges stated separately.
• The same RFQ sent to every maker.

Browse robot joint modules and robot arms to find candidates, then compare them side by side in Robot Parts.