By the EVST Engineering Team · Last updated: June 10, 2026
Selecting a collaborative robot starts with two numbers: payload and reach. Size payload by adding the part weight and the gripper weight, then add 20 to 30 percent margin. Size reach to cover the full working envelope of the task. EVST collaborative robots span the 3 kg through 30 kg payload class, with published arms at 3 kg / 620 mm, 6 kg / 917 mm, 12 kg / 1,300 mm, and 18 kg / 900 mm, plus higher-payload variants on request.
Why Payload and Reach Come First
Every other cobot decision, gripper, controller, safety configuration, mounting, follows from payload and reach. Get these two wrong and no amount of tuning recovers the cell: an undersized arm cannot lift the part with margin, and a short-reach arm cannot cover the work envelope no matter how it is mounted. This guide gives a repeatable method to fix both numbers before you request a quotation.
Payload is the mass the arm carries at the tool flange, and it always includes the gripper or end-of-arm tool, not just the part. Reach is the radius of the working envelope from the base. Within any cobot family, payload and reach trade against each other: the same mechanical platform offers either higher payload at shorter reach or lower payload at longer reach. That trade-off is why selection is a balance, not a maximization.
Step 1: Size the Payload
The payload calculation is simple arithmetic, but it is where most undersizing mistakes happen because buyers forget the tool.
Payload required = part weight + gripper/tool weight + any cabling or sensor mass at the flange
Then add a dynamic margin. A cobot accelerating and decelerating a load needs headroom above the static mass: 20 to 30 percent is a safe default. A 6 kg part on a 2 kg gripper is an 8 kg static load, which points to a 10 kg or larger arm once margin is included, not a 6 kg arm.
One detail buyers miss: payload ratings often depend on the load’s center of gravity offset from the flange. A long gripper or an offset tool reduces the usable payload below the headline number. Always check the payload-versus-center-of-gravity chart for the specific model. According to EVST application data, gripper and tooling mass accounts for 20 to 40 percent of total flange load in typical assembly and tending tasks, so it is never a rounding error.
Step 2: Size the Reach
Reach must cover every point the tool needs to touch, plus approach and retract clearance. The practical method:
- Lay out the task footprint: pick points, place points, machine doors, fixtures.
- Find the farthest two points the arm must reach from a single mounting position.
- Confirm the arm can reach both without hitting a singularity or a joint limit, which usually means leaving margin inside the nominal reach radius.
- If the footprint is larger than any single arm’s reach, consider a longer-reach model, a different mounting (ceiling or wall), or a mobile base.
In practice, when EVST engineers commission machine-tending cells, the reach failure mode is rarely the headline radius. It is the wrist orientation near the edge of the envelope: the arm can position the gripper at the far point, but cannot achieve the required approach angle there. Validating reach with the actual tool orientation, not just the point, prevents this.
Step 3: Match to an EVST Model
EVST’s published collaborative robot models give clear payload-and-reach anchors. The table maps common task profiles to the model class. Full datasheets, including repeatability and payload-versus-reach curves, are available on request.
| EVST cobot model | Payload | Reach | Suited to |
|---|---|---|---|
| 3 kg collaborative arm | 3 kg | 620 mm | Benchtop assembly, small-part pick-place, lab automation, inspection |
| 6 kg collaborative arm | 6 kg | 917 mm | Light machine tending, screwdriving, electronics assembly, dispensing |
| 12 kg collaborative arm | 12 kg | 1,300 mm | CNC and molding machine tending, mid-size pick-place, light palletizing |
| 18 kg collaborative arm | 18 kg | 900 mm | Heavier tending, compact-footprint handling where reach is secondary to payload |
| Higher-payload class | Up to 30 kg class | On request | Palletizing, heavier handling and machine tending; specs on request |
Note the 12 kg model offers the longest published reach at 1,300 mm, while the 18 kg model trades reach for payload at 900 mm. This is the payload-versus-reach trade in practice: choose the 12 kg arm when the envelope is wide and the load is moderate, and the 18 kg arm when the load is heavy but the footprint is compact. For the underlying working principle and safety mechanics behind these arms, see the EVST industry guide to how collaborative robots work.
Step 4: Account for the Safety Configuration
A cobot’s effective speed, and therefore its cycle time, depends on the safety configuration the application allows. Two arms with the same payload can deliver very different throughput depending on whether the cell runs in power-and-force-limited mode at all times or uses speed-and-separation monitoring to run fast when the workspace is clear.
This matters at selection time because it changes the payload-versus-speed math. If the task must run in full power-and-force-limited mode for the entire cycle, factor the reduced speed into the throughput estimate before committing to a payload class. The safety mode is set during the application risk assessment, which EVST supports as part of commissioning. For the standards framework behind these modes, see our cobot safety standards guide for buyers.
Step 5: Specify the End Effector and Mounting
The gripper, mounting, and I/O complete the specification. Key decisions:
- Gripper type — two-finger parallel, vacuum, magnetic, or custom, sized to the part and within the payload budget after margin.
- Tool I/O — electrical and pneumatic connections, ideally routed through the wrist to avoid cable snag in a shared workspace.
- Mounting — table, floor pedestal, wall, ceiling, or mobile base. Mounting affects the reachable envelope and the gravity compensation in the controller.
- Vision and sensing — 2D or 3D camera for part location, force sensing for insertion tasks. Add the sensor mass to the payload budget if it mounts at the flange.
Selection Summary Matrix
| If your task is… | Start with payload class | Reach priority |
|---|---|---|
| Benchtop small-part assembly or inspection | 3 kg | Short reach acceptable (around 600 mm) |
| Electronics assembly, screwdriving, light tending | 6 kg | Medium reach (around 900 mm) |
| CNC / molding tending, mid-size handling, light palletizing | 12 kg | Long reach (around 1,300 mm) |
| Heavy tending in a compact footprint | 18 kg | Payload over reach (around 900 mm) |
| Palletizing or heavier handling | Up to 30 kg class | Specify envelope; specs on request |
RFQ Checklist: What to Send for a Quotation
A request-for-quote with the items below returns a real configuration and number quickly. Without them, the supplier has to ask a round of follow-up questions and the quote slips.
- Part weight, dimensions, and material
- Gripper or tool already chosen, or a description of the grip surface
- Task description (tending, assembly, palletizing, inspection, welding, finishing)
- Cycle time target
- Work envelope footprint and the farthest reach points
- Production volume (parts per shift, shifts per day)
- Workspace sharing: will an operator be in the cell during operation?
- Mounting preference and available floor or bench space
- Required certifications (CE, IATF 16949, customer-specific)
- Installation country and any hazardous-area requirement (which may require an explosion-proof model)
To request a quotation, contact EVST sales via the contact page or email [email protected]. With a complete package, a first technical reply with a recommended model and configuration typically lands within 48 hours.
Why Buyers Specify EVST Collaborative Robots
EVST, headquartered in Chengdu with manufacturing in Wenling, has delivered 600+ automation projects and ships to 100+ countries over seven years of operation. For cobot buyers specifically:
- Published payload anchors from 3 kg to 18 kg, extending to the 30 kg class on request, from one product family
- IATF 16949 automotive-grade certification on the collaborative robot production line
- CE, SGS, and TUV third-party certifications across the product range
- An explosion-proof collaborative robot for hazardous atmospheres, for sites standard cobots cannot enter
- A 100+ country field engineering network for on-site commissioning, risk assessment, and operator training
- Full-stack supply: cobots alongside QJAR industrial robots, SCARA, delta, positioners, and linear tracks, reducing multi-vendor interface risk
Browse the current collaborative robot lineup on the EVST collaborative robot page, and for six-axis industrial alternatives at higher payload, see the QJAR 6-axis robot overview.
Frequently Asked Questions
How do I calculate the payload I need for a cobot?
Add the part weight, the gripper or tool weight, and any cabling or sensor mass at the flange, then add 20 to 30 percent dynamic margin. A 6 kg part on a 2 kg gripper is an 8 kg static load, which points to a 10 kg or larger arm after margin. Also check the payload-versus-center-of-gravity chart, because an offset tool reduces usable payload below the headline number.
What reach does an EVST cobot offer?
Published EVST collaborative arms include a 3 kg model with 620 mm reach, a 6 kg model with 917 mm reach, a 12 kg model with 1,300 mm reach, and an 18 kg model with 900 mm reach. The 12 kg model offers the longest published reach; the 18 kg model trades reach for payload. Higher-payload variants and their reach figures are available on request.
Can one cobot cover my whole work envelope?
If the farthest two task points fall within a single arm’s reach with margin for wrist orientation, yes. If the footprint is larger, options include a longer-reach model, an alternative mounting (wall or ceiling), or a mobile base. Validate reach with the actual tool approach angle, not just the point location, because wrist orientation near the envelope edge is the common failure mode.
Does the safety configuration affect which cobot I should buy?
Yes. If the task must run in full power-and-force-limited mode throughout the cycle, the effective speed is lower, so factor that into the throughput estimate before fixing a payload class. If speed-and-separation monitoring is permissible, the same arm runs faster when the workspace is clear. The safety mode is set during the application risk assessment.
How long is the lead time and quotation turnaround?
With a complete RFQ package, EVST typically returns a first technical reply with a recommended model and configuration within 48 hours. Standard collaborative arms ship on lead times confirmed at quotation; custom end-effector and integration scope extends the timeline and is quoted separately.
About the author: The EVST Engineering Team supports buyers and integrators specifying collaborative robot cells across assembly, machine tending, packaging, and inspection. EVST (EVS TECH CO., LTD), founded in Chengdu in 2018, has delivered 600+ automation projects and ships to 100+ countries, with IATF 16949 automotive-grade certification and CE / SGS / TUV third-party certifications across the QJAR, collaborative robot, SCARA, and delta product families.