1. 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.

2. 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 BPA facility

3. 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.

4. 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.

5. 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:
Easy height adjustment
Easy mounting/dismounting [no tools required]
Design must prevent rotation/misalignment with drive wheels.

6. 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.

7. Customer Interview/Feedback
Initial meeting: 20 November 2015
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
Second meeting to detail desired project outcomes.
Design envelope established.
Initial solutions/ideas discussed.
Operational Demonstration: 02 February 2016
Demonstration of the cart climbing and steep incline.
Demonstration of the cart “passing” a standard suspension tower.
PDS Presentation and Update: 24 February 2016
Discussed factor of safety based on ANSI B77.1 and 29 CFR PSU team suggested factor of safety of 4:1. BPA will advise when an agreement has been made by all parties.
BPA approved redesign of cart arms which have braces added to provide structural support.
BPA approved cross bar design that uses ball-lock pin to replace cotter pin.
BPA approved 2 different designs for pinch wheel assemblies.

8. 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:
PSU team to determine alternative to ball- lock pin mechanism and present to BPA for approval.
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.

9. 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:
PSU team to complete detailed design of cross-bar.
PSU team to complete FEA analysis of cross-bar.
Analysis of changes to the arms will determine whether these cross-bars can be eliminated from the cart design.

10. Concept Evaluation & Selection
Pinch Wheel Assembly
Two options presented to BPA on 2/24/16
Option A
Option B

11. 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

12. 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

13. 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

14. Detailed Design Pinch Wheel Assembly
Re-designed pinch wheels to be presented to BPA
Combines features of A & B for mounting and height adjustment

15. Detailed Design [ cont.]
Support Arms
FEA analysis of proposed design of the support arms to be completed to determine whether it will handle impact load on arms.
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.
Drawings will be completed within two weeks for fabrication
Cross-Bar
New design of cross-bar will be utilized if FEA analysis of support arms suggest it is needed.
FEA analysis of cross-bar will be completed if cross bars are deemed necessary.

16. Next Steps… Pinch Wheel Assembly Support Arms Cross-bar
Present design to BPA and obtain approval.
Complete FEA analysis of assembly.
Create drawings for fabrication.
Support Arms
Complete FEA analysis for impact loading on arms.
Make a decision on need for Cross-bar based on FEA results.
Cross-bar

17. Questions??