Hello, today we're going to talk about software to simulate mechanisms and analyze mechanisms. So let's get started. Okay, the software that I'm introducing to the class is this GIM software, G-I-M, I'm guessing that's how we pronounce it.
It's located, you can download it from the website and you can all... from our ILEARN website and there's also the tutorial that you can look at there. This was developed by this university and if you use it for a publication or project something there, you're going to go online.
Please recognize the group, this group, for their free sharing in the software. You have a couple options when it comes to software for representing mechanisms. I'm going to point out two quickly as we get started. I guess I should mention three. So the classic approach is Adams.
We don't have Adams at the moment, but it's probably the strongest software. Another one is MotionSolve made by Altair Hyperworks. And we've got a few seats of this in one of our better labs, I say our better labs, one of the Clement Hall labs. And I did note on MotionSolve, you can see it's integrated multi-body solutions, and you can get a free student edition for Motion Solve if you choose. You'd be developing this.
I need to tell you, you need to be developing this on your own. So you could download a free student edition and play with that on your own. Another software that's probably the most popular for, I would recommend, but you have to spend a little bit, is this...
I'll turn this little thing here and it's called, not Simwise, what is it? It's called two-body dynamics. Go back to this.
It's called motion works. Couldn't think of the name of it. Motion or excuse me, working model, working model.
So it's this working model 2d and you can get this student the student edition for Six months $29 or 12 months $49. It's a little bit of investment But that's a nice software if you actually purchased the book you would get if you purchased the book you would get Working model along with that textbook and there are some examples in the textbook on using that however That's not the option we're going to use in this class for no particular reason. We'll be using the GEM software. I think the software is easy.
We'll all be fairly similar. Probably this one being free would be the clunkiest, maybe the most constrained in terms of what it will do. But it is free, and you can always get access to it and use it for your projects. So to open GEM, you need to go to the download GEM, extract it, and then start.
Jim on your computer. That's what I'm doing here. So the first thing that we see is this general purpose workspace. And I'm going to be jumping, you know, I'm going to be jumping to the tutorial a few times. You're going to see this general purpose workspace.
And there's a couple parts to Jim. You can see you've got the standard new start a new file open from existing files, save your current. file and there's a couple steps that you can do geometry in geometry you create your mechanism or they actually provide a library you can download some mechanisms already built and start modifying those so you create and modify here in geometry kinematics and do kinematics simulation the dynamics will do dynamic simulations so in kinematics courses motion and dynamics you include forces there's a link of synthesis In synthesis, you actually specify the motion you want to get from your mechanism, and that will then solve or give you mechanisms that will do that problem.
And then finally, there's this workspace analysis. In this short little video, I plan on talking a little bit, showing you a little bit about geometry, a little bit about kinematics, and a little bit about synthesis. I'll record a second video that will talk a little more specifically on synthesis using GEM. All this material comes from the tutorial and then also just kind of clicking around and learning on your own I'm not very comfortable with Jim.
I mean, I don't use Jim a lot, but it's a good software And I think you could pick it up pretty quickly after reading the tutorial. Okay, so let's start with Geometry and I'm over here. I've got the my screen. I've got the tutorial open actually.
And so the first page I can see what is GIM. It tells me is this mechanism analysis software. It's very nice. Application of the software, access to the software, and again it's noting if you use their stuff the only thing they ask is that you cite them in any kind of publications and they give the citations there.
Has the kinematic analysis module, which is the heart of GIM. I can see this geometry in motion is what that means. And so they first start talking about the geometry module. So let's look at that.
So we're going to look at the geometry module here. So I'm going to create a very simple mechanism, and there's a couple ways to do it. The way I do it is I first create key points that are going to recognize my mechanism.
And let's say I want to create a, let's just say a simple four bar we've seen. Let's think about, I'm going to try to create something that looks like the Let's see. Okay, I'm going to stretch a little bit. We just did the elliptical machine. So I think I'm going to try to create a mechanism that looks like the elliptical machine.
So I'm going to place a couple points that I think are key points on the elliptical machine. This is the input handle. Up here is where you grab with your hand.
Here's where it's fixed to ground. Down here is where it attaches to the lower leg link. I'm going to run the lower leg link, say, over to here.
And then... And then that attaches to the crank, which comes up, and let's say the crank is here. So I've placed those points, key points, and then I'm going to start creating links between them. By the way, if I want to modify one of those points, I click this modify icon.
I can come to any of these. I double-clicked it, and I can either move it around, or I can specify its location. It gives an orientation, but for a point, I don't know that orientation makes much sense. So I can work with these guys as follows. I'd like this to be in a line.
I guess I'd have to think about how to make that in a line. Maybe I can do it by making all of them have a common X value. Okay, next I'm ready to start creating my links.
So to create my links or elements, I'll select... this icon and my first element is going to be the handle. So it's going to start at this point, it's going to run up to this point and then carry on, in this case to that point. And I'm done. Now I'm not quite sure how to tell it is done, so I'm just going to click on it there.
I guess I just clicked on that last link twice and you can see I've got this link, that's my handle. Now I'm ready to create a second element. And that's already selected, so I'll go down and start it here.
It's going up to there and then I click on that endpoint twice to get it to stop and then I'm going to create one more So go from there to there click on it twice that's done now at the moment This is just a just a rigid link of chains. So next I want to insert some type of no Kinematic pair, you know some type of joint and here I've got a revolute joint prismatic a double slider a sliding revolute joint You see my different options here. I want to start with these revolutes.
I'm going to select a revolute, and I will click on that point again. And that now gave me a revolute between those two guys. I'm going to click on this, and that broke then the link there and gave it a link. Now, I've noticed for connecting to ground, they don't give it explicitly. So if your link ends in space, you can connect it to ground just by clicking on it.
So it kind of assumes defaults that ground is there, and we'll try to do the same thing here. Yeah, okay. So there you have it. If for some reason I don't like something, I could click delete, come around and choose it. And then down here are some constraints that I could add to the device, and then I could delete these constraints down here as well.
Okay. And this modify was just looking at the modify. I'm not sure if I can.
I don't know if I can modify that. I was wondering if I could make the ground come out. Okay.
Anyhow, that's our mechanism. Again, you stand here. There's the crank in the back, and then the user puts their input up here. So now I'm ready to do some analysis.
So I've completed my geometry. Now I'm ready to do my analysis. So I'll go to kinematics.
So I've clicked the kinematics icon. And I have a couple options. I can do single position analysis where I'll select. In all cases, it's the same.
I can do single position, controlled motion where I define it, or some automatic motion. And we'll try some different things. Oh, I need to show you one thing.
Sorry about that. Save changes. It just said save changes.
Okay. So when I go back, notice right off the bat, when I built this thing, it gave me the degrees of freedom and redundancies. So it's pretty nice.
I don't know if you were following as I was building, but those things change as I build. For example, if I come in and say, well, I'm going to attach another link to ground, we kind of know what would happen. Let's say I'm going to fix that to ground.
What happens? Well, look, I've lost all degrees of freedom. And I've lost those redundancies. I'm going to try to get rid of that thing.
Okay, well I did it the hard way, so now I got to go back and create it. So I'm going to recreate the point here. I want to edit that point, make sure he's on the line.
Recreate the link, because I'm just going to delete this. I suspect I could have done a better job at that. Now recreate the link. It goes from here to here to here. Double click on the end to stop it.
It looks like it by default picked up that revolution, but I still need to connect to ground. So select that. Now I'm back. Okay, so and I'm back to one degree of freedom.
So now I go to kinematics. I'm going to start with automatic motion. And for my automatic motion, it's suggesting some input.
What I need to do is select my input actuator, and I'm going to let it be the handle here. And so that's giving me some motion. I can see my possible motion in the machine.
And then finally I'm ready to I can animate the system if I want, like so. And so now my you know, this is the motion that I would get. It's giving me some key points along the way. I can pull information off.
Oops, slowing down. That might be my computer slowing down, actually. Or I could step through those points.
So that's kind of nice. There's several things I can see. I wouldn't know that just arbitrarily that mechanism would have worked the way I'd hoped, but it looks like this one does.
Looks like this one does. I think if I were to add a middle point, it would track. Notice how it's tracking the location, all these middle points.
For fun, let's go back to geometry to go back to the initial spot. I'm wondering if we can add a point to the middle of this link. Let's say the foot's going to be right there.
I'm going to add a point there. I think I just added. It looks like I added something. Now I'm going to go back to my kinematics.
Do an automatic motion. Yes. See, what just happened, it's now giving me the... the trajectory of every point that I followed.
So now that point seems to have disappeared on the drawing. That's where I want the foot to be, but you can see it's giving me the path of the foot. So, you know, I could ask the question, they call it elliptical machine. Is that elliptical? Not quite.
It's kind of there, but it's not. We could, if we made this, one of these a slider, it would get elliptical. It's elliptical like, we'll call it elliptical like machine. Okay. So I get that motion.
There should be a way that I could you could find where you could get those absolute numbers and plots of those. That's the main idea. In this case we made this be the input. I could have chosen this link to be... Oh, no, that's back.
I could have chosen this link to be the input. That's odd. See that points back. Anyhow, once again, all those things are all given to me. Finally the controlled motion.
If I go with controlled motion... Again, I can choose an input and now I have the option of giving the range. So it looks like this one is, I can't start the change the initial condition, but I can change the final.
So it's starting at 60 to 63 degrees. I can make it go to zero. And that would show me then the motion for going from this 63. It must be missing the negative. That's not, oh, it must be missing a decimal point because that's actually in the negative quadrant. Sometimes it's a little hard to see.
But here I'm going over that smaller portion of motion. That's why I specify. And then note, it's also giving me the velocity right now, the angular velocity, angular acceleration of that link. And I could modify, I suppose, some of those as well.
Let's say I want to go to 90 farther, go to 180, 270. Okay, so I'm going to end that portion of motion. Okay, so that's how the kinematics works, and you can pull out some of these parameters. You know, you can also always choose, you could choose different things to be the inputs. This shows absolute rotation, one of the links that are connected to ground.
Here's a relative or floating actuator slider. We don't have any of those. I'm going to stop that. So I'm about done with this set of notes. The last thing I want to show you, you probably could take a little time and play with other mechanism types.
What I want to do next is look at their library. So I can I just selected open from the library and actually they have planar spatial computed gosh and the like but let's just stick with our planar and they give us a variety of One degree of freedom mechanisms to choose from two degree of freedom mechanisms three degree of freedom mechanisms and so on zero Oh trusses. Yeah, they do some truss analysis static analysis as well. We've just created a four revolute a four bar so far These are all four bars actually, but a four revolute four bar. Let's choose another one.
These would be one of our what we call one of the slider cranks. Let's choose this guy for fun. And it just returned a default mechanism. We should have the ability to go in and in geometry, we should have the ability to go in and move these points around. If you want to change the device, okay?
So here I'm changing where that link is. So this will give you the chance to pick a general topology you like. We call that a topology, but then start changing dimensions. So here I'm doing dimensional changes, okay?
So let's go back to what we had. Looks like it started there. Let's go to the kinematics, look at the motion for a moment. Okay, so that's the motion that's returned by default.
And we can go back to the geometry now and start modifying that. So I've clicked this modify and I'm gonna start moving things around so I can make a new mechanism. There's a new kind of mechanism like so and go back and look at the behavior of this guy and You'll notice it's pretty easy to get motion that becomes quite not I'm going to say not intuitive based on the mechanism.
And that's the beauty of mechanisms. Really, the power was that I could start creating complex motion. A single link is going to give me circular motion. A single link pinned to ground is always going to give me circular motion.
A slider connected to ground is always going to give me linear motion. But if I want anything else or any alternative way of doing it, with just a small number of links, I start getting complex motion. this.
So that's a summary of a quick overview on gym. The third topic that we want to look at, stuff this guy, the third topic that we're going to look at is synthesis, creating a mechanism given the desired motion. So in other words, you know, I want to maybe create something that's near a straight line or some particular path.
What's the mechanism that gives that? And I'll do that in the following.