Rhino tread snapping?
 

Has anyone had issues with the rhino treads snapping? We busted one during a practice match when we started pushing another team.

We hope that it's just due to the fact that it was a heavily used track that has a lot of wear during build season and post build season.

Re: Rhino tread snapping?
 

We at AndyMark have not heard of anyone else breaking a tread. These treads are rated at 600 pounds of break strength, with a safety factor of at least 2. The white (or clear) colored timing belts are reinforced with a continuous loop of steel cables.

Can you provide more information regarding how your tread broke?

Andy B.

Re: Rhino tread snapping?
 

Will do! Honestly, I still haven't heard the full details (it broke late last night, I wasn't there), but I expect to get the entire story (as well as a picture of the treads) today when I go in. My preliminary understanding is just that we went into a head on bumper to bumper collision with another robot, and in that collision we heard a snap. The carpet ripped underneath the robot - we aren't sure if that was due to the force of the tracks snapping or perhaps a symptom of the same issue that broke the tracks (maybe something sharp?). Our drivetrain uses 2 CIMs/side, but I don't remember the gearing (it's nothing crazy though).

However, that is comforting that they are rated for 600lbs - makes it sound more like a freak accident than anything!

Thanks for the support!

Re: Rhino tread snapping?
 

I too would like to see a photo of this snapped belt.

Re: Rhino tread snapping?
 

We had no issues with our treads they were flawless deep into back to back regionals....so that's 28 matches plus several practice matches.

We did have to replace all revision 3 with revision 4 pulleys

Re: Rhino tread snapping?
 

Just curious if you HAD TO change all to rev 4 or you chose to change them to rev 4... in other words, did all of them break?

Re: Rhino tread snapping?
 

We went into competition with revision 3 (not my call I wanted then all changed out prior only had 4 and we ordered 8 more) and yes we ended up breaking all of them and replaced as we went with rev 4

Re: Rhino tread snapping?
 

What is this Rev 4 and 3?

Re: Rhino tread snapping?
 

Rev 3 is referring to the pulleys which shipped with the Rhino originally. Rev 4 is referring to the new pulleys that were designed to eliminate the failures that some teams were seeing with rev 3.

Re: Rhino tread snapping?
 

This is the main reason my team stopped using tank tracks back in 2007. We were using almost identical belts to the ones Andymark sells, and we would typically break at least one every competition we went to (and since the ones we ordered were custom, they were closer to $300 a piece).
After years of experimenting, we discovered that the issue seems to be caused by either too much or too little tension on the belts. Failure modes can also be caused by attempting to drive while getting pushed sideways by another robot.

Try adjusting the tension on your tracks using the turnbuckle and see if that helps (the tracks should be snug, not too loose or too tight). Also avoid situations where you get pushed from the side of the robot.

Finally, while it's certainly possible to build a reliable tank drive system, my advice to all teams using tank treads would be to make sure you have spare treads with you at your events, or you may regret it later.

Re: Rhino tread snapping?
 

We havent had issues with the blue rhino track belts. But we did have an issue with the black drive belts, we noticed during practice the robot drove to the right a little more and couldnt find out why, but the belt stretched somehow during a match and made driving almost impossible. Luckily we had extra belts we ordered. We learned that anything can and will break, so we keep extras of nearly everything at compeition. But after St Joe last weekend, a few teams I know learned to bring backups of 99% of your parents, even RoboRios can break for no reason.

Re: Rhino tread snapping?
 

So it appears that my story was a little bit off. It was NOT a head on collision - it was the same kind of situation cbale2000 describes:

Does anyone know what tension we should have the belts at such that they won't fall off but aren't dangerously tight?

Attached are photos of the snapped belt (I apologize for how huge they are).

Re: Rhino tread snapping?
 

AndyMark Page for Track Drive Tensioning Here

Re: Rhino tread snapping?
 

From the visible damage to the side of the teeth/V-guide on the pulley face of the belt my guess is that the belt was forced to ride up onto the teeth of the sprocket dramatically increasing the belt tension and causing it to fail catastrophically.

Re: Rhino tread snapping?
 

I'll admit that I had both my Dad (w/ 60) and Step-Dad (w/ 5207) working together like heck for several hours to build the drawbridges that didn't want to get built at my rookie FTA event at Arizona North Regional this past week. My Step-Mom is also a Mentor (w/ 60) and my Mom (working on her for 5207) came up to Flagstaff to see the event and her baby boy at his rookie FTA event. Didn't realize that bringing backup parents were a normality :D


On topic...that is an amazingly straight break, almost like it was cut by something.

Re: Rhino tread snapping?
 

Don't. HUGE photos are exactly what is called for in this instance; it makes what happened easier to see.

Are all 3 of those images the same 'end' of the belt, or are we seeing different ends in images 1 and 3? I suspect the latter but want to hear it from you.

Re: Rhino tread snapping?
 

I see the same thing you do I suspect. 1 & 2 look to be the same end of the belt, just flipped over. 3 looks to be the other end as it looks to have the missing "chunk" from 1 & 2.

Re: Rhino tread snapping?
 

Yes, I can confirm this. Should have labelled the pics when I put them up - sorry about that!

Re: Rhino tread snapping?
 

OK, Thanks.

From the markings I see on the central "lumps" of the clear side of the belt, I theorize that the belt slid sideways on the wheels, so when the drivetrain was powered up they rode up onto the wheels. This stretched the belt to catastrophic failure. I am thinking that an under-tensioned belt could do this.

I am not trying to cast apsersions or 'blame'; just hypothesizing (= guessing) as to how this might have happened.

Anyone else have a theory?

Re: Rhino tread snapping?
 

Don, I think your theory is correct.

Our experience (this season only) with tracks is that low tension can cause the belt to slip off the side of the pulley when the robot is pushed sideways while moving forward or backward. This subsequently increases tension, either locking that side of the drivetrain if you are lucky (as we were), or causing extreme stress on the misaligned belt if you are not. The latter case happened here, I think.

We've been checking belt tension between matches. We also modified our turnbuckles to include lock washers and jam nuts.

Re: Rhino tread snapping?
 

Another failure mode to consider when talking about side-loading on belts is belt impingement on the frame itself. On many of our tank tread robots in years past, the belt could come partially out of alignment, sticking out past the bottom of the frame during a T-bone, but afterwords could self-correct; however if the frame had a sharp edge on the bottom when pushing occurred and the driver attempts to drive, the result can start enough of a cut in the tread that it compromises the entire belt and cause it to fail in a similar method to the previously posted pictures.

In addition to proper tensioning, I recommend checking the bottoms of the drive plates for sharp edges and clean up what you can. ;)