A linear motor purchase is decided by a small set of datasheet numbers that actually predict field behaviour: peak force (Fp), continuous force (Fc), motor constant (Km), maximum speed, coil thermal class, air gap, magnetic track length, encoder resolution, and the integrated temperature sensor (PTC or KTY) [S1][S3].
Selection is rarely one-line: a working speed profile (trapezoidal or triangular), the load mass, the stroke, and the duty cycle have to be reduced to those nine parameters before the catalog filter does any useful work [S1][S7]. Engineers who skip that step routinely oversize or undersize the coil unit by a factor of two or more [S1].
Peak force, continuous force, and the motor constant Km
Peak force Fp is the maximum thrust the coil can deliver for short transients, while continuous force Fc is the thermal-limited thrust the winding can sustain without tripping the insulation class, and the two are listed separately on every reputable iron-core datasheet [S1][S3]. The motor constant Km, defined as the ratio of output force to the square root of input power (N/√W), is the single best cross-vendor figure of merit, because it folds electrical and mechanical efficiencies into one number and lets you compare an iron-core and an ironless coil on equal terms [S6].
For a trapezoidal move of a 0.5 kg payload across 20 mm in 100 ms on a 20 deg incline, the calculated peak force lands in the tens of newtons and the continuous force in single-digit newtons, which is why a FAULHABER-style selection flow asks for both numbers before any catalog search is started [S1]. Sizing tools such as LinMot Designer 1.11.0 (released 2026-01) accept the same peak/continuous pair as inputs and return a filtered list of matching coil units, magnet track lengths, and servo drives [S5].
Coil thermal class, winding temperature, and the F/v curve
Coil winding temperature is the silent failure mode of every direct-drive axis: as the copper heats, resistance climbs, force drops, and above the insulation class the winding burns out, so the datasheet's stated continuous force is only valid if the cooling path is real [S1]. Iron-core vendors specify PTC thermistors (typically 1 kΩ at 25 deg C, switching near 130-155 deg C) and KTY84-130 silicon sensors on the coil front face, and the analog Hall or digital Hall module on the slider reads back position through the same cable harness [S3].
Buyers should request the F/v (force versus velocity) curve for the candidate coil, not just the headline peak/continuous numbers, because attraction force between iron teeth and magnets can exceed 1,000 N on a 100 mm wide stack and that load transfers directly into the linear bearing choice [S3][S4]. A matching sizing tool, run with the actual motion profile, will plot the operating point on the F/v curve and flag any segment that breaches the continuous envelope [S5].
Magnet track length, air gap, and mechanical interface
Magnet track length sets the maximum usable stroke and the effective field overlap; coupling two shorter tracks end-to-end is supported on iron-core platforms but introduces a small dead zone at the joint that must be designed around [S3]. Air gap between coil teeth and magnet track is typically 0.5-1.0 mm on iron-core units, and mounting surface flatness below 0.05 mm/m is required to keep that gap uniform, otherwise peak force variation along the stroke can exceed 10% [S3].
Stainless steel cover plates, magnetic-field shielding plates, and water-cooling interfaces are listed as additional parts rather than as core components, and they change the thermal budget and the minimum bend radius for the power cable [S3]. The coil unit, magnet plate, and Hall module each have a polarization key, and a reverse-polarity connection during pre-commissioning is the most common field failure for first-time installers [S3].
Encoder, position feedback, and the linear actuator chain
Encoder resolution, not raw motor speed, is the parameter that decides whether a stage hits its repeatability target, and precision stages routinely specify 0.1-1 µm linear scales read through an external linear encoder rather than the motor's internal Hall sensors [S4][S8]. Hall modules (analog or digital) provide commutation and coarse position, while the high-resolution linear encoder closes the position loop, and the two feedback channels are wired into the same servo drive [S3].
When the application is a complete axis rather than a bare coil, the datasheet chain to verify is the linear actuator stack: motor + bearing + encoder + drive + cabling, with the bearing preload and the encoder signal integrity (twisted pair, shielding, max cable length) called out in the same document [S4]. A linear motor actuator that meets the force spec can still fail repeatability if the encoder cable shares a tray with the power wires [S4].
System wiring, braking, and electrical safety
Wiring and cable management on a linear motor are not afterthoughts: the system is a stationary magnet track plus a moving coil or slider, so the power cable has to flex for the full stroke, and standard drag-chain ratings (typically 5-10 million cycles) apply [S2]. Voltage spikes from the PWM drive are clamped at the coil terminals, and a missing or undersized regen resistor will push the bus voltage past the drive's trip level on every decel [S3].
Because the coil is friction-free, a controlled or mechanical brake is required for any vertical or power-loss-safe axis, and the brake voltage, holding force, and release time must be on the same datasheet page as the motor [S4]. EMC, protective earth, and the PTC/KTY temperature sensor wiring are documented in the iron-core manual with specific terminal pinouts, and CE, RoHS, REACH, UKCA, and CSA certifications are listed for the global build [S3].
Decision matrix: which parameter to weigh first
For a high-acceleration point-to-point axis (pick-and-place, gantry), rank peak force > continuous force > Km > encoder resolution, because acceleration dominates the move time [S1][S4]. For a constant-velocity scan or printing axis, rank continuous force > thermal class > F/v curve flatness > peak force, because the motor sits at one operating point for long dwells [S1][S4].
For a cleanroom or medical axis, rank encoder resolution > cabling bend rating > material certifications (RoHS, REACH, biocompatible covers) > raw force, because particle emission and signal integrity outweigh thrust [S3][S8]. For a vertical or safety-rated axis, rank brake holding force > regen resistor sizing > PTC/KTY trip class > continuous force, because failure must be controlled on power loss [S3][S4].
Procurement checklist before issuing the PO
Request from each shortlisted vendor: the F/v curve, the empirical continuous-force test at the actual mounting orientation, the 3D CAD model in STEP format, the wiring harness drawing with pin numbers, and the integrated temperature-sensor type (PTC or KTY84-130) [S3][S7]. Cross-check the published Km against an independent calculation, and confirm the magnet track length, the air-gap tolerance, and the bearing preload are listed on the same datasheet page rather than buried in a separate mechanical drawing [S3][S7].
Confirm that the servo drive in the quote is matched to the coil's voltage, current, and feedback type, and that the regen resistor, if external, is sized for the worst-case decel of the load [S3]. A 2026-06 sourcing guide notes that buyers who rely only on standard datasheet metrics without empirical test data report the highest field-failure rate, and the same guide flags CAD-model turnaround as a practical proxy for a vendor's application-engineering depth [S7]. Two trackable signals to watch over the next quarter: the release of updated LinMot Designer revisions and any new iron-core platforms that publish standardized F/v curves across the full track-length range [S5][S7].
This topic is covered further in Plunger Pump Power End: Crankshaft Layouts and Drive Options.