autocat final project

8/12/2019 autocat final project

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Intro

The goal of this project was to design and manufacture seven remote control cars. These cars

were built using the resources in the shop in building 35. Even though this was a small scale

project, many decisions were made from a manufacturing point of view, where something like

this would typically be mass produced.

The team first focused on designing the car to be as simple as possible. This meant fewer parts to

manufacture and assembly down the line. We also made sure to design in modules so that each

module could be assembled separately, then put together at the end. This greatly helped later.

Next we went to fabrication where we decided all of our manufacturing methods and started to

make parts. Once this was well on its way we started to test the overall assembly. Once the car

was ready to drive we tested the car overall and made the necessary changes.

Design and Manufacturing

As stated previously, our design philosophy was easy manufacture, easy assembly. Our simple

components and individual sub-assemblies are evidence of the execution of this philosophy and

will be further described below.

Our chassis was simple water-jetted aluminum with thermoformed skidplate. Front end assembly

is one sub unit consisting of wheels, tires, suspension, steering control, and bumper. This entire

assembly attaches with just two screws that both fasten the whole front assembly and align all

components. The steering yoke mount is made of sheet metal and also serves to properly space

our suspension.

The rear assembly is also an entire sub-unit and consists of the motor, drive gear, rear axle, and

rear wheel/tire units all neatly confined to a C-channel section. C-channel was chosen as the

main structure for this rear sub-assembly because it can be purchased off the shelf and quickly

machined to have the features required. This entire sub-assembly easily attaches to the chassis

via two tapered head screws.


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Our control box was designed to be made out of a single piece of sheet metal. After water jetting

the flat pattern, six bends are made and a delrin handle is attached to two upright flanges. These

two flanges each serve dual purposes. The front flange is the mount for the servo, and the rear

flange is the mount for the banana clip. The electronic components housed in the control box are

all attached with double sided tape to the base of the box. The battery sits velcroed to one of the

side flanges of the control box. The angled flanges on the rear of the control box serve the

purpose of helping to align the banana clips for quick attachment and removal.

Our design process started with several ideas, but we ultimately focused on an elegant, and easy

to assemble design. As well, we focused on having complete sub-assemblies in anticipation of

mass producing this item and reducing assembly times and bottlenecks in the process.

Our design has minimal parts, ease of access for all fasteners, and ease of adjustability on

components such as steering (toe-in, toe-out), steering yoke tension, wheel bearing tension, and

king-pin pivot tension.

Project Time Estimates

Getting this project done in time involved a lot of individual and group efforts. A decent amount

of time was spent as a group during the preliminary design stage of the project, as well as other

progress review meetings.

Individual and subgroup efforts were put into CAD/CAM modeling, part fabrication, assembly,

and testing and troubleshooting, based on the level of proficiency in a particular area.

The total amount of man-hours spent on the project was about 524 hours.

Table 1 below provides a summary of the tasks performed, estimates of the amount of time spent,

and individual contributions towards the success of the project.


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Table 1: Task and Time Sheet

NB: See original table in Dropbox: Time Estimate for Project.xlsx

Group Dynamics

Team 1 Members

The Tumbler team consists of seven brilliant MIT graduate students with expertise on

mechanical design, CAD drawing, fabrication, and modeling. This year, they made the best ever

car f or Professor Martin Culpeppers class 2.810.

Figure 1: Kyle, Obehi, David, Yan, Desoto, Ryan, Nick

Group Strategy

The tumbler teams success is based on a wise job distribution and the synergy that it creates.

Ryan is the one who organizes the whole team, assigns team member tasks to do and makes sure

everything is on the right track. David and Nick are the two super design experts. They bring rich

experience together with design principles from course 2.75 to make the best design ever. Yan

and Obehi are two great modeling analysts. They also collaborate with Ryan on documentation

and with David & Nick on CAD drawing. Kyle is a person who really has talent in fabrication.

His naval background trains him to be on schedule, which helps guarantee the accomplishment

of tasks in a timely manner. Joe is able to stand by and think about questions in a different way,

which brings great value into design and fabrication.


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At the beginning, the tumbler team held several preliminary groups meeting to come up with the

best possible design by applying principles such as the golden ratio and research on previous car

projects. In the manufacturing process, each team member was able to learn and perform

injection molding for plastic wheels, water j et cutting for cars chassis, sheet metal bending for

control box, thermal forming, and assembly for the whole car. Communication among the team

were efficient through emails, group text messages, and weekly meeting. Individual team

member consistently performed their specific responsibility to the best of their abilities and

shared the documents and drawings through Dropbox to allow the teamwork transaction and

revision control to take place. Individuals contribution and team synergy make a difference in

helping the Tumbler team achieve its ultimate objective.


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Exploded Views:

Figure 2: Front Assembly Exploded View

Figure 3: Control Box Exploded View


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Figure 4: Rear Exploded View

Lessons Learned

In the design stage, we could have more carefully considered tolerancing, as it played a huge role

during assembly, leading to longer assembly times.

We also often rushed into assembling the car without careful consideration of the entire parts of

the car, and so often had to disassemble and reassemble, wasting time. Also, some parts which

needed to be ordered when a design had been fixed, were not ordered at the right times, and led

to delays in car assembly.

Also, as a group of seven, scheduling for meetings proved difficult sometimes, but better use of

scheduling tools like doodle could have been taken advantage of.

Conclusion

Overall, the car came out well. Many iterations on the design were made as issues came up in

manufacturing and assembly. This meant that changes were being made late in the semester, but

the car ultimately worked very well. This took a collaborative effort of all all the group members.Everyone is satisfied with the performance of the car and are looking forward to race day.


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Our Components

Figure 5: Rear Tire

Figure 6: Rear Wheel Hub


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Figure 7: Rear Axles

Figure 8: Front Suspension


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Figure 9: Front Wheel Hub

Figure 10: Front Bumper


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Figure 11: Steering Yoke

Figure 12: Chassis


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Figure 13: C-channel

Figure 14: Control Box - Flat Pattern


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Figure 15: Control Box - Folded

Figure 16: Control Box Handle


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Figure 17: Banana Clip Mount

Documents

autocat final project