Phase 4

Within this final phase of the project, the goal is to create the rotation mechanism to move the entire assembly, consisting of the following; lifting mechanism, grasping mechanism, and the payload, which all have been designed earlier within the project.

Design Constraints

Within Phase 4 many constraints were involved with this portion of the project. Constraints are placed to set as a guideline to not only challenge, but to ensure direction and the ability to accommodate any given circumstance. The explicit constraints placed upon this phase of the project include:

Involving phase duration the team was given two weeks to complete this phase of the project
The team may receive a 10” diameter circle of 0.75” thick MDF and two drop zone boards (also 0.75” thick MDF). The circle has a 1/8” diameter hole in the center, added during the manufacturing process, that our rotary table can pivot on should you the group choose to use it. This piece serves as the ground and you may modify as needed drilling additional holes to anchor gears, servos, etc.
The rotary table must be gear-driven by the third servo, while also having the servo travel through at least 150° of rotation during the pickup/drop-off sequence.
Each mechanism must rotate 180*(N-2)/N degrees, where N is the number of groups in the class.

Not only are explicit constraints entailed within phase 4, but there are implicit constraints the team has encountered as well, such as:

The servo cannot exceed 180 degrees of rotation
The servo must at rotate at least 150 degrees

As far as a team imposed constraint the team has decided on laser engraving into the wood of our final designs. The laser engraving will take place at the end of this phase. Laser engraving will be a unique challenge to furthermore enhance our knowledge and experience with laser engraving.

Brain Storming

For this Phase of the project, our brainstorming was less design based and more concept based. Instead of brainstorming completely different designs, we were more brainstorming different gear ratios, configurations, and number of gears

Gear Ratio

Options:

With the specifications of the constraints, we had to make the servo rotate between 150 and 180 degrees to make the arm move 140 degrees. This could have been done with a variety of gear ratios. After some quick math our best options we thought were 15:14 (150 degree servo rotation), 9:7 (180 degree servo rotation), and 8:7 (160 degree servo rotation). Of course there were a variety of options in between, but we decided on 8:7 based on sizing and the servo's constraints.

Number of Gears

Two Gears:

Pros:

Less to fit on 10 inch platform
Less materials and manufacturing

Cons:

Servo rotation is opposite arm rotation

Three Gears:

Pros:

Servo rotates same direction as arm
Can stagger gears if needed to fit on platform

Cons:

More manufacturing

Gear Train Calculations

Below are the gear calculations for our design. With nine groups in our class, we calculated that the arm had to rotate 140 degrees. With the servo having to rotate between 150 and 180 degrees, we had to find a gear ratio that would allow the mechanism to perform the way we needed. We decided to have the servo rotate 160 degrees making the ratio 8:7. With that we ended up with a 32 tooth drive gear and a 28 tooth gear rotating the arm. To fit all three gears onto the base we decided to use a diametral pitch of 10, making the total diameter of the gears lined up 4.6 inches. With a 10 inch base, the gears will be 0.4 in from the edge

Design Renderings

Claw in Position 1

(pickup)

Claw in Position 2

(drop)

Video of Claw Moving from Position 1 to Position 2

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