Servo Motor Compatibility Checklist Before PO

Use this pre-PO checklist to verify flange, inertia, encoder, and control assumptions before locking a rotary table supplier.

Do not release PO on catalog claims alone. Release PO only after compatibility is backed by measurement and documented evidence.

Mechanical fit is only half the decision. Many rotary-table schedule slips begin after PO, when controls and tuning constraints show up too late.

I wrote this checklist for buyer teams that need a hard pass/fail gate before commercial release.

Applicability, Date, and Limits

Last verified date: 2026-05-11.
Applies to: new RFQ, retrofit replacement, and supplier-switch decisions for servo-driven rotary axes.
Does not replace: full machine safety validation, controls functional-safety design, or legal warranty terms.
Decision boundary: this checklist is a compatibility gate before PO; final tuning and process validation still require project execution.

Scope and Decision Boundary

Use this checklist for:

servo hollow rotary table projects,
retrofit replacement of an existing rotary axis,
supplier switch under timeline pressure.

This is not a replacement for full machine safety validation. It is a pre-PO compatibility gate to prevent avoidable integration failures.

Pre-PO Compatibility Gate (Pass/Fail)

Checkpoint	Required evidence	Starter pass threshold (example)	Fail trigger
Motor model match	Supplier confirmation against exact motor SKU	Exact model code and brake option match	Generic "equivalent motor" with no model map
Flange and pilot interface	Controlled drawing revision	Zero critical mismatch on bolt circle, pilot, shaft interface	Any critical dimension unresolved
Reflected inertia screen	Calculation sheet + duty profile	High-dynamic indexing projects start with `<=10:1` load-to-motor inertia; moderate duty can screen at `<=20:1` then verify by tuning	Ratio out of screen and no tuning proof
Encoder and protocol fit	Interface control note	Protocol and signal level match controller stack	"Adapter later" answer without design note
Reducer ratio suitability	Torque/speed envelope sheet	Meets required speed and peak torque under duty peaks	Rated values only at non-project conditions
Repeatability allocation	Test method + target	Rotary axis repeatability budgeted at `<=25%` of process angular tolerance	No tolerance budget allocation
Backlash allocation	Measurement method statement	Backlash limit defined as percentage of process tolerance (commonly `<=40%` of axis budget)	Backlash not measured bidirectionally
Thermal stability	Warm-up test condition	Drift budget defined after thermal soak under representative duty	Performance only measured at cold start

These thresholds are practical screening values used by many commissioning teams. Final limits must be locked to your actual process tolerance and drive-vendor guidance.

How to Measure Before PO (Minimum Method)

Ask suppliers to provide a minimum evidence pack with the same method across candidates:

Warm up the axis under representative duty for at least 20-30 minutes.
Run bidirectional indexing cycles (CW/CCW) for at least 30 repetitions.
Record max, min, mean, and P95 for repeatability and settling behavior.
Measure backlash after controlled direction reversal sequence.
Report all values with instrument type and test environment.

If suppliers use different methods, numbers are not comparable.

Compatibility Risk Matrix for Buyer Review

Risk pattern	Typical root cause	Business impact	Required action before PO
"Fits mechanically but tunes poorly"	Inertia and ratio mismatch	Commissioning delay and cycle-time loss	Force tuning evidence using your duty profile
"Protocol mismatch discovered late"	Controller assumptions not frozen	Rewiring/reprogramming rework	Lock interface control document revision
"Repeatability meets catalog but not process"	Measurement condition mismatch	Scrap/rework risk	Define one shared measurement protocol
"Replacement motor changed quietly"	Obsolescence handling not defined	Unexpected redesign in production	Add approved equivalence list in PO annex

Minimum Technical Annex to Attach to PO

Add a one-page annex and require supplier acknowledgment. Include these fields:

Annex item	Example content
Approved motor list	Primary model + approved equivalent list
Mechanical interface revision	Drawing ID + revision + critical dimensions
Inertia and ratio assumptions	Calculation file ID and boundary conditions
Protocol and encoder map	Interface document revision
Acceptance criteria	Repeatability, backlash, thermal drift limits
Test report format	Required data fields and submission timing
Change-control rule	Any motor/interface change requires written approval