Does anyone know the sizes of the two gears I have circled in this picture: https://drive.google.com/file/d/0B-UMlMKf_f9yMEFQVGthNURtS0k/view?usp=sharing ,and where I can order the two gears?
Not sure what the gear size is. But my closest guess is that it is the 84t gear they mention in the description of the product.
On the VexPro website, it states that there is a total of 84 tooth spacing. For my team, we had a 11 tooth pinion gear on the motor, and this corresponded with a a 72 tooth gear, which we also ordered from the VexPro website. These details and four different gear ratios should be on the VexPro website on the description for the clamping gearbox, and the gears should be on another page. Here is the link to the gears: http://www.vexrobotics.com/vexpro/motion/vexpro-gears/1-2-hex-bore.html
Where did you get this picture from? If I had to take a guess the big gear on the drive shaft looks like an 84 tooth hex gear, assuming that those are 4" omni’s. Also I’m pretty sure that there are 12 teeth on that pinion gear. I would suggest VexPro for gears, you can also buy the omni’s there if you want.
And 84t gear would be larger than 4" omni wheels. That is a 72 tooth gear mating with a 12 tooth gear.
Gear diameter = (teeth + 2)/pitch. Vex gears are 20 pitch, so an 84t gear has a diameter of (84+2)/20 = 86/20 = 4.3" diameter. A 72t gear by comparison is 74/20 = 3.7" diameter.
Here is the link to the clamping gearbox page.
It has a number of options for gears, but by counting teeth and checking material, you should be able to cut it down to specific parts.
The total number of teeth needed on the two gears need to add up to 84. The 11 & 13 tooth pinions (smaller of the two gears) shown on linked site are a special case. They cut on 12 & 14 T diameters respectively. The big gear is either 70 or 72 based on commonly available cim pinion gears.
A 72 t gear on a 4" wheel is a risky proposition. Any trash picked up from the floor will jam the gears. Gears are trash magnets.