ELMERS WOBBLER - Home Model Engine Machinist

3. ELMER’S WOBBLERAn oscillating/key stock engine is commonly referred to as a ‘Wobbler’. During thischapter we will gain a fundamental understanding of how an oscillating engine works, whilstexploring Elmer’s Wobbler.3.1 OPERATIONThe key to comprehending how the Wobbler operates is to take a look at themovement produced when the engine is running. The back and forth movement that theengine demonstrates is described as an ‘oscillating’ action; whereby the cylinder seems towobble, hence the term Wobbler.Why this oscillating action occurs is the underlying principle of the Wobbler. Figure1.0 shows three ports on the frame of the Wobbler of critical concern:BACFigure 1.0 (Basic Frame to Show Port Operation)PortABCFunctionAir/steam inlet port from sourceAir/steam inlet port to the cylinderExhaust portTable 1.0 (Port Functions for Figure 1.0)Air/steam is directed into the frame at port A, which travels through to port B asshown in Figure 1.1. Port B corresponds with a port on the cylinder, allowing for air/steam toenter and force the piston sidewards, filling the space in the cylinder with compressedair/steam.Figure 1.1 (Air/steam Entry to Cylinder from Frame)3

The air/steam now needs to escape the cylinder. In Figure 1.1 we can see that the porton the cylinder is adjacent to port B. Therefore in order for the air/steam within the cylinderto escape, the cylinder must move so the cylinder port lines up with port C.The piston rod has no flexible movement, besides being able to move side to sidewithin the cylinder; due to the rods attachment to the crankshaft. As the crankshaft rotates therigid movement of the piston rod causes the cylinder to rock on its pivoting point.This oscillating movement allows the cylinder port to position in line with port C onthe frame, demonstrated in Figure 1.2. This alignment allows for the compressed air/steam toescape whilst the piston returns to its ‘original’ position.Figure 1.2 (Oscillating Movement)4

3.2 COMPUTER AIDED DESIGNTo increase the productivity of any method there must be a substantial elevation of theprocess used. This is evident with the methods used for constructing an engineering drawing.If we take the literal phase ‘time is money’ we can apprehend that advancements intechnology have allowed accuracy, removal of common mistakes, efficiency and speed to beincreased.This in return has allowed processes to excel reducing the time taken forinterpretation and modification. Computer-aided design (CAD) has significantly reduced theneed for draftsmen and has allowed engineers to construct their own drafts.CAD technology allows three dimensional design, in different axes, surfaces, verticesand edges; which permits designers to be able to create a three dimensional engineeringdrawing with a vast amount of intricate detail compared to a drawn pictorial sketch whichvaguely creates a understanding of the layout. Furthermore increasing technology hasallowed designers to use computer-aided design to construct three-dimensional solid shapeswith complex and impressive geometry called ‘3D solid modelling’.Solid Modelling of the oscillating engine has allowed for a more in-depthunderstanding of Elmer Verburg’s Wobbler. The platform used for CAD within this project is‘Solidworks 2010’ whereby all dimensions are derived from Elmer’s engine plan. (SeeAPPENDIX A Chapter 2. ELMERS WOBBLER UNIT CONVERSION)3.2.1 FRAMEACBFigure 1.3 (Frontal-view of Elmer’s Wobbler Frame)The frame is the fundamental component when addressing Elmer’s Wobbler. This canalso be said for almost all oscillating engines. Besides being evident in the name, the framenot only supports and holds the engine together, but separates the cylinder and the flywheel.If we look at Figure 1.3 we can see the extrude cut ‘A’ is the insertion point for thebearing, ‘B’ is the insertion point for the cylinder pin. The extrude cuts represented as ‘C’ arethe air/steam inlet port to the cylinder and exhaust port.5

AFigure 1.4 (Rearward-view of Elmer’s Wobbler Frame)Also if we look at Figure 1.4, point ‘A’ shows the chamfer, which the springwill press against.Figure 1.5 (Inlet Port from Source on Elmer’s Wobbler Frame)Furthermore, Figure 1.5 on CAD allows for the visualisation described previous inFigure 1.1. The inlet port from the air/steam source can be seen, where knowledge gainedand CAD Solid modelling enables us to see the link between the two ports on the frame.6

3.2.4 CYLINDERFigure 1.8 (Exploded view of Elmer’s Wobbler Cylinder)If we go back to Figure 1.3, point ‘B’ on the frame is the insertion point of thecylinder. Figure 1.8 shows that the cylinder assembly consists of two sub-assemblies; thecylinder and cylinder pin.The importance of the cylinder is on the face which mates to the front of the frame.BAFigure 1.9 (Side-view of Elmer’s Wobbler Cylinder)The side-view allows us to distinguish the point of entry and exit of compressedsteam/air. The oscillating movement allows the cylinder port ‘A’ to position itself over theexhaust and the air/steam inlet port.Point ‘B’ shown on Figure 1.9 is the insertion point of the cylinder pivot; this isthreaded to match the thread on the cylinder pin.8

3.2.5 CYLINDER PIN AND NUTThe cylinder pin on Elmer’s design is attached to the cylinder and enters the frame,whereby the nut attaches to cylinder pin. The area between the nut and the frame highlightedin Figure 2.0 is where the spring is allocated.Figure 2.0 (Side-view of Elmer’s Wobbler Cylinder Pin and Nut)The cylinder pin allows for the cylinder to ‘pivot’ or permits the oscillating movementto occur. This is only possible due to forces exerted on the spring.To better grasp this concept we must gain a perspective of compression. Compressivestrength is the ability of a material to withstand ‘pushing’ or ‘inward’ forces. The greater thecompressive strength of a material the greater force required to compress the material.Figure 2.1 (Compression)With our understanding of solids, we can look at Figure 2.1 on an atomic level,whereby the grey circles in Figure 2.2 represent the atoms within a material.9

Figure 2.2 (Atomic-view of Compression)We know atoms within solids try to find a position of equilibrium and distancebetween one another. So, when a material undergoes compression, forces arise to counteractthe compressive forces and ‘restore order’.If we relate this to Elmer’s Wobbler we can say, as the nut tightens, it pushes or exertsa compressive force upon the spring, which in return the atoms oppose this force. This resultsin the spring pushing against the face of the frame.As long as the spring is not compressed beyond its elastic limit, these forces willremain. Figure 2.3 demonstrates the forces surrounding the cylinder pin, spring and nut andhow these aid in holding the cylinder and frame together.Figure 2.3(Compressive Forces Acting Upon Elmer’s Wobbler)Although we have highlighted the fact that this allows for the movement of thecylinder, it’s most important purpose is to create a negligible or minimal gap between theframe and cylinder.The understanding behind this is simple; as we know the compressed air will travelinto and from the frame to the cylinder. Therefore by having no gap between these twosurfaces, there is no loss of air.10

3.2.6 PISTON AND CONRODABFigure 2.4 (Elmer’s Wobbler Piston and Conrod Assembly)The conrod, shown as ‘A’ in Figure 2.0 connects to ‘B’ the piston. This assemblyconnects to the crankshaft allowing linear motion to be converted to rotational movement.We must understand the piston and the connecting rod’s movement is linear, wherebywe can say a push and pull type of movement is transferred so the connecting rod can rotatethe crank.Figure 2.5 (Top-view of Elmer’s Wobbler Piston and Conrod Assembly)As we can see the piston is directly connected to the base of the conrod. Figure 2.1shows the rearward-view demonstrating this. We can appreciate that this face is within thecylinder.3.2.7 ASSEMBLYElmer Verburg ensured that his designs were open for interpretation, whereby Elmerencouraged an innovative and intuitive approach. This was evident within Elmer’s Engines,whereby the appendix is entitled ‘Creating Your Own Designs’, which contained variationsof different components applicable to all fifty-two engine types.Bearing this in mind and the designs obtained (See APPENDIX A Chapter 1.ELMERS WOBBLER) we do not have a complete Wobbler, as using fabricated dimensionswould distort the purpose of this chapter. This was to gain the underlying knowledge andessential understanding of the operation of an oscillating engine through Elmer’s Wobblerdesigns, thus avoiding any engineering or rendering to what has been available.11