Algodoo

Suggestion -- Zoom OUT just before you save your scene on your computer. That way, a good thumbnail picture of your scene will show on Algobox. You did not do that for this scene before saving it, and that's why the thumbnail picture looks blank! The last displayed image that you see on your computer before saving the file is the same image that will show on Algobox when your scene is being displayed.

You did it right this time for the updated file. Good job!