Wankel Rotary Engine

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A rotary engine with the front left open. Turn the handle and the eccentric shaft swings the rotor round inside its housing, while the rotor's internal gear rolls round a fixed gear on the rear housing. The rotor turns once for every three turns of the shaft, and its three apex seals stay on the wall of the housing all the way round. Follow one flank and you see the four strokes: it draws in past the intake at the top left, squeezes the charge at the top, passes the two spark plugs on the right and pushes out through the exhaust at the bottom left. Through three windows in the rear housing you can watch the gears mesh. The housing curve and the rotor flanks are calculated, not drawn: the rotor is the exact inner envelope of the epitrochoid, with the same ratio of rotor size to offset as a Mazda 13B.

• 16 printed parts

• 11 × 21 × 20 cm assembled (L × W × H)

• ≈ 0.4 kg filament in total

• 190 mm bed length for the rotor housing, which prints flat; the other parts fit a 170 mm bed

Parts

Rotor housing: The epitrochoid bore the rotor runs in: 144 mm tall and 108 mm across at the waist. Cooling fins round the outside, a boss for the intake and one for the exhaust on the left, two for the spark plugs on the right, and a foot that sits in the stand.

• Size: 190 × 149 × 25 mm

• Print: Flat on the bed, no supports: the port and plug holes have pointed tops.

• Filament: ≈ 98 g

Rear housing: The back wall the rotor slides on. The fixed 24-tooth phasing gear and the rear bearing are part of it, and three windows let you see the gears mesh. Nine M3 nuts go in the hexagons at the back.

• Size: 168 × 134 × 14 mm

• Print: Back face down, gear up.

• Filament: ≈ 63 g

Front frame: A lip round the bore that keeps the rotor in, and a bar across it with the front bearing. Everything else at the front is open.

• Size: 168 × 134 × 13 mm

• Print: Flat side down, bearing hub up.

• Filament: ≈ 37 g

Rotor: The inner envelope of the housing curve, 0.45 mm smaller all round, 24 mm wide. A combustion pocket in each flank, a slot for an apex seal at each tip, a Ø32.5 mm bore for the lobe and a 36-tooth internal gear (module 1.5) in the back face.

• Size: 109 × 107 × 24 mm

• Print: Front face down, so the gear teeth print on top without supports.

• Filament: ≈ 65 g

Apex seal × 3: A strip with a round tip that sits in the slot at each tip of the rotor, 0.2 mm off the housing wall. Glued in.

• Size: 24 × 5 × 2 mm

• Print: On its side.

• Filament: ≈ 1 g

Eccentric shaft: The rear journal (Ø12) and the lobe (Ø32, 9 mm off the axis) that the rotor turns on. The front shaft is glued into the socket in the lobe.

• Size: 39 × 32 × 32 mm

• Print: Lobe face down, journal up.

• Filament: ≈ 8 g

Front shaft: The front journal with a D-shaped key at the back, which only fits the lobe one way, and a D at the front for the pulley.

• Size: 30 × 12 × 12 mm

• Print: Standing on its front end.

• Filament: ≈ 2 g

Rear collar: Slides onto the D at the back of the shaft and keeps it from sliding forward.

• Size: 22 × 22 × 8 mm

• Print: Flat.

• Filament: ≈ 2 g

Pulley with handle: The front pulley with the handle you turn the engine by. Three turns of the handle turn the rotor once.

• Size: 52 × 52 × 31 mm

• Print: Back face down, handle up.

• Filament: ≈ 12 g

Spark plug × 2: Two of them, leading and trailing, pushed into the bosses on the right.

• Size: 31 × 12 × 10 mm

• Print: Standing on its tip.

• Filament: ≈ 2 g

Intake with velocity stack: Pushes into the intake port at the top left.

• Size: 32 × 29 × 29 mm

• Print: Standing on its spigot.

• Filament: ≈ 5 g

Exhaust pipe: Pushes into the exhaust port at the bottom left.

• Size: 46 × 22 × 22 mm

• Print: Upside down, on the end of the pipe.

• Filament: ≈ 7 g

Stand: A base with a socket for the foot of the rotor housing. Two M3 screws from below hold the engine.

• Size: 160 × 110 × 14 mm

• Print: Flat on the bed. It needs a 160 × 110 mm bed.

• Filament: ≈ 73 g

What else you need

• 9 M3 × 35 screws with nuts, through the front frame, the rotor housing and the rear housing.

• 2 M3 × 12 screws from under the stand into the foot. They cut their own thread.

• Superglue for the apex seals and the shaft key, and a little grease for the rotor bore and the gears.

Print settings

• 0.20 mm layer height (0.12 mm for the gears looks better)

• 3 walls

• 15% gyroid infill

• PLA or PETG material

For a 0.4 mm nozzle. Filament amounts are estimates for these settings.

How to build it

1. Print the parts: Nothing needs supports. The rotor housing needs a 150 × 190 mm bed. Clean any elephant's foot off the rotor, the lobe and the gear teeth, and check that the shaft journals turn freely in the bearing holes.

2. Seals in the rotor: Glue an apex seal into each of the three slots with its round edge outwards, flush with the front and back of the rotor.

3. Rotor on the shaft: Slide the rotor over the lobe of the eccentric shaft from the front, gear side first. Push the key of the front shaft into the socket in the lobe and glue it. The rotor should spin freely on the lobe.

4. Housing: Press nine M3 nuts into the hexagons at the back of the rear housing. Lay the rotor housing on it with the bolt holes lined up, and slide in the screws from the front so they stand up as guides.

5. Rotor in the housing: Grease the gear teeth. Lower the rotor and shaft into the housing, rear journal first through the fixed gear. Turn the rotor a little until its gear drops over the fixed gear and its three tips sit against the housing wall.

6. Front frame and pulley: Put the front frame over the screws and the front journal, and tighten the nuts evenly. Push the rear collar onto the back of the shaft and glue it, leaving a paper-thin gap. Push the pulley onto the D at the front.

7. Finish it: Push the spark plugs, the intake and the exhaust into their bosses, set the engine in the stand and fix it with two M3 × 12 from below. Turn the handle clockwise: the rotor turns the same way, once for every three turns.

The engine has small parts: keep them away from small children. Keep fingers out of the open front while someone turns the handle.

More

3D viewer, colour preview and the full guide: https://shapekit.cc/wankel-engine.html

Licence: CC BY-NC 4.0. Print it, remix it and share it with credit to Shapekit. Please don't sell the files or the prints.

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