Final Project ReportEML 4024C

Engineering Design and PracticeSummer 2015

Authored by:James CiancioloSidney Feldman

Eduardo LarrazabalDavid Shamblin

Due Date: August 7, 2015

Table of FiguresFigure 1: Piston Cap Sketch............................................................................................................4

Figure 2: Finished Piston Cap..........................................................................................................5Figure 3: Finished Pin......................................................................................................................5Figure 4: Piston Rod Sketch............................................................................................................5Figure 5: Finished Piston Rod.........................................................................................................6Figure 6: Flywheel Sketch...............................................................................................................6Figure 7: Fin Sketch.........................................................................................................................6Figure 8: Flywheel with fins............................................................................................................7Figure 9: Finished Flywheel............................................................................................................7Figure 10: Muffler Sketch...............................................................................................................7Figure 11: Muffler Cut.....................................................................................................................8Figure 12: Extruded Muffler............................................................................................................8Figure 13: Muffler Sketch 2............................................................................................................8Figure 14: Finished Muffler.............................................................................................................9Figure 15: Carburetor Sketch...........................................................................................................9Figure 16: Extruded Carburetor.......................................................................................................9Figure 17: Finished Carburetor......................................................................................................10Figure 18: Engline Block Extruded...............................................................................................10Figure 19: Engine Block with Fins................................................................................................10Figure 20: Engine Block holes......................................................................................................11Figure 21: Engine Block Exhaust..................................................................................................11Figure 22: Engine Block Carburetor Adaptor...............................................................................11Figure 23: Finished Engine Block.................................................................................................12Figure 24: Spring...........................................................................................................................12Figure 25: Finished Spring............................................................................................................12Figure 26: Crankcase 1..................................................................................................................13Figure 27: Crankcase 2..................................................................................................................13Figure 28: Gasket...........................................................................................................................13Figure 29: Crankshaft....................................................................................................................14Figure 30: Assembly 1...................................................................................................................15Figure 31: Assembly 2...................................................................................................................15Figure 32: Assembly 3...................................................................................................................15Figure 33: Assembly 4...................................................................................................................16Figure 34: Assembly 5...................................................................................................................16Figure 35: Assembly 6...................................................................................................................16Figure 36: Assembly 7...................................................................................................................17Figure 37: Assembly 9...................................................................................................................17Figure 38: Assembly 8...................................................................................................................17Figure 39: Exploded View.............................................................................................................18Figure 40: Table of Material and Mass Properties........................................................................19Figure 41: Displacement Graph.....................................................................................................20Figure 42: Velocity Graph.............................................................................................................20Figure 43: Acceleration Graph......................................................................................................20Figure 44: Strucutal Analysis 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Figure 45: Structural Assembly 2..................................................................................................21Figure 46: Reference 1...................................................................................................................23Figure 47: Reference 2...................................................................................................................23Figure 48: Reference 4...................................................................................................................24Figure 49: Reference 3...................................................................................................................24Figure 50: Reference 6...................................................................................................................25Figure 51: Reference 5...................................................................................................................25Figure 52: Reference 7...................................................................................................................26Figure 53: Reference 8...................................................................................................................26Figure 54: Reference 9...................................................................................................................27Figure 55: Reference 10.................................................................................................................27

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Introduction

The project was to create a functional 3D model of a two stroke weed wacker motor assembly using SolidWorks. Motion analysis was then performed to report the kinematic and dynamic quantities present when the mechanism was in operation. The intension behind this project was to test everything that has been learned over the semester within Solidworks. It also showed firsthand how many mechanical objects can be created and tested before any physical pieces are ever needed.

Background

What is a two stroke engine?It’s an engine that takes two strokes to complete a full cycle (up and down motion of rod for one revolution of crankshaft).  

It follows:Intake→Compression→Exhaust

As opposed to a 4 stroke engineIntake→Compression→Combustion→Exhaust

Mechanical Design

Parts

Piston:

The piston head was made by first creating a circle and extruding it.

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Figure 1: Piston Cap Sketch

Another two circles were created and extrude cuts were applied to give the piston head its shell as well as the two holes for the cylinder.

For the pin, two circles were created on the same plane and the extrude tool was applied.

For the piston rod, hole diameters and total length were measured before a sketch was made.

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Figure 2: Finished Piston Cap

Figure 3: Finished Pin

Figure 4: Piston Rod Sketch

Extrude and extrude cuts were then applied to create the finished piston rod.

Flywheel:

The initial flywheel was created using a closed sketch and the revolve feature.

The fin was then sketched on the bottom face of the flywheel with a circular pattern and then extruded upward with a chamfer effect.

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Figure 5: Finished Piston Rod

Figure 6: Flywheel Sketch

Figure 7: Fin Sketch

Another chamfer was applied to each fin to give them the required angle and a fillet was used on each fin to produce the rounded edges.

The keyhole was then made using a circle on the bottom face with an extrude cut and a chamfer effect. A drawing was then created, mirrored, and cut extruded with an offset to finish the keyhole.

Muffler:

All parts were measured using digital calipers for precision. To start the muffler, a square was made 2.37 inches tall by 2.38 wide and later extruded to the desired value.

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Figure 8: Flywheel with fins

Figure 9: Finished Flywheel

Figure 10: Muffler Sketch

A cut extrude was made on the sides to mimic the shape of the muffler. The cut was done through all.

For the next part, a plane was created at the desired distance from the front face and a square was created and extruded and united with the existing part.

A similar cut extrude to step 2 was done on the last part to polish the muffler. After the cut, two holes were created on the outer box and cut through. This is the result from the cut.

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Figure 11: Muffler Cut

Figure 12: Extruded Muffler

Figure 13: Muffler Sketch 2

After filleting the top and bottom faces and shelling the muffler, this was the final result for the piece.

Carburetor Adaptor:

The adaptor was a complicated part to make. The group decided to use the engine block as a reference, since it had the same dimensions as the carburetor. The sketch from the block was copied and later modified to fit the desired dimensions. It can be seen the whole sketch is fully constrained.

A lofted cut was later done on the extruded piece from the back face to the center and then another lofted cut was done from the middle to the front face.

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Figure 14: Finished Muffler

Figure 15: Carburetor Sketch

Figure 16: Extruded Carburetor

A cut extrude was done on the bigger circles to match the carburetor. Also, another cut extrusion was done for the smaller circles. They were cut through all. The rest of the piece consisted of fillets through the entire piece.

Engine Block:

The Engine Block was started by creating a square on the top plane and extruding down, then filleting the edges to create the top shape. Next a cylinder was extruded from the bottom surface and extruded as well.

Next, the fins were created by sketching and extruding the bottom fin first and then using a linear pattern to create the rest.

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Figure 17: Finished Carburetor

Figure 18: Engline Block Extruded

Figure 19: Engine Block with Fins

Then the holes were cut into the solid extrusion for the piston cylinder and the holes for the screws.

The connection point for the exhaust was created by extruding a cylinder and then making a lofted cut to create the cut as can be seen in the image. Also a few extrusions were made on the sides which give space for holes to be cut into later on.

The connection point for the carburetor adaptor was created by sketching the shape seen to the right and extruding the surface out. The lofted cut in the center was made in the same fashion as the previous one.

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Figure 20: Engine Block holes

Figure 21: Engine Block Exhaust

Figure 22: Engine Block Carburetor Adaptor

Finally the cylinder was cut out as well as the channels. Numerous fillets were made in order to cut down on concentrated loads as well as for aesthetic purposes. Other cuts, extrudes, and fillets were used for aesthetic purposes as well.

Spring:

The spring was made using a helix and a circle. The circle was extruded along the helix.

The spring was finished by sketching the last two pieces of the spring and using a swept extrusion that followed it.

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Figure 23: Finished Engine Block

Figure 24: Spring

Figure 25: Finished Spring

Crankcase:

The crankcase was made by sketching and then extruding a piece from aluminum. For the purposes of this project, the most meaningful parts were those that mated with other parts. The smaller diameter of the center hole was extruded to accommodate the bearings and crank shaft.

The larger diameter in the back was made to allow rotational movement of the crank shaft and translation of the piston rod. A hole on the top was added to let the piston move up and down. The back of the crank case is left open, as in regular operation, it is covered and sealed by the plastic enclosure of the trimmer.

Gasket:

A rubber gasket was extruded using the sketch on top of the crankcase. In the assembly, this would mate between the crankcase and cylinder.

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Figure 26: Crankcase 1

Figure 27: Crankcase 2

Figure 28: Gasket

Crankshaft:

A crankshaft was created from stainless steel. The crankshaft contains a keyhole which allows proper mating with the flywheel. The rod on the back receives the combustion force from the piston and converts that to rotational energy used by the trimmer.

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Figure 29: Crankshaft

Figure 30: Assembly 1

Figure 31: Assembly 2

Figure 32: Assembly 3

Assembly

For the piston assembly there were only four mates. To attach the pin to the piston head a tangent and concentric mate were used.

Then to complete the assembly for the piston, the piston rod was mated to both the pin and a plane created using concentric and distance mates.

The crankcase was the first piece added to the assembly, as it would mate with the most pieces.

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Figure 33: Assembly 4

Figure 34: Assembly 5

Figure 35: Assembly 6

An assembly was made with the crankshaft and bearings. The bearings were mated concentrically with the shaft. A coincident mate was added with the face of one bearing and the front face of the rear element of the crankshaft. The other bearing was mated coincidentally with the groove toward the front of the shaft.

The flywheel was added concentrically with the shaft and groves on the flywheel were mated coincidentally with a key slot on the shaft.

The gasket was added coincidentally with the face of the crankcase and concentrically with the screw holes.

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Figure 36: Assembly 7

Figure 37: Assembly 8

Figure 38: Assembly 9

The engine block was mated coincidentally with the gasket and concentrically with the screw holes.

The piston assembly was added by mating it concentrically with the rod on the rear of the crankshaft and concentrically mating the head of the piston with the center of the engine block.

Finally, the peripheral parts were added with concentric and coincident mates.

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Figure 39: Exploded View

Exploded view

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Figure 40: Table of Material and Mass Properties

Mechanism Model Analysis

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Figure 41: Displacement Graph

Figure 42: Velocity Graph

Figure 43: Acceleration Graph

Mechanism Kinematics and Dynamics

Mechanism was applied by attaching a rotary motor to the crank shaft and having it rotate counterclockwise about the z-axis. The rotation of the crankshaft transferred to linear motion in the piston head. For the kinematics/dynamic analysis a point on the piston head was chosen, and the displacement, velocity, and acceleration was found. By choosing a point on the top of the piston head, the full stroke of the motor can be found. The top dead center of the engine is 80mm below the origin of the assembly, and the bottom dead center is 55mm, thus the full distance traveled by the piston is 25mm. Using a diameter of approximately 34.3mm, it was found the engine that was modeled was 23cc.

The linear velocity of the motor, as can be seen, is maximum when the piston is halfway through its motion and minimum at either TDC or BDC.

The acceleration of the piston head is maximum at TDC and BDC. Which makes sense, because as the piston slows down and speeds up at those positions is where the greatest amount of force will be felt.

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Figure 44: Strucutal Analysis 1

Figure 45: Structural Assembly 2

Structural AnalysisA structural stress analysis was performed on the rod of the piston, as it would be taking a large amount of the loads in various directions from the axis of the rod.

The results showed a maximum stress of 146.3 kN/m^2 that developed on the sharp corners of the rod and along the center axis. This was to be expected as the greatest shear and moments would develop at the thinnest parts toward the center, given its general symmetry.

An additional structural analysis was performed on the deformation experienced by the crankcase and showed maximum deformations at the most extreme corners of the structure. The value for the displacement was .2805 mm. This made sense as the vibrations from the engine operation would produce the largest displacements on the crank case at the furthest distances.

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Conclusion

The creation and assembly for the two-stroke weed wacker motor was an excellent way to test students’ skills with Solidworks.  The results obtained for the weight of the motor were very close to that of the actual model. Using a diameter of approximately 34.3mm, it was found the engine that was modeled was 23cc. Motion analysis produced accurate results from the single rotary motor used. Stress and deformation analysis produced reasonable results with maximum and minimum values where expected.

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Figure 46: Reference 1 Figure 47: Reference 2

References

Spark plug: https://grabcad.com/library/zenoah-g270-rc-1

Bearings: http://www.mcmaster.com/#standard-ball-and-roller-bearings/=ye5ljf

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Figure 49: Reference 3 Figure 48: Reference 4

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Figure 51: Reference 5 Figure 50: Reference 6

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Figure 52: Reference 7 Figure 53: Reference 8

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Figure 55: Reference 9 Figure 54: Reference 10

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