pic: Banebot P60 Failure

[thefro526]

loading photo ...

[Lowfategg]

Another thing to look out for is the roll pins that hold the outer ring gear to the front plate. The wall on the roll pin holes bend and lets the flats on the ring gear slip which ends up rounding the whole front of the gear. I can see it already happening to this gearbox.

Install a torque limiting sprocket to take care of some of that shock load at ends of travel if your using chain.

[billbo911]

This is copied directly from the Banebots P60 64:1 RS550 page.

Maximum torque recommendation

We recommend maximum torque not exceed 35 ft-lb for all P60 Series Gearboxes

Yep, that's what happens when you stress things past their design spec.

[Swampdude]

We stripped our 256:1 today also....

[Mike Schreiber]

That's a shame considering how long they take to get...

[Hawiian Cadder]

we did that to a 144-1 p80 once, made quite a lot of rattle. we used 81-1 and then a 3-1 chain reduction to solve this problem (it will take 10 times what we expect.)

[thefro526]

Originally Posted by Lowfategg

Another thing to look out for is the roll pins that hold the outer ring gear to the front plate. The wall on the roll pin holes bend and lets the flats on the ring gear slip which ends up rounding the whole front of the gear. I can see it already happening to this gearbox.

Install a torque limiting sprocket to take care of some of that shock load at ends of travel if your using chain.

The 4 roll pins have already stripped out of the front bearing mount, but I believe that we may be able to press new roll pins in - I'm not sure yet.

Our mechanism is designed so that the gearboxes themselves should never "see" more than 15-20ft-lbs of torque. The majority of the damage done to these gearboxes was done when I was testing an arm fix and went from full speed up to full speed down, something that the operator does not do in competition.

[billbo911]

Out of curiosity, did you have the end of the shaft supported?

[sanddrag]

Originally Posted by billbo911

Out of curiosity, did you have the end of the shaft supported?

And can we get a picture of the whole arm?

[thefro526]

Originally Posted by billbo911

Out of curiosity, did you have the end of the shaft supported?

The end of the shaft is not supported right now, but the point where the sprocket attaches is only about 3/4" from the face of the gearbox. There isn't really any way for us to support the end of the shaft, and we're not sure if we need to yet.

Originally Posted by sanddrag

And can we get a picture of the whole arm?

I don't have any pictures of the arm handy but here is a video: http://www.youtube.com/watch?v=s8SR93PZ_Ac

I believe that the gearbox failed during testing of our aluminum lower link fix. The arm is geared to approximately 90* per second max speed, and at that speed I abruptly reversed the arm causing one of the gearboxes to fail. We plan on limiting the speed of the arm once all of the sensors are installed so that this can not happen again. Strangely enough the arm was put through nearly 40 cycles after that test and there was some binding when un-powered, but powered the arm worked fine.

[AdamHeard]

Originally Posted by thefro526

The end of the shaft is not supported right now, but the point where the sprocket attaches is only about 3/4" from the face of the gearbox. There isn't really any way for us to support the end of the shaft, and we're not sure if we need to yet.



I don't have any pictures of the arm handy but here is a video: http://www.youtube.com/watch?v=s8SR93PZ_Ac

I believe that the gearbox failed during testing of our aluminum lower link fix. The arm is geared to approximately 90* per second max speed, and at that speed I abruptly reversed the arm causing one of the gearboxes to fail. We plan on limiting the speed of the arm once all of the sensors are installed so that this can not happen again. Strangely enough the arm was put through nearly 40 cycles after that test and there was some binding when un-powered, but powered the arm worked fine.

I would modify your system before ship, this isn't the kind of failure you want to ignore.

High reduction banebots gearboxes are a bad idea, I'd solve it before ship.

[dez250]

Originally Posted by thefro526

Our mechanism is designed so that the gearboxes themselves should never "see" more than 15-20ft-lbs of torque. The majority of the damage done to these gearboxes was done when I was testing an arm fix and went from full speed up to full speed down, something that the operator does not do in competition.

If it can happen it will happen. I am with Adam on this one and would redesign it so you can't see more torque than the transmission is spec'd for. Just because you normally wouldn't operate in this fashion, if it does happen, I wouldn't want to be the one begging a team for a spare transmission at competition.

[Madison]

What is the overall ratio? How heavy and long is the arm? Is it counterbalanced?

I'm just curious about the conditions prior to failure. We have a similar implementation using a BB 81:1 gearbox and have beat on it pretty hard over the last two days. We haven't experienced any problems yet, but if our implementation is similar to your, I may tear the gearbox apart and take a peak inside.

[Chris is me]

Dustin,

Aren't you already slowing down the arm in software? All you need is another stage of chain reduction and you'll dramatically decrease the load on the gearbox, increase the output torque on the arm, and fix every problem you have.

[thefro526]

Originally Posted by Madison

What is the overall ratio? How heavy and long is the arm? Is it counterbalanced?

I'm just curious about the conditions prior to failure. We have a similar implementation using a BB 81:1 gearbox and have beat on it pretty hard over the last two days. We haven't experienced any problems yet, but if our implementation is similar to your, I may tear the gearbox apart and take a peak inside.

The overall ratio is approximately 819.2:1. The Banebot Transmission itself is a 256:1 ratio, and there is a 3.2:1 ratio after the transmission which drives the arm. The arms themselves are approximately 57" long with a 7lb load on the end. We also have some surgical tubing on the arm so it's effectively lifting a 1lb load at the end of the arm, and that load is being lifted by two RS775-18's through two 256:1 transmissions.

Originally Posted by Chris is me

Dustin,

Aren't you already slowing down the arm in software? All you need is another stage of chain reduction and you'll dramatically decrease the load on the gearbox, increase the output torque on the arm, and fix every problem you have.

We were planning on slowing the arm down in software if we found the need to. We may implement a 2nd reduction after the transmissions, but we'll need to see if this is physically possible with our system. A more likely solution is to swap the 15 tooth drive sprocket on the transmission to a 10 tooth drive sprocket which would give us an effective 4.8:1 ratio after the transmission.

I just want to say that they did not fail under "normal" use, they failed during a test in which I tried to get them to fail. I cycled our arm at the highest load point from 100% forward to 100% backwards a half dozen times before getting any sort of play in either transmission. One transmission failed, while the other was fine. (The drive sprocket for the arm was not tightened properly during re-assembly which appears to have caused one side to see more force than the other, but I'm not sure).

Note: This picture wasn't meant to start a discussion about our system, but to provide a visual record of a failed P60.