Shifting transmissions

[liam.larkin]

I have been playing with a number of possible drive train designs for our team (272) for this upcoming year and for the future. A few of them lend themselves to the utilization of shifting transmissions. I have had little luck in the past with these style transmissions often under utilizing them and not fully taking advantage of their unique capabilities.

I have been looking at the ball shifter offered by VEX as a new possibility. Does anyone have experience with these. Are the stock gear ratios adequate? Is the design robust enough for a typical FRC competition/game? Has anyone modified them (ratios, gear material) with success? What about the stock gearing itself, spur or helical, undercut, overall backlash, tip relief, contact ratios? Any additional information and/or is appreciated.

[MichaelBick]

The Vex ball shifters are relatively new, so I doubt many people have experience with them yet, much less throughout a full season. Two other options are the AM supershifters and the new WCP shifters. The AM supershifters have been used by many teams succesfully. The WCP shifters are new, however there is a lot of data that suggest they will be a solid choice. The gears used in their transmissions have been used by many teams(many powerhouses too). The gearbox design is based off the designs developed by 1323 and 973(not sure if 2415 and 1477 helped too). The design has been changed quite a bit for production, but I talked to Adam Heard from 973 and he said it should perform just as well.

The stock gearboxes are adequate based on what you plan to do with it. If you want to direct drive they might be a little bit slow or fast. The gear ratios are relatively easy to change, as long as you get gears that add up to the same tooth count. The gears should work fine(WCP has sold the same kind of 7075, black ano, teflon coating gears for a while), however again they haven't been tested during a season yet. They use spur gears(helical isn't really needed in FRC).

[msimon785]

For the first time this year, shifting transmissions from a variety of suppliers and in a variety of configurations are available to teams off the shelf. As such, I suspect a disproportionately high number of teams will be employing 2-speed drivetrains.

I'll also give my vote to the WCP gearboxes. 1515 is using the 2-speed WCD model this year. In all likelihood, we'll stick to the stock ratios (30-45, 15-60). This leads to fairly optimized speeds with 4" wheels. With that said, as Michael mentioned, changing ratios in a shifting transmission is as easy as finding 2 gears that add up to the same tooth count.

I suppose your choice of gearbox will, in the end, reflect the way in which you use it. If you are direct driving, and building out of 2x1 tubing, the WCP option is proven by a number of powerhouse teams. WCP uses hobbed and coated and Type III anodized 7075 gears that 1323 and other teams have been using in the past few years. While I haven't tested them yet, they are purported to be of great quality. The Vex ball-shifters are equally applicable, but can also be more easily used in dead-axle and non-direct drive applications. As an alternative, the AndyMark product line has seen many seasons of wear and is probably your safest bet.