Why Payload and Reach Are the First Specifications You Should Lock Down

When specifying a collaborative robot (cobot) for an integration project, payload and reach are the two most critical parameters. They dictate the robot's physical capability, cycle time, and ultimately the success of the application. However, these two specs are often in tension: increasing payload typically reduces maximum reach, and vice versa. As an integrator, you need to understand this trade-off to select the right arm for the job—and to communicate requirements clearly to your sourcing team.

The Payload-Reach Trade-off Explained

Every cobot arm has a torque limit at each joint. To lift a heavier payload, the motors and gearboxes must be larger, which adds mass. That mass must be supported by the structure, reducing the effective reach at which the arm can handle the rated payload. Manufacturers often publish a payload-reach curve: the maximum payload decreases as you extend the arm further from the base. For example, a cobot rated at 10 kg payload might only handle 5 kg at its full reach. Always check the payload at the specific reach you need, not just the headline payload.

Key Criteria for Selecting Payload and Reach

• End-effector weight: The payload specification includes the weight of the gripper, tooling, and any cables. Subtract these from the rated payload to determine the net payload available for the workpiece.
• Center of gravity (CoG): Payload capacity drops if the CoG is offset from the tool flange. Check the manufacturer's CoG offset charts.
• Dynamic vs static payload: Acceleration and deceleration forces increase the effective load on the joints. For high-speed applications, derate the payload further.
• Reach definition: Reach is usually measured from the base mounting surface to the center of the tool flange at full extension. Ensure this matches your workspace layout.
• Mounting orientation: Ceiling or wall mounting can change the payload-reach relationship due to gravity effects. Verify with the manufacturer's data.

What to Specify Before Ordering

Before you request quotes from Chinese factories or distributors, prepare a clear specification sheet. Include:

• Required net payload (workpiece + end-effector) in kg.
• Required reach at that payload, measured from the base to the tool center point (TCP).
• Maximum acceleration and speed requirements.
• Mounting orientation (floor, ceiling, wall).
• Environmental conditions (temperature, humidity, washdown).
• Communication protocol (EtherCAT, PROFINET, etc.) and I/O needs.
• Safety requirements (ISO/TS 15066 compliance, force limits).

This specification will help suppliers recommend the right model and avoid costly over- or under-specification.

Cost Considerations

Payload and reach directly impact cost. Higher payload and longer reach require larger motors, gearboxes, and structural components, increasing the bill of materials. Additionally, arms with higher payloads often have higher inertia, requiring more powerful controllers and safety systems. When sourcing from China, consider:

• Volume pricing: Factories offer significant discounts for bulk orders (e.g., 10+ units).
• Customization: Some factories can modify arm lengths or payload capacities for OEM projects, but this increases lead time and cost.
• Total cost of ownership: A cheaper arm with lower payload may require slower speeds or additional robots, increasing integration and maintenance costs.

Sourcing Tips for Chinese Cobot Factories

China is home to a growing number of collaborative robot manufacturers, many of which offer competitive pricing and customization. To ensure a successful sourcing experience:

• Request detailed payload-reach curves: Reputable factories provide these. If they don't, be cautious.
• Ask for test reports: Verify payload capacity at your required reach with a third-party or in-house test.
• Check certifications: Ensure the cobot meets safety standards (e.g., ISO 10218, ISO/TS 15066) for your target market.
• Evaluate after-sales support: Confirm spare parts availability and technical support responsiveness.
• Visit the factory or request a video audit: Assess production quality and testing procedures.

Common Pitfalls to Avoid

• Using headline payload: Always use the payload at your required reach and CoG.
• Ignoring end-effector weight: A 2 kg gripper on a 5 kg payload robot leaves only 3 kg for the workpiece.
• Overlooking acceleration effects: High-speed moves can reduce effective payload by 20-30%.
• Assuming all reaches are equal: Reach is measured differently by some manufacturers; clarify the measurement point.

Bottom Line

Payload and reach are not independent specs—they define the cobot's usable workspace. As an integrator, you must specify the net payload at the exact reach and orientation required for your application. When sourcing from Chinese factories, demand detailed performance data, verify certifications, and consider total cost of ownership. Getting these two parameters right upfront will save you from costly redesigns and ensure a successful integration.