New Tutorials

Along with the new release of MOMDYN onto the App Store and Play Store, I have created two new tutorials, for a simple pendulum, and a mass-spring-damper. These will be permanent pages (not blog posts), and I'm going to incorporate them and their corresponding Youtube videos directly into the app. Check out the videos below, and go download the app! (or join the beta, its free, just send me an email).

Version 1.0 ... Live in the App Store!

Guess what? As of today, the 16th of September, 2020, MOMDYN is available for the public on the iOS App Store! Check out that screenshot below, first (and only) result for multibody dynamics, how's that for fulfilling a life goal? 

I'm expecting to go live on the Play store in the next few days as well, then I'll have two buttons like a proper app. You'll see I'm charging $4.99, why? Because I can. The beta will stay free though, a willing tester will always be worth more to me than 5 bucks. If you're interested in joining the beta test, send me an email.

This is a culmination of almost a year of work for me, first while on sabbatical, and more recently in the early morning and late at night when I'm not working my regular job. I'm pretty excited to give it a run out in the wild west of mobile apps. Wish me luck!

What's new in version 0.10?

 Version 0.10 is up on Test Flight for iOS beta testers, and the Android version will be following shortly. This will be the *last* beta version before I release to the public on the App stores! This version contains all the basic features that I want for MOMDYN, and while I expect to keep on improving, I'm excited to finally release it into the wild. A little clip of the most recent version in action below. 

What you'll see in this latest version:

• Rigid Body Cylinder
• Rigid Body Cone
• Tabbed interface update

The cylinder and cone are very similar to the existing Rigid Body Box interface, replacing the two width and height arguments with a single radius argument. I had to do a bit of work to figure out how to make a nice wireframe graphic for these, which you can see some of at this Google Colaboratory notebook. A screenshot of that notebook is below, I used IPywidgets and the interact function to create the slider bars which rotate the cylinder and cone in the plot (note, you have to visit the link to use the interactions).

The new tabbed interface is purely aesthetic, I think putting them at the bottom better aligns with the visual qualities of a lot of modern iOS and Android apps. Also a few subtle changes to color themes, and made the report tabs all fit on a single line.

As I near release, I'll make note that I'm still looking for testers. I'll be doing this myself for the next couple of weeks, tapping my way through all the menus I can think of and seeing what breaks. Would like to have a few more folks to cover my blind spots. Besides that, I'm interested in what the users really want for future releases. I have my own ideas (more bodies and joints, 3-D diagram, ...), but the product really should be community driven. If you're interested, send me an email at mobilemultibodydynamics@gmail.com, and I'll add you to the list, its free, all I ask is you send me good useful feedback.

Spinning T-Handle

Just posted a new video to Youtube showing some of the new features in an upcoming MOMDYN update. Here I show combining a rigid cylinder and box to create a body similar to the T-handle from a famous video taken on the space station. Basically shows if you take a T shaped object and rotate it about its center axis, it is unstable. This is especially apparent in the zero gravity setting.

Video linked below. I'll have the beta app update in the next few days with the new cylinder and cone bodies, and some aesthetic updates (few last kinks to work out). 

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.