1.3 Design Process

During the prototype phase, our team has gone through multiple iterations for our design. Our process began with the initial brainstorming found in the project proposal which used the analysis of the following link lengths (L1 = 32mm, L2 = 16mm, L3 = 32mm, L4 = 20mm, LP (ternary) = 40mm) to determine the geometry of each arm that the climbing robot would have. Our initial design decided on having 6 legs that would have different instances of rotation to allow for constant contact with the wall, however, we decided that doubling up and making two layers of legs (12 legs total) would allow for a more even distribution of force and fully ensure that there would always be contact with the two parallel walls. To allow for variability in the leg's distance from the wall, a spring and rubber foot will be implemented at the end of each leg for compliance. This will keep the system from receiving unnecessary stress and be able to keep each individual leg on the wall for a longer period of time. 

For powering all of the individual legs, it was decided that using a gear train would be the easiest and most efficient to implement. This would allow for all twelve legs to be powered by one individual motor. The gear would act as link 2 with there being an offset location from the center for the ternary link (L3) to connect to.  Figures 1, 2, and 3 show initial sketches from team members regarding how the legs and gears would be implemented. 

Figure 1: Gear system and leg link order

Figure 2: Gear system with spring and rubber feet

Figure 3: Additional initial design

Taking these dimensions and ideas, the first prototype that was created was a single leg to ensure that the motion was achievable. A CAD model was designed for just one leg and includes an input gear, an idler gear that transfers motion from the input, and a leg gear (L2) that receives the transferred motion to move the leg. Figure 4 below shows the initial model in Solidworks. 

Figure 4: Single leg prototype

The model was then created by laser cutting all of the parts from scrap wood at TIW and assembled using screws and wooden dowels as axles. The result can be seen in Figure 5 below. The result was a design that was not very stable and often had gears come loose. It was determined that bearings were needed to get better motion and ensure that gears and links stayed in place. The prototype however was able to achieve the motion determined in the initial analysis. 

Figure 5: Assembled single leg prototype

With further analysis, it was determined that improved motion could be found by once again changing the link lengths to get a longer and flatter vertical movement for each leg. The new link lengths that the second prototype used were (L1 = 30mm, L2 = 10mm, L3 = 30mm, L4 = 12mm, LP(ternary) = 65mm, theta between LP and L3 = 80 degrees ). This greatly improved the motion as can be seen in figure 6 below. This prototype has 4 legs powered by a hand crank that simulates the input power from a motor that the final iteration will use. 

Figure 6: Four leg prototype

The Solidworks assembly was once again laser cut and assembled but just with two legs to ensure that motion on the input side could be translated to the opposite side properly. Figure 7 below shows the completed prototype in motion. This iteration uses bearings to smooth the motion. The design also uses wooden dowels as axles that are press fit throughout the prototype to keep everything well put together. This final prototype iteration should prove that it is possible to do all of the required 12 legs. For the final product, springs will be added to the ends of each leg with rubber tops to improve compliance with the parallel walls that the robot is climbing up. 

Figure 7: Assembled two leg prototype. 

The final iteration just expanded the design seen in figure 6 by adding 2 more legs and then adding a second layer of legs for the total of 12 legs. The final iteration is also motorized instead of hand powered so a switch, battery, and motor were needed. A 1:3 gear ratio was used for the motor to slow down the motor and allow it to be strong enough to power all the gears and arms. The motor was then placed in the center of the gear train so that motion would translate more smoothly throughout the robot. A battery mount was added to the bottom of the robot to ensure equal weight  distribution for climbing up and also serves as a way to space out and secure the plates that make up the robot. A switch housing was added between the battery and also allowed for wire management. A CAD model can be seen from different angles below in figures 8 and 9. 

Figure 8: Front view of final iteration

Figure 9: Isometric view of final iteration

To manufacture and assemble the final iteration, the gears and plates were laser cut out of acrylic and the small and ternary links were laser cut out of wood to allow for visual variation in the final product. The battery holder, switch enclosure, and motor mount were all 3D printed. The rest of the parts were bought/available from class materials which included the motor, batter, switch, bearings, axles, spacers, and nuts/bolts. Figure 10 below shows the completed and assembled product. One change that was made from the original vision was that instead of springs, foam material was used to add compliance to the arms. This was done to simplify the design due to time constraints and ease of implementation. 

Figure 10: Final iteration complete