GEAR MATES

[denisvan]

WOULD SOMEONE PLEEZ OUTLINE THE STEPS TO APPLY GEAR MATES. NONE OF THE BOOKS THAT I HAVE EXPLAIN HOW TO APPLY THEM, THEY EXPLAIN WHAT THEY ARE BUT NOT HOW TO APPLY AND THE PROMPTS ARE NOT DESCRIPTIVE ENUFF FOR ME. COULD YOU PLEASE LIST THE STEPS TO MATE 2 GEARS TOGETHER (GEARTEETH) SO THAT YOU CAN ROTATE ONE AND THE OTHER TURNS. I CAN'T FIND THIS INFO ANYWHERE AND "HELP" DOESN'T HELP. AS USUAL IT IS TOO VAGUE.

 

[jimshaw]

Denisvan,


I agree, it is not very intuitive, but it has a lot to do with what other constraints you have in the assembly as well. First, you must locate the gears so they can rotate but not translate. An easy way to do this is to locate them on existing shafts with concentric mates (or datum axis with coincident mates). Lastly, locate it along the shaft, for example using a coincident face mate.


Next, select a circular face from each gear part - for example, either the outer diameter or the root diameter:


View attachment 5855


SW will automatically insert the gear ratio based on the diameter of the surface you selected, but you can enter the gear ratio as needed.


Now, drag one of the gears around, and it should move the other correspondingly.


Here I have a simple setup, showing the highlighted faces used for the mate, and the gear ratio (which was auto calculated, since I modeled no teeth). In this case the gears are tangent to each other (as a result of their location) but they do not have to be (like when modelingbelt pulleys):


View attachment 5856


Let us know how this works for you,


Jim
http://www.linkedin.com/in/shawengineering
Edited by: jimshaw

 

[denisvan]

Thank you, that did help. I was selecting the shaft dia. that the gear was on when I should have been selecting the O.D. of the gear itself. When I tried rotating the gears I got some weird reactions. I figured out that the gear centers needed to be constrained to keep them from flopping around. When you do a motion study do you have to select all the gears that are mating as well as the one that is designated with the motor or will they spin by virtue of the gear mates?

 

[jimshaw]

denisvan,


Just assign a motor to the circumference of the driving gear, and the driven gear will automatically rotate with it as a result of the gear mate. If other gears are keyed (i.e. fully constrained) onto the the same shaft as the driven gear they will rotate as well. They may also drive subsequent gears if those are gear mated to more gears in your gear train.


Just like in real life, the shafts should be underconstrained (to allow rotation) but the gears should be keyed to the shaft - this can be done literally if you have modeled the keyway/keys, or implicitly using datum features.


Just think about the costraints in real life, and mimic that in your CAD. This method SHOULD be used for all CAD assemblies, and MUST be used for Rigid Body Dynamics (aka SW's "motion analysis").


Make sense?


Jim


http://www.linkedin.com/in/shawengineering

 

[denisvan]

Absolutely! I tried the motion study after I sent the post and found it to be as you said. I applied gear mates to the entire geartrain, then spun the driver gear manually and the entire geartrain spun, but not when I applied the motor to it, but when I selected the drive gear for the motion study, I selected the face of the gear. I will now try it again and apply the motor to the O.D.(circumference) of the gear.
One thing that surprised me was that the gear teeth did not stay in perfect mesh when the gears were spinning, I expected them to stay in mesh, they are meshed as they should be when viewing the geartrain static.

 

[jimshaw]

If your gears start in mesh but don't end in mesh, then your gear ratio does not match your CAD model. Double check your numbers.


Jim