paper: WCP/VexPro Gear Calculator

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WCP/VexPro Gear Calculator
by: TheHolyHades1

Shows all compatible gears sold by WCP/VexPro with the same Center-Center spacing, for easier gearbox design.

Compiled using the calculator found on WCP’s website. Please let me know if there are any mistakes.

WCP Vex Gear Calculator.xlsx (16 KB)

Nice work! One thing to note is that the 11 and 13 tooth pinions have the center distance as the 12 and 14 tooth pinions, respectively. This means anywhere a 12 tooth pinon will work, an 11 tooth pinion will also work, and same for the 13/14.

This is a cool calculator. It would be neat to see it integrated with JVN’s design calculator to figure out gear reductions as you plan your drive/mechanisms.

This WCP gear calculator has the same mistake.

Out of curiosity, how exactly do these gears work? How does the PD remain the same with fewer teeth?

Good catch, fixed it now.

The gears are addendum modified, which is where the addendum, and in some cases the dedendum is altered from its nominal dimension. This adjusts the shape of the gear tooth, and can be used to alter pitch diameter, reduce undercut, create stub teeth, etc. Paul Copioli had a few posts this fall, detailing more of whats going there.


I spent a while researching trying to figure that out, and the best explanation I could come up with is that the 11 and 13 T gears extend the involutes of their teeth and modify the addendums of the gear such that they contact the other gear at the same distance a corresponding 12 or 14 T gear would. So, basically, they make the teeth of an 11 or 13 T gear longer and modify the profile of the gear to make sure the gear teeth can still mesh properly. But I don’t claim to really understand it, as there’s really very little information on the internet about gear tooth design.

I’m hoping Paul Copioli can jump in here, I’m also interested to learn what’s “really” going on.

EDIT: Other people beat me. And I thought CD wasn’t supposed to be busy this time of year…

Profile shifting is the term you’re looking for. See here for an explanation of the method, and here for some diagrams and equations. Basically, you cut fewer teeth on a given diameter blank than would ordinarily be expected; the profile shift describes the different tooth shape that is required. (One common reason to do this is to avoid the undercut that is evident on low-tooth-count gears, especially with 14.5° pressure angles.)