Concept of Design

Millipede Characteristics:

• Arthropods known for slow but steady movement.

• Large number of legs provide stability on various surfaces.

Walker Concept and Theme:

• Inspired by millipedes' characteristics.

• Emulates distinctive leg movements: each leg pair moves at same speed but with different cycles.

Prototype Description:

• Exhibits stable crawling behavior akin to millipedes.

• Features 8 legs moving in different cycles.

Final Prototype

PVA and DFA Analysis

Subassembly: Gear Train

Our gear train consists of eight gears that rotate with the same angular velocity as represented by Figure 3. This ensures that all of the gears that drive the motion of the leg have the same cycle. The motor gear has 30 teeth (Nm = 30) while all other gears have 50 teeth (Ni = 50). Using the number of teeth for each motor, it is possible to calculate the gear ratios of each leg.

From the gear ratios from above, it is possible to confirm that all 8 legs have the same gear ratio and ultimately the same cycle. Coordination of motion between different elements was achieved by utilizing gears of the same teeth number. The direction of these gears were meticulously determined by the number of gears connected from the input gear (motor gear) to the output gear (leg crank gear). By shifting the initial starting position of each gear, we were able to create different cycles for each leg.

Subassembly: Klann-Linkage

The Klann-Linkage was chosen for our leg mechanism, since it converts rotary motion into a linear motion almost perfectly. Our team had to scale the linkage sizes and the joint positions of the Klann-Linkage so that it had optimum linear motion when in contact with the walls and 3 satisfied the size constraints of this project.

The individual links that made up this Klann-Linkage were also fairly easy to design. While we have spotted several other teams with the same Klann-Linkage mechanism, our robot is unique in a way that it has 8 legs. Moreover, 4 of these legs are oriented upside-down to enable greater stability, making it ideal for not only the horizontal crawl but also the vertical climb.

Final Velocity Estimation

In order to make the problem tractable, we have made the following assumptions:

• The mechanism moves slowly, so the peak torque is determined primarily by the weight of the mechanism

• The weight of each leg is negligible, so we can assume that the majority of the torque on the gearbox will only be due to the legs that are touching the ground.

• No power losses

Our robot has 8 legs, with N=4 on the ground at any given time. The torque from four of the legs will contribute to the torque on the motor. The gear ratio mv is 0.6 (going from motor to legs). The peak torques are therefore given by:

Although the batteries run the motor at 9.6 V, data from 9V is acceptable assuming the batteries will not be fully charged.

At motor torque of 0.429 Nm,

For a motor angular velocity of 8.77 rad/s and a gear ratio of 0.6, we get a crank angular velocity of 5.26 rad/s.

Since the required velocity is 2m/min, the calculated velocity is sufficient for the robot to climb/crawl the wall during the allotted time.

Challenges

Initial Design Approach:

• Began with clamping mechanism but shifted to walking mechanism due to concerns about friction from cam follower.

• Selected Klann linkage for walking mechanism due to foot path.

• Initial prototype had 4 legs; increased to 8 to overcome counter moment issue.

• Considered weight increase and complexity with more legs.

Human-Centered Design Approach:

• Iterative process from design to prototype until viable solution found.

Fabrication Challenges:

• Laser-cut chassis required high precision and tolerancing to avoid toggle positions in walking mechanisms.

• Tolerance issues from laser cutting at Sidney Lu caused problems in assembly, stability, and functionality.

• Determined optimal hole size through trial and testing for smooth motion and stable structure.

Adapting to Climbing Challenges:

• Challenge in achieving balance between normal force for vertical climb.

• Increased length of leg link to enhance outward force against wall, aiding stability.

• Used sponge to marginally help with vertical climb.

Drive Train Solution:

• Wooden shaft chosen over metal for lighter weight.

• Square-shaped wooden shaft with 3D-printed attachments ensured smooth rotation.

• Achieved purpose of creating lighter walker with consistent gear rotation speed.

Exploded view