Rotating objects on a Pivot Point

[ianhughes7UFVF]

Hi

I posted this before, but I am not sure I could provide the file correctly and I don't think I explained the problem.

Here is a share link to the file, that you can download to look at the project:

http://a360.co/2AOsIyI

Basically I need to convert this:

... from the legs and body being straight up, to this:

Basically the legs have a pivot to the body of 36 degrees, which equates to the legs and body angling 18 degrees to get the effect. I want to add the center foot in so I need to tilt the body forward, the two side legs back, and tilt the feet forward.

So I really need to be able to pivot the individual parts of the design, the body, legs and feet.

Any help will be greatly appreciated as I am having lots of trouble getting anything to pivot.

Kind Regards

Ian

[TrippyLighting]

When looking at ambitious designs like this that start of on the wrong foot almost with the first sketch I look at, I am always wondering how to approach that.

Can I get this to work ? Sure! Do I want to take the time to sift through all the assemblies an components to correct the mistakes ? Probably not!

Origins and sketches are the very first things I look at.

1. In a mechanical design such as this, Sketches should be fully constrained and dimensioned.

2. #1 can only be achieved when the sketch is somehow referenced to the Sketch origin.

 Neither is the case right with the first sketch in this design.

In fact there is  very little in this sketch that is constrained at all.

You let us know where you want to go from here.

If you prefer to just get advise on how to assemble this, that's fine. If you want to learn how to do thing properly and ensure that things fit and your assembly does not blow up when assembled then maybe you want to take a step back.

[jeff_strater · Accepted solution]

It's a rainy Saturday here in Oregon, so what the heck...  I spent a bit of time making a screencast showing how I would go about adding joints to this model.  I only did part of it, hopefully it is enough to get you started, and you can figure the rest out on your own.

PS love the model - did you come up with the construction of it on your own, or did you work from some existing plans/documentation/etc?

Jeff

[ianhughes7UFVF]

Hi

I appreciate your frankness. With alot of my work up to this point I have been doing things as correctly as I have been taught here. So I do feel I have come along way from the disasters I started out with.

With the Foot Frame you were looking at, they were supplied to me as dxfs and with a lot of open joints, and alot of headaches :(.

With the frames I have been doing, I have started by guaranteeing that the first part is set to the origin and built from there, they were usually parts that sat flat horizontally to start off so it made it easy, and they always had a center point. I was unsure what to do with this object considering its a vertical plate and where to center it on the origin. So I carried on with it, also only expecting to use it as a individual project for display.

Although that has changed and it has been used for the larger project.

Constraining objects is something I have never understood. A good explanation of that would be great.

Kind Regards

Ian

[ianhughes7UFVF]

Hi

I appreciate the time you have taken and will have a good look at your solution shortly.

I greatly appreciate the effort you have taken.

I will reply in more detail shortly. I have to go out for an hour.

But I am totally grateful for the screencast.

Kind Regards

Ian

[TrippyLighting]

---

@ianhughes7UFVF wrote:

Hi

... With alot of my work up to this point I have been doing things as correctly as I have been taught here. So I do feel I have come along way from the disasters I started out with.

With the Foot Frame you were looking at, they were supplied to me as dxfs and with a lot of open joints, and alot of headaches :(.

...  

---

I remember earlier encounters of this model, and , yes you definitely seem to have applied rule #1 and there appear to very few "lose" sketches. That is good!

I am sorry if I came across a little harsh. I am German and for the most part I've been told way too many times that most German engineers are like that. We don't beat around the bush!

As I said, this is an ambitious project for a Fusion 360 beginner. When starting to assemble this I started with the foot with the intention to ground it hoping that its origin would be at ground level. Thay was not the case, so I investigated further  and when I saw the sketch my heart sank!

Now that I know that this came to you as a DXF - sorry to hear that 😉 - I'll see if I can find other things that could be stumbling blocks.

So in other words the Jedi (you) has returned and there is new hope 😉

[ianhughes7UFVF]

Hi

First of all, Thanks Jeff for the demo on how to make the joints move. That's exactly what I need to do.

The Frame, legs and feet were all provided to me as dxf's. Its the story of my life with the work I am doing. Most of the work, is other R2 builders providing me with files for simular frames and I am building them up to demonstrate to the R2 builders community what they look like. So the frame, is the result of one dxf that I had to brake up into stacks of individual dxfs to insert into the project and build up the frame. All those parts are made from a light material called styrofoam, so a builder can make a really light R2 from it. I would add skins on, but I don't believe fusion can wrap a 2mm skin around the frame.

As far as the parts go, the foot moves, the leg and the hub are joined and the body moves, so you were close.

So now I can work on the frame and correct those issues and present it properly. I especially like the fact that fusion shows the angles as the leg and foot need to be set at 36 degrees.

And thanks Peter. Your frankness has been just what I needed. To tidy up my projects has made them a hundred percent better for a beginner. Now with advice from Jeff I can see that there are definite extra things I need to do, especially constraining components better and setting pivots in place well early in a project, not at the end.

Thank you chaps. You have my respect.

May the Force be with you 🙂

Kind Regards

Ian

[TrippyLighting]

Are these models for presentation only or are you going to hot-wire-cut these ?

I can see the dilemma with the DXF's. I looked at one and it exhibits a number of problems even though you might have already cleaned it up.

For presentational purposes that might be OK and even for manufacturing them out styrofoam it might be OK. Styrofoam is rather forgiving.

However If you'd laser cut this out of a harder material, having precise dimensions, and proper assembly clearance it rather essential.

then it really pays to actually clean up these DXF's and constrain and dimension them. But I can see that this is a good bit of extra work that might after all not be needed.

Thank you again for your explanation! However, now that you've encountered these difficulties it might be time to educate these R2 builders that you receive these DXF files from. How do these folks create their DXF files ? Presumably they also use some form of CAD system and if those R2 builders would all work with Fusion 360 this whole process might be a lot less wasteful and painful for everyone.

[ianhughes7UFVF]

Hi

These are presentation only at the moment.

I run a threads on astromech.net which is the world wide forum for R2 builders. It is about frame designs, and parts designs, and I display already designed frames and concept frames on it. There are a surprising lot of fusion users on the forum, but they don't collaborate that much.

Nearly all the dxfs I have been given have had issues, and I have had a friend with rhino trying to clean them up before I get them, yet they still have issues.

I personally wish I had started with fusion before anything else, and learnt to use it properly from the start. It would have so many headaches.

I think people on astromech are definitely seeing the advantage of using fusion though. With the recent work I am doing with the frame build ups and getting the parts to pivot, its definitely helping.

Kind Regards

Ian

[ianhughes7UFVF]

Hi

I am working through adjusting my fusion file of the frame and the pivot movements, and I can see I need to make a rigid group of the frame and hub to get the movement I need.

One slight problem still is getting the correct angle of the body and the leg and feet.

The main angle of tilt is 36 degrees when R2 is in three leg mode. Which means the outer legs tilt 18 degrees backward and the body tilts 18 degrees forward, and the feet tilt 18 degrees forward.

With the demonstration, Jeff, you showed that you grounded the body to work with the leg parts.

Is it possible to get the body to have the 18 degrees tilt to get the final appearance correct.

Instead of

Hopefully I am not pushing the limits of what can be done here.

Kind Regards

Ian

[jeff_strater · Accepted solution]

Yes, absolutely, you can do that.  I just chose to ground the body for convenience.  It's a good idea to ground something in your model.  But, even that is optional.  In this example, I grounded the right foot assembly:

I had to make a rigid group out of the body, but other than that, the workflow is the same.

Jeff

PS - I had no idea that astromech.net existed.  Seems pretty cool.  Keep us updated here on your progress!

[ianhughes7UFVF]

Hi

Thanks for that. A logical solution to the problem it appears.

astromech.net is where most people who want to build life size R2's go. There is stacks of support, advice and they have a parts section where you can buy nearly every part of the R2 if you want to build one up.

There are a couple of popular guys on there using fusion as their packages, that are far along with its usage.

I will keep you updated as I go.

Kind Regards

Ian

[ianhughes7UFVF]

Hi

I am still working on the design.

I have been able to follow your instructions so far, but for the life of me I cannot get the foot to angle the 18 degrees in contrast to the 36 degrees at the top of the leg.

Here is a link to where I am at.

http://a360.co/2jcpYRa

Sorry for being dense.

Kind Regards

Ian

[jeff_strater · Accepted solution]

@ianhughes7UFVF,

Here is an overly-long and rambling screencast.  I kinda did it without practicing.  Sorry about that...

I think there are a couple of mistakes here.  One is an admittedly frustrating aspect of how Ground works in Fusion.  There has been lots of debate on this, internal as well as on the forum.  But, the sad fact is that grounding a sub-assembly does, basically, nothing.  You have to make a rigid group out of the sub-assembly, and ground one of the "leaf-level" components (with no children).

Second, the relationship here between the joints in the Motion Link, and the Joint Limits is causing problems.  I had to delete the Motion Link, and the limits, and re-add them to get it to work.

screencast:

Jeff

[jeff_strater · Accepted solution]

OK, so I thought more about this, and went back to the model.  I can get to the same state with much less fooling around.  All that is really needed is to do the stuff with grounding the foot properly, and change the joint limits on one of the joints (it was set with a minimum and maximum both of 36, which essentially freezes it in place), and edit the Motion Link (to get the 2-1 ratio, and also to uncheck the Reverse flag).  Much simpler.  Ignore the previous screencast, unless you want to understand the thought process that went into analyzing the design...

Jeff

[ianhughes7UFVF]

Hi

I just watch your screencasts and that is totally clear on how to sort out my mistakes.

I am totally looking forward to fiddling with the design tonight. Unfortunately I am work and not able to get to my computer.

You made it very clear on how to correct the problem.

One question, though, at the end you drag the component, to show how the frame moves manually. When I try that nothing moved. Is there a crl or alt or key and mouse configuration that allows one to do that?

Kind Regards

Ian

[jeff_strater]

Hi @ianhughes7UFVF,

There is no magic involved in component drag.  You should be able to just click on a face and drag it.  My guess, based on the model you shared earlier, was one of two things:  Either the grounding was not effective, and the whole model moves when you drag it (I think that's how the model behaved when I first got it), or else it was because you had one of the revolute joints essentially locked - setting its min and max to the same values.  And, because that joint was locked, and there was a motion link to the other revolute joint, it meant the entire model was locked.  That's my theory.  Let me know if you find otherwise, when you get back to it.

Jeff

[ianhughes7UFVF]

Hi

Thanks for that, I was able to correct the design and now I could move the frame properly.

But ....... When I try and work on the other side, moving up the time line, I fall into major issues.

http://a360.co/2AXC8Ie

Is the problem, that I have mirrored the foot, leg and hub, and is that creating it so its all going funny.

Kind Regards

Ian

[jeff_strater · Accepted solution]

Hi @ianhughes7UFVF,

For some reason that I cannot figure out, when I try to download this design, I never get an email notification to download the file.  I have no idea why.  So, I just started on my version, where it left off.

To answer your question, no, the mirror should not affect the ability to join the components together, assuming that the mirror was at the component level, not at the body level. Looking at the earlier versions of your design, this look OK.

You do have to re-create the rigid groups, unfortunately, because those do not get mirrored.  No joints get mirrored today.

One trick, that only really applies to designs like this, I think, is you can make an as-built rigid joint between the left and right legs, since they move in tandem.  So, you don't need revolute joints and Motion Links for the left side of the design.  The sub-trick, here is, just like for Ground, you have to make the rigid joints between leaf-level parts in the design.

Here is another screencast:

Hope this helps!

Jeff

[ianhughes7UFVF]

Hi

Thank you,Thank you,Thank you,Thank you,Thank you,Thank you,Thank you,Thank you.

That really sorted it out and I was able to tidy up the rest of the frame.

Making each mirrored side mad the whole process simple and tidy.

I really appreciate your help.

Here is the result:

The last thing to do now is cad up the Center Foot for it and add that on and then I am finished.

I am so appreciative of your time and patience.

Kind Regards

Ian

PS. I wish I could download your screencasts and keep them permanantly, but after another 5 or 6 frames I should know how to do it with your direction here.