VEXPro 2014: After The Season

[T^2]

You know the drill.


3-CIM Ball Shifter

This product was a bit of a mixed bag, but the upsides outnumbered the downsides. The gearbox is light, generally reliable, and has a good variety of speed options. We used ours in a WCD with WCProducts bearing blocks, and once the drivetrain was together, we never had a problem with it. We were fast in high gear, pushy in low gear, and only once had to run maintenance on the gearboxes themselves (see next paragraph). Definitely a solid choice for teams wishing to save time on custom gearboxes. I maintain my stance that the ballshift mechanism is both faster and more robust than shifting with dogs.

Most, but not all, of the problems we encountered with these gearboxes arose from user error. Notably, the mounting nuts on the sides (or rather, the top and bottom, when mounted with the stock 3rd-stage plate we used) are not meant for high loads, and will tear through the shell if used in that manner. We found two significant problems that are, I feel, an inherent part of the design. First, the stock 3rd-stage mounting plate's holes for mounting to the frame (of a WCD, in our case) are asymmetric: one is horizontally 1.976 inches from the 3rd-stage output, and the other is 2.024 inches horizontally from the same. This is compensated for by an increase in the hole size. I cannot possibly imagine why the holes could not be symmetric.

The second issue, which is a bit more important, is that the gearbox feels as though it is not designed with a west coast drive in mind. Attaching a WCP center bearing block to the system requires using low-profile 10-32 nuts on the inside of the plate, which are difficult to access with chain in the way. (There might be a better way to do this, but I can't find any documents that say so.) Furthermore, the 3rd-stage shaft runs through two bearings that insert in the same direction: one is a press-fit into the nylon shell, and the other is a slip-fit into the bearing block. If the press-fit fails, as it did for all four of our gearboxes, then the entire output shaft assembly will partially slide out of the robot until about half of the output gear is in mesh. To solve this, we had to Loctite the outside bearing into the bearing block. I'd really rather not.

Speaking of Loctite, this year's ballshift shaft assemblies are an improvement over last year's. We noticed no issue with the shaft coming out of the housing, unlike last year. However, this wasn't the case with all teams; at Champs, I helped another team perform an emergency Loctite replacement on one of their drive gearboxes because the shaft had extracted itself. Overall, I can say that while a better job was done this year with regards to Loctite application, I still wish for a mechanical connection between the shaft and its housing.

Last note: while we didn't use it ourselves, multiple teams with whom I spoke were satisfied with the new plastic encoder gear.


VersaPlanetary Gearbox

The advantages to these are the same as last year; I'll focus on the problems with the new stuff. The 7:1 gear stages we ordered had weak welds, which cracked in short order. I'm sure this will get fixed soon. The main problem we experienced this year was with the new plastic motor mounting plates. While a step up from last year's system, the plates were difficult to attach to the gearboxes because their mounting holes had extremely thin walls around them; tightening the mounting screws just a bit too much led to fracturing. Please either make these out of aluminum, or improve the wall thickness. (Doing both would be best; one of the secondary disadvantages of the plastic plates is their poor rate of heat flow for purposes of motor cooling.)

We found out the hard way that these gearboxes are not meant to take heavy loads while powered by MiniCIMs. They're great for intakes, though.

WCP Cam

Amazing. I wish the hex shaft on the steel model could be a bit longer, though.


Wish List

A 17t #25 sprocket option, for chain-in-tube drives.
A stock butterfly module, paired with a stock frame that can use it.
A hall-effect sensor magnet with the same center hole, but a smaller outer diameter.


That's about it for what 1678 used. If anyone could elaborate on the quality of the VersaWheel DT, the dual-input VersaPlanetary, or the plastic pulleys, that'd be great.