Weekly Challenge Group

My first thought was there could a single hinge in space around which the door could be pivoted between the two locations. This turned out to be impossible. However a single hinge could be used for one edge of the door then a ball linkage used to guide the opposite side of the door.

This was carefully laid out using Inventor. Consists of a pivoting link on the upper edge of the door connected to another pivot located on the wall above the door. Then a link with ball joints at each end from the bottom of the door to a point on the floor some distance away.

The door movement interferes with the floor. This of course was a non-issue according to the criteria given but I decided to cut away the floor for clarity.

Now the problem with this arrangement is the same face is presented on both positions, which violates the criteria. This was not realized until after completion. However a similar mechanism could be generated to accomplish the originally stated goals. Time constraints prevent me from continuing so I present my incorrect results for the sake of generating interest.

Excellent Bob!

It is much more detailed than is necessary for this exercise.

It's very good that you noticed the issue of the final position, which does not respect the problem statement. Precisely "the interpretation of the problem statement" and the licenses that one can take (or sometimes, the restrictions that are added unnecessarily) are the "lesson to be learned" in this simple exercise.

Kind regards!

Here I provide one more solution, but I must clarify that this solution (like any other) is not the important thing in this exercise.

Simply put, "one solution works for one problem" and what I try to provide with this exercise is "one rule that works for all problems."

The important thing is our way of thinking and we will make a good contribution to this when we have finished the presentation of proposals.

Kind regards!

Hello everyone,

I share with you my "first failed attempt" based only on curved guides.

I got too excited about the drawing and realized too late that I wasn't fulfilling the problem statement!

But I will trust what Marcelo always tells us: a solution, even when it doesn't work, is useful... as long as we realize why it doesn't work!

Excellent work Eduardo, especially if you manage to learn from the "mistake" and reach a valid solution!

I suppose everyone has already realized "the generalized mistake" we have been making: we think of a mechanism, we get excited about drawing it... and then we notice that "it doesn't meet the requirements"...

We present to you (as a work team) a progress that respects the recommendation that Marcelo always makes to us:

First you have to design a movement (among many alternatives) and then, design possible mechanisms (also among many) to carry out said movement (at least, approximately)!

I love that they are methodically applying design practices!

As long as they start by "solving the mechanism" and accept the movement that it provides (the opposite of what is recommended), they will fall, like many, into designs that are "more of the same", incapable of even exploring something innovative.

Well done!

It is surprising that it can be solved with a single degree of freedom and, therefore, a single motor!

A simple rotating arm + a vertical guide!!!

PS: Of course, there are details to discuss such as small "elastic aids" to get out of deadlocks and avoid ambiguities.

Very well thought!

I notice a slight change in strategy. Yesterday a triangular rotating frame was observed to support the movement. Now they have simply controlled 3 strategic points of the rectangle.

It's true! We changed our mind after carefully observing the movement and noticing that:

1) a vertex of the gate simply went down and up through a straight line...

2) another vertex described a semicircle...

3) the plane of the rectangle always contained the line along which the first point moved...

The happiness was short-lived when we discovered that the final position of the rectangle was a kind of dead point for "this mechanism" and that it caused the ambiguity of the movement of the rectangle when it wanted to return (reverse the direction of rotation of the motor).

We corroborated this using SolidWorks MOTION, which by reversing the direction of rotation eventually moved the rectangle in the undesired direction:

The solution (virtual, in Motion) consisted of adding a spring that "helps to get out of the dead center in the correct direction" which, in a real mechanism, could be an elastic support that fulfills this function (not along the entire length of the spring). movement but only during final support).

Motion simulation with motor and spring:

Reworked so the correct sides are presented.

Similar method as before. A pivot along one edge and a ball link for the opposite edge. There are obvious issues if this were destined for the real world but it achieves the desired motion with no ambiguities.

Grabcad would not let me post the video on this post but It can be found here:

move-wall-weekly-challange

Excellent Bob!

We will get a lot of benefit from this exercise.

I guess I'll wait until tomorrow or the day after to close it and start telling you some interesting questions.

Kind regards!

Marc and I provided another possible "movement design" that, of course, could be executed by various alternative mechanisms.

Hello friends!

I share with you two materials that will allow us to take advantage of this weekly challenge:

1. Reflections on what was done in:

https://grabcad.com/tutorials/dof-in-engineering-problems-1

2. Strategies to improve the design process in:

https://grabcad.com/tutorials/dof-in-engineering-problems-2

I want to thank you all for your participation, whether by presenting proposals or simply observing what has been done. I hope that we can take real advantage of this brief experience by exchanging ideas, impressions and, of course, constructive criticism in the comments of both tutorials.

My intention is always to "try to leave something useful" as a result of these types of "challenging" experiences. If anyone identifies with any of the practices that I consider "improvable"... I hope to help them and not lose that opportunity for improvement!

Kind regards!

Marcelo

PS: the truth is that it takes me time to create these tutorials and that is why I did not want to wait to have the last one ready, referring to the design of the mechanism once the movement has been designed. It will be available in a few days!

When shall we see some sort of final solutions for the problem or at least some discussion regarding the mechanisms required:

"Problem statement:

...It is requested to design a mechanism capable of moving it between both positions."

Simple definition of mechanism:

"an assembly of moving parts performing a complete functional motion, often being part of a large machine; linkage..." https://www.dictionary.com/browse/mechanism

While several concepts were presented, No other complete mechanisms were described. Much discussion was devoted to the methodology of conceptualizing the problem. No discussion was devoted to the actual mechanisms. Maybe I misunderstood and it is a problem with semantics. Maybe a single mechanism per se was not the end goal.

Hello Bob!

He hoped that the participants could complete the work, after raising the concepts, also proposing a concrete mechanism.

In any case, some concepts, such as that of @Ofitec Team, suggest enough about the mechanism: a 180° rotating arm that would include the drive motor, and a vertical sliding guide that also limits overturning in the plane of the rectangle. They also added an elastic element to facilitate exit from dead center in a vertical position.

PS: If @Ofitec Team or @Eduardo Marconi or @Clau 67 do not present a more concrete mechanism option, I will do it myself based on one of their concepts.

Sorry colleagues that we have not completed our proposal!

Work obligations worked against us, but we promise to upload something soon so that the challenge is not left unfinished.

Greetings!

Hello everyone!

To continue the talk started by Bob, I bring you a new case that tries to clarify the stages of conceptual design:

1) Movement design: in this case, applying the resource of "movement components" (two 90 degree turns in this case). 3 variants of the same movement are shown, which consist of sequentially applying the components, in any order, and then applying them simultaneously.

2) Schematic design of the mechanism: this is a schematic option that only shows the fundamental linkages to implement the previous "motion design", taking into account that "it is one option among many possible ones."

3) Specific design of the mechanism: add to the above the possible drives "for the case of 2 Degrees of Freedom". That is, a motor or actuator associated with each DOF that allows programming any of the designed movements (by individual components sequentially, in any order, and also by simultaneous components in infinite superposition possibilities).

Note: if one degree of freedom is mechanically linked to the other, this mechanism becomes 1 DOF and only requires one motor or actuator, at the cost of "losing flexibility" of movement because it specifically relates both components (turns of 90 degrees) of the movement making them simultaneous.

Movement design, resolved by components applied sequentially:

The same movement design, resolved by components applied sequentially, reversing their order:

The same movement design, resolved by components but applied simultaneously (there are infinite ways to do it):

Schematic design of the mechanism without motors/actuators or linkage of their degrees of freedom:

Design of the mechanism in greater detail for the option of 2 degrees of freedom driven by a gearmotor and a linear actuator (this is only an example that does not intend to specify the technologies, which is usual in the subsequent "basic stage" of the design):

Final comment: if we wanted to continue advancing in the definitions, it would be essential to "abandon the generality of the case" and move on to propose a specific case with its real context and characteristics, which would lead to "filtering many of the generic solutions" for different reasons such as interferences with the context; space swept by the moving object; etc. etc.

A very specific case in its "conceptual stage" would have many fewer permissions (degrees of freedom) in its statement than the example we have proposed here. A very generic example was proposed, precisely, to facilitate "the exploration of multiple solutions" that becomes more complex in a less permissive case.

Conversion of the mechanism to 1 Degree of Freedom:

So that it is not just words, I share with you a simple way to convert the previous 2 DOF mechanism to another 1 DOF mechanism by linking the rotation movement in the vertical axis (powered by a cylinder) with the rotation in the horizontal axis (eliminating the gearmotor) through a linkage with spherical ends (shown schematically).

I hope that some of this simple experience (with a very limited, but didactic, generic example) has been useful to you.

Kind regards!

Marcelo

I found the experience very useful!

Something very important that has been left pending in this proposal (which resulted from 1 degree of freedom) is to indicate the place and form of its motorization/drive to check if it implies a uniform advance or if it has dead spots or other inconveniences for mobility.

We must remember very classic cases such as the connecting rod-crank mechanism used in internal combustion engines. The basic "mechanism", understood as the set of links, is unique and results from 1 degree of freedom, but its behavior changes greatly depending on the place and way in which it is motorized/actuated. For example, if we drive it with a rotary motor on the crank (as happens in air compressors) the mechanism has a fluid movement even when passing through its dead points. But if we operate it from the free end of the connecting rod (as happens in internal combustion engines, through the explosion of the fuel that drives the piston) the mechanism "locks" in both dead points (upper and lower) and even It can come out of them in an ambiguous way (turning in one direction or another). For this reason, internal combustion engines require "a mass that provides momentum in a certain direction of rotation" to be able to pass through dead spots without problems.

If driven by a simple motor at the main pivot point (the stationary end), mine has no dead spots and has a continuous fluid movement. The relationship of the rotation angle to the relative position of the door is almost linear. Therefore, the rotational force required would remain nearly constant.

Because the ball link stationary end had an infinite number of solutions along a single plane it was originally tried adjacent to the main pivot. This resulted in dead spots and very acute included angles. (Something that would generated unnecessary high forces in the real world.) Moving it one time to a random position opposite the initial door position as shown resulted in good motion with no extreme included angles.

The geometric construction (descriptive geometry) required to develop this mechanism was advanced but quite easy with the 3d CAD system. I shudder to imaging doing it on the drawing board with a T-square.

The main criteria that drove me to this solution was that the only thing that really mattered was the starting and ending door positions. The intermediate paths were inconsequential. Trying to predetermine an intermediate path, in my mind, only limited the possibilities.

Excellent Bob, thank you!

Many of these questions are very important lessons for anyone learning about mechanisms. Just seeing a final version that works is good, but knowing the issues that had to be overcome to achieve it is even better.

Greetings!