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Group A Christopher Back Joseph Ashwin Franklin Kwong voon Wong Chen Lin Machines and Mechanisms II MAE 512 Final Project SHRIMP Robot Front Leg Design

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Introduction Design Constraints and Requirements Synthesis Description Synthesis Design Process Synthesis Results Prototype Development Analysis Description Analysis Design Process Analysis Results Overall Performance of Mechanism Designs Overview

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Introduction The Goal of this project is to design and optimize the four-bar system used in the front leg of the SHRIMP legged-wheel robot in order to allow the robot to climb over the obstacles of heights (H=2R, H=4R, H=2R) We are also required to come up with a four bar system that reduced the peak torque required and reduced the fluctuations of the torque through one cycle.

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Design Constraints And Requirements Device must be a Four-bar linkage that either be a Crank-Rocker or Double Crank Must agree with Grashof Criteria to be able to predict behavior Must pass through all necessary points to climb an obstacles The Device must be compact (Sum of 4 links must be small) Should have base points located within the body of robot. The linkage system should have reduced peak torque and torque fluctuations to avoid active control of motor

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3 Position Motion Generation by Analytical Synthesis

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Synthesis Matrix Form(3 point) M+W +Z =P1; M+W*exp(b2) +Z*exp(a2) =P2; M+W*exp(b2+b3)+Z*exp(a2+a3) =P3; N+ U +S =P1; N+U*exp(g2) +S*exp(a2) =P2; N+U*exp(g2+g3)+S*exp(a2+a3) =P3;

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Mechanism Synthesis Procedure: Pose problem as 3 point precision problem Make use of 3 point synthesis equations Free choices are (db2,db3,dg2,dg3,da2 da3) Assign arbitrary values for (db3,dg3,da2 and da3) Vary angles (db2 and dg2) to determine a possible range for feasible mechanisms. We also needed to see if these feasible mechanisms have base pivots M and N within the chassis of the robot. We made use of a series of surface plots to perform our search.

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Figure 1: Surface Plot of DB2,DG2 and usability criterion

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Figure 2: Surface plot of a narrow band for search of DB2, DG2, and usability criterion

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Figure 3: Surface plot of DG2,DB2 and sum of the link lengths

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Figure 4: Surface plots of base pivots M and N against usability criterion

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Results from Initial Synthesis Analysis: We see that the values for M and N indicate that there are no feasible mechanisms that have a base pivot within the chassis of the robot The surface plot analysis still gave us some ideas regarding the angle ranges for possible designs.

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Mechanism Synthesis cont… We now posed problem as a two point synthesis problem using the appropriate synthesis equations. Now we have free choices as (db2,dg2 and da2) Varying these parameters we performed a search for the base pivots (M and N) locations within chassis. To do this we again made use of surface plots

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Figure 5: Real and Imaginary parts of M and N

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Figure 6: Shows the region of M (0.3 < Rm<1) and the Im(.75<1m<1.25) are all feasible

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Mechanism Synthesis Continued: From previous set of surface plots we obtained a feasible region for M and N location. Now we manually tune the angles to obtain a desired output path. We know that using the synthesis equations does not guarantee the mechanism will pass through the desired points in the same configuration. To check if mechanism passes through the required points we make use of a series of animations.

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Path trace of mechanism for H=2R case

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Path trace of mechanism for H=4R case

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Path trace for mechanism for H=6R case

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Matlab Animation

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Prototype Development Height of Stairs = 2R

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Prototype Development Height of Stairs = 4R

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Prototype Development Height of Stairs = 6R

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Prototype Development Static Balancing

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Position Analysis Loop Closure Equations Velocity Analysis Differentiation of Loop Closure Equations Force Analysis Newton Euler Method Torque Variations for a Crank Rocker Lowest Peak Torque Least Torque Fluctuation Balancing to reduce Torque Fluctuation Analysis

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Purpose was to identify which parameter effects Torque variation to improve design Sensitivity Analysis

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Peak Torque VariationsLowest Torque Behavior of Mechanism Designs Case H=2R

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Peak Torque VariationsLowest Torque Behavior of Mechanism Designs Case H=4R

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Peak Torque VariationsLowest Torque Behavior of Mechanism Designs Case H=6R

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Lowest Peak Torque coincides with least Fluctuation Static Balancing - to reduce Fluctuation and decrease fatigue and strain on the Mechanism Moved CG to point of rotation Reduced fluctuation but increase in peak Torque Behavior of Mechanism Designs Fluctuation Reduction

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Lowest Peak Torque Behavior of Mechanism Designs Case H=6R Least Fluctuation after balancing

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Lowest Peak Torque Behavior of Mechanism Designs Case H=4R Least Fluctuation after balancing

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Lowest Peak Torque Behavior of Mechanism Designs Case H=2R Least Fluctuation after balancing

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Our Design trace a path that will allowed the Front Leg to Climb the stair Although the Front leg will climb higher than it need, it can be an advantage when we have higher flight The performance of our design can better be better determined with a real prototype The Fourbar criteria limits our imagination to come out with better design Overall Performance of SHRIMP Robot Front Leg Design

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Questions?

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