Banebot 56mm gearbox - double D - RELOADED

[DonRotolo]

Can someone please confirm for me: The 3:1 carrier plate is used in 12:1 transmissions, the 4:1 plate in 16:1 transmissions. You need one or the other if you are going to have new carrier plates made, but not both.

Is that right?

The thought is to get a price quote from a local machine shop based on Dr. Joe's prints. I plan on getting the 3:1 carrier plates plus the shafts, all at RC40.

Thanks,
Don

[MrForbes]

the 12:1 transmission uses a 4:1 first stage, and a 3:1 second stage. The 16:1 transmission uses two 4:1 stages. The first stage carrier plate has much less load on it than the second stage, so you don't need a new first stage plate.

If you decide to replace the vulnerable carrier, you need a new 3:1 second stage carrier made if you are using 12:1 transmissions.

[eugenebrooks]

The following table provides comparison data for 1040, 4140 and 4340 steel, that makes it clear what the best choice is if you are concerned about part failure.

http://www.auto-ware.com/techref/materials.html

[Donut]

Originally Posted by squirrel

One possible method of ensuring that the motors are started in a controlled way, would be to have the programming team put a limit on how fast the PWM outputs to the drive motor speed controllers increase. If they allow only a small change per unit time, then the gearboxes cannot be damaged by sudden direction reversals, even if the driver gets a bit exuberant (and I do realize how exciting the matches are!). Look into this, hopefully some of the programmers here can come up with some code to control motor acceleration rate.

For any team this should help to reduce some of the problems with the end plate tha are occurring, and really I think this is good practice regardless of what motors/transmissions you're using. If teams need help with this just ask, I know some teams (ours included) have been doing this for at least a few years.

[jskene]

With reference to Dr. Brooks' table in the above post of various steel properties, what degree of hardness do we need in the gearbox plate? This will help us decide which metal to start with.

We have access to a waterjet and a computerized furnace, and hope to make some parts. Hopefully we can make several.

[ZZII 527]

Originally Posted by jskene

With reference to Dr. Brooks' table in the above post of various steel properties, what degree of hardness do we need in the gearbox plate? This will help us decide which metal to start with.

We have access to a waterjet and a computerized furnace, and hope to make some parts. Hopefully we can make several.

Somewhere earlier in the thread, Joe Johnson posted some target hardnesses for different situations:

1 CIM 12:1 or 16:1 - HRC23. Any harder and the shaft becomes the weak link. But this should be enough to handle the torque of one motor in cyclic loads.

2 CIM 12:1 or 16:1 - HRC40 on the carrier and the shaft for the worst-case scenarios. Any harder and the steel may be too brittle.

Also, there are drawings in the first post for a plate/shaft with a square hole/end instead of the double-D, which will help with the stress distribution.

Dr. Brooks' team has made some HRC40 plates and shafts out of 4130 and my team now has two made out of A2 tool steel. I think 4130 or similar is the more appropriate choice, since C40 is almost off the charts low for tool steel. I got it because McMaster carriers 5/32" (4mm) precision-ground stock. Other teams and BaneBots are in the process of making and testing new parts.

[WaterFreak]

just wanted to post something so I get notified on updates.

we are using the 2 CIM adapter setup and I am now VERY concerned about our robot.

Will keep my fingers crossed that a timely solution presents itself, otherwise....

[RichardCMongler]

One possible method of ensuring that the motors are started in a controlled way, would be to have the programming team put a limit on how fast the PWM outputs to the drive motor speed controllers increase. If they allow only a small change per unit time, then the gearboxes cannot be damaged by sudden direction reversals, even if the driver gets a bit exuberant (and I do realize how exciting the matches are!). Look into this, hopefully some of the programmers here can come up with some code to control motor acceleration rate.

http://www.chiefdelphi.com/forums/sh...ad.php?t=53488

[Joe Johnson]

Originally Posted by WaterFreak

just wanted to post something so I get notified on updates.

we are using the 2 CIM adapter setup and I am now VERY concerned about our robot.

Will keep my fingers crossed that a timely solution presents itself, otherwise....

I certainly understand your concern, but I believe that you will be just fine.

#1 the failure is not instantenous, but rather works itself overtime. The rate that it fails is a function of robot design (heavier robots with grippier tires make things worse) and robot driving (repeated rapid changes increase the rate). There are many many robots out there that would never know there was any issue with these transmissions if they we did not tell them (even 2-CIM per side teams).

#2 the fialure only hurts the carrier, not the rest of the transmission. This will allow teams to drive as is and implement the solution when we finally get to that point. (we are working out the details -- stay tuned).

#3 while we are still working out the details of exactly what is need to address the problem, the early reports from teams that have implemented various bit of the plan have been very encouraging. Again, let me repeat that FIRST and Banebots are very much committed to working with teams to address this problem in a timely manner.

Stay tuned.

Joe J.

[WaterFreak]

Originally Posted by Joe Johnson

I certainly understand your concern, but I believe that you will be just fine.

#1 the failure is not instantenous, but rather works itself overtime. The rate that it fails is a function of robot design (heavier robots with grippier tires make things worse) and robot driving (repeated rapid changes increase the rate). There are many many robots out there that would never know there was any issue with these transmissions if they we did not tell them (even 2-CIM per side teams).

#2 the fialure only hurts the carrier, not the rest of the transmission. This will allow teams to drive as is and implement the solution when we finally get to that point. (we are working out the details -- stay tuned).

#3 while we are still working out the details of exactly what is need to address the problem, the early reports from teams that have implemented various bit of the plan have been very encouraging. Again, let me repeat that FIRST and Banebots are very much committed to working with teams to address this problem in a timely manner.

Stay tuned.

Joe J.

Joe - thanks for those words.

I have read through ALL of the posts and see that many people (with FAR more brain cells than I have in this area) are working on the problem and a re VERY motivated to come up with a reasonable solution.

Our robot is definately going to fall into the "heavy" category and, we are using the High Traction wheels from IFI along with a set of the Coolie-Dualie Wheels from AndyMark. We may consider adding some "software" to our program to limit the forward/backward transitions to try and prevent some of the potential for damage.

In the meantime, our team is going to at least talk about some Risk Mitigation strategies today and come up with a "Plan B".

Keep plugging away, am sure there are a LOT of teams all in the same boat.

[eugenebrooks]

Originally Posted by jskene

With reference to Dr. Brooks' table in the above post of various steel properties, what degree of hardness do we need in the gearbox plate? This will help us decide which metal to start with.

We have access to a waterjet and a computerized furnace, and hope to make some parts. Hopefully we can make several.

Reading from Mil Spec MIL-H-6875H

4340 1550F soak for half hour, oil quench, 850F temper, tensile is 200-220 ksi
4130 1600F soak for half hour, oil quench, 850F temper, tensile is 160-170 ksi
4140 1600F soak for half hour, oil quench, 850F temper, tensile is 180-200 ksi

Seal the parts in a stainless bag, flushed with argon, that is easily cut with shears while glowing so you can drop the parts in the oil quickly without them cooling off in air before the dunk. Tempering cooler will increase strength, but as you approach 700F the parts become brittle. These strengths are way above the strength of the factory shaft. You should make both parts, and use a square hole, to get the full benefit of the improved materials/geometry.

[ZZII 527]

Here's a really cool McMaster white paper on steel properties and heat treatment:

http://www.mcmaster.com/addlcontent/...p?doc=88645KAC

If that link doesn't work, search the catalog for: 88645KAC

[Arkorobotics]

If I took out the CIM spacer cut it down to the right size to fit and cut down the CIM's shaft to be flush with the gear, and Lubricated it would this help prevent Binding and a risk of the plate breaking?

[ZZII 527]

Originally Posted by Arkorobotics

If I took out the CIM spacer cut it down to the right size to fit and cut down the CIM's shaft to be flush with the gear, and Lubricated it would this help prevent Binding and a risk of the plate breaking?

Probably not. This would help the gearbox and motor run smoother, but it will transmit torque as well or better than it did before, meaning the double-D could still deform over time.

Update on the tempered C40-hardness A2 tool steel carriers: We finally got around to re-mounting and testing today. The HS kids enjoyed the opportunity to do wheelies and driving it like crazy in a confined area. After about 5-10 minutes of driving, a sprocket bolt fell off (somebody forgot locktite) and everyone suddenly had to leave instead of fixing it.

I wouldn't call this definitively tested, but they didn't fracture and there is no backlash to be seen right now. More testing to come tomorrow.

Our drivetrain is 1 CIM, 12:1, going to a 6WD. See attached pic.

Edit: Yes, I know the shafts aren't well supported. O_o

[Arkorobotics]

Originally Posted by ZZII 527

Probably not. This would help the gearbox and motor run smoother, but it will transmit torque as well or better than it did before, meaning the double-D could still deform over time.

Update on the tempered C40-hardness A2 tool steel carriers: We finally got around to re-mounting and testing today. The HS kids enjoyed the opportunity to do wheelies and driving it like crazy in a confined area. After about 5-10 minutes of driving, a sprocket bolt fell off (somebody forgot locktite) and everyone suddenly had to leave instead of fixing it.

I wouldn't call this definitively tested, but they didn't fracture and there is no backlash to be seen right now. More testing to come tomorrow.

Our drivetrain is 1 CIM, 12:1, going to a 6WD. See attached pic.

Funny thing is that it does run smoother and no signs of binding, yet (hopefully never). How much torque does it really take to backlash it and break it?