Project 1: Backhoe Loader MechanismEML 4024C: Engineering Design Practice
The backhoe loader project was intended to demonstrate the modeling, simulation and motion study analysis of 3D representation of a backhoe loader. Solidworks was used to model the individual parts comprising the cab, front loader, excavator, wheels, and support arms. Each of these had moving components, as seen in the animation video, and a motion study in addition to a kinematic, dynamic and static analysis was done for the front loader. The modeling and analysis of this project was done to a 1:16 scale, due to referencing a scaled model.
Excavator Boom: The frame of the excavator boom is used to transmit torque from the dipper to the main body and support arms. This component needed to be tall, and long, but not thick, to transfer the load with minimal material, so the shell command was used to hollow out space from the extruded surface. In addition, this boom needed pin joints for two hydraulic components to connect to the cab, and the excavator dipper. The boom controls the height of the dipper, and therefore the height and extension of the bucket scoop, by changing the angle of the boom relative to ground. The boom is also able to pivot and rotate horizontally to move material from one side of the cab to the other.
Excavator Dipper: Similar to the excavator boom, the excavator dipper transfers the torque applied from lifting material a horizontal distance from the scoop to where the dipper connects to the boom. The mechanical design also consisted of extrudes, with a shell, in addition to two hydraulic components that connect to the boom and the scoop, and a mounting pivot to the boom. The dipper controls the height and position of the scoop by changing the angle of the dipper relative to boom.
Bucket Scoop: The Scoop pivots about a joint at the end of the dipper, in order to ‘scoop’ up and dump out material from the bucket scoop. The scoop is controlled through one hydraulic cylinder that forces a mounting bracket to rotate the scoop. This scoop contains teeth to help dig into the ground, and mounting brackets for the dipper. This dipper is also shelled but with only one open face, in order to also contain liquids, with the coordination of boom, dipper and scoop angles to keep the scoop horizontal while transferring it. The scoop, boom, and dipper assembly allow the scoop to move in three degrees of freedom, translation away from the cab, angle of rotation of the scoop, and the horizontal rotation to either side of the cab. We used a mid-plane boss extrude,
for the general shape, and mirror features to create the brackets.
Loader Boom: The loader boom also transfers torque to the cab, however is much closer to the center of gravity, and does not have as long of a torque arm, so is able to lift heavier items, thus the wide loader shovel in comparison to the bucket scoop. This arm has four hydraulic cylinders, two each from the cab, and to the shovel.
Loader Shovel: the loader shovel is designed to be driven into a material, before the hydraulics rotate the shovel to better contain the material. Similar to the bucket scoop, this shovel has only one open face to maximize the carrying capacity, however its assembly onto the boom and cab only allow it two degrees of freedom, rotation of the scoop and angle relative to cab, and thus needs to be coordinated with maneuvering the backhoe in order to be effective.
Bucket scoop support and control panel: The bucket scoop support serve to decrease the moment arm from the bucket scoop to ground, and therefore increase the maximum load from the bucket scoop. The support arms have feet that rotate about a pin axis, in order to provide a flat mounting surface. The arms rotate from the back of the cab and out to either side. They, and the bucket scoop are operated by the back control panel. Extruded boss, swept, and cuts were made from sketches to create the frame and pivot joints as well as the back control panel.
Axles and wheels: The axles and wheels connect to the main cab component and the rim component attaches to the rubber tires. The rims involve creating multiple circles with different extrusion levels, as well as the lug nuts.
Cab: The cab serves as the base and engine compartment for the backhoe loader. It contains wheel covers, and a step up into the roll cage.
Roll Cage: The roll cage is the compartment for the driver to sit, and includes the frame around the driver to protect them from outside elements. Also a steering wheel, and joysticks would be located here in front of the chair.
Loader Arm Assembly:
The front loader comprised of the following parts: Scoop, Inner and outer Hydraulic Cylinders (1-3), Excavator Boom, Excavator dipper, Mounting bracket, and Arm Base.
Connecting to the cab assembly, is the arm base which allows the excavator assembly to rotate to either side of the cab. The cylinder at the back of this arm base rotates inside a cutaway of the Arm Support Dock. I chose to create multiple extrudes, the first being a simple block as seen below. And to the right is the second extrude, which will be later mirrored to mount the Boom on to.
On the left is the second extrude which will be mirrored across the front plane, in order to give two mounting locations. Also an additional sketch and extrude was made for the pivoting section. This half cylinder fits inside the arm support dock to help support the weight of the excavator arm. The third picture shows the cylinder which rotates inside the cut extrude of the arm support dock.
The final step to complete this part is to fillet the edges shown below, to distribute stresses.
The first step to create the excavator boom was to create an extrusion of the solid frame, but first we needed the dimensions we took from the caliper measurements as seen below. This sketch used different constraints such as concentric, fix, horizontal, and perpendicular to constrain the arcs to form the shape.
Then, using an offset extrudes, these faces were made with the help of the mirror feature across the front plane again, as seen in the second image.
To connect these two faces, initially we decided to use individual pins, made specific for the purpose of connecting either the arm base, hydraulics or to the excavator dipper, however this caused problems with the motion study, so a simpler alternate of extrusions connecting them proved to help the animation process. Also, fillets were added to more realistically display the model.
The excavator dipper part has two solid faces, as well as a connecting frame which is hollowed out. To create it, we first used constraints to define a sketch matching the measurements we took with calipers of the 1:16 model. Next, we extruded this sketch at a distance away from the front plane, for both sides of the frame.
Because this piece might undergo rotational stresses, the frame also needs horizontal framework, as seen in this next extrude. However this needed to be shelled out to give a realistic metal plate thickness.
Also, extruded cuts were used to make the holes where the hydraulics, excavator scoop, and boom will be mounted. To do this, first a sketch was made with the dimensions used for the holes, and then cut extruded through both surfaces.
The final step was to add fillets to create rounded edges.
The general shape of the scoop was made with a sketch about the front plane. Because the model was not directly to scale, this shape was altered as the excavator arm was assembled. This sketch was extruded and
then shelled in order to create the open face, with a certain wall thickness.
To create the teeth, a sketch of one tooth profile was made, and then extruded to be patterned across the scoop face.
To attach this scoop to the dipper, two mounting brackets needed to be added, one for the hydraulic, and another for a pin connection. This was done using extrudes, and “combined” together with the scoop. Holes were included in the sketch at the dimensions of the pins to go through them. Final steps included fillets such as the ones shown below.
This piece began with the arm connecting to the scoop, and then a connecting bar was added to create a bar where a moment arm could rotate the scoop with hydraulic motion. The sketch below was extruded and a mirror feature was used to create the opposite arm across the front plane
To create the connecting bar, an extruded boss was created to go through the top hole. This was mirrored just as the arm bar was.
Also, stopping cylinders were added to constrain the movement of the bars that connect this to the dipper. These were essentially disks extruded at a distance and then filleted and the bars chamfered as seen below to give the shapes desired.
Scoop Lever 2
This scoop lever is very similar to the previous, connecting from the scoop to the hydraulic cylinder, however this part does not connect to the dipper, but instead lower on the scoop. One of these was made, and inserted twice into the assembly. This was one of the simplest parts, as it only included one sketch using a “straight slot” and then fillets to round it to the shape measured on our model.
Below is a rendered image of the two scoop levers, connected to the dipper and scoop.
Outer Hydraulic Cylinder.
The hydraulic pistons were simplified in order to more predictably control the motion in the motion study. The dimensions of the first circles are of the rod on which it is mounted, and the outer diameter of the cylinder.
Then the actual piston cylinder was extruded from a new “plane 1” a distance which was later modified to include the full range of motion of the inner cylinder through the range of motions.
Then to make this cylinder hollow, a cut extrude was used to make room for the inner hydraulic cylinder to move through.
Inner Hydraulic Cylinder.
Similar to the outer cylinder, the inner cylinder also used the same geometry for the connection to the pin, and can be seen in the above first two steps, however this cylinder was solid instead of hollow, so only required one extrude from the plane perpendicular to the mounting pin.
This same geometry was used for all of the hydraulic cylinders, with modifications for the length of the cylinder length to match the appropriate motion associated with the sliding in and out to extend and retract the connected members.
The support leg was simplified to not include hydraulic cylinders, and instead rotates simply at a pin joint freely
The first step was a simple shape extrude seen from the sketch below
A new sketch was made to imitate the leg shape, and also extruded
The leg mounts to the foot and back support, so needed two extruded cuts for these holes.
The support foot is the piece that contacts the ground from the support leg. A parallelogram shape was created first for the support foot and then extruded. But a Cut extrude of a simple rectangle sketch along the back face is what provided the section cut out as seen below.
A second boss extrude created a mounting pin for the support leg, and the result was merged to form one solid body, and the third extrude created the large foot surface to contact the ground. Lastly, chamfers were added to complete the geometry of the foot platform.
Back Control Panel
The first step in creating the back control panel was to create three extrudes using sketches constrained by dimensions, equal, horizontal, tangent and coincident constraints.
Next, an exrude cut was made using coincident tangent vertical and horizantal constraints. After that the controls were made with six extrudes made using sketches constrained by coincident, and diameter constraints. Then, the dome tool was used to round out the top of the control stick. Next an extrude was created using a sketch constraind by midpoint, vertical, horizontal and deminsion constraints.
After that the swept tool was used by ussing a path sketch constrained by deninsions and a profile sketch constrained by diameter and coincident constraints. Finaly an extrude cut was created using a sketch constrained by vertical, coincident and demision constraints.
The first step in creating the back support was extruding a sketch constrained with symetric, vertical, horizontal, coincident, tangent, midpoint, and demension constraints. Next, a cut extrude was made using a sketch constrained with symetric, vertical, horizontal, coincident, midpoint, and demension constraints. Then an extrude was cresated using a sketch constrained with symetrical, coincident, vertical, horizontal, eqaul, midpoint, and demension constraints.
An extrude cut was then made using a sketch constrained with diameter and coincident constraints. Next, an extrude was created and mirrored about a plane using a sketch constrained by diameter and distances. Finally an offset extrude cut was made using diameter and coincident constraints.
The roll cage was created with a ton of extrudes that are on the faces of other extrudes, and are too numerous to describe individually, so I will show the sketches. This roll cage was symmetrical about the front plane, so many of the sketches used the mirror tool across the dotted lines shown.
The Vertical bars created here were sketched and mirrored across the front plane with an offset.
The roof was created on a plane from the top of the vertical bars,
The Steering wheel column were also mirrored across the front plane, but the mount was sketched and extruded from the new face created by the column seen below.
The cab was created with a few boss extrudes and cut extrudes in order to contour the seat to a normal human being’s gluteus maximus and back muscles and fat. A basic shape was sketched to resemble the back of the chair. Then another sketch was created to resemble the bottom of the chair.
Then by sketching arcs onto the plane face created, with extrude cuts created the contour of the chair.
Then the base was a simple rectangle extruded from the bottom of the chair base.
Then fillets made the chair smooth and comfortable for the driver. These fillets are crucial to not cut off blood flow of the driver’s thigh and lower leg, causing muscle cramps and spasms, as sharp edges would have done, even though it was made from foam.
First a circle was extruded, and then hollowed out with two cut extrudes to create a more thin rubber tire geometry.
Then the tread pattern was drawn on a new plane tangent to a line of the tire. This tread pattern was then extruded, and then patterned around the 360 degrees of the circular outer surface
The back tire is 1.61 times the size of the front tire, and steps are repeated, but adjusted to scale.
Axle and Rim
The rim was created first, with simple circular extrudes, as well as a rod to act as the axle.
A circular pattern was used to imitate each of the lug nuts on the wheel.
Then the mirror feature tool was used to make this part symmetrical on either side.
The back axle rim is 1.61 X larger than the front axle.
The first step in creating the cab was making a sketch of the basic shape using demensions coincident, midpoint, vertical and horizontal constraints and then extruding. Next we made an extrude cut to make the arm mounting hole and cylindar mounts using a sketch constrained by diminsions, coincident and vertical constraints. Next, three extruded cuts were made to form the grill using a three different sketches constrained using vertical, horizontal, coincident, and dimension constraints.
Then , an extrude was created to make the fenders using a sketch constrained using coincident constraints and then it was filleted using the fillet tool to make them more relistic. An extrude was created to make the rest of the fender after that using the geometry already in place.
An etrude cut was then made to create the axle well using a sketch constraind with vertical, horizontal, coincident, and deminsion constraints. Finaly, an extrude cut was made so that the rollcage would fit propperly to the cab. This extrude was made using a sketch constrained by parelel, eqaul, horizontal, coincident, midpoint, and deminsion constraints.
Front loader arm
The first step in creating the loader arm was to extrude a sketch with the dimensions taken from the calipers. Constrains that used, were, tangential, coincident, equal, and horizontal. Next, an extrude was created using a sketch constrained by diameter and coincident constraints.
Then, an offset extrude cut was made using a sketch constrained with certain dimentions and coincident constraints. Next, an extrude was created using a sketch constraind by diameter and coincident constraints. Then, a plane was created and the body was mirrored about the plane.
After that sketches constrained by eqaul,horizontal, verticle, perpindicular, coincident, parelel and deminsions were extruded.
Next a offset cut extrude was created using a sketch constrained by coincident, horizontal and dimension constraints. The chamfer and filet tool was used to make the arm more realistic. An extrude was then made using diameter and distance constraints. Finaly the feture was mirrored about the plane.
The first step to create the front shovel was to create an extrusion of the solid frame, but first we needed the dimensions we took from the caliper measurements as seen below. This sketch used different constraints such as horizontal, vertical and coincident to constrain the sketch to form the shape. Then using an offset cut extrude, the bucket portion was hollowed out.
Next, using sketches constrained with verticle, horizontal, coincident, and distance constraints we extruded a frame rail.
Then, using a sketch constrained by diameter and distance we cut extrude the lower mounting point. Then we used a sketch constrained by distance, eqaul, vertical, horizontal, parelel, and coincident constraints we extruded the rest of the frame rails. Finaly, we extruded the top mount using a sketch constrained by diameter and coincednt constraints and filleted the edges to give a more relistic look.
In order to create the final assembly, every single part that was created need to be constrained within one assembly. The purpose of having every part in one assembly is that if assemblies are put within assemblies, the assembly will break apart during the motion analysis. For the assembly, a singular part was chosen to be the fixed center of the assembly. The part that was selected for this assembly was the solid cab. From there the roll cage, steering wheel and chair were assembled onto the cab.
Followed by the wheels and axles, the framework for the rest of the loaders was put into place. For the front loader, a set of pistons were connected to each other to constrain the motion of loader. The front loader was the connected to the cab by constraining a set of pins to the front of cab to enable rotation. The back excavator was connected to a control panel that was on the back of the cab. The connection was created through a rotating pin that allowed the excavator to rotate side to side. The different pieces of the excavator were also connected through pin connections as well as pistons that enabled different types of motion. The scoop was connected in the same manner with different pin connections that enabled rotation. Shown below are two views of the final assembly.
Figure 1238: Front Assembly View
Figure 1249: Back Assembly View
In order to create these type of connections and prevent any undesired movements, different kinds of mates were used. These mates are used to connect faces to faces, edges to edges, and various constraints. For this assembly four kinds of mates were used, concentric, coincident, parallel and symmetric. Examples of these mates are shown below.
Figure 12570: Coincident Mate
Figure 12671: Concentric Mate
Figure 1272: Parallel Mate
Figure 12873: Symmetric Mate
Shown below is an exploded view of the final assembly. This was created by manually separating every part that was constrained together during the assembly phase. This view is useful because it shows every part that was used during the design phase and where it fits into the final assembly.
Figure 12974: Exploded Assembly-Back View
Figure 175: Exploded Assembly- Front View
Mechanical Model Analysis
Shown below are the tabulated results of the mass properties for the assembly as well as each of the parts that are encompassed in the final assembly. Among these properties include the volume, surface area, density, mass, center of gravity and numerous moments of inertia. It is important to note that each of the
given results are 1/16 of the actual values given that the assembly was modeled 1/16th to scale. The majority of the backhoe loader are different kinds of steel, creating a low cost solution for assembling the backhoe loader (as well as giving a more constant density for the overall system). The diesel tank which is mounted on both sides has been made out of polished aluminum, which is a lighter metal that also won’t rust over time. The tires are made of PW-MT11030, which is a type of textured rubber/plastic.
The overall weight of the entire assembly was found to be 10,425.8 lbs., which is a direct result of the amounts of steel that were used in larger areas of the assembly, such as the cab or the front loader. In an attempt to decrease the weight of the assembly the tires were hollowed out. This results in one back tire having a weight of 46.328 lbs., a mere 0.444% of the assembly. The majority of the weight comes from the solid cab, which is the hub of all the different connections within the assembly. The weight of this part comes out to be 6630.624 lbs., over 50% of the entire weight.
A possible solution for decreasing the overall weight of the assembly would be to create a cab that is not 100% solid. The actual design of a backhoe loader involves the cab being more of the framework housing parts such as the motor and chassis as opposed to a solid body used to create connections. It is noted that bodies such as crane bicep and crane forearm weigh 102.4 lbs and 81.92 lbs respectively which is a direct effect to the bodies being hollowed out framework for different bodies such as the pistons which regulate the motion of the excavator arm. Shown below are the mass properties for the overall assembly and each part used to create the final assembly. Table 1 shows the mass properties of the final assembly, showing not only the standard mass properties but numerous different moments of inertia taken at different pointing including the center of mass. Table 2 displays the mass properties for each type of material. Here it is shown the distribution of mass and density through the final assembly. It is shown here that the solid cab is the source of the largest mass and density throughout the system and how the different types of materials can affect the entire system.
Table 1: Mass Properties of Final AssemblyVolume 79.9Surface Area 630.97Average Density 0.247955Mass 20.18Center of GravityX Y Z
3.97 1.46 0.8Moment of Inertia at Center of MassIxx Ixy Ixz
1 0.06 0Iyx Iyy Iyz
-0.06 1 0.01Izx Izy Izz
0 -0.01 1Principle Moment of InertiaPx Py Pz
46.99 197.54 216.66Moment of Inertia at Center of Mass & Output
Coord. SystemLxx Lxy Lxz
47.57 9.34 0.22Lyx Lyy Lyz
9.34 196.96 0.19Lzx Lzy Lzz
0.22 0.19 216.65Moment of Inertia at Output Coord. System
Ixx Ixy Ixz103.53 126.37 63.99
Iyx Iyy Iyz126.37 527.18 23.71
Izx Izy Izz63.99 23.71 577.21
Table 2: Mass Properties of Assembly PartsCenter of Mass
The Backhoe Loader assembly required three motors too replicate the motion of the excavator. The real-life excavator uses hydraulics to create pressure on a side of the piston to push or pull the piston which in turn moved the part connected to it. For this project rotational motors were used to simplify the motors as an actuator would have been harder to find the appropriate positions, the rotational motors allowed an angle of rotation to be chosen and an amount of time to get to this angle. The Team decided to modify parts of the Excavator for design purposes such-as the scoop connection to the hydraulic piston, a linkage system was made to provide a higher moment and to keep the parts from running into themselves, this also provided a more realistic look to this portion of the model. The model has much more motion than is displayed in the rendered video because the front loader, wheels, seat, steering wheel, and support arm all can move in the assembly but for this report was not required. In the path analysis the paths can be seen and how they become more complex as parts are added to the analysis.
Forearm Crane Motor
The Forearm Crane Motor is used to provide the ability for the excavator to dig into the ground, the motor allows the forearm to become more horizontal. Without this motor the crane assembly would only have the ability to act on objects above the ground level, or lift the scoop up once it is in a hole. The path of the Forearm is a simple 2D motion, it can rotate around the pin that connects it to the main cab this creates a side to side motion or a horizontal arc, it also rotates vertically around the pin connecting to the hinge system this makes a vertical arc. This point was selected because it provides the most extreme motion and leads to the motion of the next part in the assembly.
Figure 176: Horizontal Point Motion
Figure 177: Vertical Motion of Bicep Point
Figure 178 : Angular Displacement of the Forearm
Figure 179: Graphs of the Motors Motion of the Forearm
Bicep Crane Motor
The Bicep Crane Motor allows the excavator to reach out further with the bucket. This motor provides a scooping motion to allow the scoop to dig and pick up dirt or other material. This part has the same motion as the Forearm except more complex.
Figure180: Motion of the Bicep Point
This is the complex motion in the x-direction of the endpoint of the Bicep arm. The motion caused from the hinge to swing the excavator side to side is very similar to that of the Forearm motion, the plot below is of the angular displacement of the end of the bicep arm where the scoop attaches. This point was selected because it combines the motion of the Forearm and Bicep of the crane while still showing the farthest path of the motion.
Figure 181: Angular Displacement of the Bicep
Figure 182: Graphs of the Motors Motion of the Bicep
The scoop is the part that allows the excavator to do the job that is designed for, digging or picking up material. The motor here allows the scoop to act on a material in the most efficient way (digging). The motion path for this is very similar to that of the Bicep because they are so close to each other, but the extra hinge and hydraulic allows for extra motion. This selected point combines all the parts in the excavator assembly and how the motion of all of them combine and how the paths build off of each other to create a system that provides a complex motion.
Figure 183: Motion of the Scoop Point
This path shows the scooping motion that the scoop takes as it completes its motion.
Figure 13084: Angular Displacement of the Scoop
This plot of the angular displacement shows that the motor of the scoop doesn’t have much to do until it starts to “dig” but when it does that is when almost of the motors strength is needed and the forces are strongest.
Figure 13185: Graphs of the Motors Motion of the Scoop
Arm Base Motor
The Arm Base motor allows the entire excavator arm to rotate around the connection. All the parts will display a similar arc with slightly different radius. This motor allows the collected material to be dumped to the side to allow a larger hole to be dig easier.
Figure 13286: Graphs of the Motion of the Arm Base Motor
By choosing to use a 1:16 scale of a backhoe loader, a more manageable resource was present to deconstruct and analyze every aspect of the model. This also provided the ability to create a more detailed model which in turn more accurately showed every aspect of the backhoe loader. As shown above, the backhoe loader was constructed in numerous different parts but were divided up into 4 main sections. These sections include the front loader, the cab and the roll cage, the wheels and axles, and the back crane. By dividing the final part into these smaller parts, it’s easier to construct each detail of the overall part.
When constructing the final assembly for part, each individual part was integrated into a final assembly. The parts were constrained together by using different sorts of pistons and pins as well as concentric constraints to attach two faces together. Following the completion of the final assembly, a motion analysis was conducted onto the back crane. By using numerous motors on different areas of the crane at different time frames, a simulation of the motion involved in moving the crane was performed. Through this simulation, the mass properties including density, moment of inertia and mass were found of the final assembled part as well as each individual part. In addition, a specific point was selected in the assembly and a kinematics/dynamics analysis was performed in order to find the velocity, position and acceleration at that specific point. The purpose of this analysis was to understand how the entire motion of an object is affects one point which can further have effects on the entire body itself.