A centered Watt linkage uses opposing transverse links and a central rocker to keep an axle centered more closely than a single Panhard rod. This calculator performs only a single-link travel-angle and chord-setback check for an entered tie-link length.
Related Resources for Actuator Projects
For separate actuator-driven fixtures or automation projects, check force, travel and limit controls through the full motion. These resources do not describe a conversion of the suspension linkage to actuator drive.
For those separate projects, define the load path, required travel, control method and environment before choosing an actuator.
A crank or cam may tolerate continuous rotation through a difficult part of the cycle, while a linear actuator has defined end positions and internal limits. That difference matters when the mechanism needs repeatability or must not drive into a hard stop.
- Map actuator stroke to the actual output travel before choosing a model.
- Check for binding, changing leverage, and peak load near the ends of travel.
- Decide whether timed motion is acceptable or position feedback is required.
For a FIRGELLI design review, calculate the load case with the FIRGELLI actuator force calculator and plan the switching or controller arrangement with the linear actuator wiring diagram generator. If an actuator or cylinder is already installed, the linear actuator replacement finder helps keep the comparison tied to real dimensions.
Watt's Link Rear Suspension Interactive Calculator
Enter tie-link length and vertical travel magnitude. Outputs are single-link geometry references—not complete Watt-link closure, axle lateral motion, roll-center migration or suspension design.
Equation Used
- The geometric formulas require a vertical offset magnitude no greater than the link length. Inputs outside that range do not describe a possible single-link position, even if clipped values remain on screen.
- The link starts horizontal for the single-link geometry check.
- Fifteen degrees is a declared comparison limit, not a universal suspension criterion.
- Chord setback is for one rotating link, not predicted axle lateral shift.
- Central-rocker length, chassis pivot spacing, asymmetric wheel travel, compliance, roll center, loads and interference are omitted.
Watt-Link Rear-Suspension Context
U.S. Patent 8,696,002 describes a vehicle Watt linkage with two equal horizontal bars and a central vertical link, noting that opposing curved movements compensate to approximate a centered vertical path. That coupled behavior requires more geometry than this two-input tool contains.
What This Calculator Represents
The tool checks one entered tie link against a vertical offset, compares its angle with a declared 15-degree reference and reports the corresponding one-link chord setback.
Single-Link Geometry Calculation
margin=L sin15deg-h
L_min=h/sin15deg
setback=L-sqrt(L^2-h^2)
Setback is not complete Watt-link axle motion.
Worked Reference
For L=320 mm and h=80 mm, single-link angle is about 14.5 degrees, margin to the declared 15-degree offset is about 2.8 mm, minimum length about 309 mm and chord setback about 10.2 mm.
Assumptions and Limits
- Calculated: one-link angle, 15-degree comparison, minimum length and chord setback.
- Illustrated: opposing links and central rocker as topology context.
- Not calculated: coupled closure, axle path, roll center, compliance, loads, bump/roll asymmetry or packaging.
Frequently Asked Questions
Is chord setback axle lateral shift?
No.
Is 15 degrees a universal limit?
No; it is a declared comparison.
Does the tool solve the central rocker?
The animation solves an illustrative coupled linkage. The numerical outputs evaluate one link only and do not report the central rocker or axle coordinates.
Are equal left/right links enforced?
Only one length is entered.
Are roll and one-wheel bump modeled?
No.
Can this design a suspension?
No.
References
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