Banebot 56mm gearbox - double D related

[MrForbes]

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.

[Jonathan Norris]

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.

[Nitroxextreme]

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.

[sanddrag]

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.

[dapub]

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

[Joe Johnson]

Originally Posted by dapub

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

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.

[cbpetrovic]

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

[MrForbes]

Originally Posted by squirrel

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.

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.

[haroony341]

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.

[cbpetrovic]

Originally Posted by squirrel

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.

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