Banebot 56mm gearbox - double D related

[Joe Johnson]

I have been talking with a lot of folks. A plan is starting to take shape.

I have 2 teams that have agreed to do some additional testing for us (thanks to #1279 & #1618).

By the way, I have confirmed that FIRST had these gearboxes almost 9 months ago and they say they did extensive testing on real robots with both the 1-CIM and 2-CIM set up. It is still possible that the one confirmed field failure is a fluke of some kind and not representative of the loading we expect to see in the field.

We will work hard to understand the extent of the problem and to come up with a way to address the issues.

Joe J.

[sanddrag]

Is there any room to make the plate thicker? Or, what if we go to hex instead? Forgive me, I haven't actually looked inside the thing yet.

[haroony341]

team 2234 at Episcopal Academy had originally planned to use Banebot's dual CIM gearbox attached to the 56mm planetary gearbox but we no decided to scrap the idea, and go with AndyMark's dual speed transmission. more than just the double-D connection, the larger sized gears in the planetary box were worn down almost instantly. we had only done a few tests with no load at all and the gearbox just locked up. we found that the one of the gear's tooth was bent. we chipped it off as a temporary solution. but a few days later, after just one failed load test, it locked up instantly, and each of the gears had something wrong with it.

hopefully we'll have better luck with the new transmissions

[Rich Kressly]

Originally Posted by haroony341

team 2234 at Episcopal Academy had originally planned to use Banebot's dual CIM gearbox attached to the 56mm planetary gearbox but we no decided to scrap the idea, and go with AndyMark's dual speed transmission. more than just the double-D connection, the larger sized gears in the planetary box were worn down almost instantly. we had only done a few tests with no load at all and the gearbox just locked up. we found that the one of the gear's tooth was bent. we chipped it off as a temporary solution. but a few days later, after just one failed load test, it locked up instantly, and each of the gears had something wrong with it.

hopefully we'll have better luck with the new transmissions

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.

[Mike Schroeder]

Originally Posted by Rich Kressly

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 itemd 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 the team's decision to go with AM single speeds.

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

[Joe Johnson]

Originally Posted by "Big Mike"

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

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.

[RaMoore]

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.

[Joe Johnson]

Originally Posted by RaMoore

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.

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.

[Rosiebotboss]

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.

[Joe Johnson]

Originally Posted by Rosiebotboss

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.

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.

[MrForbes]

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.

[sanddrag]

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.

[MrForbes]

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.

[MrForbes]

Originally Posted by sanddrag

Once again, forgive me I haven't had a chance to tear into the thing yet

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)

[Rosiebotboss]

Originally Posted by Rosiebotboss

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.

The official reply form BB regarding the alloy. The emailwas in my InBox this morning after requesting the info yesterday:

Dear Dana P. Henry,
We are working with the manufacturer right now but we do not have the information as of yet. We apologize for the delay.

Sincere thanks,
BaneBots, LLC

So......we are still looking for the alloy information. To quote Dr. Joe, "Got lab?"