Feature Showcase - Free Motion Joint

In today's episode I demonstrate how to use MOMDYN to create a free motion joint, sometimes called a 6-degree-of-freedom (6-DOF) joint. This represents the motion of an object (any object) as it moves freely through the air; say, for example, my iPhone when I throw it across the room.

That is exactly what I did in a video that I created to demonstrate the new feature, which is embedded after the jump. I also plot some of the data in a notebook that can be accessed in Google Colaboratory. I hope you will be interested in experimenting in that notebook, and maybe recreating some of it yourself (just make sure your phone lands on a soft spot). 

For more information on how to implement the new feature in your own model, keep reading.

What's new in version 0.9?

New MOMDYN version will be out for beta testing in the next few days. Version 0.9 will include these new features:

• Planar joint (two translational states, one rotational)
• Free motion joint (six degrees of freedom)
• Playback speed setting
• Approximate size setting

The first two are what I'll call the motion joints, used for rigid body motions with both translation and rotation. I used the free motion joint to generate the flying box at the right, similar to the spinning box example I posted previously, but now with 3-D translational dynamics. With quaternions!

The second two are tied to the visualization, but not to the model itself. Playback speed will allow you to slow down or speed up the animation, and approximate size dictates the size of fonts, thickness of lines, etc.

Feature Showcase - External Force

In version 0.8 I have added external and actuated forces and moments. What took me so long, you ask? I don't know, I guess it seemed like low hanging fruit, so I didn't really prioritize it, but here they are.

I added a video to the MOMDYN Youtube channel demonstrating an external force to create a form of the classic Duffing oscillator. The video doesn't cover much of the theory, as its more focused on using the app, but to suffice to say you can get some wild and chaotic dynamics out of a seemingly simple system. Read on after the jump for more discussion of the dynamics you see in the video.

Whats new in version 0.8?

I'm back in business! Had a little hard drive issue on the laptop I use to build and distribute, so I've been working on the code but hadn't been able to update the beta test release for a little while. Thats all resolved now though, and the updated version should be live in the next day or so. Four new load types are included:

• External Force
• Actuated Force
• External Moment
• Actuated Moment

Feature Showcase - Model Export

From a prior entry in the blog, version 0.7 includes the ability to export data and scripts from the app. These can be shared with your peers, or transferred to a desktop environment to do more advanced analysis. I added a quick video at the link below with a demonstration of this in action.

https://www.youtube.com/watch?v=b3Xu8DHAMuU

Tutorial video - revolute and prismatic joints

I uploaded a video to Youtube which shows new joint mechanics that have been added in the last couple of releases. Joints in MOMDYN combine attributes of various features of the classic interface. A revolute joint creates a new frame along with the associated symbolic constants and time varying properties. A prismatic joint creates a vector and point. Each can include spring-damper physics, which is included in the demo. 

What's new in version 0.7?

The newest MOMDYN beta release is the first to include the capability to export data and code from the model to share with colleagues, or to transfer your analysis to a desktop environment. From the menu dialog, there is now an export button, in which there are three options.

• Model : used to share and import to the MOMDYN app
• Simulation : tabular data for each state variable
• Python : source code that can be executed on a desktop

On iOS, open the “Files” app and navigate to “On My iPhone/momdyn/momdyn/Documents” to view exported files. To import another user’s model, place the momdyn_model.py file into your “On My iPhone/momdyn/momdyn/user” folder, then it will be visible in the import menu on the welcome screen.