In my Intro to Design class we learned all about gears. It was a while back, but I remember that gear ratios, speed, and torque are all directly related to the diameter of the gear, what kind of teeth it has on it, and how many teeth are on it. If you do a YouTube search on any of those things you’ll find all kinds of stuff. I would tell you here but it’s a lot lol. Plus a video with diagrams and pictures would be much more helpful to you.
gears are very interesting, but also quite complicated, for me anyway. If you really want to know more about gears, the link below is a good place to start. You can also request information from them that will certainly help you. It is not a subject that you can explain briefly.
Well, gears are very intriguing parts of machines but involve strenuous calculations when being designed. Moreover, these calculations vary depending on the type of gear set (a gear and its corresponding pinion). For instance, one may calculate for circular pitch using Pç=πd/N for spur gears while Pñ =P/cos§ goes for norminal diametral pitch for helical gears. I've made a simple involute spur gear design (although on Solidworks 2017), you may want to access it here
what are you trying to do with your gears? there are many different kinds and variations depending on the intended use. For example, if all you are trying to do is increase/reduce speed between the driver and driven shafts you may be able to get away with simple spur gears, but if you are trying to drive a heavy load at high speeds (as in a vehicle) you might want to go with ring & pinion helical bevel gears.
You need to be clear about what type of gear you need, the standard and the use that you are going to give it, then you look for which is the most suitable for you, personally I design very small mechanisms and used the NIHS standard for Siusa watchmaking and I draw them since Inventor doesn't have these very small standards