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Mechanism Analysis Charles Hunter AME40423 Mechanisms and Machines September 10, 2010 Abstract The purpose of this project was to graphically reproduce the mechanism within three different machines and determine the degree of freedom, F, and the mobility, M, numbers for each. The machines chosen were the Precor Elliptical Fitness Crosstrainer EFX 576i, Precor Adaptive Motion Machine AMT 100i, and Precor Seated Row machine. Diagrams of the mechanisms are given with a short description of the analysis for each.

1 Engineering Analysis There is only one equation required to analyze the mechanisms in order to determine the degree of freedom. Gruebler’s Criterion to compute the degree of freedom is, (

)

( )

(1)

where N is the number of links, P1 is the number of P1 contacts, and P2 is the number of P2 contacts on the mechanism. The mobility of the mechanism cannot be found using an equation. The analysis for the


mobility was found through observation. The mobility number is equal to the minimum number of links which need to be grounded in order for the mechanism to be considered a structure.

2 Results The Precor Elliptical mechanism diagram is shown in Figure 1. The mechanism consists of 6 links, 6 P1 contacts, and 0 P2 contacts. All of the links are held together with pin contacts except there is a sliding contact between the 6th link and the ground. Using Gruebler’s Criterion, equation 1, the degree of freedom number was calculated to be 3. The mobility number was observed to also equal 3. The 5th, 4th, and 3rd link could all be grounded to render the elliptical immobile.

Figure 1: Precor Elliptical Fitness Crosstrainer EFX 576i Mechanism Diagram


The Precor Adaptive Motion Machine mechanism diagram is shown in Figure 2. The mechanism consists of 6 links, 6 P1 contacts, and 0 P2 contacts. All of the links are held together with pin contacts. Using Gruebler’s Criterion, the degree of freedom number was calculated to be 3. The mobility number was observed to be 3 as well. The 1st, 2nd, and 3rd link could all be grounded for the Adaptive Motion Machine to become a structure.

Figure 2: Precor Motion Machine AMT 100i Mechanism Diagram

The Precor Seated Row mechanism diagram is shown in Figure 3. The mechanism consists of 6 links, 7 P1 contacts, and 0 P2 contacts. All of the links are held together with pin contacts. Using Gruebler’s Criterion, the degree of freedom number was calculated to be 1. The


mobility number was determined to be 1. If one of the links were held immobile, the mechanism would be considered a structure.

Figure 3: Precor Seated Row Mechanism Diagram


Mechanism Analysis