Hey, I’m currently working on a project built around SDS’s bevel gears, and I’m curious as to how strong they are.
To any teams using SDS’s MK4/i modules, have you ever needed to replace the gears? Have you noticed any wear over the course of a season?
I’ve been looking across CD for some time now and can’t find any mention of teams replacing the bevel gears in their modules. This is in stark contrast to my own experience with poorly spaced $8 a pair cheapo gears. I’ll be putting them under a fairly comparative load, but if they’re on the disposable side my project will likely be unpractical/infeasible.
Haven’t used SDS’s gears specifically, but they’re pretty typical of what most gears are made of, which is 1045 steel. We have something a bit higher strength on our modules and they’ve never shown any apparent wear, even after many hours of use, but these are plenty strong. 1045 is pretty tough carbon steel (on the low end for carbon content) and is well suited to applications like this. Our WCP modules use 4140 steel for the bevel gears, which is a bit more fatigue resistant but otherwise fairly comparable (though higher carbon.) Both types of steel are just fine for this application. Unless you’re going to demand a lot more of them than a swerve drive does, I’d say you have nothing to worry about.
You can calculate the strength of a gear tooth using the material and Pitch or Module of the gears. You need both parameters to estimate gear strength, as the tooth size and material are both important. I don’t know if Lewis gear calcs are valid for bevel gears, but I’m sure the equations are out there to calculate the lifetime.
Another thing to keep in mind when designing gears into an application is how they are held in place and are they properly meshed. As I type I can think of a bunch of examples where the gear failure had more to do with the case/bearings/gearbox allowing the gears to move away from each other rather than “If the gears were only stronger, they wouldn’t have broken”.
I would bet a crisp dollar bill that the majority of the FRC gear failures are primarily caused by poor engagement management and case flexure.
As I recall the SDS bevel gears are a 1.5 module, 45:15 tooth pair. So you can look up that size from another manufacturer to get a starting point for strength ratings:
I don’t know if SDS uses the same material or heat treatment though, so use these numbers with caution.
To answer your question, we ran them all season, 2 districte events, district champs, Worlds and IRI and have very little noticeable wear on them. In fact they look to be good enough to run another season.
FYI: 1045 has 0.45% Carbon and 4140 has 0.40% Carbon. (Yup, those alloy #'s have a direct meaning.)
Other components of the alloy may make 4140 more or less fatigue resistant, but the low Carbon content and strength correlation is inaccurate.