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A mechanical design to harness the lifting force is a collection of balloons tied together as their lifting force is directly attached to each other. This created a unified lifting of all the balloons pulling together. The resulting energy output is greater than the energy needs to sustain the process.


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The trick to this is to picture in your mind a simple phase diagram tracking the rotation of the cam; that these are all circular cams and not lobed cams make this a little easier!

The point of rotation is centred in the lower left quadrant on all three, so all we are doing is tracking the difference between them all.

The movement of the followers on b) and d) will be near identical in range and phase - there will be a very slight difference in both as as the latter is constrained to the arc of the retaining rod and runs on a wheel, but this is likely to be negligible. I would be quite careful n any analysis on cam c) as, depending on the loads involved, this is at high risk of fatigue - actually they all are, but this will have the loading alternating identically from one side to the other in a sinusoidal fashion whereas for the others the loading less "extreme" (though that does depend on how close to the horizontal d) gets!)

Whilst a) and c) look the same at first glance, they are significantly different; one follows the eccentric wheel vertically above the axis of rotation, the other follows the highest point of the cam regardless of phase. 

So, looking at the "pressure angle" as asked in the question, at the snapshot moment in time that this image is displaying, b) and c) will have the pressure angle all acting vertically, a) slightly to the right and a) slightly tot he left - effectively exactly as shown in Roger's post above (duplicated below)...but this is where it becomes a little "ambiguous".

On 1/10/2022 at 6:13 PM, Roger Casas Robert said:

Is it a vector perpendicular to the tangent line appearing in the matching point between the shaft and the follower, for each case?


The question is asking about the pressure angle on the follower, NOT on the cam. It is unclear to me what the question actually seeks and this will be clearer for you from the lectures you have attended and the guidance given by your tutor. If I was analysing the CAM followers at this point in time shown, I would resolve these and determine that:

a) is a resolved force creating a bending moment; effectively as a cantilever load.

b) is purely a compressive load

c) is the resolved hypotenuse of the contact point and the linear guide of the follower, again creating a bending moment both on the shaft and on the leg of the "T"

d) will always act perpendicular to the contact point tangent of the follower wheel regardless of position.

Remember, the only one that will remain consistent throughout, regardless of the phase of the cam is d) - again if it reaches horizontal, that could be an issue.

Hope this helps!

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