Group B Tedros Ghebretnsae Xinyan Li Zhen Yu Tang Ankit Panwar.

Group BTedros Ghebretnsae

Xinyan LiZhen Yu TangAnkit Panwar

Design a fourbar to move from point A to B Point B is at a height, H=6R,4R,2R Single motor drives the input crank Preferable a Grashoff crank rocker or double

crank The Chassis is fixed What is required from the motor• Compactness• Dynamically well behaved

Links: Aluminum T6061Area of each link: 1 cm2

Weight of wheel: 1 kg

Two most important constraints were:• the ground link had to lie inside the chassis• the lower arm should travel from without

colliding with the step. First choice was whether to synthesize the

mechanism for two or three points. The main advantage for the two point

mechanism was that there were more free choices.

Whereas with the three point, there was a better control

This was the first method employed by us. Total variables: 18, total equations: 12 The free choices were α2 , α3 , β2 , β3 , γ2

and γ3

The problems with this method:• no constraints on the ground link• the arms were colliding with the step• None of the solutions satisfied our design

requirements

Next we employed the same technique but with fixed ground.

The values of the betas (α2 and α3 for the upper blue link, β2 and β3 for the lower black link) were found first

The known variables were the ground link and the coupler angles γ2 and γ.

We were able to get the solution for all the three points which satisfied the design requirements.

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The problem with this method was that the arm moves from point one to point two, but fails to trace the last point.

The reason why this method fails is that it does not always guarantee that the fourbar will pass through all the three points

The plot shows the same fourbar mechanism but in the crossed configuration

Whereas the previous plots were for the uncrossed configuration

Total variables: 14, total equations: 8 The free choices were C, S (this is the part extended

beyond the joint of U and C), β2, γ2 and γ3

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Steps taken:• Determination of Position, Velocity and

acceleration of all the center of masses and also that of the wheel

• Formulation of Torque versus input Theta 2• Plotting Torque versus Theta 2 using Matlab for

different height H(6R, 4R and 2R)• Analyze the plotted Torque and • Determine and select the feasible one for the

given mechanism size and orientation

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For heights 4R and 2R The Torque seems to stabilize for theta

greater than 100 For those values of theta, it was managed

to lower the Torque to little more than zero value which in turn means less work is needed to do the task, and hence a small Motor would work

For height equal to 6R Unstable torque. There is a lot of fluctuation in magnitude

and direction There is a big range between max and min

valuesTheta2 values Values between 50 and 100 resulted in

great fluctuation of the torque with extreme high values and lack of stability