Gears not meshing correctly

elizabeth_giovanardi

This is more of a mechanics question than a CAD question I would assume, but I'm hoping someone out there can help. I did a project last year with my CAD students where they had to design, assemble, and animate a gear train. This required discussing center-to-center distances, pitch, etc. One student created the gear train shown here; all gears have the same diametral pitch and the center distances are also correct, but we cannot get the yellow gear to align properly with the black gear. Like I said earlier, I suspect this is an issue with gear properties and not a CAD issue. This happened with another student as well who tried to make a 'loop' or 'chain' of gears. Please let me know how to prevent this problem in the future; my students got frustrated. Thanks for any help or suggestions!https://cad.onshape.com/documents/c2d2c44336c91d0d97e953ce/w/6bf83d6cc9f1343a02006936/e/dad2357144311e03be347210?renderMode=0&uiState=627bbdf4411a9867bab3cd76

This was inspired by the lesson posted in the edu forum posted here by Domenico_D:  https://forum.onshape.com/profile/Domenico_D

ChuckKey

Deleted.

antlu65

Do you have any requirements or restrictions for the gear train, other than having the gear teeth mesh properly? Try this modified gear train linked here: I adjusted the tooth count on the largest (black) gear until it meshed with the purple and yellow gears - trial and error on my part. (I have z=65 and alignment angle = 83.75 degrees with respect to the purple gear, using this custom feature - which I think would work well for your scenario).

elizabeth_giovanardi

Thanks for the response. The students had to use the Spur Gear Feature Script to create spur gears with 20 DP. They had to calculate the center-to-center distance, use mates, etc. I see that your gear train now works. Do you (or anyone else) know why that gear size works, but not the ones my students used? Basically is there a way to figure this out without relying on trial and error since I'm trying to teach them about gear properties while also teaching how to use feature scripts and assemblies. Thanks!

antlu65

Off the top of my head, I don't know how to calculate the number of teeth needed to have a gear mesh with other gears in a 'loop' configuration like your students are creating. Could possibly derive an expression, but I think it would be outside the scope of your lessons.

If your students get stuck trying to find gears that fit into these 'loops', you might suggest that they set some of the problematic gears to have the same (or nearly the same) number of teeth - introducing symmetry can help simplify the problem. Heuristically, it seems like it would be easier to find a gear that fits the blue and grey gears (or the red and purple gears). While it would be more difficult to find a gear that fits your black and blue gears. Sorry, that's all I've got.

elizabeth_giovanardi

I understand what you're saying. Thanks for the help! I guess I'll have them keep it symmetric rather than guess-and-check.