Gear Generator

[pfleming]

I like the simplicity and intuitiveness of Fusion as it makes it very easy to use for those of us without a whole lot of previous CAD experience. I’m now crossing over from conventional subtractive machining to 3D printing and would like to see mechanical parts and surface finishing techniques available that can be directly accessed via menu (ie on on the Mac version of Fusion too) and not require scripts. I will enter a few suggestions separately for vote.

At the moment the only mechanical feature available in the create menu is “threads”. I would like to suggest a gear generator that can generate correctly modelled mechanical gears. Given that 3D printing isn’t limited by conventional gear manufacturing techniques, apart from simple spur gears I would like to see more complex gears available such as double herringbone, helical, worm, bevel (of various types), and racks. I would like both metric and imperial gears available and the menu to default to standard gear values with basic parameters eg Pressure Angle = 20 degrees, DP = 16, tooth N = 32 will produce a standard involute spur gear, however also have the option of changing some additional parameters to modify the gear geometry when that is required.

Gears follow relatively simple mathematical rules and I think this should be relatively straight forward to code and implement.

Thanks

[roambotics_scott]

There is a «spur gear» script but I totally agree and want something that works like threading (though ideally with a third option that isn't modeled but looks it).

Not so trivial but I'd really love to have something like this that can cover non-circular gears, spirals, bevels, herringbones, and harmonic drives would be particularly awesome.

[pfleming]

I don't believe the spur gear script works with Macs. 

[roambotics_scott]

For some reason there are two in mine.. only the first one works for me but it definitely works (Ultimate build 2.0.1462).

[pfleming]

Ok cool, that seems to be working now, thanks! I guess it's a start, but it's very basic and the presentation isn't something I've ever encountered before. For some bizarre reason, with Fusion in metric, the DP and gear thickness are in cm. Not being a dress maker it's something I'm not used to seeing 😉

I don't know if it's possible to further develop this so that both imperial and metric gears are available in standard gear nomenclature?

[roambotics_scott]

Yeah it's definitely not very usable in the current state. 

There was a demo about a year ago (https://www.youtube.com/watch?v=eKdTTE4j8so) that looked much more promising but I'm not sure what ever happened to it.

[HughesTooling]

If you work in mm I've figured out to get gears using module divide the module by 25.4 then divide by 2.54. So if you want a 1.25 module gear with 10 teeth it's (25.4/1.25)/2.54 = 8. The gear generated will have an OD of 15mm and the pitch diameter will be 1.25x10.

Mark.

[charegb]

Hi,

We have a lot of this tech in house with Design Acclerators for Inventor. 

http://knowledge.autodesk.com/support/inventor-products/learn-explore/caas/CloudHelp/cloudhelp/2014/...

We have the same team (see Vasek's video linked by scott above. Vasek leads this team) working on Fusion now and we definetly plan to do this. Its just a matter of time and priority now. We are working on Simulation first and then we will work on this next.

Thanks,

Bankim

[madengineer13]

A robust gear generator would be fantastic.   I would also need bevel, helical, and worm gears at a minimum.  it would also be great if it did rack and pinion, hypoid,  and bevel gear sets other than 90 degrees.  

[roambotics_scott]

I'd really love to see the more complex stuff like herringbone and maybe even strain wave gearing (though that would take a bit of flexible / soft body physics)

[Bruce]

id like some gear simulation added too..

[HughesTooling]

You can simulate gear motion using a Motion Link and setting a ratio. Here's an example of what's possible.

 https://screencast.autodesk.com/Embed/Timeline/346fe87e-1603-4819-8339-20b1e04d845d

Mark

[roambotics_scott]

That's cute for making a movie but a rigid body simulation would be way better (and could actually help dial in the tooth parameters and even motor size and gearing ratio)

[HughesTooling]

I'm not sure how you'd make a joint/constraint work for a gear, even on gear with few teeth there's a minimum of 2 points of contact and on gears with a lot of teeth even more. The gears in this picture have 6 points of contact and that varies as they rotate.

Mark

[roambotics_scott]

Simple - constrained multi-body dynamics simulation with collision detection.

Make each gear a rigid body (with fixed joints or moving about a rigid / fixed shaft). Drive one, detect the collisions between the teeth, compute the contact forces, and integrate forward in time (with Verlet or whatever your favorite method happens to be).

Game engines do it all the time and if you put in tolerances (easily modeled with a sigmoidal step function or infinite potential with exponential fall-off, Lennard-Jones, or whatever you like) and mass distributions, you can find the moment of inertia tensor for each body and accurately model the dynamics. 

You have to worry about numerical stability and physical realism but they're solved problems. People regularly do molecular dynamics simulations with much more complicated constraint networks and force fields with tens of thousands of bodies. Modeling a handful of bodies is childs play in contrast and could be done in real time on a single core with the right software.

[HughesTooling]

 OK thanks, I understood most of that.

Now how about some fun.

[phazaar]

It still shocks me that these (this and similar things like screws and bolts) aren't some of the first features to hit CAD software in era of the 3D printer. Yes, it's great to be able to 'pretend' a joint is a particular fixing or that two cylinders with a animation ratio are actually gears operating on one another, but that helps hobbiest, prototypers, and businesses relying on 3D printing alone a grand total of 0. 

Would love to see this implemented, and fast.

[roambotics_scott]

I definitely get that the dev team is busy but it does seem like no small oversight that this isn't in the stable branch especially given that I saw a demo of spur gear design that was integrated into the app (/ not a script or plugin) well over a year ago.

The annoying thing is that getting good teeth isn't that hard with the right mathematical tools, but in the absence of that, you've gotta go through some gymnastics to try to manage it.

Simulation is a trickier thing but the rigid body dynamics really isn't that hard. I definitely agree though - linking two rotations and manually specifying the gear ratio makes for nice animations but doesn't feel remotely satisfying.

Scripting doesn't really cover this well at all but it'd be really great to be able to setup the gears, get further along in the design process, and then adjust the gear ratio (ideally linking the gears in contact). Actually - if that were built in then there'd be no need to do the rigid or soft body dynamics (at least for the first pass) - the user just sets up the two (or N) gears that are in contact and they're automatically constrained to mesh with eachother. That seems totally doable and would make a nice summer intern project.

[HughesTooling]

Here's a link to the demo gear design plugin, seems odd to demo it on youtube then not release it. Noticed in the demo it is using diametric pitch, would need an option for modual as well.

https://youtu.be/eKdTTE4j8so

[robertbaruch]

I'm was bit confused about the gear generator script (SpurGear). You see, the formula for diametral pitch is:

Diametral pitch = (Number of teeth) / (diameter of pitch circle).

You can see that the diametral pitch has units of inverse length (actually, it's teeth per unit length of diameter). The script, however, seems to be asking for a length, so I'm not quite sure what it's really asking for.

Suppose I want a gear with 24 teeth and a pitch diameter of 10 cm. That's a diametral pitch of 2.4 teeth per cm. So if I enter 2.4 cm into the diametral pitch box, and 24 teeth, I end up with a gear that's 10.8 cm across, which seems about right.

Now if I enter, instead, 2.4 mm for diametral pitch (thinking that I really wanted 2.4 teeth PER mm), I end up with a gear that's 10 times as large. NO! So whatever I wanted, I'd have to enter something that's clearly not the diametral pitch into the diametral pitch box. And that's not really a good thing.

I modified the script so that it asks for circular pitch instead, which is in units of length per tooth. Circular pitch is the pitch circumference divided by the number of teeth. The script then calculates diametral pitch ( = pi / diametral pitch), and now the script works as expected. Zip of the script attached. Unzip into your install's API/Scripts directory.

BetterSpurGear.zip