Axis experiments and Ball Drop issue

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BillM
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Axis experiments and Ball Drop issue

Post by BillM »

Art:

I decided to use Fusion 360 to create objects for use with Ticker.

I’m creating Ticker projects to understand/test several things:
Creating STLs from Fusion 360. (pretty straight forward)
Creation of Assets from STL’s
Differing apparent definitions of coordinate systems
Creating Switch and Ball-drop assets

Using Fusion 360, I created tapered cones (20mm base tapering to ~9mm with a 4mm hole). Three cones were created: Cone Base on XY plane with axis along +Z; Cone Base on XZ plane with axis along +Y axis; Cone Base on YZ plane with axis along +X axis. I exported these cones as STLs.

Using Ticker Asset Creation I imported the individual files. I got unexpected results for the Cone along the +Z-axis. The cone appeared upside down. I recreated the cone in Fusion 360 with the cone aligned with the -Z-axis. This one did appear as I expected.

During Asset Creation I shifted the cone X-axis and Y-axis to shift their bases to be at zero which then creates shafts that are half buried in the bases of the cones.

I used the same cones to create switches and also ball droppers to experiment with.

I created a project, AxisOrientationBallDropsV01, by importing the cones and also the ball dropper based cones. Each object was created with only Position Lock on. I arranged the cones near the top left to right X-axis, Y-axis, Z-axis. I arranged the ball dropper cones further down on the work area in the same right to left order.

For the ball droppers, I selected a rep rate of 2 seconds, 10mm Objects. Default objects on X-axis dropper, Spheres on Y-Axis dropper, Random objects on Z-axis.

The Experiment:

When I started the simulation I was surprised that all of the objects rotated toward me and placed their respective shafts to be parallel to the XY plane. I’m trying to understand why this happened. I could easily prevent this rotation by simply locking their orientation.

A separate oddity was with the ball croppers. The Y-axis dropper had Sphere selected but dropped cubes instead.

There is another variation of this experiment that discovered a possible bug...but more of that later if I create a simpler scenario to illustrate the problem.

Appreciate the time you are taking both in developing and debugging the Ticker program. Once I understand the program better

Bill

Attached are zip files of the project file as well as the Assets for the cones.
Attachments
Assets-AxisTest.zip
Assets used in the creation of the AxisOrientationBallDropsV01 project.
(407.61 KiB) Downloaded 125 times
AxisOrientationBallDropsV01.zip
Project file to explore Axes, Asset creation, ball drop characteristics
(341.93 KiB) Downloaded 135 times
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ArtF
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Re: Axis experiments and Ball Drop issue

Post by ArtF »

Hi Bill:

I'm in late, let me give you a quick responce before I review your files.

>>I decided to use Fusion 360 to create objects for use with Ticker.

I too use Fusion 360.

>>I’m creating Ticker projects to understand/test several things:
>>Creating STLs from Fusion 360. (pretty straight forward)
>>Creation of Assets from STL’s

Always good to know, and Fusion is very good on STL's, the original Ball dropper
is from fusion.

>>Using Fusion 360, I created tapered cones (20mm base tapering to ~9mm with a 4mm hole). Three cones were created: Cone Base on XY plane >>with axis along +Z; Cone Base on XZ plane with axis along +Y axis; Cone Base on YZ plane with axis along +X axis. I exported these cones as STLs.
>>Using Ticker Asset Creation I imported the individual files. I got unexpected results for the Cone along the +Z-axis. The cone appeared upside >>down. I recreated the cone in Fusion 360 with the cone aligned with the -Z-axis. This one did appear as I expected.

In Ticker, the Z-- axis is the one going toward you, Z++ goes into the screen.

>>During Asset Creation I shifted the cone X-axis and Y-axis to shift their bases to be at zero which then creates shafts that are half buried in the >>bases of the cones.

Yes, the shaft placement is Asset creation is really to set the Z axis to whatever axis it should be as
it could reasonably be created in any orientation by many programs. For objects that typically wouldn't have shafts
you can either select "hide shaft" or just set it tiny so it isn't seen. (You can modify the shafts length overrides for Z--- and Z++ maxes.
All shafts are created as Z axis objects for ticker. The orientation stage of import is for that exact reason, to make sure Z is proper aligned.

>>I used the same cones to create switches and also ball droppers to experiment with.

>>The Experiment:
>>When I started the simulation I was surprised that all of the objects rotated toward me and placed their respective shafts to be parallel to the XY >>plane. I’m trying to understand why this happened. I could easily prevent this rotation by simply locking their orientation.

Ill check the file, but its possibly a force reaction to the ball being ejected ( or cube. ). There is a checkbox for droppers and switches called "UnMovable" which should be used unless the dropper or switch is on a shaft connected to another mass, in which case normal physics should
be in effect. Ill let you know what I think when I review the files. If no using unmovable, the droppers and switches are basically pivoting on
a point in space, any force may cause them to pivot around in space.

>>A separate oddity was with the ball croppers. The Y-axis dropper had Sphere selected but dropped cubes instead.

Known bug, I just haven't fixed it yet, the Sphere checkbox should read Cube, balls are used by default.

>>There is another variation of this experiment that discovered a possible bug...but more of that later if I create a simpler scenario to illustrate the >>problem.

No problem, let me know as you see apparent bugs, I am building a list for the next recoding.

>>Appreciate the time you are taking both in developing and debugging the Ticker program. Once I understand the program better

In truth it is an educational experience for me, I had never written this type of code, and the bullet physics library is notoriously hard
to figure out the esoterics of its insides as documentation is sparse, the challenge has been fascinating. Writing my own constraints has forced me to learn more about physics and matrix operation than I figured I could. When you get old enough, the whole thing is about the challenge. :)

Art
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Re: Axis experiments and Ball Drop issue

Post by ArtF »

Hi Bill:

I have tested the first axis file. Does look strange doesn't it? When you look deeper though, it starts to make sense.
If you turn on the "Forces" display to see the following it starts to be clear and makes more physical sense.

Look at the first cone only. Look at the shaft with "forces" display on as the simulation starts. You'll see a small blue line
pulling downward, this is the gravity force. If the center of the shaft was at the center of the cone, it wouldn't move, but
when shafts are created their is no guarantee that the shaft's center will be on plane with the cones center. They rarely are
in fact, so in this case the shafts center is slightly outward from the cones center ( towards the viewer) so the gravity pulling down on the shafts
center is about 2mm toward you in the case of the first cone. You will see this as the gravity force (blue line) is not centered at the
cones center. The cone, for its part being locked to IT'S center as a pivot,
see's there is a downward force about 2mm to the front of its center from the shaft, so it tips over. The shafts offset is
then vertical in the axis of gravity. About what would happen if masses of the two are centered on the shaft at cone center.
It is the offset from shaft center to cone center in this case that makes it tip. This isn't necessarily a problem, other than
one must use orientation or "unmovable" in this case. If the shaft was extended to a "thing"..gear, worktop, other asset
and that item has mass, the cone would simply sit connected to the whole.

You can test this by moving the shaft inwards a bit and trying to make it balanced in length on the plane of the cones center
with an even amount hanging on either side (in Z).... So basically, the cone is correct on its pivot, and the shaft is simply tipping it over
so the longest part of the shaft from center is facing downwards.. Delete the shaft and the cone stops tipping. Lower the mass of the shaft
and the tipping is slower or only partially till the cones mass equalizes the gravitic force difference.

(Hurts the head , doesnt it.. :) )

Art
BillM
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Re: Axis experiments and Ball Drop issue

Post by BillM »

Art

Thanks for the mind bending explanation. I think I'll recreate the assets and let the system calculate the shaft position as it normally would at the center of gravity. The tapered cones has allowed me to verify the consistency of coordinate systems between Fusion 360 and Ticker.

In order to recreate my Denison double three-legged gravity I'll have to play around with pivot points and center of mass.

I've studying your intro videos again for details I probably missed the first few times I looked at them.

Bill
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ArtF
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Re: Axis experiments and Ball Drop issue

Post by ArtF »

Bill:

Yes, the video's, though over an hour of me droning on, skip a fair bit of theory..
Ask anytime if confused.

Art
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