How to Use This Mechanism Library

Start with the motion you need, not the part you think you need. A four-bar linkage, crank-slider, cam, Geneva drive, rack and pinion, and lead screw can all convert motion, but they do it with very different force profiles, accuracy limits, wear points, and packaging requirements. The purpose of this page is to help you narrow that choice quickly by watching how each mechanism behaves and then checking whether its assumptions match your build.

For example, if you need intermittent indexing on a rotary table, a Geneva mechanism may be simpler than servo-controlled motion when the index positions are fixed and the dwell period is valuable. If you need a door, hatch, or panel to travel through a controlled arc, a linkage may be better than forcing a linear actuator directly onto the hinge line. If you need high reduction and continuous rotation, gears or worm drives may be more appropriate than a linkage, but backlash, lubrication, and side loading become important design concerns.

When reviewing an animation, pause mentally at the worst-case position. That is usually where the transmission angle is poor, the actuator is close to stall, the cam follower is climbing fastest, or the linkage is near a toggle point. A mechanism that looks smooth in free motion may still fail when friction, misalignment, side load, acceleration, or a real payload is added.

What's Covered in the Guide

• How to search and interpret the mechanism animations
• A practical mechanism selection table
• Engineering checks before copying a mechanism
• Application examples and design assumptions
• Common mistakes to avoid
• The complete interactive mechanism index
• Mechanism selection FAQ

Choosing the Right Mechanism Family

The table below is not a substitute for calculation, but it is a useful first filter. Use it to decide which categories are worth exploring in the animation index, then validate the geometry with real dimensions, loads, cycle rate, and safety factors.

Engineering Checks Before You Copy a Mechanism

An animation shows the kinematic idea, but your finished machine still depends on materials, tolerances, loads, lubrication, and mounting stiffness. Before adopting any mechanism from the index, define the following assumptions:

• Required output motion: travel, angle, dwell time, velocity profile, and whether the motion must be repeatable under load.
• Load case: static load, peak dynamic load, impact, gravity direction, and whether the load changes during the stroke.
• Duty cycle: occasional movement, continuous cycling, or high-speed operation. A mechanism that survives a demo may wear rapidly in a production machine.
• Mounting stiffness: flexible brackets introduce misalignment. Linkages and gear trains are especially sensitive to frame deflection.
• Guidance: do not ask a driving actuator, gear, or crank pin to also behave as the main linear guide unless it is designed for that side load.
• Adjustment method: slots, eccentric bushings, shims, or turnbuckles can make commissioning much easier than fixed holes everywhere.

For force-sensitive designs, convert loads into consistent units before comparing concepts. FIRGELLI's force unit converter is useful when a drawing, supplier part, or test result mixes newtons, pounds-force, and kilogram-force. For current draw on actuator-driven prototypes, the current unit converter helps keep electrical estimates consistent.

Practical Examples

Example 1: Small hatch or lifting panel

Assume a lightweight panel must open through an arc and stop reliably at the end positions. A direct linear actuator connection may work, but only if the actuator has a useful moment arm throughout the stroke. If the actuator line of action passes too close to the hinge, the required force can rise sharply near closed position. A four-bar linkage or bell crank can improve packaging and force angle, but it adds pivots that must be aligned and lubricated. For beams or arms that may flex, check deflection with a method such as the cantilever beam deflection calculator before assuming the mechanism will stay square under load.

Example 2: Reciprocating pusher or feeder

A crank-slider is attractive because it converts continuous motor rotation into a repeatable stroke. It is not ideal if constant linear speed is required, because the slider naturally slows near each end and moves fastest near mid-stroke. That behavior is useful for some feeders and pumps, but it can cause impact or material handling problems in others. If you are sizing the geometry, compare crank radius, rod length, and stroke using the crank-slider mechanism calculator.

Example 3: Rotary indexing table

A Geneva drive can provide positive mechanical indexing with a dwell period between moves. The tradeoff is engagement shock: the drive pin enters the slot, accelerates the wheel, then leaves it. At low speed this can be simple and robust; at high speed it may require careful material choice, lubrication, and shock control. To compare index count, dwell angle, and geometry, use the Geneva mechanism calculator. If your design is closer to a controlled release or counting mechanism, also review the stud escapement explanation.

Example 4: Gear reduction before an actuator or output shaft

Gear trains are often chosen to increase torque or reduce speed, but every reduction stage adds friction, backlash, and shaft loading. A high gear ratio may solve a torque problem while creating a positioning problem. For early estimates, compare options with the gear ratio calculator and guide, then verify that the selected shafts, bearings, and housings can handle the loads.

Common Mistakes to Avoid

• Ignoring toggle positions: A linkage near a straight-line toggle can create very high forces with very little output movement. That may be useful for clamping, but dangerous for an actuator or motor if it is not intentional.
• Using pivots as bearings without enough support: A bolt through two thin plates may work in a prototype and loosen quickly in service. Add bushings, shoulder bolts, spacers, or proper bearings where cycle count matters.
• Forgetting clearance through the full path: Check the swept envelope of every link, coupler, follower, and fastener head, not just the start and end positions.
• Assuming the animation shows scale: Many mechanism animations are schematic. Real link lengths, pressure angles, cam radii, gear tooth counts, and joint offsets must be engineered for the application.
• Underestimating dynamic loads: Starting, stopping, reversing, and impact can exceed the static load by a large margin. Use conservative assumptions until measured test data is available.
• Skipping life-cycle thinking: If a mechanism cycles often, estimate service life early. For actuator-driven systems, the actuator life cycle estimator can help frame duty-cycle assumptions.

Complete Interactive Mechanism Index

The searchable index below includes animated demonstrations and engineering explanations of classical machine elements, steam-era engines, modern linkages, gear systems, cam mechanisms, escapements, couplings, and many other mechanisms. Search by the motion you need, the component name, or a category such as cams, gears, linkages, indexing, or escapements.

Mechanism Selection FAQ

What is the best mechanism for converting rotary motion to linear motion?

There is no single best choice. A crank-slider is simple and repeatable, a rack and pinion gives a direct relationship between rotation and travel, a lead screw provides high mechanical advantage, and a cam can create a custom motion profile. Choose based on stroke, speed profile, load, accuracy, duty cycle, and available space.

How do I know whether a linkage will bind?

Check the full range of motion, not just the endpoints. Watch for poor transmission angles, links approaching a straight-line toggle, joints running out of angular misalignment, and frame deflection under load. A cardboard model, CAD motion study, or simple pinned prototype can reveal binding before metal parts are made.

When should I use a Geneva mechanism instead of a servo motor?

Use a Geneva mechanism when you need fixed mechanical index positions and a repeatable dwell period with relatively simple control. Use a servo when you need programmable positions, adjustable speed profiles, soft starts, or frequent changes to the index pattern.

Why does my mechanism work by hand but stall with a motor or actuator?

Hand testing often hides peak loads because you naturally slow down, wiggle parts through misalignment, or avoid the worst load point. Motors and actuators follow their mounted path. Check friction, side load, pivot alignment, acceleration, and whether the drive has enough force or torque at the least favorable position.

How much safety factor should I use?

It depends on the consequence of failure, shock loading, uncertainty in the load, and duty cycle. For early prototypes, use conservative assumptions and test. If the mechanism lifts people, supports critical loads, or operates near users, follow the relevant engineering standards and have the design reviewed by a qualified professional.