To the OP:

For the gears, there are just some basic things you need to know, all of which can be find on suppliers’ websites:

- the pressure angle
- diametric pitch (DP) (these 2 need to match)
- outside diameter
- pitch diameter
- face width
- number of teeth
- bore size and key

The pressure angle is the angle between the contact plane of the teeth and the line out from the center of the gear to the point of contact. The diametric pitch is the number of teeth per inch of the gear’s pitch diameter, which tells you (with circumference calculations) the distance between teeth. All you need to do is make sure these match and are suitable for your application. For FIRST purposes, 20 DP and 14.5º pressure angle is just fine.

The outside diameter and face width will just tell you how much clearance you need for your gear.

The pitch diameter is the diameter at which the teeth interact. If one gear has a pitch diameter of 1" and therefore a pitch radius of .5", while the other has a pitch diameter of 3" and therefore a pitch radius of 1.5", their centers must be 2" apart. That should be pretty straightforward once you know how it works. Just for fun, if these gears are 20 DP, then the first one has 20 teeth and the second has 60.

The number of teeth then tells you the gear ratio. In the above example, 20:60 simplifies to 1:3. So your gear ratio is 3, 3:1, 1:3 however you want to say. You just need to keep straight which way it goes. The bigger gear always turns slower but carries more torque. Conversely, the smaller gear turns faster but carries less torque. The gear ratio is exactly the ratio between these speeds and torques (ignoring inefficiencies).

Finally, the bore size and key type are important for making sure you have the shafts you need. You can always make the bore bigger, but it’s awfully hard to make it smaller. The key can be an ANSI keyway or hex key, both of which you can do yourself with a broach (don’t actually know much about that).

As for finding/making the gears. Aside from Andymark’s (somewhat limited) selection, you can find a lot of stuff at McMaster Carr, Grainger, and Martin Sprocket, if you look in their catalogs, which provide all of the above information. As for making them yourself, you’ll have to ask someone else. You can probably find information about the tooth profile in aforementioned machine design textbooks. I know 148 did some cool stuff with sheet metal, and there are probably other ways to do it too (wire EDM, others?). And who knows how pricey.

Well that was kind of long…