A bell crank lifts the hook in an eccentric rod off a rockshaft wrist pin, allowing the valve gear to be moved by hand. The animation shows this release and reconnection. The separate calculator converts angle and elapsed time at constant shaft speed; it does not calculate release timing.
Unhooking Device and Angular Timing Calculator
Watch the manual hook release and calculate a separate angle/time comparison at constant rotational speed.
Equation Used
- Rotational speed is constant and positive.
- The selected angle is an entered interval, not a proven trip datum.
- The entered time is converted to angular sweep only.
- Hook geometry, latch engagement, cutoff, forces, wear and safety are excluded.
The animation illustrates manual release; the calculator converts selected angle and time independently.
Bell crank, lifting link and eccentric-rod hook
For uniform rotation at n revolutions per minute, one revolution takes T=60000/n milliseconds. A selected angular interval theta therefore takes t=theta T/360. Conversely, an entered time interval dt corresponds to a sweep dtheta=360 dt/T.
In Hiscox figure 268, lowering the short bell-crank handle raises the eccentric-rod hook clear of the rockshaft wrist pin. The rockshaft can then be operated by a hand lever. The drawing shows illustrative fixed link lengths during a stopped-drive release, not an automatic cutoff event.
Use and boundary
Use the calculator to translate between angle and time at constant shaft speed. These conversions do not determine hook dimensions, engagement force or a release event.
Uniform-rotation conversions
T_ms=60000/n; t_interval=theta T_ms/360; dtheta=360 dt/T_ms; rate=360/T_ms.
Default selected-value example
At 60 rpm, one revolution takes 1000 ms. A selected 60-degree interval takes 166.7 ms. An entered 10 ms interval corresponds to 3.6 degrees of uniform rotation.
Manual release and timing comparison
The release handle lifts the hook through a connecting link. The illustration holds the drive end at rest while the rockshaft is moved by hand, then returns the wrist pin to alignment before lowering the hook. Its dimensions and hand motion are illustrative. Hook strength, wear, operating loads and running-engine procedures are not calculated.
Questions
Is the selected angle a release angle?
No. It is a selected interval for constant-speed conversion, independent of the manual hook-release sequence.
Does the entered time establish release duration?
No. It only converts elapsed time to angular sweep under constant speed.
Is any undercut safe?
No safety or latch-retention conclusion is produced.
Reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), page 78, figure 268: simple unhooking device.
- OpenStax University Physics: Rotation Angle and Angular Velocity — definitions connecting angular displacement, angular velocity and elapsed time.
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