Tumbling Acrobat – Working out the Movement

Thu, 19 Jul 2012

After spending a day cutting and sticking without much success I've decided to take a step back and try to work out the geometry of this classic tumbling toy.
I've been sent various YouTube links by helpful friends of the website so I've been poring over various online videos. I screen grabbed shots of this  YouTube video by Ian B Dunne and looped it to more easily see what is going on. 


I've then taken the individual frames and dropped them into Illustrator.

In essence, the tumbler has three parts. the body with the sliding weight, the arms and the legs. I traced the three parts and experimented with different stills from the YouTube video to work out where the joints should be. 

I've animated the frames together and included the coin weight to show its motion. You can see it rolling back and forth with the body tube.

There is one point in the motion that might be a problem. When the body reaches the point shown in the still, the arms need to swing over the body to the other side ready for the hands to touch the floor. Gravity won't do the job. Inertia might but failing that I'm hoping that a strip of paper where the purple dotted line is will pull the arms over as the body drops down. Time will tell.

By checking the geometry of the parts in the animation I can see the range of motion that the arms and legs need. When I put the second prototype together I'll use these angles in the hopes that the model will work straight from the drawing board. Hah.

In the tumbling boy automata, who stars in a few YouTube videos, there is a strange 'tail' fixed behind the legs. Rather that using that design I'm going to be using a really big foot. 

Tomorrow – back to card.

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Comments (6)

  • Shelley Noble July 20, 2012 at 4:04 am

    See—THIS is why I LOVE THIS

    See—THIS is why I LOVE THIS BLOG, Rob!! It is fantastic to get a peek inside the workings of your design/engineering process! Way to go!!! Can't wait for this model too.

  • kalpesh July 20, 2012 at 12:37 pm

    it’s great!!! best wishes for

    it's great!!! best wishes for the work…

    looking forward for it…

  • chris.aaslid October 5, 2012 at 3:13 am

    Came across this, and

    Came across this, and couldn't help but think of you. Gakken (a Japanese company) seems to have just recently re-released this toy. There's a video showing how it works on the make magazine store website:


  • cool022883 March 13, 2013 at 10:19 pm

    i was on the US version of

    i was on the US version of amazon.com and found a book called krazy karakuri by andrew dewar


    and along with several other models it says it has models that tumble.i ordered the book today so when it comes i will see if it might have any useful information for the completion of this project

    • umehta January 15, 2015 at 2:18 am

      So Cool, what did you

      So Cool, what did you discover in this book: Krazy Karakuri?

      • cool022883 January 17, 2015 at 1:25 am

        nothing that will help with

        nothing that will help with this model its mostly ramp walkers the tumblers are just like weighted toys that when you make them flip in the air they land on there feet so its nothing like the tumbling effect rob was going for with this model

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