Fall 2016 Biped Trade Off Study- String for Lateral Balancing
String Material
By: Hector Martinez (Manufacturing Engineer)
Approved by: Ijya Karki (Project Manager)
Table of Contents
Introduction
For the Biped Project, we have considered the following materials for our Biped lateral balancing system. The system requires two weights attached to a servo through a lever and string. The purpose of this study is to choose a suitable string material to support the two weights, and allow the proper range of motion to allow the system to work properly, i.e. make the robot balance.
Material Chart
| Material | Costs | Safe Load | Pro | Con |
| Manila Rope (Fiber Rope) | $0.05 – 2.23 /ft | .15kN (5mm dia)
~15.2kg |
1. Durable
2. Flexible 3. Biodegradable 4. Cheap |
1. Shrinks when wet
2. Difficult to unknot when wet 3. Fibrous 4. Only found in braided strands |
| Nylon | $0.22 – 0.68 / ft | .326kN (5mm dia)
~33.2kg |
1. Elastic and shock absorbing
2. Long lasting 3. Rot proof 4. Chemical resistance 5. Can be bought in single strand |
1. Weak against UV rays
2. Susceptible to heat 3. Loses strength when wet |
| Polyester | $0.10 – 0.36 / ft | .284kN (5mm dia)
~28.9kg |
1. Rot and UV resistant
2. Retains properties wet or dry 3. Abrasion resistant |
1. Not suitable for heavy duty applications
2. Susceptible to chemicals 3. not elastic, not very shock absorbent |
Conclusion
Based on the research we have decided to use Nylon. The elastic and shock absorbing properties of Nylon make it perfect for a toy robot that will inevitably be used and played with and may be put through some rough times. Nylon also has the highest Safe Load rating of the three materials, and even though it is highly unlikely the rope will be used anywhere near this rating, it’s only a few cents more per square foot. The biggest reason for choosing Nylon is the ability to purchase it in a single strand. This allows us to use it in areas where space is an issue, having to use string/rope that is braided makes it difficult to use in such applications.
Resources
1. http://www.knotandrope.com/store/pc/Manila-Rope-c3.htm?pageStyle=m&ProdSort=19&page=2&idCategory=3&viewAll=yes
2. http://www.engineeringtoolbox.com/manila-rope-strength-d_1512.html
3. http://www.engineeringtoolbox.com/nylon-rope-strength-d_1513.html
4. https://knotandrope.com/store/pc/home.asp?gclid=Cj0KEQjwqfvABRC6gJ3T_4mwspoBEiQAyoQPkf52P_avp4P23eVobtda_agXx5x95YtQhVcXsBSvCBsaAkE-8P8HAQ
5. https://survivalblog.com/ropes_and_rope_making_by_be/https://www.usnetting.com/rope/selection-guide/#polyester