AGV Chassis Wheel Alignment & Datum Inspection: An FAI Guide

An AGV chassis can look square on a welding table and still create a difficult vehicle build. Wheel modules may bolt on individually, yet their axes may not relate correctly to one another. A payload interface may be flat when clamped for inspection but relax after the clamps are removed. A hole pattern may pass a coordinate check while the actual drive module cannot seat against its locating surface.

That is why an AGV chassis first-article inspection should be organized around function rather than around the easiest dimensions to measure. The inspection plan needs to reproduce the chassis state that matters to the OEM: how it is supported, where it is located, which interfaces carry the wheel modules and what evidence is required before the chassis enters vehicle assembly.

This guide stays deliberately narrow. It addresses wheel coplanarity, axle relationships, datum strategy and first-article evidence. Material selection, navigation architecture, controls and the broader choices involved in AGV chassis design belong in separate reviews.

Start with the vehicle coordinate system

Before the supplier balloons a drawing, the OEM should identify the coordinate system used by the mechanical, controls and calibration teams. A practical drawing normally needs a primary plane, a longitudinal direction and a lateral origin. Those references should come from stable, accessible features rather than from a cover edge or a welded surface that has no assembly function.

The primary plane might be established by defined support pads or mounting interfaces. A centerline may be created from machined targets, qualified holes or symmetric features. The correct choice depends on how the wheel modules, battery structure and payload deck are assembled.

Avoid creating one datum scheme for fabrication and an unrelated scheme for vehicle calibration. When two schemes are necessary, document the transformation between them. Otherwise a supplier can produce a compliant report that does not help the integration team diagnose tracking or wheel-load problems.

Define the measurement state before the tolerance

A welded chassis changes shape according to support and restraint. The inspection instruction should therefore say whether the chassis is measured free-state, supported at defined pads, leveled on adjustable points or restrained in a released fixture. It should also state which installed components are present.

This distinction is not paperwork. A heavily restrained frame can appear flat while storing enough stress to move after release. A completely unsupported frame can show twist that disappears when installed on its intended support points. Neither result is meaningful unless it matches the drawing definition.

Use a simple inspection-state note that covers:

• Drawing and model revision.
• Support-point locations and support method.
• Permitted clamps or restraint forces, if any.
• Installed inserts, brackets and machined pads.
• Whether coating is present and which interfaces are masked.
• Stabilization conditions required by the OEM measurement procedure.

Inspect wheel interfaces as a related system

Each wheel mount may be correct in isolation while the complete set is wrong as a system. The FAI should evaluate the relationships that govern vehicle behavior: wheel mounting planes, axle directions, lateral spacing, fore-aft position and height relative to the primary chassis plane.

For driven wheels, the important characteristic may be the axis generated by two locating features rather than the nominal center of a clearance-hole pattern. For casters, mounting-plane orientation and the location of the swivel axis may matter more than the outline of the bracket. The released drawing should make that intent measurable.

Functional question	Drawing definition to provide	Suitable evidence
Will all wheel modules seat correctly?	Mounting-plane datums, local flatness or profile requirement, and keep-out zones	Surface or coordinate report plus seating check
Are drive axes correctly related?	Axis-generating features and relationship to chassis datums	Coordinate measurement or qualified functional gauge
Will wheels share the intended ground plane?	Support state and wheel-interface height relationship	Height map or simulated module-interface check
Can the OEM repeat the setup?	Datum targets, support diagram and measurement sequence	Annotated setup photographs and inspection procedure
Is the hole pattern usable?	Locating versus clearance features and positional controls	Pattern gauge, coordinate report or mating check

The OEM should choose acceptance limits from vehicle dynamics, module drawings and the released tolerance analysis. A fabricator should not invent limits from a generic AGV rule.

Separate coplanarity from local flatness

Wheel coplanarity and mounting-pad flatness answer different questions. Local flatness describes one interface. Coplanarity describes how several interfaces relate to a common reference. Both may matter, but combining them into one vague note makes inspection ambiguous.

A pad may be locally flat but positioned at the wrong height. Conversely, several small formed interfaces may establish an acceptable common plane even though none resembles a precision-machined surface. Define the characteristic that predicts assembly and select the production process accordingly.

If interfaces are machined after welding, the inspection sequence should distinguish the welded condition from the finished condition. Record which datums locate the chassis for machining and how the shop protects that datum chain during subsequent finishing and handling.

Make axle alignment inspectable

An axle direction cannot be verified reliably when the drawing only dimensions two loose hole centers. Identify the features that establish the module orientation. These may be dowel holes, a machined shoulder, a locating edge or a controlled mounting pattern.

The inspection method must fit the feature. A coordinate measuring system can calculate axes from several points, but the report should explain the construction. A functional gauge can reproduce the module interface quickly, but the gauge itself needs control and traceability. For low-volume development builds, a mating module or qualified surrogate may provide the most useful evidence when its use is defined in advance.

Do not use assembly bolts to force a module into alignment unless the OEM has intentionally designed that adjustment. Clearance holes, slots and shim packs need documented setting and acceptance instructions so the first vehicle and later builds follow the same process.

Plan the FAI around process-changing operations

Measure critical geometry after the operations capable of changing it. Welding, stress relief where specified, machining, hardware insertion and coating can each affect interfaces in different ways. An early in-process check may help control fabrication, but it cannot replace final-state evidence when later operations affect the feature.

The first article should use production-intent material, tooling, weld sequence, machining setup, inserted hardware and finish. If engineers hand-correct the first frame, document the correction and incorporate it into the released process. Otherwise the accepted article does not demonstrate repeatability.

A useful FAI package can include:

• Ballooned released drawing and model revision.
• Inspection-state and support diagram.
• Results for wheel planes, locating patterns and generated axes.
• Material and finish documentation required by the purchase order.
• Weld and machining traveler references where requested.
• Records of nonconformances, approved deviations and reinspection.
• Identification of the production tooling or gauge revision.
• Photographs showing datum targets and the measurement setup.

Use an FAI and RFQ checklist before releasing the purchase order

An RFQ should not leave the supplier to guess which dimensions matter to motion performance. Review the following items before quotation and again before the first article begins.

Review item	OEM or integrator input	Fabricator response
Vehicle datum scheme	Released drawing and functional explanation	Proposed setup and accessible targets
Wheel-module interfaces	Mating drawings, loads and locating method	Manufacturing and inspection approach
Chassis support state	Installation and measurement condition	Fixture or surface-plate plan
CTQ evidence	Required report format and sampling plan	Measurement capability and deliverables
Post-weld machining	Finished-interface requirements	Datum transfer and machining sequence
Finish boundaries	Masking and grounding requirements	Finish traveler and protection plan
Change control	Approval route for deviations and revisions	Revision-identification method

The downloadable robotics frame FAI and datum checklist can help structure this conversation, while the robotics sheet metal quality-plan guide explains how to connect CTQs with evidence across a wider mechanical kit.

Keep mechanical fabrication and vehicle validation boundaries clear

DRAmetal fabricates mechanical scope to the OEM’s released drawings, models, specifications and approved inspection plan. We can review manufacturability, propose measurement methods and supply agreed fabrication records. The OEM or system integrator owns vehicle architecture, loads, steering and control behavior, safety functions, applicable certification decisions and final validation in the real operating environment. Qualified electrical and safety personnel must approve work within their disciplines.

For a production-oriented review, start with the AGV chassis manufacturing page and the wider robotics manufacturing hub. Include the released chassis model, wheel-module interface drawings, support state, CTQs, quantity, finish, inspection deliverables and destination when you contact DRAmetal. That package makes a wheel-alignment discussion concrete before tooling and inspection plans are committed.