A rotating cam pin sits between two inward-facing ratchet racks. A governor raises or lowers the suspended rack frame to select a direction of feed. At the neutral height, the pin clears both racks and the regulating-valve connection stays still.
Cam to Double-rack Frame with Governor Interactive Calculator
Choose the cam-pin radius, engagement half-angle and shaft speed. The animation shows neutral, right feed, neutral and left feed. Results describe one selected engagement and the mean feed if that rack remains selected.
Equation Used
- Ideal point pin, rigid rack and maintained tooth contact during the selected driving interval.
- A selected rack advances one pitch per revolution; neutral advances neither.
- The drawing prescribes four stages: neutral, upper selected, neutral, lower selected. It does not solve governor dynamics.
- Finite pin radius, tooth stress, contact impact, friction, backlash and valve load are not calculated.
- The engagement geometry is an educational construction, not a dimensional reconstruction of a historical machine.
Brown figure 84 and Hiscox figure 995 show a rotating pin driving a governor-selected ratchet frame. Compare the advance per engagement, mean selected feed, revolution time and driving interval.
A governor selects which rack receives the drive
Brown figure 84 describes a double rack frame suspended from rod A. The rotating cam is midway between the racks at neutral, so neither receives motion. Raising or lowering the suspension brings one rack into range. The frame then feeds left or right and moves a throttle or regulating-valve connection. Hiscox figure 995 illustrates the same principle as a ratchet governor.
The pin rotates continuously while the rack frame advances only during selected tooth contact. The four-stage demonstration changes the suspension position to show both feed directions and the intervening neutral states.
A mechanical regulating feed
The historical references describe this motion as a connection between a governor and a regulating valve or gate. The cam supplies the motion; the governor selects the corrective direction. Neutral stops the feed without stopping the rotating shaft.
This calculator illustrates that selection principle. It does not establish control accuracy, stable speed, valve sizing or compatibility with a specific engine.
Step distance and selected feed rate
For an ideal point pin on an orbit of radius r, the horizontal distance traversed through an engagement interval extending γ to either side of the orbit top or bottom is p = 2r sin γ. The illustrated rack pitch equals p.
If the same rack stays selected, there is one step per shaft revolution. At N rpm, mean feed magnitude is pN/60 and revolution time is 60/N. The driving portion is 2γ/360. At neutral, feed is zero. Direction depends on the rack selected.
These quantities describe the selected ratchet feed. Regulation accuracy also depends on the governor, engine and valve dynamics, which are not calculated here.
A 20 mm pin radius
At r = 20 mm and γ = 30°, one selected revolution advances 20 mm. At 100 rpm, continuously selecting that same rack gives an ideal mean feed magnitude of 33.33 mm/s. One shaft revolution takes 0.60 s, and driving contact occupies 16.67% of the turn.
The animation alternates selection to show both directions. That demonstration has a different net feed from holding one rack selected continuously. Its motion is slowed by a factor of 2.5 for inspection.
What remains outside the model
A real pin has a finite radius and teeth have clearances and shaped entry and exit surfaces. Their stresses, impact, wear and load limits need separate design work. The small displayed contact marker represents an ideal point, not a specified pin diameter.
The governor, engine, valve and process also form a feedback system. This geometric demonstration cannot predict hunting, settling time or regulation accuracy. The vertical suspension motion is prescribed to explain selection.
Questions about the ratchet frame
Why does the cam turn while the frame stays still?
At neutral, the cam pin clears both racks. In a selected state, feed occurs only during the driving contact interval.
Why does the frame also move vertically?
The suspension selects the upper or lower rack by moving it into the pin orbit. The horizontal motion is the feed to the regulating connection.
Where are the pinions?
This reference mechanism has a rotating pin cam and ratchet teeth, not two continuously meshing output pinions.
Does the animation predict how a governor responds to a speed error?
No. It prescribes neutral and opposing selection states to demonstrate the mechanism. Governor feedback behavior requires a separate dynamic model.
Primary mechanism references
Brown, figure 84, Digital Mechanism and Gear Library: suspended double rack, neutral clearance, raised/lowered selection and connection to a regulating valve.
Hiscox, Mechanical Movements, Powers and Devices, page 253, figure 995: ratchet governor with rotating pin cam and suspension rod.
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