Banebot 56mm gearbox - double D related
 

There are threads here, here and here that are all discussing the same issue. Will the double D joint between the last carrier and the output shaft survive?

There are sub-questions:
Will the 12:1 1 CIM joint fail? If so what can be done to fix it?
Will the 16:1 1 CIM joint fail? If so what can be done to fix it?
Will the 12:1 2 CIM joint fail? If so what can be done to fix it?
Will the 16:1 2 CIM joint fail? If so what can be done to fix it?

We can debate who is to blame and how could this have happened all day long. It is not going to get us the answers to the question, nor is it going to get us to a solution.

Here is the state of things:


Data Point 1: Hardness test of shaft and carrier:

Output shaft: RC 23, RC 23.3, RC 23.2
Carrier Plate with D: RA 45.9, RA 46.9, RA 45.8

Rockwell C to Tensile Yield:
RC 22 – 115 Ksi
RC 23 – 117 Ksi
RC 24 – 119 Ksi
RC 25 – 123 Ksi
RC 26 – 125 Ksi

Rockwell A to Tensile Yeild:
RA 45.0 – 62 Ksi
RA 45.5 – 63 Ksi
RA 46.0 – 64 Ksi
RA 46.5 – 65 Ksi
RA 47.0 – 66 Ksi
RA 47.5 – 67 Ksi
RA 48.0 – 68 Ksi

Data Point 2: Calculations & Date = Prediction
Using calculations + above hardness tests of the joint, I predicted that with the 12:1 gearbox should fail at about 3.1N-m input into the gearbox. Since 3.1N-m = 28in-lbs = roughly 1.5X CIM_stall_torque, alarm bells began ringing.



Data Point 3: static failure test
Using a test set up and a torque wrench, I was able to determine that the join failed with a single loading of between 3X and 5X CIM_stall_torque. This is better than predicted but not that encouraging considering that the "failure" was basically a spungy type event, allowing for actual failure to begin at lower than 3X. See picture.

Data Point 4: Cycling Failure test
Using the same test set up, I was able to show that the joint will fail at 2X CIM_stall_torque with repeated loading. See Picture.

Data Point 5: Failure in the field
This still did not mean that teams would see failures in the field because we don't know the dyanmic loading that we expect to actually see during real world conditions. I typically use 2x as the dynamic load factor, but that is not a law of physics it is just a rule of thumb. So... ...we needed confirmation.

Team 166 uploaded a picture that confirmed this problem will be seen by teams. This is after 3 hours of driving. Team 166 did not say what ratio & how many CIMs they used, but I suspect it was 16:1 with 1 CIM. Will someone from 166 confirm this please.

Where do we go from here?
Now, what do we have to do going forward? I believe that we can get a quick 2X in the output by simply getting harder carrier plates (RC 23 or higher). I believe that will almost certainly get us to the 12:1 1-CIM case as well as the 16:1 1-CIM case.

What it does to the 2 CIM cases, I can't predict. My best educated guess is that for most teams the this will address the problem for the 2-CIM cases too, but I have to be honest, the picture from 166 has me worried. If they were in fact using the 16:1 1-CIM set up, then going to a 2X hardness will be exactly matched by a 2X in loading due to the 2-CIMs.

We need more testing and we need more thought on solutions.

More Information
For your information, Banebots is well aware of this. They are working hard with FIRST, their suppliers, and yours truly to get a good solution out there to teams. Everyone is sorry. Beating us all up will not help. Calling them will only take time away from fixing the problem. We are working on it.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

In the pictures of the failed plates, it looks like the shaft is not fully engaged with the plate. In addition to hardening the plate, it might be worthwhile to look into some type of mod to the shaft to get full engagement.

Re: Banebot 56mm gearbox - double D related
 

May I add that this same problem is happening with the 42mm gearbox's, which many teams planed to use with the FP motor to power an arm. It will fail on you quicker than the 56mm drive gearbox's. If I was on or mentoring a team planing on using these gearbox's I would tell them to grab a pair of single speed Andymark gearbox's which for the same price accept 2 CIMs or 1 Bike CIM and 1 CIM.

Re: Banebot 56mm gearbox - double D related
 

I have been following the banebot transmission failure threads for some time now and now I feel teams need to take action.

We are currently running 2 CIMs on each gearbox...so we definately need to get parts made. At the moment are transmissions are on the robot and not easily accessable, but we will get to them to replace the Double D plate. We have yet to have an issue...but are going to take precautions now.

Does anyone have a CAD drawing of the piece that needs to be made?

It is my hope that teams which have the resources...get many of these plates made to help out other teams who are not as lucky.

I would love to not have to worry about it and wait for BaneBots, but their response time (at least with me) was not acceptable. Teams need to start production now so the plates can be replaced BEFORE regionals.

Re: Banebot 56mm gearbox - double D related
 

Is this a problem only with a 2 motor setup? Should we be concerned if we are just using one CIM per gearbox?:confused:

Re: Banebot 56mm gearbox - double D related
 

Dr. Joe.

We are using 1 CIM w/ 12:1 ratio.

An ME here would like to know how you calculated the stress. Below is his observation from the photos as well as conversations with me.

"The initial interface is 2 lines of contact (essentially zero area) between the shaft and the D hole. It is only after material begins to deform (ever so slightly) that area contact is made. I am curious what he uses for stress area and how he determines it."


C. B. Petrovic

Re: Banebot 56mm gearbox - double D related
 

Is the double D shaft pressed into that plate, or it just sits in there? Howabout the planet pins? This part that fails is just a 2D geometry plate? Is it easy to swap out? We have a lasercutting sponsor. There is a chance we may be able to set up a large production run of lasercut plates available for a small cost. Is laser accurate enough (draft angle)? What kind of material would it take to make this plate never break? How would it have to be treated/hardened? Joe, talk to me. :) I want this to be a good year for FIRST. A robot that drives without worry is the key to success.

Re: Banebot 56mm gearbox - double D related
 

From the data we have to this point, it looks like it could be a problem over time for even the single motor CIM drives if driven hard back and forth for many cycles. I think it will take significant cycles to fail but based on the experience of Team 166, I think it will fail.

The good news is that when it fails it doesn't seem to take the rest of the gearbox down with it. It is not ideal but it is something.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

I assumed a linear stress distribution normal to the joint surface starting at the center line and increasing to a peak at the corner of the D. I then integrated the torque to get the sum (on both sided of the D) which had to resist the torque on the joint. I found an engineering rule of thumb that allowed me to estimate failure of the joint by saying the material will start moving at 1.5X the tensile yeild stress. Once the material begins to move, the stress distribution changes but the joint is losing the battle. So I used the torque that made my linear stress distribution have a stress in the corner greater than 1.5X Stess_Tensile_Yeild

I hope that helps.

Joe J.

Re: Banebot 56mm gearbox - homebrew hardening?
 

Would a homebrew hardening of the plate be of use in helping this problem? Heating it to red-hot and tossing it into a bucket of cold water seems like a fun experiment. Into potentially explosive oil could be even more exciting (just kidding, this could/would be very dangerous). http://www.efunda.com/processes/heat...ing/direct.cfm

Re: Banebot 56mm gearbox - double D related
 

Is there any possibility FIRST would let us use last year's transmissions as a solution?

This is so bad I can't even understand how this mistake could happen. We have been planning for a year and getting ready for this year’s competition and we may be sunk before we even take the field. Why were these things not tested before the switch was made?

boooo:(

Re: Banebot 56mm gearbox - double D related
 

This plate looks like it could be manufactured out of 4140 pre hard (Rc 28 - 32) fairly easily. 4140 Rc 28 - 32 should give Sy of around 120 - 130 ksi. A wire EDM could do all features with high precision. Comments?

Could you provide drawing for us to use?

thanks

Ron Reich 166

Re: Banebot 56mm gearbox - double D related
 

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.

Re: Banebot 56mm gearbox - double D related
 

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.

Re: Banebot 56mm gearbox - double D related
 

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

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.

Re: Banebot 56mm gearbox - double D related
 

We did it three times to guarantee that we got hardening all the way to the core of the material. To harden the material further we would have to use higher temperatures and cool it faster and we felt this was unnecessary. Before hardening we were able to easily shave pieces of steel off the edges (using a pocket knife) and after the third quenching we could no longer shave large pieces of material off.

We didn’t temper the material following the third quenching because hardening the material to the point we would need to temper it is beyond our capabilities.

We will repeat the test with one of our unhardened carriers and post results soon.

Re: Banebot 56mm gearbox - double D related
 

Thanks for reminding me about the pocket knife test. I forgot that bit.

I am not a hardening expert by any stretch. From what I remembered from the one class I had that cover this, I thought that only the last one mattered. But I think I was mistaken. I will think some more about it and try to make a new hardened part tomorrow -- at least one will be using your 3rd time's the charm method.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

Hi Joe,

We are using the 56mm gearboxes with the 16:1 reduction, no chains, one per wheel. I am currently very concerned about this issue, but as you keep re-iterating to do, we are avoiding panic (although I am currently investigating other transmission options, should we decide we need to change our design).

My team has very little machining capability, and no sponsors with the capability to do machining such as manufacturing harder plates for us.

A (sort of) solution that springs to mind is that perhaps Banebots could make the current plates with the "double D" available on their website for sale (preferably at "cost"). Given the ease with which the 56mm planetaries are dis-assembled and re-assembled, having spare plates would potentially function as a "fix" for those teams with a few extra dollars in their budget but did not want to/could not afford to buy a full set of replacement gearboxes. 1/2 way through the competition, one should be able to dismount the transmissions, check for the "bow-tie", and if needed swap the plates.

Just a suggestion - I look forward to an official response/fix/etc... from FIRST and BaneBots, as well as the results of your own, clearly extensive and dedicated, testing and trouble shooting.

Thank you for your continued support with this issue, Joe, and good luck to everyone else who is dealing with this issue.

//Dillon Compton
Team 1394

Re: Banebot 56mm gearbox - double D related
 

We just repeated our test with the unhardened carriers and we successfully broke our gearbox. :(

We could clearly notice the damage by the 50th cycle. I'll add pictures as soon as I get a chance. We feel that hardening definitely helped, but whether it is a "fix" more testing will tell.

Re: Banebot 56mm gearbox - double D related
 

So after reading all the posted information and an experiencing an appropriate amount of panic, we are ditching the 56 mm planetary gearboxes for a pair of Andy Marks.

It does not make much sense to us to have worked hard over the last year to build a better organization, recruit more team members, mentors, and sponsors and hope a fundamental piece in the KOP will hold up. Imagine the frustration, tears and anger that would follow if the transmissions fail. Oh and the Rule 7 updated posted today did not make us all warm and fuzzy either!!

Switching was a no brainer.

Re: Banebot 56mm gearbox - double D related
 

We will be manufacturing many of these carrier plates out of 4140 steel. We are going to purchase 2 foot long stock of it and maybe make as many as we can out of it.

I don't know about drawings for them, but we will create one if we can't find it.

We suspect it will increase the strength about twice as much.

Re: Banebot 56mm gearbox - double D related
 

I saw this mentioned on another threat in a previous post, has anyone tried welding the two (gear and plate) together? Are there any significant downsides to attempting this, as it seems like a relatively simple (if welding is available) fix...

Also, has anyone tried pinning the two? That idea was tossed around this evening, milling and pinning at three or four points the gear to the plate. This would support the central pivot on the double D, if nothing else.


Just some thoughts, drawing and (hopefully good) results forthcomming

Re: Banebot 56mm gearbox - double D related
 

About hardening, I don't think the 3 times repeating will get you a lot of extra depth, but I'm going off my one class a couple years ago, same as Dr. Joe. If you're not heating it high enough to transform the metal and break your previous hardening, then your hardening isn't going to work. If you are heating it hot enough, then you're breaking down the previous hardening. I suspect what you might be doing is a poor man's version of carburizing, building up a layer of carbon from the volatilized motor oil, then letting it soak in by heating up the part again.

At any rate, some brief googling gives me a little better info for those trying the homebrew hardening. The austenizing point is apparently slightly past where the metal stops being magnetic. So heat a bit past where a magnet won't stick to it anymore. I'm also curious if the carrier can withstand a water quench if anyone has a carrier they wouldn't mind possibly warping or cracking.

Re: Banebot 56mm gearbox - double D related
 

Good suggestions.

My thought on welding is that it will be hard to do without damage to the bearings and if the bearing survive the heat, I am not sure that the joint will be that much stronger -- the problem is the base metal gets pushed out of the way.

Pins are another thought. It may be that a pin in the middle of the rounds could take more torque without taking away more than they give. I think it would take an FEA to be sure as the loading gets pretty complex for pen and paper guys like me. Anyone up for an FEA optimization problem? How many pins and where to locate them to reduce the stress by a factor of 2?

PM me and I will coordinate efforts.

Thanks. Keep the ideas coming.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

This is pretty great news. Now we have a clear this fails / this does not case.

Well Done. I had forgotten to tell RaMoore when I asked them to do this that we will get them new parts to replace the damaged ones.

As to pictures. Yes, we need them.

What we need now is a mat'l lab that can reverse engineer the mat'l of the shaft and of the carrier plate ASAP. Does anyone know of a lab that will do this quick and free?

If we know the material it may be possible to design a heat treating process that can give us the harness we need. If that is possible, then one possible path toward a solution is to locate a heat treat source that will set up a carrier exchange program.

But, first things first, anyone Got Lab?

Joe J.

Re: Banebot 56mm gearbox - double D related
 

I read in one of the close threads (please forgive me for being lazy and not finding the specific post) that when a team tried to pin the two pieces together, they actually broke their drill bits on the output shaft. I'm not sure what bits they were using specifically (as they didn't mention), so this may or may not be problem in terms of teams doing this themselves.

Re: Banebot 56mm gearbox - double D related
 

That was us. It was a very makeshift job with ordinary 1/16" bits. The carrier drilled fine, but trying to go through the harder shaft, they broke. But other teams with better bits might have good results. Also, I think someone mentioned milling slots for the pins instead of drilling straight through.

Re: Banebot 56mm gearbox - double D related
 

The shaft is probably hard enough that it would need to be ground (or milled with a carbide cutter) to make the slots in it for pins.

Pins will act kind of like splines...the angle is better than the double D configuration. Perhaps spreading the load out among two pins, the double D, and fixing any end play problems, would be enough to make it work?

although the end play stuff gets more disconcerting the more I look at it, when I reassembled the transmission that I took apart for the exploded view this morning, it had somewhere around .030" play between the bearing and the snap ring on the shaft. There is a lot of slop there, the bearings are a press fit on the shaft, and it may be necessary to also press the inner bearing onto the shaft fully while supporting the outer bearing, and then install a selective washer between the inner bearing and the shaft snap ring.

This is kind of like working on car transmissions....which I've done a bit of.

Re: Banebot 56mm gearbox - double D related
 

Pictures of unhardened carrier as promised.

The damage is not as extensive as other teams have seen, but a clear difference from the hardened one.

As for the repeated cycles of heat, we tested with the knife scratch and it did seem to change it, for whatever the reason. I don't think any of us has had a class on the subject just some practical experience and some googling. I think we could try Kevin Sevcik suggested method for hardening if we can get it that hot.

Re: Banebot 56mm gearbox - double D related
 

We have four 56mm BB trannies running our mecanum drive. The 8" AM mecanums are directly mounted to the BB drive shaft which is supported on the outboard end quite securely. (photos at http://www.chiefdelphi.com/forums/sh...highlight=1346 )We "broke in" the gearboxes for at least 30 minutes of continuous operation before installing them.

We have been running our robot for... well... less than 30 minutes and noticed one or two of the trannies were beginning to show significant backlash.

We took the transmission apart and noticed that while the final drive plate had not failed completly it was very close to failure as discussed in this thread.

This is after very low use with ONE CIM in a relatively low dynamic loading (no chain to snap) environment.

We have noticed that the two BB's that came in the KOP have less backlash. They also fit much more nicely onto the CIMs than the two we bought in early January. Perhaps there is variation from batch to batch to deal with as well.

In any case, here is one more report of BB 56mm failing (or at least coming close enough to failure to count) under ONE CIM load... and at extremely low cycles, too.

We are also pondering solutions, but it seems manufacturing a new plate, or having one manufactured is what we are going to have to do if we want to use these trannies.

Jason

Re: Banebot 56mm gearbox - double D related
 

I have access to an EDM (actually, three), and I could look into making a whole bunch of these plates out of something super hard (haha... im not a metals expert here :P) If someone had a CAD drawing, that would be great...

Just last night we had to burn threads into some stuff... the scrap we found was hard :)

~Dave

Re: Banebot 56mm gearbox - double D related
 

I have to say that although the thought of our transmissions going out on us has me pretty worried, the collaborative effort I'm seeing to solve this problem is bringing a tear to my eye! sniff sniff.

Think about it, this is what FIRST is about! The whole stick a tube on a spider leg thing is just a distraction. This is all part of the master plan...(enter Twilight Zone music here)

Re: Banebot 56mm gearbox - double D related
 

My sentiments exactly (see my post in the BaneBots Return Policy thread and accept my word that I did not read yours first). This problem will be solved by one of the largest problem-solving machines in the world...the FIRST community.

Re: Banebot 56mm gearbox - double D related
 

Kevin is right about this. We have a heat treating furnace in our
shop that we have used to heat treat axles and shafts for several
seasons now. You soak the metal at a temperature above the transition
temperature to non-magnetic long enough for complete transformation
and then you quench, once, in oil or water as required by the material.
If you are not getting the metal above the temperature that ceases
to stick to a magnet, you are not doing much useful. We in fact use
a magnet on a soaked sample in the furnace to check that our
temperature meter is not off, we crank it up 25 degrees at a time
until the sample goes non-magnetic, and then give it another 50 degrees
for margin.

The shaft in the 56 mm transmission is already hardened. A high
speed steel cutter makes absolutely no progress on it. We learned
this when we attemped to turn a shaft into a square hole to mate to
a 4130 carrier plate that we made for a test of hardended material.
We ended up having to make a new shaft from 4130, and we will
heat treat the material tomorrow. If you heat the shaft from the
transmission you are likely to only temper it to a softer state.

Contrary to prior posts, water quench cools more quickly than oil
quench. Oil quench is dicated for some materials because water
cools too quickly and causes distortion. I would use oil for machined
parts that you do not want to risk distortion during quench. This part
is very thin. There is absolutely no need to water quench it. Oil will
cool it off quickly enough.

After a proper heat soak, and getting the part into the quench
before exposure to air cools the metal below the transition temperature
is really important, you have to temper. A temper at 800 degrees
is what we use on our axles. We do this in the furnace to get a
precise temperature, but they come out a dark blue and this is one
way you can tell what temper you have.

I don't know what the carrier plate in the bane bots tranny is made
of, so I don't know if it can be hardened. We made a carrier plate
and axle of 4130, with a square hole, and we will see what a proper
heat treatment of these parts gets us.

Eugene

Re: Banebot 56mm gearbox - double D related
 

Here are a couple of slides with a solution cooked up by one of our MEs...





C. B. Petrovic - Team 166

Re: Banebot 56mm gearbox - double D related
 

Dr. Joe...

When we reported the gross failure of one of the drive systems, we failed to mention that we pulled the other three gearboxes off and observed the same damage, although to a lesser degree.

Ron Reich, a new ME mentor on the team, had done the research and determined that the 4140 prehardened steel would provide double the resistance to stress that the original carrier plates can withstand.

We will be having new plates made and as soon as we get them, we'll report back on how well that works.

C. B. Petrovic - Team 166

Re: Banebot 56mm gearbox - double D related
 

Jim,

Yes, you are right. When we first assembled the motors onto the gearboxes, we needed shims to get the spacing right. This was done in accordance with the message from Banebots. After making hasty repairs to the failed plate, we discovered that the .040 shim was not necessary, nor were any mods made to the spacer, pinion or CIM shaft.

After pulling the remaining 3 gearboxes apart, all of which had the .040 spacers, we found these to have similar wear/failure patterns. Reassembly no longer required the shims.

We should have used our heads and run them no-load for a period of time for break-in purposes.

Oh, well, add this one to the "lessons learned" list!

C. B. Petrovic

Re: Banebot 56mm gearbox - double D related
 

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?"

Re: Banebot 56mm gearbox - double D related
 

We routinely add an acceleration limiter to our motor control software to lower the maximum torque that is transferred to the drivetrain during rapid forward/reverse speed changes. This should reduce the instantaneous load on the problematic gearbox plate, but I don't know whether it will be enough to solve the problem.

I'll have the team dissect gearbox to see what damage we have sustained so far (~ 2 hours of driving).

Re: Banebot 56mm gearbox - double D related
 

I had a chance to read up on this issue last night and also talk to Joe this morning. I'm coming in late to this party, but am offering help or advice. Here are a couple of things I see...

1. Just how bad is this problem? What is the % of failure rate here?

2. What is the best fix? It's great to see that is what is focused on in this thread. Best means quickest and easiest for teams, not just the best exact design (for instance, the crossed-dowel fix is a nice design, but difficult to implement since the shaft is hard).

3. Specs for a fix are needed quickly. I'm very interested to see what would CB Petrovic comes up with the 4140 material solution. If I had to pick the "best" fix, that may be it... to re-create a bunch of plates out of 4140.

which brings us to this...

4. IF someone can get a fix (prints and a CAD file) done quickly, there could be ways to mass-produce new parts to get out to teams. I would suggest that a well-toleranced print be made, along with an acurrate CAD file (.stp version). Then, someone could go to http://www.mfg.com and post this as an RFQ. They could ask for quotes to be returned within 1-2 days, and finished parts to be required within one week. We at AndyMark have used www.mfg.com as a fabrication resource of multiple parts and have had good experiences 90% of the time. The bid could be awarded to multiple suppliers, each providing 1-2,000 parts. My guess would be that this part would cost anywhere between $8-$14 if someone was making 1,000 in this short lead time situation.

Once parts were made, boxes of them could be sent out to regions, and then teams could drive a couple of hours to get their part from a central location.

Andy B.

Re: Banebot 56mm gearbox - double D related
 

That sounds like a plan..... :)

Some things to consider: The 12:1 and 16:1 output planet carriers are different, because the planet gears are a different size, so the pins are in a different location. Would the replacements be available for both the KOP 12:1 and the upgrade 16:1 transmissions? or would teams have to settle for using 12:1 only?

If you're not familiar with the transmission design, it is a two stage planetary, with a 4:1 first stage, and a 3:1 second stage. An upgrade 4:1 second stage is available from Banebots, and apparently some teams have decided to use it, and apparently it has the same problem with planet carrier plate failure under some conditions. The stages are mostly interchangeable, except that the pinion for the CIM motor is only made for the 4:1 stage (as far as I know), and also I believe it is the only one that will fit in the motor mounting end of the transmission.

Should the replacement plate be made significantly softer than the shaft, to act as a sacrificial part?

Would it include the planet gear pins, or would the teams have to press them out of the old plate, and into the new plate?

Is anyone going to consider the end play issue now, or wait until it causes problems in regionals?

Re: Banebot 56mm gearbox - double D related
 

Thanks Andy for taking the high road in your posting.

For the "newbies" that are keeping up with this thread: this is what FIRST is about, a perfect example of gracious professionalism. Someone recognized a problem and posted it here. Instead of finger pointing (yes, there was some in the beginning but that quickly subsided), the dialog quickly turned to "Ok, what now? Let's come up with a solution." That posting mobilized an army of engineers, students, teachers and teams working together for the common good.

Back to Andy.....Andy, thank you for taking the high road here. You very easily could have said, "Hey, teams!! AndyMark has an alternative design here. We can provide......." You can guess what the rest of the sales pitch would be. But, no. Andy has offered a solution instead of a sales pitch. THAT is GP in action!!

Re: Banebot 56mm gearbox - double D related
 

Hi,

I know this will not help all of the teams, but since we were already machining our own shafts for a direct drive application we decided to hex the end of the shaft and the carrier plates. The parts will be made by Thursday and will hopefully be tested out Thursday night for a couple hours. We will be making the plates out of 4140.

I don't have access to modeling software until Thursday, so the only drawing I can post is a quick sketch, I will also post the IGES files we sent out for machining. The files will only be useful for the carrier pin hole dimensions as we have a hex in the plate instead of the double d. Also please note that the dimensions in this file were calculated using the SINE Law by measuring the pin diameter and the outer dimension between two pins of the pentagon, so if anyone can double check the dimensions...

By Thursday I will be able to post some results of the the strength of the modified shaft and carrier plate and ensure that the parts as dimensioned on this sketch and in the IGES files mate into the existing transmission.

Re: Banebot 56mm gearbox - double D related
 

Andy,
I will have a STEP file and associated print with tolerances made by one of the best engineers I know (he's a Delphi guy that I could never quite get involved in FIRST... ...maybe some day).

I am also getting the shaft drawn up in CAD too.

Here is my thought process. I am looking for options here. We don't really have a bound on the problem yet. I believe it is likely that an RC 23 carrier plate will be the solution for teams with 1-CIM. But there are teams that have counted on using the 2-CIM with 16:1 ratio. Also, hoping for a good test outcome is not a plan -- it is just a hope. So, I am looking for options in case the tests show that an RC23 carrier is not enough. In this case, there is no more we can do with the carrier alone because we will just push the failure to the shaft. So... ...I am starting to think about the next step in case we have to take that step.


2 questions for folks with the right knowledge base:
#1 should we make the joint square to increase the surface area (and thereby lower the stress)? I have found an 11/32" square broach (8.73mm). Going from a 9mm D to a 8.73mm square will lower the stress to 46% of the current value (an increase in the failure torque of 2.15 (50% of the reduction is from 4 sides taking torque rather than 2 and the extra 4% reduction is that by going to the smaller distance between the flats, you get a larger load surface).

#2 I am thinking that we should have a target hardness of RC 40. This is a Tensile yield of 180Ksi (1250 Mpa). Is this too brittle? I am thinking it is probably ok. My reasoning is that I know that Forkbolts for car door latches are hardened to RC30-38. If RC38 is good enough to take the impact loading from a car crash, I think that RC38 is not too far. It is a small step from 38 to 40. Please share your educated gut feelings with us (provided you have an educated gut).

Joe J

Re: Banebot 56mm gearbox - double D related
 

It is great to know that there great minds working on the solution. We are a team of very limited resources (financially and know how) and we rely heavily on the items provided in the KOP. The thought of a filed gearbox will most certainly means a pedal powered robot for us, but on board human players are now allowed :) Hopefully a solution will be found soon!

On behalf of our team, I want to say thanks in advance to everyone working on this problem! It is posts like this that give teams a "heads up", practical advice on a workaround or an alternate solution. This is just one of the reasons the FIRST community is in a class all its own.

Re: Banebot 56mm gearbox - double D related
 

I have had good success with STEP files. IGES is fine but circles are often not circles, arcs are not arcs, etc. It is a pain sometimes -- especially if you have to modify the part or if you have to measure things.

For what it is worth.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

This is the beginning of a failure but it is still a long way from a robot making a perfect circle. Will you please continue the test until a failure that stops the robot occurs? If you take pictures periodically and post them, all the better. If you send me your address, I will send you a replacement for the carrier.

This will be a very good set of data to capture the failure and to test possible solutions (with perhaps something to test coming in a few days).

Thanks.
Joe J.

Re: Banebot 56mm gearbox - double D related
 

Can anyone else see these slides? I can not.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

In reference to the hardening question, I have spoken to our local heat treating facility and they recommend a hardness of RC40. The implication of this is that you should probably start by using standard 4140 (vs. prehard @ approx. RC23) and have the parts heat treated professionally after machining. Speaking from my own experience, 4140 will become too brittle (break vs. deform) for this application at RC>45.

Re: Banebot 56mm gearbox - double D related
 

This is a very strong case that the gearboxes will indeed fail in the field.

As to the low cycles, I have not observed this particular robot in action but based on other mechanum wheel robots I have seen (I can't get to YouTube from this PC), I am not sure that the loading was infact "low cycles"*

In these types of drives, even though the motion of the robot is smooth and continous, the voltages commanded to the motors are often rapid step changes from Full Forward to Full Reverse back to Full Forward -- Again, I am not denying that there is an issue, I am just saying that even though it is direct drive and only 30minutes, it may infact be many many high impact loadings on the gearbox.

For what it is worth.

Joe J.

*Don't jump on me here for burrying my head in the sand. I am have been working this issue since I first saw the joint the day after kickoff. It is only recently that I have been able to get others to join me.

Re: Banebot 56mm gearbox - double D related
 

Joe,

A target harness approaching RC 40 should be fine. We have run
welded axles, 4130 flanges welded with 4130 rod onto 4130 axles
for several seasons. We harden these and then temper at 800F.
Tempered at 900F, a little softer, the RC is 36 and the tensile yield
strength is 161,000 psi. We temper at 800, slightly off the charts, so
to speak, but safely above the brittle zone, to get just a little more
strength. We have bent these axles in competition with direct robot
impact on a cantelevered wheel setup, but have never broken one.

Hardening the carrier plates to a value approaching RC 40 is probably
just right. Using 4140, or even better 4340, is best for this application.
We are using 4130 because this is the material we have on hand.

Here is a link to useful heat treatment info:
http://www.aerospacemetals.com/steelalloys.html


Eugene

Re: Banebot 56mm gearbox - double D related
 

Great data. Thanks.

I have just spoken with a materials guy at Delphi. He has recommended 1040, hardened (he advises oil quench since the parts are relatively thin) then tempered to RC 40-42.

This is from a source I will call "usually reliable" but I am really out of my comfort zone on this one.

Everyone with expertise in this area please feel free to comment.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

We are 2nd year team that is planning on using the 56 Trans in direct drive. I am new to posting as well. One possible solution we came up with is to reduce end play by adding a shim between the motor and the drive gear. This pushes the whole mechanism forward so ultimately the drive shaft is set "into" the Double D. We don't have a drive train to test yet. If other teams could make comment or possibly test this solution we be most grateful. We feel the end play is allowing the failure to occur. Also my technical adviser suggests crucible packed with charcoal, bone, or other carbonized material and forge heated for 8 hrs or more. We are concerned about warping the plate. We are opting to not heat treat and have andymark trannies just in case we have to redo the drive train.

Re: Banebot 56mm gearbox - double D related
 

I always had a feeling metallurgy was one of the dark arts.....

As for the shim idea, it sounds reasonable to me at first glance, but I have not had a chance to take a close look at the fit of the motor and gear. I think it would be relatively easy to figure out the shim thickness required, although you'd have to pull the gear off the motor shaft to install it, or change it if it's wrong. Also putting the shim there would be best from the viewpoint of having full gear tooth engagement. Adding the shim in the second stage planetary would allow partial sun gear/planet gear contact.

Re: Banebot 56mm gearbox - double D related
 

An update on the heat-treating front: Yesterday, I tempered the 42mm plate, which seems to be some type of tool steel, and managed to get a significant increase in hardness, although my first attempt was too brittle. I will try again when I get another sample, but in the mean time I tested the 56mm plates too. Unfortunately, they are definitely NOT tool steel and will not harden much without adding carbon. Some data:

56mm carrier before heat treatment: HRA 46.1, 46.5, 46.5
56mm carrier, 950C for 15 minutes, oil quenched: HRA 49.3, 49.9, 49.4
56mm carrier, 950C for 15 minutes, water quenched: HRA 57.1, 57.9, 58.5 (about a C16)

It's a slight improvement, but not the C40 we are looking for or even the C23 of the shaft. Case hardening is still an option, but not an easy one. I suspect the solution will be an entirely new plate made of something harder and with a tighter fit for the shaft. I will probably shift my focus to this avenue now, although hardening is still an easy solution for the tool-steel 42mm carrier.

Good luck all!

Re: Banebot 56mm gearbox - double D related
 

I was pondering making the shaft to plate joint a press fit. I think it would be relatively easy to get the size for round part of the hole figured out, but I wonder what the tolerance is on the flats on the shaft. If they vary by more than a thousandth of an inch, it would be challenging to get a reliable fit.

It would be really nice from the viewpoint of the wear we are seeing....I know in automotive transmissions, once splines start to get loose, they wear out quickly.

Re: Banebot 56mm gearbox - double D related
 

I think that we have pretty much put to bed the idea that the carriers can be easily hardened (by teams or even by a "swap service" of some kind).

I think the urgency of getting the mat'l analysis is lessened.

As to the tight fit, this is going to help some but my theoretical analysis/calculations do not show a significant improvent in this case (nothing like what I expect we need).

Here is my current thinking of most likely patches:
#1 harder carriers (= to the shaft hardness) address all the 1-CIM cases (16:1 & 12:1)
#2 harder (perhaps RC 40-45) carriers plus redesigned joint (e.g. square hole) plus harder (again perhaps RC 40-45) shafts (with mating joint) address all the 2-CIM cases (IF, and this is a big IF, tests show 2-CIMs stress the joint beyond what is done in #1 -- note that motor torque is not the only thing that determines the torque this joint sees, friction is another and it may limit the torque that the joint sees to something close to the 1-CIM number)

Stay tuned.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

I'm ordering O1 and A2 tool steel to test with. I can cut them on the waterjet, but the tolerances will not be great. Maybe start small and work my way up to a nice press fit? I'm hoping with the same material as the 42mm plates, I can treat them to be just about any hardness I want. The A2 may be hard enough (B89-99) without any treatment.

I am not going to try 4140 because I think other people are on top of that and I don't know where to get 5/32" by tomorrow.

I should also mention that our original 56mm carriers showed only the very tiny beginnings of deformation after driving around yesterday evening (1 CIM, 12:1), although we haven't done high-cycle testing.

Re: Banebot 56mm gearbox - double D related
 

Dunno what's u, I can see these from my house, I'm at the school now and cannot. Let's try this.

Re: Banebot 56mm gearbox - double D related
 

So, unbeknownst to me, one of our mentors has connections and is trying to get the 52mm carrier plate spectrally analyzed to determine alloying materials and carbon content, hopefully by tomorrow or friday if I'm really lucky. I'll keep everyone posted as soon as I have results.

Re: Banebot 56mm gearbox - double D related
 

Can we start a pool? If so I will take 1018. Didn't do any analysis, but it is in that range of hardness and won't harden with plain quenching. I'm very interested to see the results. I wish I could have gotten to the machines here, but I have more MechE connections than materials connections.

Re: Banebot 56mm gearbox - double D related
 

Got em now, but I am at home. Must be a firewall issue.

Joe J.

Re: Banebot 56mm gearbox - double D related
 

Interesting. I quoted the message to get the actual links, and when I tried to open them directly, I got a 404 Not Found error.

Re: Banebot 56mm gearbox - double D related
 

This thread is getting way too long. I fear that folks with dial up will miss the shipping date waiting for it to load.

Also, there is a lot of valuable information but it is pretty diffuse.

I am closing this thread. But no worries. I will start another one here:

Banebot 56mm gearbox - double D - RELOADED

It has what I think is the best information we have up to this point.

Joe J.