Weird Gearbox Sound

[thinker&planner]

Originally Posted by maxnz

I just checked the battery and it tested at 39%.

39%, at what load?

As batteries age, they may appear to still be good (have a high voltage) but under high load they drop voltage very quickly.

If you're using the CTRE Battery Beak, use the % or voltage at whatever the highest load is (18A?). That should give you a better idea of what it will actually run at during driving.

[maxnz]

Originally Posted by thinker&planner

39%, at what load?

As batteries age, they may appear to still be good (have a high voltage) but under high load they drop voltage very quickly.

If you're using the CTRE Battery Beak, use the % or voltage at whatever the highest load is (18A?). That should give you a better idea of what it will actually run at during driving.

I'll check the battery again as soon as I can, probably in 30 minutes. The battery tested at 95% that morning before we started, if that helps at all.

[Jon Stratis]

If you'd like, I'd be happy to stop by after work sometime this week - I know you have very little time to get it fixed before States, only 6 hours of robot access outside of the bag!

My first guess is a dead battery, and we can look through your driver station logs pretty quickly without unbagging the robot to see if that was the case.

My second guess would be some sort of mechanical interference or damage, something that would require the robot outside of the bag and running to figure out, eating up work time!

Let me known in a PM if you want me to swing by after 5 one of these days, I'm available all week (except for Friday, when I'll see you guys at load-in!).

Edit for those curious: the Minnesota State High School League State Tournament is held every may, a few weeks after champs, and is a bag and tag event, following the district bag and tag rules of 6 hours of robot access leading up to the event. This is done to keep the playing field level for the event, as someone last competing in week 1 would otherwise have significantly more time than someone competing at Champs would. It's not perfect, but the best we can do!

[maxnz]

Originally Posted by Jon Stratis

If you'd like, I'd be happy to stop by after work sometime this week - I know you have very little time to get it fixed before States, only 6 hours of robot access outside of the bag!

My first guess is a dead battery, and we can look through your driver station logs pretty quickly without unbagging the robot to see if that was the case.

My second guess would be some sort of mechanical interference or damage, something that would require the robot outside of the bag and running to figure out, eating up work time!

Let me known in a PM if you want me to swing by after 5 one of these days, I'm available all week (except for Friday, when I'll see you guys at load-in!).

We have the pepfest on Thursday (2:15) if you want to come by then. We'll have it unbagged then. Thanks for the offer!

[Jon K.]

As someone who has seen more matches than most (close up, on the field) I would check your pulleys and belts. It sounds, and looks, more like the belts were slipping than a gearbox gear broke. While I don't think the cold would have had that much of an effect, with the intermittent driving, there could have been some issues with heating and cooling of parts unevenly.

[maxnz]

We have had the belts slipping a few times this season, and this wasn't that. That was what I checked for first when it started acting weird.

[maxnz]

So, we had a little parade through the school this morning where we ran the robot, and the robot seemed fine. The stuttered movement never happened, so we think that that was due to the low battery.

As for the gearbox, it still had the weird sound like there was sand or something in the gearbox. The other gearbox sounded similar this morning. It ran fine, but we don't know what the sound is from.

[happyWobot]

Originally Posted by maxnz

So, we had a little parade through the school this morning where we ran the robot, and the robot seemed fine. The stuttered movement never happened, so we think that that was due to the low battery.

As for the gearbox, it still had the weird sound like there was sand or something in the gearbox. The other gearbox sounded similar this morning. It ran fine, but we don't know what the sound is from.

You said this was a TB Mini, correct? Back out the screws holding the plastic cover in place about 1/4 turn each. Run the robot and see if that changes anything. If not back them out another 1/4 turn. I ran into a situation this year with a brand new mini that if I over tightened the case the transmission would make noise. I think something is at a very low clearance and that the plastic cover changes shape if overtightened causing it to come in contact with one of the gears. Any chance your mini is 12.75:1?

[maxnz]

Originally Posted by happyWobot

You said this was a TB Mini, correct? Back out the screws holding the plastic cover in place about 1/4 turn each. Run the robot and see if that changes anything. If not back them out another 1/4 turn. I ran into a situation this year with a brand new mini that if I over tightened the case the transmission would make noise. I think something is at a very low clearance and that the plastic cover changes shape if overtightened causing it to come in contact with one of the gears. Any chance your mini is 12.75:1?

Yup, a Toughbox Mini. It is set at the standard gear reduction that is detailed in the assembly manual. If I remember correctly, it is 12.75:1 or something similar. We can try that tomorrow when we unbag the robot at state. Did it sound similar to what it sounded like in the video I posted?

[happyWobot]

Originally Posted by maxnz

Yup, a Toughbox Mini. It is set at the standard gear reduction that is detailed in the assembly manual. If I remember correctly, it is 12.75:1 or something similar. We can try that tomorrow when we unbag the robot at state. Did it sound similar to what it sounded like in the video I posted?

If you mean the sound at the end of the video, yes, that sounds familiar.


Has it always made the noise since the case was constructed?

If not, is there any chance some students went on a bolt tightening exercise recently?

Did you tape over the small holes on the back side to prevent debris from getting in?



I experienced the noise with a brand new case. Took it apart and reconstructed it twice. Discovered that if I tightened the plastic cover too much the noise was louder. I had a second case that was also brand new purchased at the same time. It made not a sound. Both were constructed at the same time, in tandem, and were identical as best as I could observe. I let off on the case bolts just till the noise was barely noticeable, then installed it CIMs and all into the chassis.

It actually got quieter over time. I had several theories about what it was, first was that the tightening of the case was causing the plastic to deform in a way that made it come in contact with one of the gears. The second was that the weight of the CIMS were doing something similar to the plastic cover. The third thing was that if there was some sort of contact or vibration, that the plastic cover was magnifying the sound like a drum.

I know for certain it was not the gears. The gears were clean with freshly applied grease. With the cover off it did not make a peep when turned. The gearing is ridiculously simple, the shafts confirmed to be mounted into the bearings until firmly seated. With the cover on, once tightened all the way down, it would make that rattle. Like as if gear teeth were coming contact with some part of the cover.

If you find that the noise goes away by loosening the cover just a bit, tighten it back down until the noise starts again and then just back off a touch. We got through two qualifiers, a district Championship and worlds and never once had an issue with either one.

[maxnz]

Originally Posted by happyWobot

If you mean the sound at the end of the video, yes, that sounds familiar.


Has it always made the noise since the case was constructed?

If not, is there any chance some students went on a bolt tightening exercise recently?

Did you tape over the small holes on the back side to prevent debris from getting in?



I experienced the noise with a brand new case. Took it apart and reconstructed it twice. Discovered that if I tightened the plastic cover too much the noise was louder. I had a second case that was also brand new purchased at the same time. It made not a sound. Both were constructed at the same time, in tandem, and were identical as best as I could observe. I let off on the case bolts just till the noise was barely noticeable, then installed it CIMs and all into the chassis.

It actually got quieter over time. I had several theories about what it was, first was that the tightening of the case was causing the plastic to deform in a way that made it come in contact with one of the gears. The second was that the weight of the CIMS were doing something similar to the plastic cover. The third thing was that if there was some sort of contact or vibration, that the plastic cover was magnifying the sound like a drum.

I know for certain it was not the gears. The gears were clean with freshly applied grease. With the cover off it did not make a peep when turned. The gearing is ridiculously simple, the shafts confirmed to be mounted into the bearings until firmly seated. With the cover on, once tightened all the way down, it would make that rattle. Like as if gear teeth were coming contact with some part of the cover.

If you find that the noise goes away by loosening the cover just a bit, tighten it back down until the noise starts again and then just back off a touch. We got through two qualifiers, a district Championship and worlds and never once had an issue with either one.

As far as I know, it only started making that sound on Saturday. They both sounded like the first sound until then. We did tighten bolts last week, but they were the ones holding the plate to the chassis. The other gearbox sounded similar to the weird one yesterday morning, but not as 'bad'.

Also, what holes are you speaking of?

Originally Posted by Jon K.

If you are still experiencing these sounds, I would definitely take the gearboxes off and double check the gears. It's highly unlikely that you have managed to sheer teeth off the steel gears in the TB Mini, but this is the year of the strange failures.

A couple of quick questions:

Did you run the gearboxes in for about 30 minutes prior to greasing them?
Have you done any maintenance on the gearboxes this season?
-Running outside might have introduced a foreign contaminant into the gearbox, and it might be worth cleaning the gearboxes out and greasing them again after checking the teeth.
Have you checked the tightness of the screws holding the CIM motors on?

As for greasing, the gears already had some grease on them from previous years, so we didn't think much about regreasing them. We did take apart the gearbox in question at our regional because a key fell out (making one of the motors hot, indicating something was wrong). We took it apart, added a key, added a washer (to each CIM) to keep the keys in, then reassembled it and added it back onto the robot.

[Jon K.]

Originally Posted by maxnz

As for greasing, the gears already had some grease on them from previous years, so we didn't think much about regreasing them. We did take apart the gearbox in question at our regional because a key fell out (making one of the motors hot, indicating something was wrong). We took it apart, added a key, added a washer (to each CIM) to keep the keys in, then reassembled it and added it back onto the robot.

I would definitely pop open the gearboxes and give them a good once over, clean the gears off and the housings out, and then reapply some red tacky grease. There are a few holes on the outside of the housing that allow you to tighten the screws down, etc. Those holes do have the risk of debris entering, although it is rare that it is enough to cause more extreme sounds like those in the video.

[cbale2000]

So, a few thoughts based on experience:

1. The first part of the video seemed like an electrical issue, like a dead battery or a short. The behavior was not indicative of a mechanical failure, at least none I've seen.
2. The sounds in the second part sounds like one of three things, it could be either one of the motors not being powered (assuming you use 2 per gearbox), a CIM that has lost it's key between the shaft and the pinion gear (and is free-spinning), or gears not engaging each other in the gearbox for some reason (probably due to lost teeth or loose motors).

I would be curious if the issue persists if the robot is up on blocks (wheels not touching anything), I would also be curious if you could identify a certain action that causes the issue to happen consistently (turning the robot, for example) or if it just happens at random. I would also suggest monitoring battery voltage during such tests through the driver station.


On a somewhat related note, our team experienced some odd behavior (seemingly random jerkiness during acceleration) with our drive system this year when using Talon SRX controllers in CAN configuration. We later realized the issue only occurred when the controllers were fed a 100% power command. We changed the code to limit the max output to 99.9999% power and the issue vanished.

[Jon K.]

If you are still experiencing these sounds, I would definitely take the gearboxes off and double check the gears. It's highly unlikely that you have managed to sheer teeth off the steel gears in the TB Mini, but this is the year of the strange failures.

A couple of quick questions:

Did you run the gearboxes in for about 30 minutes prior to greasing them?
Have you done any maintenance on the gearboxes this season?
-Running outside might have introduced a foreign contaminant into the gearbox, and it might be worth cleaning the gearboxes out and greasing them again after checking the teeth.
Have you checked the tightness of the screws holding the CIM motors on?

[Monochron]

It kind of looks to me like nothing more than a brown-out. The stuttering and flickery RSL are the normal symptoms of brownout, and a difference in gearbox sound (because you aren't giving the motors your normal 11-13 volts) is expected. If your battery read as 39% (3.9V?) then you were probably well below brownout levels.

The fact that no one else mentioned this has me worried that I missed something obvious though