Breaking the First Helical Gearset Gearboxes!

[Jim]

Thanks to Team 537, Sussex WI for two valuable services rendered
1) Staging the mock competition yesterday for nearby teams. It was a blast and we are all glad that you do this! It helps remind us of all the organization that still needs to get done for a smooth work-flow at the real competitions

2) Trading us (Thanks Sami) the globe motor for your first helical gearset gearboxes. (Still checking on the availability of a spare victor 884) Thanks to your mock competition, we found at least ONE of our achille's heels.

WARNING TO ALL TEAMS USING THESE GEARBOXES:
We are using the set up as intended from FIRST with the DMs as the prime mover. In our case, one side of the box is mounted against a mounting plate. We blew out the bearing carrier on the unsupported side, TWICE (left side in one match, right side in another match).

We had done driver trials the day before and thought that after the first one let go, we must have started the crack the day before.

When the second one let go, we knew we had "issues". Real competition had found the weak link.

Our solution was to create a backing plate of aluminum with a small lip at the bottom. (Thanks to Loren and Heidi!)

The plate helps strengthen the box to the thrust load and the lip at the bottom helps with the force in that direction as the meshing gears try to move away from each other.

I will recommend tonight that we make more of these plates as a service to other teams.

[Adam Y.]

Can I see what exactly happened with a picture????

[Jim]

I am asking around for a picture now. I will let you know.

[Gamer930]

Dang Geocities took them down. PM me if you want them

Sorry the pictures are so big. Trying to do this at school. Unsure how the Geocities bandwith is going to workout. If you want I can e-mail them when I get home. PM me with your e-mail address.

[jrgrim12]

We had this happen yesterday for the first time. Our problem came from not having the wheel captured so it can't move. If you have it just like first did then you need to make sure the shaft can't be pushed from the side. You need to place a spacer between the wheel and the side of your robot so if the tire gets hit from the side the wheel and shaft won't move. Because if it does the side of that plastic can't handle those forces. It just wasn't designed to. I hope this helps.

[AdamT]

If you look throught the forum *I don't remember which section* this happened to another team, and they did the same thing with a metal plate...if I run across it again, I will post a link. The previous discussion was complete with pictures...

[f22flyboy]

I also recall that, but they said it broke under a no-load situation, and the lateral forces of the helical gears broke the plastic.

[Dick Linn]

Hope you had the internal gearbox spacers very precise so that the gears can't shift significantly when moving from forward to reverse. I think someone on this site calculated the end (axial)thrust of the gears and it was in the neighborhood of a couple hundred pounds...I can't recall. That could tear up the plastic. Also make sure nothing is misaligned and that the gearbox is securely but not overly tightened.

We used shaft clamp collars and machine washers to snug up everything onto the axle, not the spring or star washers or whatever you call them that came in the kit. We also were careful not to allow any axial play in the shafts, but then we have some dual-setscrew sprockets on the shafts between the wheels and the gearbox for our 4 wheel drive.

We didn't dop extensive testing, but a couple of us smaller guys (115 to 125 lbs.) rode up and down the ramp on top of the 'bot a couple of times and nothing seemed to come apart (one at a time. mind you). Note that with the sprockets between the frame rails and the wheels, the axles are cantilevered out from the frame a good inch or more beyond where they would be on a 2 wheel drive. I guess time will tell if it all holds up.

[f22flyboy]

I have noticed after extended operation, especially in high gear, the aluminum tubing provided as spacers for the helical gears is worn down. I have been shimming it with steel washers as a temporary fix, but we are trying to find some steel tubing with 5/8" interior diameter to replace the spacers at competition. Does anyone know where some can be bought, and if so I advise teams using the same tubing in their drivetrain to either make sure both there shafts and gears are securely pinned, or replace the aluminum tube spacers.

[Dick Linn]

I suspect that is why the Bellville spring washers were included in the kit. Although we didn't use them, I think they should be inside the gearbox to preload things and absorb shock.