A connecting rod joins a rotating crank to a piston that slides along a straight guide. Explore how crank angle and rod length determine piston position and rod angle.
Inline Slider-Crank Geometry Calculator
Vary rod length, stroke, crank angle and rotational speed. Position and rod angle use zero-offset rigid-link geometry; mean piston speed is a cycle average. No force, stress, bearing, combustion or life result is calculated.
Equation Used
- The crankshaft and cylinder axes have zero offset.
- The crank and connecting rod are rigid and pin joints have no clearance.
- The entered ranges keep L greater than r, allowing full rotation.
The crank and rod keep fixed pin-to-pin lengths while the piston follows its horizontal guide. The results describe this motion and average piston speed; they do not predict forces or service life.
Exact rigid-link closure
The crank pin travels on a circle of radius r=S/2. A rigid rod of length L connects that pin to a piston pin constrained to the horizontal cylinder axis. The square-root term in the position equation is the rod's horizontal projection, so the drawing and the result cards use the same geometry.
Autoplay shows an illustrative sweep while the result cards keep the selected crank angle. Changing the angle input or manually scrubbing updates the selected position and its results. Pin-center lengths remain invariant; member thicknesses, guides and supports are schematic.
Kinematic inspection, not engine rating
Use the screen to inspect displacement, rod obliquity, rod ratio and cycle-average piston speed for the entered geometry. It does not establish material, section, bearing, lubrication, balance, thermal, combustion or durability requirements.
Inline slider-crank equations
Rod angle is beta=asin[(r/L)sin(theta)]. Mean piston speed is 2SN/60 after converting stroke S to metres. It is an average over a complete revolution, not the derivative of position at the selected angle.
Reading the geometry
At 0 degrees the piston is at the outer dead center and displayed travel is zero. At 180 degrees it is at the inner dead center and travel equals the entered stroke. Intermediate travel is not sinusoidal because the finite rod changes its angle.
Model boundary
The model omits offset, elastic deformation, joint clearance, bearing dimensions, reciprocating mass, gas pressure, inertia force, friction and vibration. Rod ratio L/S is a geometric comparison only; it is not a horsepower, reliability or suitability rating.
Slider-crank questions
Does the rod change length during playback?
No. Its two pin centers remain exactly L apart.
Is mean piston speed the speed at this angle?
No. It is the distance travelled per cycle divided by cycle time.
Can this calculator size a connecting rod?
No. It supplies kinematics only.
Kinematics references
- Ohio University ME 301 Kinematics Notes: slider-crank vector-loop position and velocity analysis.
- Cornell Reuleaux Collection, Slider Crank: mechanism topology and historical model.
- Colorado State University Slider Crank Model: stroke, crank radius, rod length and dead-center definitions.
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