Weird Gearbox Sound

[maxnz]

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

[thinker&planner]

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.

[ctt956]

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?

[maxnz]

Originally Posted by thinker&planner

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.

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.

[ctt956]

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?

[maxnz]

Originally Posted by ctt956

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?

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).

[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.

[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.

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

[ctt956]

Originally Posted by maxnz

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).

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.

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.

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.

[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.