Non-circular racks?

[Timothy Moulton]

Hi,

I would like to create an arbitrary profile gear and matching rack to counter some non-linearity that appears in the linkage it is driving. Any thoughts as to how I could do this? It would be awesome if I could input a table or a spline and tooth along the profile. Any help would be greatly appreciated. For that matter, I can't seem to find the rack option at all in Gearotic 2.0. Mind pointing me to the right place?

Thanks

Tim

[ArtF]

Hi Tim:

  There is a button on the non-circular gears page to make  rack. You cannot however make an elliptical or arbitrary shaped
gear that will run on the rack. The racks are proper pressure angled racks, for an elliptical or non circular gear to run on a
rack that rack would be specially deigned with teeth reflective of the quickly varying pressure angle of a non-circular gear..

  It IS possible mathamatically.. Ill add it to my list to investigate the capabiility, I hadnt considered it before really..

Art

[JustinO]

Hi Tim,

Sounds interesting, can you tell us about the linkage?

It sounds like you have the transfer function in one form or another, (splines, a table). Do you have it explicitly?

The relationship of linkages and non circular gears is fascinating.

I've been working on a linkage with very particular kinematics, and have the transfer function I need to drive it, but I haven't yet made the NCGs that will deliver the function from a linear source. I'll need a considerable quantity of solitude and caffeine.

--Justin

[Timothy Moulton]

Thanks Art. I am sure that list is very long. I hadn't really considered this until recently either. Is there a way to make arbitrary shaped rotary gears? I can see the elliptical and logarithmic, but it would be great to be able to input a spline or a CSV file to dictate the shape. I have a laser cutter and love making stuff with the output from Gearotic. Keep up the great work!

Justin, I have an older version of it in SciLab, but a little updating is in order. Currently it is not too complicated. This is for a fun project (gokart steering rack where it really isn't needed) but I am working on it because I have a paying project coming up in the fall that could benefit from this.

It is fascinating to think about. I would love to have it in my arsenal of design variables. I have worked on several concept projects that use straight line linkages, but the speed for the straight line output varies considerably most of the time. This would be a very cool capability to add.

Thanks again.

tim

[ArtF]

Tim:

  Youll find a new button appearing lately thats greyed out labeled "CAD". Thats the module when complete that
will hopefully allow you to draw a gear ( or import a poly to make one) which will make a mating gear to it.
The CAD module will be for changing spoke shapes or drawing pockets and such. It wont be complete for quite
a while as the 3d and 4th axis machining modules are in front of it for development. It will be an interesting
development year for g2 starting this fall. The 3d module to replace the current cnc screen is well underway
this summer, but nothing will be released till September or so..

Thx
Art

[Bloy]

Hi Art,
Heh!  Looking forward to this fall now... and summer isn't near complete.

Soon you will have a complete CAD/CAM package!

Thanks,
John

[ArtF]

John:

  Thats my hope, but theres many good cad packages out there so Id expect mine to
be a bit different. It will focus more on mating shapes, and mechanisms. As I picture
what I want to do its quite a different process than Ive seen in CAD before.
  But we'll see what comes of it, I let the code and requests guide me and to be truthfull
I rarely know the end results look or feel before I get there. If it works for me I release it,
if not I start over with something else, I write a lot of code, and delete much of it. :-)

  In the end Ill be happy if G2 is well received and users find it usefull and fun. So far
Ive been lucky enough to find that works. This group has been nothing but supportive
of my experiments and helpfull with my mistakes. Cant ask for more than that so Ill keep
building. :)

Art