Bonneville Power Administration Aerial Line Cart Progress Report
Bonneville Power Administration Aerial Line Cart Progress Report Class of 2016 Portland State University Mechanical Engineering CAPSTONE Project Presenters: Rob Lawrence and Sam Levin Team members: Austin F. , Joshua P. , Stephen R. , Mackenzie L. , Bao P. , Carlos J.
Project Background Aerial Line Cart [Spacer Cart] • The cart is used to perform repairs of high voltage transmission lines. • The cart was created in-house by BPA to address the needs of the linemen while performing repairs. • PSU ME Capstone tasked with performing a redesign to address safety/ergonomic problems. Marty Lyons demonstrating the use of a Spacer Cart at 25 degrees @ BPA facility
Project Scope Structural Issues • Over time, the cart develops stress fractures due to impact and shock loads distributed to the cart arms when it encounters obstacles on the transmission line. • PSU team to create a design that ensures frame is structurally resilient and able to withstand impact loads. Verification to be done with FEA analysis.
Project Scope [Cont. ] Cross-Bar • Current design of cross-bar uses cotter pin to hold the position in place on the arms • Cotter pin is difficult to place/remove • PSU team tasked with changing locking mechanism.
Project Scope [Cont. ] Pinch Wheel Assembly • Pinch wheels are used to maintain contact between drive wheels and the line. • Difficult to adjust height for different diameter lines • Pinch wheel assembly tends to rotate on frame arm out of alignment with drive wheel • PSU team tasked with designing a removable assembly. Design must include: o Easy height adjustment o Easy mounting/dismounting [no tools required] o Design must prevent rotation/misalignment with drive wheels.
Project Scope [Cont. ] Factor of Safety • BPA utilizes an 8: 1 factor of safety based upon internal standards • PSU team tasked with researching applicable standards to come up with an alternate factor of safety.
Customer Interview/Feedback Initial meeting: 20 November 2015 o o o Project Team met with customer representative Meeting held with a the current version of the spacer cart available for on ground demonstration and physical inspection. Documentation regarding current issues was distributed to the team. Follow up meeting: 13 January 2016 o o o Second meeting to detail desired project outcomes. Design envelope established. Initial solutions/ideas discussed. Operational Demonstration: 02 February 2016 o o Demonstration of the cart climbing and steep incline. Demonstration of the cart “passing” a standard suspension tower. PDS Presentation and Update: 24 February 2016 o Discussed factor of safety based on ANSI B 77. 1 and 29 CFR 1926. PSU team suggested factor of safety of 4: 1. BPA will advise when an agreement has been made by all parties. o BPA approved redesign of cart arms which have braces added to provide structural support. o BPA approved cross bar design that uses ball-lock pin to replace cotter pin. o BPA approved 2 different designs for pinch wheel assemblies.
Concept Evaluation & Selection Ideas for Structural Improvements • BPA likes the use of angled bars to provide support against impact. They have approved this design • BPA is worried about the use of the ball-lock pin to connect each independent arm, since there will be a stress concentration on the hinge and pin • Next Steps: o PSU team to determine alternative to balllock pin mechanism and present to BPA for approval. o FEA analysis to be completed regarding impact load to the cart arms. FEA analysis will be used to determine whether the cross-bars can be eliminated.
Concept Evaluation & Selection Cross-Bar • Use of a bolt-action mechanism to locate the cross-bar joining each arm • Use of a ball-lock pin instead of cotter pin to secure cross-bar in place • BPA approved both changes to the current design • Next Steps: o PSU team to complete detailed design of cross-bar. o PSU team to complete FEA analysis of cross-bar. o Analysis of changes to the arms will determine whether these cross-bars can be eliminated from the cart design.
Concept Evaluation & Selection Pinch Wheel Assembly Two options presented to BPA on 2/24/16 Option A Option B
Concept Evaluation & Selection Pinch Wheel Assembly [cont. ] • Option A builds off of the original design but flips the orientation of the wheel. It also uses a ball-lock pin so that it can be mounted/removed easily • Height adjustment is still done using nut/screw
Concept Evaluation & Selection Pinch Wheel Assembly [cont. ] • Option B uses a series of indexing pins for mounting/removal of the wheel assembly • Provides 2 pinch wheels to ensure constant contact at any angle • Uses ACME screw with attached handle for height adjustment
Concept Evaluation & Selection Pinch Wheel Assembly [cont. ] • BPA chose a hybrid system, using the layout of a single wheel from Option A combined with the ACME screw and handle of option B
Detailed Design Pinch Wheel Assembly • Re-designed pinch wheels to be presented to BPA • Combines features of A & B for mounting and height adjustment
Detailed Design [ cont. ] Support Arms o FEA analysis of proposed design of the support arms to be completed to determine whether it will handle impact load on arms. o Based on results of FEA analysis, a decision will be made on whether the cross bars are needed on the cart for arm alignment/support. o Drawings will be completed within two weeks for fabrication Cross-Bar o New design of cross-bar will be utilized if FEA analysis of support arms suggest it is needed. o FEA analysis of cross-bar will be completed if cross bars are deemed necessary.
Next Steps… Pinch Wheel Assembly o Present design to BPA and obtain approval. o Complete FEA analysis of assembly. o Create drawings for fabrication. Support Arms o Complete FEA analysis for impact loading on arms. o Create drawings for fabrication. o Make a decision on need for Cross-bar based on FEA results. Cross-bar o Complete FEA analysis for impact loading on arms. o Create drawings for fabrication.
Questions? ?
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