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Assignment 1 for EGB321
Analysis and redesign for spider robot (Semester 1, 2019)
Figure 1. Picture of a robot spider and its legs (1/4 whole body). It contains gears, 4-bar linkages and 6-bar linkages.
Figure 2. Schematic diagram for the spider leg, where all components are shown, note that the size is not in scale.
The combination of Four-bar linkages and gears can be widely used in mechanisms and machines. One example is the robot spider which is mainly composed with gears and 4-bar & 6-bar linkages. To fully understand the working principles and mechanics, you are required to analyse a linkage mechanism. With the knowledge from EGB321, you are also required to re-design the mechanism.
You are required to design, analyse and verify a mechanism (Linkage) to fulfil the above task. In completing this assignment, you must complete following steps:
I: Measure parameters and understanding of the linkages (Total 20%):
a) Find out the corresponding joint points (O1, O2, O3, A, B, C, D) of schematic diagram in Fig. 2; Label all of them in right panel of Fig. 1 (10%).
b) Measure the lengths of 4-bar linkage of the spider leg (red lines), calculate the DOF of 6-bar linkages (including all red and blue lines of Fig. 2), and then determine Grashof condition of the 4-bar linkage. (10%);
II: Analyze the four-bar linkage obtained in Section I (Total 50%)
Let (see details of re-arranged diagram in Fig. 3, the links are re-orientated for easy-looking):
Link 1: O1O2, the positive direction is from O1 to O2, O1 is the origin point with coordinate of (0, 0);
Link 2: the link connecting Point A and the fixed pivot O1;
Link 4: the link connecting Point B and the fixed pivot O2; ? : is the link angle measured from initial x(+) direction counter clockwise to the particular link.
Figure3. Diagram for the part of spider leg (O1, O2, A, B, C correspond to the joint points as in Fig. 2), note that the length of links are not in scale.
When ?2 = 45° (O2O1A), to calculate:
a) ?3 and ?4 using the formulas, and also graphically get these values (using a separate graph paper). Note, only the values for open configurations are required, it is the same for the following analysis (10%);
b) if the angular velocity ?2 = 2 rad/second (anticlockwise) for Link 2 at that instant, to calculate: i) angular velocities for all other links of the 4-bar linkage; ii) velocities of Points B and C. (20%);
c) if the angular velocity ?2= 2 rad/second (anticlockwise) and angular acceleration a2 = 0 rad/s2 for Link 2 at that instant, to calculate angular accelerations for all other links(10%);
d) Develop a MATLAB script to calculate ?3 and ?4. (10%)
III: Re-design the four-bar linkage (Total 20%)
If we would like the spider robot run faster, under the condition that all parameters are unchanged except the length of O2B (the positions of O2 and B can’t be changed), should the length of O2B be increased or decreased? Use Norton Linkage software (or Matlab, or Solidworks) to verify your answer by monitoring the velocity of vB or vC
(as a function of ?2) when O2B is varied. (20%)
IV: Demonstration the redesigned spiders by modifying 4-bar linkage (Total 10%)
Practically verify the result by replacing O2B and/or AC; you need to fabricate your own links to replace O2B/AC to see if the spider can run faster. In order to reduce the complexity and the work load, please ensure to keep all other components unchanged except O2B/AC parts, no any other component is added or attached on spider. The positions of O2 and A can’t be changed, but the positions for B and C are changeable. There is no limitation for the used materials.
Marking notice for Part IV:
• Your group will get full mark (10) if the re-designed spider can walk/run 2 m with time of 28 second (standard time)
• Corresponding mark will be deduced depending on the performance of the re-designed spider
• Zero mark if the re-designed spider can’t run/walk, or the spider wasn’t re-designed, or the group is absent.
The redesigned spider from each group will make a competition at the week 7, the spider which can run 2m with the shortest time will be the winner. For the fastest 3 groups, each will win \$50 gift card.
OTHER REQUIREMENTS
Group work
The study shall involve the following broad steps:
This assignment is to be completed by groups containing minimally 4 and maximally 5 students due to the limited number of spider robots. The work must be entirely the work of your own group. It is your responsibility to manage the project so that all group members participate equally.
There will be no replacement if you damage or lost the spider robot, and each group can only have one spider.
Report and Cardboard model
problem. Well labelled/annotated diagrams or graphs will be favourably regarded compared to excessively verbal descriptions.
part IV.