Sketchy physics - rotating a crank

I’m having problems with rotating a crank in sketchy physics. Any help?

  1. I draw a 3D Circle, a crank and create a group
  2. Adding the “motor” on the axe
  3. play = Ok
  4. Add to columns to support the crank (with a hole where the crank pass through)
  5. play (a small movement and nothing)
  6. I Add a “Hinge” to the columns (join between Column1 + Hinge1 and Column2 + Hinge2)
  7. not working :frowning:
    It could be nice also to have a good tutorial.

here after the picture of the SU project

and a example of a classical whirligig whale

Thank you

Hi there,

From your illustration, it seems like the hinge is off center. (to the rotating axis).
-Which will hinder the rotation.
The hinge is added to the columns, but they are apparently not lined up to fit the line/center of rotation. (sorry for my English…)

But it would be much better for the problem solving if you could upload your model. Thanks

As for tutorials here is one:

(I have some more somewhere… see where this gets you first :slight_smile: )

Hi Piiil60,

thanks for your help, I found also a very interesting tutorial here:,d.bGg

I found two things to help me in the resolution of my issues:

  1. “drill” a hole in a 3D object is not “understood” as an empty space by SP.
    To create a hole, we must group objects in order to design the hole.

  2. by using the “Debug” option, I realized that the crank is not viewed by SP as a wire but as a cube (an envelope all around the crank). So I resolved my problem by setting the state of the columns to “ignore”.
    Now the crank and the circle move freely.

I will continue with the rest of the project and of course, I will keep you inform!

Best rgds,

Thanks Phil.
Looking forward to see your project.

There are models with SP at the 3D Warehouse too.

Lots to study there.
Good hunt to you!


I designed a quick rough version (just to be sure that the model works fine)

Now, I’m ready to work on a whirligig model


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Thanks for sharing :slight_smile:

Been kind of busy here in this heatwave, but/and would like to try your model.
Maybe you could upload the file here for everybody?Thanks.
(instead of signing up for Dropbox…)
Wish I had more time for all this fun stuff!


I worked all the day on the project and no way to design a real case!

what I learned today:

  • if the model is too small, there is no physical interaction (may be due to tiny numbers in the formulas); so I multiply the size of the whirligig by 100
  • if you want to attach 2 joints to the same 3D object,
    • joint 1 + Group 3D Object
    • joint 1 + Define parent
    • Explore the new 3D object group, clik on the 3D object to isolate it
    • joint 2 + Group 3D Object inside the first group
    • joint 2 + Define parent

Sorry but I don’t know how to attach a file directly in the forum, so I used Drop Box again

That is a charming whirligig!
Well you can upload here:

-or drag and drop.

Several years since I tried SP so I don’t remember much…
It was lots of work to learn. That I remember :slight_smile:
Maybe this model to study is close to your project?

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I finally solved my problems with the whirligig.
What I learned today (stay positive :slight_smile: )

  • It’s very important to set the joint very precisely (an offset can have a huge impact)
  • when nothing works, set a name to the joints, you can play manually the animation … and keep calm :slight_smile:
  • Check examples on the warehouse … if you don’t find exaclty your solution, at least you will see people doing things really more complex that what you are trying to achieve

It could be nice to have a dedicated forum for SP; there are so many things that we can do (… and so little documentation :()
I hope that a new 64 bits will come soon (now I have to work with SU 8 with SP and SU 2015 for my other projects) - No way to install on the same computer SU 2015 32 and 64 bits


Here after the whale in SU (748.8 KB)

Preview of my new projects in progress …

Thanks for model.
-I did find out how to download from Dropbox though ( Dooh, didn’t have to sign up)

So I ended up spending time on SP in my weekend too… :wink:
-and learned something too, I think…

Your solution to transferring the red/blue plane rotation to the green/blue plane is quite interesting and innovative.
Well, I wish I had more time right now, but must go to work today.

Your new projects, do the wheels spin too? :wink:

About other forums:
maybe you have been here: SketchyPhysics • sketchUcation • 1
or here: SketchyPhysicsWiki | Fandom



I agree