Banebot 56mm gearbox - double D related

[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)

[Joe Johnson]

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.

[B. Flaherty]

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.

[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?"

[jskene]

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).

[Andy Baker]

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.

[MrForbes]

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?

[Rosiebotboss]

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!!

[Jadium]

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.

[Joe Johnson]

Originally Posted by Jadium

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.

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.