The Boardman rotary engine shown by Hiscox 334 has a rotor concentric with a segmental casing and hinged pistons carried in rotor pockets. The pistons swing outward into the enlarged segment and fold inward at the smaller return segment. Their motion is rotation about a hinge, not radial sliding.
Actuator motion note for Boardman Rotary Engine Mechanism
A linear actuator could operate an external valve or control linkage associated with an engine demonstration. That is a separate motion system: the Boardman rotor shown here needs continuous rotation, and its casing-volume calculation does not size an actuator.
For structural members, the actuator load should be applied through brackets that do not introduce unintended bending. Check both static load and the extra load created when the mechanism starts, stops, or binds.
For any added control linkage, sketch its start, middle and end positions. At each position, check required force, line of action and clearance, keeping actuator loads aligned with the rod.
- 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.
Boardman Rotary Engine · Casing Geometry and Passage Timing
Explore the concentric hinged-piston arrangement in Hiscox 334. Calculate selected casing dimensions, added segment volume and piston passage timing.
Equation Used
- Rotor and casing are concentric.
- Three hinged pistons follow the source engraving.
- Pistons are thin rigid members and contact the selected casing profile.
- Outward contact is a geometric constraint, not a centrifugal force calculation.
- Added casing volume excludes the smaller return-radius circle.
The original source gives no dimensions or operating performance. Use actual engine data for power, steam consumption and operating limits.
Hinged pistons in a concentric rotor
The source engraving shows three pistons pivoted in pockets around the rotor. Steam enters at one end of the enlarged casing segment and exhausts at the other. Hiscox describes centrifugal action opening the pistons at the inlet; contact with the smaller casing segment closes them at the exhaust.
The section shows the rotor and casing centres coincident. Each blue piston turns about its visible hinge. Pale pockets show the space into which the pistons fold. The inlet, enlarged lower segment and exhaust form a visibly continuous route.
The original engraving supplies no dimensions or complete transition profile. The illustrated casing profile uses two smooth 30° transition ramps. Each thin piston is opened only as far as the casing permits, checking its entire length rather than just its tip. That is a geometric contact model, not a simulation of centrifugal acceleration, steam pressure or friction.
Use the calculator to examine this geometry
Set the enlarged bore, axial depth, enlarged-segment angle and rotor speed. Bore scales piston length and added radial depth. Axial depth and segment angle change the added casing volume. Rotor speed changes animation speed, revolution time and the rate at which the three pistons pass a given port.
The drawing is a cross-section, so changing axial depth changes the displayed dimension and volume without changing the section outline. The three-piston count follows the historical engraving.
The historical reference describes the construction without establishing an operating speed or power rating. The calculator therefore compares geometry and passage timing, not engine performance.
Selected casing profile and its added volume
Let enlarged radius R=D/2. The rotor face radius is 0.70R, the piston hinge radius 0.65R, piston length 0.50R and smaller return-segment radius 0.74R. The extra radial depth is 0.26R.
The enlarged segment spans ψ radians. Each end contains a ramp of w=π/6 radians. Across a ramp, normalized radius is ρ=a+c(3z²−2z³), with a=0.74, c=0.26 and z from 0 to 1. Between the ramps, radius is R; outside the enlarged segment it is 0.74R.
The added casing volume above the smaller-radius circle is V=(bR²/2)[(1−a²)(ψ−2w)+2w(ac+13c²/35)]. Divide mm³ by 1000 for cm³. This is a static geometric volume, not swept displacement or steam consumption per revolution.
For three pistons at n rpm, port-passage frequency is 3n/60=n/20 per second. Revolution time is 60/n seconds for positive speed; at zero speed it is reported as stopped.
Change geometry separately from speed
With an 180 mm enlarged bore, the selected hinged pistons are 45 mm long and the added radial casing depth is 23.4 mm. At 60 rpm the shaft completes one revolution per second and three pistons pass a given port per second.
Doubling bore while retaining axial depth and segment angle quadruples the added casing volume. Doubling only axial depth doubles that volume. Doubling speed changes passage frequency and revolution time but leaves all geometric volumes unchanged.
What the drawing and calculator establish
The concentric rotor carries pivoting pistons that follow the casing profile. Their illustrated motion does not establish pressure history, shaft power or vibration behaviour.
The piston-contact solution assumes thin rigid members and sufficient outward bias to follow the casing. Real thickness, seals, clearances, rubbing contact, inlet timing and pressure history require actual design data. At low or zero speed, centrifugal opening cannot be inferred from this geometric animation.
The selected smooth profile makes the folding sequence inspectable. It is not a manufacturing profile recovered from the historical engraving.
Boardman engine questions
Do the pistons slide radially?
No. In this source they swing about hinges in rotor pockets.
Is the rotor eccentric?
No. Hiscox explicitly describes a concentric rotor and outer segmental casing.
Can added casing volume be used as displacement per revolution?
No. Chamber partitioning, port timing and pressure evolution must be considered separately.
Why does zero speed retain an open piston?
It freezes a geometric contact pose. The animation does not calculate whether centrifugal or steam forces can sustain that pose.
Primary reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, device 334, printed page 92. The source identifies the concentric cylinder, pocketed swing pistons, centrifugal opening and casing-contact closure.
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