Question about partial gears or missing teeth.

[GeneJ]

Hello everyone,  I am new to Gearotic and to the forum.  I am extremely glad to have found this tool as I have been struggling to visualize the gear trains in motion prior to cutting them and "see what happens".  I have searched the archive and I am not finding the information I am looking for.  I will describe the mechanism I am trying to design and maybe someone can help me with using Gearotic to create a simulation of it.

Specifically, I am trying to make a wooden gear train to put into an over-sized pocket knife to make the blade swing open then back to the closed position.  If you ever saw one of the swiss army knife counter top displays that has blades opening and closing...that is what I am trying to accomplish, but with only one blade.

I am using a 1 RPM AC gear motor to drive the mechanism.  I drew this up with a main gear that rotates the blade though its arc.  The rotation is stopped because the gear attached to the blade only has teeth on part of the gear.  once the blade stops rotating the main drive gear then engages an idler gear that is partially toothed as well.  The idler engages the gear attached to the blade and it rotates back to the original position.  I will go to the shop later today and I can make a quick video of the one I have made if anyone needs a visual.

My question relates to using Gearotic to draw the mechanism.  I cant see how I could remove teeth from a gear so I can simulate exactly what I have made.  The design I have works but it could be improved if I could use gearotic to simulate it rather than making 100 iterations in the shop.

I know there are many "non-gear" linkages to accomplish what I want but this is just what I came up with and now I want to tweek it.  Thant you for reading and I look forward to tapping into the knowledge base here. 
Gene

[ArtF]

Hi Gene:

  At the moment there is no way to remove some of the teeth form a gear. ( You'd have to use a cad program to do that.). I do
plan to add routines to allow for such things, but it will be awhile before we can do that. The simulator cant handle other than full toothed gears
but in cad if you draw a circle centered on the shaft center of root diameter, you'll find you can just erase the teeth you want gone
when they go outside that root circle. 
You wont be able to simulate it, but at least the gear will be drawn properly. This isnt the first request for gears that can reverse
and such from teeth that mesh at different radius's and change direction, so it is on my list of things to add, but without some
sort of CAD module that is somewhat aware of the physics its a hard thing to implement.. :)

Art

[GeneJ]

Art, Thank you for the reply.  I was afraid that would be the answer.  Even though the program cannot help me with that design I have several others that do not include reciprocal motion and I look forward to learning to use Gearotic in their design.
Gene

[ArtF]

Gene:

  Im usually around if you find you need help or advice. Youll find we respond pretty quick
most of the time.Ive often looked at the issues with making gears such as you describe, the complexity is pretty
large to do them in the way I do things like escapements where I can ensure a mechanism works in a specific
way. I do have a game plan for allowing users to get more involved in the way a mechanism works, but it will
take awhile to get there.
   

Art

[GeneJ]

I can see how the partial gears can cause problems with the parameters that govern the simulation.  I have drawn the revised version of what I was trying to do and I can see why they are not used often.  The contact points on the last two teeth that mesh right when they loose contact have to experience tremendous pressure without the other teeth to share the load.  The way I have it drawn also leaves an instant at the end of the up and down arc where the motor gear is not engaged on either of the other two gears.  It seems this opens the door for unintended movement of the articulating blade if its center of gravity is not close enough to the center of rotation. 

I have done all I can on paper.  it is time to mock it up and see what happens.  Thanks again for the quick reply.

[ArtF]

Gene:

  That is one problem , the mesh point.. its easier I think if the pitch diameter changes, so a large pitch diameter takes it in one direction,
and a much smaller diameter with larger teeth meshes to reverse it. Ive seen examples and will probably try to implement it that way when
I get there.

  Post a photo if you build your device, Id love to see it...

Art

[Stephen Fornelius]

I think this would be easier overall if you just put a crank on the blade like a windshield wiper works.  Then the circular motion would go one way and then the other without any complicated gearing.