Re: Banebot 56mm gearbox - double D related
 

We have tried the homebrew hardening technique and this is looking promising as at least an improvement.

How we hardened/quenched the material:
Used two propane torches to get the steel to a red hot level (approx. 550 deg. C) and then submerged in oil (motor oil in this case). The oil rapidly cools the metal (better than water) and makes a bunch of smoke (burning oil?). The metal is submerged until cool enough to almost handle. If quenched in a small volume of oil, change oil to cool oil for next cycle. The material is then reheated to glowing red hot and then re-submerged. Process was repeated three times and then tested.

Testing procedure:
motor was clamped down and half of a torque coupling was placed on the end (two jaw, pictured). A c-clamp was clamped onto the table in between the two jaw teeth and gave approximately 90 deg. of travel before locking up. The motor was then powered 100 times back and forth into full stall. Motor shaft rotates 90 degrees and then is slammed into stall when the jaws lock up. (This really isn't good on the motor nor the trans. but that's what we want right?) The test was performed in 20 cycle intervals (since the leads got to hot to hold) until 100 cycles were achieved. Pending results show little distortion in the cut aways (pictured). Future tests are pending.

Re: Banebot 56mm gearbox - double D related
 

I happened to be there to witness this one myself. I stopped in to visit 2234 to discuss shipping and a few other things with them, but instead I found a group of rookies huddled around a frozen gearbox after nearly no-load testing. Here you have a rookie that's done its homework, has an experience FIRSTer working with them and spent more than three days trying to get something to work that was listed as a "proven solution" in the tips and best practices guide. I saw the bent planet teeth myself that were hitting the mounting hole housings between stages and I also saw a central gear move laterally about 1/8" during a bench test. Mind you when the team first got these items they spent time filing burrs off of gears just to get it all to run the first time. I'm concerned that some of this product may also be pushing the limit of acceptable tolerances.

I'm not trying to bash anyone, and I'm very glad Dr. Joe is working so hard on this. I'm sure his work will prove to be a huge benefit down the road. But, standing there with this crew, what they didn't have was time and neither an experienced mentor from another veteran team or myself could guarantee that it would run well even if they supported the shaft better, and had plates to sure up both sides of the box (which another team would have had to make for them), and they found a way to offer more motor support.

I know everyone involved is working hard on a solution and I understand that new vendors are important for a lot of reasons. However, as a rookie team mentor last year all I can say is that I'm so glad that the kit gearbox we had in 2006 was so robust. I'm equally thrilled right now with my team's decision to go with AM single speeds.

Right now, headed into week 4, teams need to know they'll run reliably and right now, in my way of thinking, that means using another product if a team can afford it.

However, I eagerly await Joe's final word and banebots' ultimate fix for these issues. Yet, the fruits of this labor will probably need to wait until next year for many teams. The clock is ticking and unfortunately it looks like teams will have to dig into their pockets this year for something they thought was already in the kit.

I'm trying to be kind here, but I'm concerned for many teams.

Re: Banebot 56mm gearbox - double D related
 

Kres, I agree, I don't want to bash anyone, but i do know that something went wrong here. coming from a team with little to no engineering support at least mechanically i have got to say that we aren't taking the chances of waiting for a fix, and are already getting the money together for AM single speed, and i would like to thank bane bots for their donations, and also hope that this doesn't end their fledgling entry into FIRST



--Big Mike

Re: Banebot 56mm gearbox - double D related
 

I brought home one of the teams unused 56mm transmissions, and my sons and I did a kitchen table dissection. We discovered that the shaft does fully engage the plate under some conditions, but we also discovered that there is about 1/32" end play in the planetary geartrain stack. So, the end play seems to be a bit excessive, and allows the shaft to disengage about one quarter of the way from the plate.

Instead of a shaft modification, perhaps a select fit washer to control end play might help.

Re: Banebot 56mm gearbox - double D related
 

we put a washer behind the gear that connects the 2 CIMs together. it did help a little bit but the 4:1 gears were constantly grinding against the dual CIM adapter where the screws hold the 2 together. and adding enough washers to keep from grinding would have pushed the gear to far forward it wouldnt be connected to the CIM gears, or the would barely be connected and cause just as many problems.

Re: Banebot 56mm gearbox - double D related
 

I am sorry that Team 2234 has had these problems.

The transmission failure you describe sounds to me like something was wrong with the transmission from the start. Teams should not have had to file burrs off of gears to get them to run. The "lock up" seems to me like it must be one of the flat washers getting eaten by the gears or else some metal shavings in the mix somehow or that it was re-assembled improperly.

I have analyzed the gear teeth loading as well as the brass material that they are made from. Do not think that brass = soft. Brass comes in many varieties. This particular brass is harder than the steel gears that they mesh with. Believe me they do not "wear down almost immediately" not unless something other issue is at play.

This is more of an infant mortality issue and a quality control issue. While this is bad, I am not as worried about these types of failures because teams discover them early and have a chance to fix them. The D joint failure is one that seems ok but breaks in a match -- much worse.

I am not recommending that teams pitch the entire 56mm transmission. I believe the system is quite workable. I remain confident that this problem will have a happy ending. There are a number of people looking into the issue and working to find a way of addressing the issues found.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

Some questions:
Why do it 3 times?

Did you "temper" the part after the final time you quenched it?

Will you do your test again only with the non-hardened carrier for a baseline?

Thanks for the data.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

Joe,

What is the alloy of the carrier plate and that of the output shaft?

This info would help those that have access to a heat treat facility.

Thanks for your help in trying to remedy this problem.

Re: Banebot 56mm gearbox - double D related
 

I really wish I knew. Hardness tests are fast and cheap. Material reverse engineering takes time and money.

I have reason to suspect that both the shaft and the carrier have enough carbon in them allow them to be hardened fairly easily (no carburizing, no cyanide powder, etc.) but don't know for sure. I certainly don't know the exact alloy which would help folks with access to ovens and whatnot.

Banebots, can you help us out here?

Joe J.

Re: Banebot 56mm gearbox - double D related
 

I got the depth mic out of it's dusty storage and kind of accurately measured the apparent end play in an unused 56mm transmission (0.058"). I also measured the depth of the step on the output shaft, and the thickness of the planet carrier plate (0.157").

I see a problem here....and a relatively easy solution towards improving the strength of the DD joint by about 30% by simply adding a selective fit thrust washer, between the output planet carrier and sun gear.

Re: Banebot 56mm gearbox - double D related
 

Once again, forgive me I haven't had a chance to tear into the thing yet, but I thought of a potential solution many teams may be able to implement and perhaps make several of to supply to other teams in trouble.

Would it be possible to machine the planet carrier and output shaft from one solid piece of steel? Start with round bar the diameter of the carrier plate, Turn it all the way down. I know it's a long ways to go but CNC can help with that. Drill new planet pin holes. Cut a keyway. Is there any reason it must be two pieces? If we did this, what material should it be made from to not yield the material due to torsional shear where small diameter meets large? I would like this to eliminate any possibility for failue in the 2 motor 12:1 scenario.

Re: Banebot 56mm gearbox - double D related
 

The output shaft is actually 1/2" (0.500") at the "outside" end, and 12mm (0.472") where it passes thru the bearings. So, you could not assemble the gearbox with your plan, unless you changed the whole bearing mounting design.

The obvious solution to the problem is to spline the shaft and plate, but then you get into interchangeability and manufacturing issues.

Re: Banebot 56mm gearbox - double D related
 

here are a few "exploded" views of the 56mm transmission. Sorry about not cleaing the grease off....and if you want higher resolution images of any specific part, let me know, I knocked these down quite a bit to fit them as attatchments

Also, I measured the end play of the output shaft in it's housing, supported by it's two ball bearings, as 0.015" (using a dial indicator)

Re: Banebot 56mm gearbox - double D related
 

Concerning homebrew hardening.

I was very intriged by the homebrew hardening results reported by RaMoore. I was hopeful that the mat'l (still unknown -- I don't have access to a material lab -- will someone out there who does take the initiative and get us the alloy data for the carrier and the output shaft) had enough carbon in it to allow us to harden it relatively easily.

So... ...I headed up to my old huants, Pontiac Central -- home of the Chief Delphi FRC team, to do some homebrew hardening of my own.

I used a MAPP torch (you can buy them at you local hardware store, essentially they work just like propane only few hundred degrees hotter) and oil quench. I got the parts glowing red and quenched them in oil.

There was a lot of smoke and all that. The parts looked nice and hardened.

But, alas, when I had them checked for hardness, they measured the same as before my excursion into the black art of heat treating.

So... ...I conclude that the material does not have the needed amount of carbon lurking in the interstices of the iron atom matrix to make the hardening magic work.

Too bad. While I was a long way from suggesting that teams go out and do this themselves, I had hopes that we could set up a service where a team send their soft carriers to some FIRST friendly heat treating shop, they'd run the carriers through their ovens, drop them in an oil bath and ship them back the next day. It may have been 2 day round trip. Might have been a winner.

There is one plus to my failed homebrew hardening. If the RaMoore's part was not hard either (and I suppose it wasn't) then the test they did showed that the gearbox as shipped would have done just fine too.

I encourage others to help us determine the issues. If you run at test, document things as best you can and share your info with us all.

Finally, I want to try to stem some of the waves of panic that are going through the FIRST community (and I am going to yell here, so get your ears ready for the shock) WE STILL DO NOT KNOW THAT THESE GEARBOXES WILL ROUTINELY FAIL IN THE FIELD.

Really. The only field failure of this type that has been reported as of right now is the one reported by Team 166 and that was not a failure where the gearbox was NO-OP but that the backlash was noticeable after 3 hours of hard driving.

I am very confident that as we learn more about this issue, we will be in a position to come up with solutions to address them.

Stay tuned.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

My team requested that I post the following information.

The attached images show the problem we have encountered with the transmissions.

We first did a 30 minute run in of the motors and transmission with no load.
Two days later, we did about 10 minutes of test driving. Full forward, full reverse, rotating, basically each combination of joystick maneuvers possible. Hopefully this data will help teams that want to keep using these transmissions find a fix. We on the other hand, have decided to switch to the AM Single Speeds.