Weird Gearbox Sound
 

We were at an outreach event this past Saturday and our robot started acting weird. Here is a video: https://drive.google.com/open?id=0By...3lnRkZwN0FFaXM

Just some notes:

• It was around 35 degrees Fahrenheit that morning
• The robot was out for about 2 hours and driven on and off for a total of about 10 minutes
• The weather was cold enough that the DJ's CD players needed to be warmed every 15 minutes to keep them working
• The robot started acting weird after about 1.5 hours in

I can give more details as needed.

Thanks!
Team 2855

Re: Weird Gearbox Sound
 

I bet it's a dead battery.
When it stuttered and the orange RSL light flashed (not the normal flash, flashing with the stuttering motors), that led me to think it's the battery.

You should be able to check the driverstation logs if you don't have the robot right now.

Re: Weird Gearbox Sound
 

Was there any condensation forming from the cold? Could the grease in the gearbox have frozen? I had a similar problem with a gearbox on an R/C truck. Either the gear or the motor output shaft had become loose(maybe both, can't remember) and the gear wasn't making constant contact with the motor. There was some dust where the gear had worn. What gearbox and motors are you using? What are the gears made of? Any plastic moving parts?

Re: Weird Gearbox Sound
 

I just checked the battery and it tested at 39%. So that could be part of the problem. We actually never replaced it with our backup the whole time.

As for the gearbox sound, they were taken around 5 seconds apart, one side, then the other. The robot hadn't been driven for about 45 minutes prior to that clip. So the grease freezing could be the source of the sound, but only one side sounded like that.

The gearbox is a Toughbox Mini. No plastic parts (other than the casing). We currently have the robot bagged for the MN State tournament, but we have a pep fest on Thursday where we will be able to drive it again.

Re: Weird Gearbox Sound
 

Was the robot driven on or near anything that could have damaged the gears, such as sand? Did the robot take a drop or any sort of impact? Could anything have happened when it wasn't in use for 45 minutes? It sounds a bit like something rattling inside of the box, maybe a piece of plastic broke off and fell inside the box somewhere?

Re: Weird Gearbox Sound
 

No sand was present, the floor was swept prior to us unbagging the robot. There was no dropping of the robot. I don't believe anything could have happened in the 45 minutes (other than it getting colder due to the weather).

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

The battery beak says 11.872@18Amps with an internal resistance of .02 ohms.

Re: Weird Gearbox Sound
 

OK, post another update when you unbag it again. (You have to bag it for some offseasons?) I think the temperature probably had something to do with it, especially since it was affecting CD players, though I've never heard of them being affected by temps just above freezing.

True. I've had this experience with nicad cordless tool batteries. They appear to take a full charge(measure at full voltage), and may even hold their charge for a while, but as soon as they're used to drive a motor...almost instantly unusably weak.

Re: Weird Gearbox Sound
 

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!

Re: Weird Gearbox Sound
 

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!

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

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?

Re: Weird Gearbox Sound
 

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?

Re: Weird Gearbox Sound
 

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?

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

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?

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.

Re: Weird Gearbox Sound
 

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.

Re: Weird Gearbox Sound
 

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. :rolleyes:

Re: Weird Gearbox Sound
 

The first part was the battery. It hasn't done that when we used it with a full battery since then.

When we recorded those sounds, we were lifting up each side individually and ran them, first the left (first sound), then the right (second sound).

I'll make sure that we (I) clean out and regrease the gearboxes tonight. I'll also check the CIM motors to see if they still have their keys. What do you recommend to clean the parts with (paper towels, something else)?

Re: Weird Gearbox Sound
 

Let me know once you get your pit set up and are ready to look at this, I can help you figure it out :)

If the grease does need to be replaced, wiping everything down with paper towels is good enough - you don't need to go to too many extremes in getting the old grease off!

Re: Weird Gearbox Sound
 

If I have my way, we'll probably start looking at it once we get approval to unbag, before the pit is completely set up if possible.

Re: Weird Gearbox Sound
 

Well, in that case make sure your lock up form us with your robot when you walk through the door - we'll be checking them before you even get to your pit!

Re: Weird Gearbox Sound
 

Will do

Re: Weird Gearbox Sound
 

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 :D

Re: Weird Gearbox Sound
 

Several people's first guess in the thread was dead battery, which is one way to cause a brown out. As there can be other root causes for brown outs, knowing that it was caused by a dead battery is a more precise (and more easily fixable) analysis.

Re: Weird Gearbox Sound
 

So today, we did an amazing job at our first ever state championship tournament (13th/30). The gearboxes worked fine. We actually have thought that maybe it has sounded like that the whole time, yet we never could hear it in our shop or at the regional.