Banebot 56mm gearbox - double D - RELOADED

[Joe Johnson]

This thread is actually a continuation of this thread.

The thread was getting so long that I was worried that folks with dial up would miss the ship date waiting for the page to load.
It is a complex issue so I will try to summarize.

History:

• FIRST sourced Banebots for the 2007 KOP transmission in the Summer of 2006 after having evaluated prototype transmissions in both the 1-CIM and 2-CIM configurations.
• Shortly after kickoff, I became concerned about the double D joint.
• Analysis and Bench tests confirmed that there was reason for concern.
• Earlier this week a team first reported excessive wear in the D joint (the bow tie effect) confirming the failure predicted by analysis and demonstrated by bench tests.
• More test were done and a few more reports of bow tied carrier plates.
• FIRST published the issue in UPDATE #5, warning teams that there is an issue and that folks were working on it.
• Much help has been offered by the FIRST community to address this problem.

The data is not 100% certain, but here is where we stand as best as I can summarize:

• In some (but not all) conditions, the double D hole in the carrier plate will plastically deform into bow tie.
• The field failures up to this point show that the bow tie opens up gradually (many cycles not several fatal blows). As it fails, more and more backlash is observed in the gearbox.
• It is reasonable to expect that bow tie will eventually (after 100's of cycles) resulting in complete failure (though as of this moment, complete failure has not reported except as a result of a torque to failure bench test I performed)
• The carrier plate is significantly softer than the shaft.
• While the exact alloy of the carrier plate is not known, it is believed that the composition of the plate does not lend itself to easy hardening.

What is next:
Couple of teams have volunteered to be best subjects.
They will run a baseline set of tests to determine the extent of the problem
These teams will act as our proving ground to evaluate proposed solutions

Working together with Banebots, FIRST, and the ChiefDelphi.com I believe we are closing in on a set of solutions to this issue. Based on my communications with Ed Yackey from Banebots, folks from FIRST, and many in the larger FIRST community, I can assure you that everyone is committed to working this issue to a successful conclusion.

So what is that solution?
I cannot say 100% for sure at this point because there are still a few unknowns that could change the answer, but this is what I believe is the most likely scenario at this point.

Plan A:

New harder (RC 23) carrier plates. Hardness equal to the hardness of the output shaft. This should result in close to a 2X increase in the max torque

Plan B:

New harder carrier plates (RC 23) with square hole (rather than round with double D) Plus modifying or making new output shafts with square drive. Should give approx. 2X increase in max torque over Plan A.

Plan C:

Same as plan B only with harder (RC 40) carrier plate and output shafts. Should give approx. 1.5X over Plan B

1-CIM motor:

It is my opinion that Plan A will address this issue

2-CIM motor:

It is my opinion that Plan A will possibly address most of these failures but in order to fully address this issue for teams that are using 2-CIMs, we may have to go to Plan B.

Status:
We are working to have a sample solutions of Plan A to test for the weekend. We are in the process of planning Plans B & C but believe me, we will have them ready when the time comes. Also, I have not listed a Plan D but trust me, we will come up with a Plan D and implement it if that is what it takes to make everything come out in the end.

Closing:
This whole thing stinks. Nobody wanted this. But, I am proud of the many people who were part of the solution. And, yes, I say solution. The proof of the pudding is in the eating but I am quite confident that we have all the ingredients of a tasty dessert on the table.

Best Regards,
Joe J.

UPDATE:
I have just attached prints of the carrier (4:1 & 3:1) and the output shaft. I have versions with a 11/32" square hole. This is a commonly available broach size that is just under the 9mm flats on the DD (11/32" = 8.73mm).

I put these prints up here for 2 reasons:

• • 1st to get more eyes to look at the prints to find dimensions we have missed or mistyped.
  • 2nd to allow teams with appropriate resources to make the parts for themselves (and hopefully report back their success or failure)

Before I start a panic, note that NONE of the plans above involve teams making these things for themselves. If a team CAN make them for themselves, they may do so, but rest assured that we will not leave those who cannot stranded.

Some notes:
The material is spec'd at 1040 hardened, tempered to RC40. That is harder than we need. There are some who feel that the parts can be made from 41XX mat'l and not hardened. That is certainly true for RC23.

The square is just under the 9mm flats so it is possible that a team can modify the existing shafts to mate with a 11/32" broached hole.

These prints were not made to correspond to my organized Plans A, B, & C so they are kind of a mish-mash. Pick and choose as you see fit.

Please check dimensions for us. Check fits and tolernances too if you know what you are doing in this area. Report errors and clarifications needed.

Note that the dowel pins on the existing carrier are undersized 4mm pins. Brian Orr (my long suffering friend who did these prints for me -- staying to 11pm and his last day of working for Delphi -- special thanks to Brian whi is not even a FIRST fanantic.) sized the hole for such undersized dowel pins. If you are going to use standard 4mm dowels, you may have to open up the holes appropriately -- press fits are tricky be careful.