Sonic Shifter - recent feedback?

[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.

[BoilerMentor]

Originally Posted by GeeTwo

The form factor, including the mounting, is the only real difference. If you use a COTS shifter, use the recommended cylinder. If you're building your own, managing space is the deciding factor.

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.

I second both these statements. I think the first stage in the gearbox is a great place for for aluminum gears.

One thing I've toyed with, but never implemented is the idea of removing material from the body of a steel gear to compensate for the weight differential. The strength of the individual tooth is really where the material decision has to be made. There are tools to make those calculations available.

In my FIRST career there are a number of things I've been conditioned to avoid because of bad experiences (none of these specifically from the three cim ball shifter situation discussed within this thread)

Aluminum gears, cantilevered shafts, and #25 roller chain are standouts on that list.

[Michael Corsetto]

Originally Posted by BoilerMentor

In my FIRST career there are a number of things I've been conditioned to avoid because of bad experiences (none of these specifically from the three cim ball shifter situation discussed within this thread)

Aluminum gears, cantilevered shafts, and #25 roller chain are standouts on that list.

I'd encourage any/all readers to avoid this "conditioning" approach.

If you want to win, steal from the best, invent the rest.

We (1678) have learned to use aluminum gears, cantilevered shafts, and #25 roller chain. We've learned mostly from Team 254 and VexPRO/WCP. These organizations have, between them, probably 10 of the best 50 mentors in the entire FRC program.

The best part is, for any reader out there, even if you are a freshman rookie in high school, these mentors are just an email or PM away. Ask 254 WHY they do cantilevered shafts every year and HOW they do it! Ask 1678 WHY we copy 254 and HOW we do it. Ask VexPRO/AM/WCP how to properly implement their products into your designs.

These resources are available. They are just an email away. You don't have to do any more guess work. You CAN be a better engineer by working harder and gleaning knowledge from people that have walked further down the path you are already on. Be encouraged that you are not alone, take advantage of the opportunities that are in front of you.

Learn from the best so you can BE the best.

-Mike

[Chris is me]

Originally Posted by BoilerMentor

In my FIRST career there are a number of things I've been conditioned to avoid because of bad experiences (none of these specifically from the three cim ball shifter situation discussed within this thread)

Aluminum gears, cantilevered shafts, and #25 roller chain are standouts on that list.

Don't blame the parts, blame your implementation. Hundreds of teams have used all of these things every year without any problems whatsoever. The only time I've shredded an aluminum gear is when it was taking huge shock loads that were far more than the gear was ever supposed to support at the end of a very large reduction. My old team has used cantilevered driveshafts since 2011 without any failures. We have never failed a 25 chain in any case, even when undertensioned and slightly misaligned. Avoid what doesn't work for you, sure, but if you can't make things work that work for everyone else, you probably have bigger problems.

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.

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.

[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.