Sonic Shifter - recent feedback?

[aldaeron]

Originally Posted by GeeTwo

It depends on how much pushing you're doing, and (more importantly) how hard the collisions are. The case where you're most likely to need steel is on the bull gear (gear nearest the wheel) and the gear that engages it. It would take a truly extreme case to require steel gears in the earlier stages, or even on the bull gear for simple pushing without collisions.

Originally Posted by Chris is me

This is entirely conjecture. Properly aligned and sized for the application, in a drivetrain you should basically never fail an aluminum gear no matter how hard you're pushing. Maybe if your output gear is 14 teeth or something crazy like that you'll have a failure, but in normal applications you'll be totally fine.

I agree with Chris - why not just run the numbers yourself instead of guessing? Here is a great presentation on shear stress in a spur gear. Matweb should have material info on 7075 aluminum and 4140 steel (not sure how to apply allowance for the ceramic coating on the aluminum gears). See what safety factor your teeth have for each gear in the gear train for each material. The less robust the mounting, the more safety factor is needed.

-matto-

[BoilerMentor]

Originally Posted by aldaeron

I agree with Chris - why not just run the numbers yourself instead of guessing? Here is a great presentation on shear stress in a spur gear. Matweb should have material info on 7075 aluminum and 4140 steel (not sure how to apply allowance for the ceramic coating on the aluminum gears). See what safety factor your teeth have for each gear in the gear train for each material. The less robust the mounting, the more safety factor is needed.

-matto-

The ceramic coating is going to mostly effect wear characteristics that might otherwise be problematic in aluminum. Running the numbers is without question the way to make the decision. Ideally if you had the resources and time, you'd validate those calculations with actual load testing. I wish Machinery's would donate a copy to each FRC team. It'd make the world a better place.

[BoilerMentor]

Originally Posted by waialua359

However, I would respectfully disagree on the automatic shifting. We tried it in 3 different seasons and will never ever go back to it. In every instance, it failed/or started to wear heavily on some parts causing shifting problems. We got tired of the constant checking and paranoia that it would fail in a match.

Based on my conversation with Paul via email, I'd agree with the assessment that the press fit between the shifter shaft and the hex output shaft was the issue. I'd like to believe that with either the upgraded shaft, or our revision with the shaft being supported by a bearing opposite the gear we wouldn't have seen the failure in competition.

I'd be very curious to hear what those failure modes were with auto shifting and if there's anything I can add to that conversation. We implemented a power cut in the shifting routine that made a world of difference in testing and I suspect would significantly decrease .

I've been preaching autoshifting very hard given the fears about brown-out and the testing results we achieved with the robot in question in this thread from 2014. If the game warrants six cim two speed drivetrains this year, I suspect we'll see dozens of matches with dead at least one dead robot because of the brown out issue. I'm fairly confident, based on our experimental data, that a six cim shifting drive will brown-out if a drive accelerates aggressively from a stop.

[kyle_hamblett]

We used 4 of them on our 2014 robot in a Mechanum setup. We haven't had any problems with them in 2 district events, district champs, 4 offseason competitions and a handful of demos. We haven't checked them for signs of wear but there are no signs of them breaking or showing age.