I was looking at building a differential swerve module, but noticed that the gears from WCP and other stores all cost from $10-25 per gear. For the gears I would need it would cost around $175. However, if I buy the gears from aliexpress, ebay, amazon, and some other sites, I can get the price down to about $70. This is a substantial decrease and they are all made from the same material and gears are something that are easily checkable for flaws so I am wondering if it is OK to save money and order from China, or if there are quality issues?
Are those valid vendors in reference to section 8.1?
Consider, for example, this:
C. must be able to ship any general (i.e., non-FIRST unique) product within five
business days of receiving a valid purchase request. It is recognized that certain
unusual circumstances (such as 1,000 FIRST Teams all ordering the same part at
once from the same VENDOR) may cause atypical delays in shipping due to
backorders for even the largest VENDORS. Such delays due to higher-than-normal
order rates are excused.
When you buy from WCP and other stores you are buying from people who stand behind their products. They also will try to keep them in stock. They may run out but they at least try. When you buy straight from China you do not know the specification for hardness and quality that the gears are made. You also may have to wait until the next production batch are made to get your order or replacements later.
Having said all of this you can buy a set and if they work they are good and you then buy more. Just plan ahead so you have time to switch if needed. If they do not work you only lost 70$.
There are good Chinese manufacturers and there are bad Chinese manufacturers. Most of VEX’s products are made in China and are of great quality.
Use your judgement. I’ve had good luck with a lot of Chinese industrial bits. Often times domestic industrial stuff are just repackaged Chinese products anyway.
+1 this is also the same for other part resellers. Some products from companies such as WCP, CRP, and Andy mark come directly from China. Gears are no exception. The biggest secret of VEX is where they buy from 
maybe you could ask the Chinese company how they were manufactured. If you were just using this for off-season development I would go for the cheaper option because it’s not during a competitive season. Test in the off-season and if they hold up well you might as well use them during the actual season.
Andymark does all of their stuff, or at least the great majority, in USA IIRC.
Buying gears off Aliexpress and stuff is rather sketchy because they can easily misunderstand what you want. Vex and WCP’s gears are extremely cheap given the fact that they are lightened, and in the case of the 20DP line, have modified profiles to survive FRC manufacturing tolerances.
That being said, I buy things from China all the time. Haven’t bought gears specifically yet but chances are they would be ok, as long as you are very clear on what you want.
Where did VEX mention they modified the 20 DP profiles in that way? I was under the impression that the only gears “modified” in that range were the smaller gears which are undercut, addendum shifted, or both.
The’re a large amount of root clearance on all their gears as far as I can tell when comparing them to “real world” gears. Vex doesn’t document it, but anybody can look at their smaller gears and compare them to industrial versions and instantly notice the changes. Larger gears seem to conform better but still have more root clearance, probably to help the 84:14 mesh properly. That mesh can have issues if you are using regular gears.