Over the 2017 season, We used large 3-CIM gearboxes from West Coast Products. We enjoyed the shifting aspect of those gearboxes, but we thought we should take advantage of our machining resources to create our own. This is the result:
High speed: (Adjusted): 17.5Ft/Sec
Low speed: (Adjusted): 6.5Ft/Sec
Total weight: 8.160Lbs.
Dimensions: 10"x5"x5.5" (Including shifter cylinder - 7.25"x5"x5" without)
If you’re going to make your own, I suggest using VexPro’s ballshifting mechanism rather than WCP’s dog shifting one. It’s much more compact.
Also, one thing you can do with a custom gearbox that no COTS WCD gearboxes currently offer is include some way to gain access to the drive belt pulleys/chain sprockets without removing the entire gearbox from the frame. Figuring out a clean, small, and convenient way to do this is a handy engineering challenge.
+1 on using the ballshifter and chain access. Looking very functional as-is. A minor change would be to remove the ring around the CIMs, or at least the top of it. I like the incorporation of the COTS shifting mechanisms a lot.
One way to save space in dogshifting (which the WCP DS gearbox does) is by putting the gear that connects to the pinions in the empty space between the 2 gears that connect to the dog gears. Doing this will save 1/2" of width for free, and you wouldn’t have to deal with the COTS ballshifter’s shorter shaft.
That said, I’ve heard that ballshifters are smoother. But either way is functional, much like your current design.
Hey, Thanks for the suggestion! We used this method to make our gearboxes thinner this year, and the pinions were not meshing as good as we would’ve liked them to… Ended up doing this at an off-season competition.
Chak’s got the right idea here. In terms of space savings, Ballshifters and dog shifters are effectively the same if you make the geometries right. Sure you may be able to get one a fraction of an inch shorter than another (I’ve managed to make both shorter than other versions of the other I had made - it’s all dependent on the specific situation), but that small of a distance usually doesn’t make one design superior over another.
When you’re deciding ballshifting vs. dog shifting, here are some more relevant factors you should form your decision around:
-Which do you have more experience designing with?
-Which fits your requirements better?
-Which has the gear sizes you’re looking for?
-Which are you more comfortable with?
-Which can you implement the quickest, simplest, and easiest for your team?
Both technologies are functionally equivalent at this point, so it’s entirely up to user preference. That being said, each team’s unique experiences and situations may make one solution more reliable and easier to execute than the other. They may be equal, but the decision is definitely not a coin flip.
