# Ghost construction for the second circle tangent during animation

Professor McCarthy shared this question 2 years ago

A construction using one of two tangents to a circle is duplicated for the other tangent and appears as a flickering ghost during animation. How can this be avoided?

I think its a bug.

Maybe this workaround help (and is robust)

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Sorry, have not seen the english tag. See advanced settings:

Continuity: if Continuity is On, GeoGebra tries to set new calculated points near the original ones

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Thank you. It works correctly now.

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The problem has returned even with Continuity On

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The screen recording would not load so here is the .ggb file

I would appreciate any ideas

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I think its a bug.

Maybe this workaround help (and is robust)

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Thank you very much. I will give this a try.

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Hi,

I rebuilt your mechanism by adding other sliders, as you can check. I’ve attached the corresponding file. I also think that the problem of the phantom geometric location certainly comes from the way you build your animation.

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Thank you very much for doing this. The dimensions are set by the patent drawing, not by my choice. I measured the perpendicular distance from the crank pivot to the slot and then used a circle of this radius on the moving point and its tangent that passes through the pin to construct the moving slot. As far as I can tell, the particular dimensions of the slot on the right causes this construction to have a singularity that results in the ghost construction. There may be another better construction.

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You may enjoy seeing the patent that I am using for this GeoGebra construction. A pdf of the patent is attached, but you can also see it at the URL https://patents.google.com/...

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I do not know how the construction is done but I think that R works fine and A_1 not. Is A_1 done in the same way, same steps that R?

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Thank you for taking the time to look at this. The construction is the same for both, I select one of two tangents to a circle come to define the line that defines the blue links. However, on the A1 side I believe the two tangents come together at the point where the ghost appears. The dimensions come from the patent drawing I am animating, but I might be able to change the dimensions to avoid this singularity. I will give it a try. Thank you.

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It seems a bug. The att'd worksheet shows the correct behaviour of locus1 when angle has a limited range. Cheers

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It seems a bug. The att'd worksheet shows the correct behaviour of locus1 when angle has a limited range, i.e. [-120degs,+120degs]. Cheers

P.S: forum platform refused my ggb upload

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Tried again

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Thank you for reproducing the error. I believe you show that over a range of input values the construction is stable and over another range it is unstable. I can say that the work-around was successful.

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I have studied your Geogebra applet and I realize that your construction is very unstable in that it is built on very free points (E, D, F) and that is why you have an unstable geometric location calculation.

Look at how I built “Baby Crawler w1” and I appended to my remarks one day ago.

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I am grateful for your attention. I reviewed your .ggb file carefully. Please notice the differences between your solution and what is needed to match the patent drawing. 1. your crank length is longer, and 2. the locations of the slots in the two coupler links are different from the patent. I understand that the construction is unstable, I am just not sure how to revise the construction without changing the design.

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Kind attention to user Seror.

Please be noticed that your "Baby_Crawler" sheet shows a different solution of the proposed one: two loci instead of one, as per attachment.

In principle Geogebra should solve any construction without drawbacks. Cheers

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You may enjoy the patent that shows the device I am trying to animate in Geogebra. It is US Patent 1,146,700 Animated Toy to A. Gund (1914). Here is the URL: https://patents.google.com/...

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I also recommend Tchebychef's work on the mechanisms:

y

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Thank you very much for these links. I am working my way to the chebyshev plantigrade machine, and beyond to the Klann and Jensen walkers. So I expect to have more questions.

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Amended my previous sheet, in compliance with above rami's drifts and by using one leg only, as per attachments. Cheers

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Nicely done. As I work on more increasingly complex walkers, I may have more questions. I am grateful for the help.

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I would like to share with you the outcome of my efforts. And again thank you for your help. You can see the animations I generated using Geogebra at my website mechanicaldesign101.com

The also appear in the Kindle Interactive book Kinematic Synthesis of Mechanisms that is available on Amazon.com.

Thanks again.

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Why don't you try embedding the applet as an iframe?

https://mechanicaldesign101...