Rubber band on rollers breaking

Our top roller on the snail bot has one rubber band breaking each test cycle. No other rollers have this problem. The rubber bands are not contacting anything except the ball and are attached the same way the bands on the other rollers attach.

Does anyone have an idea of why this is happening or if it has happened to you?

It may be the rollers are rubbing on the spacers that are on the axle. That is what happened to my team for a while. Make sure to actually rubber band then well and out of the way of where spacers may be contacting the sprockets. It sounds dumb but that’s what was happening to us

1 Like

That makes sense! I will check it out tomorrow and let you know if that’s the issue.

Ok. Also just as a side question do you know what rubber band you got? From vex? Amazon. Or do you atleast know what size they are?

I can recommend some high quality ones on amazon.
96=$6

Could you post a picture of your top roller?

And for rubber band needs, these rubber bands come in great bulk for a very cheap price. They are very reliable and come in fun colors too!
[https://www.amazon.com/Alliance-24645-Sterling-Contains-4-Inches/dp/B000CCYVO2/ref=sr_1_6?dchild=1&keywords=64+rubber+bands&qid=1610086473&sr=8-6](http://Rubber bands)

1 Like

quality rubber bands are so worth it. also check for anything that could be rubbing the bands while it spins.

To prevent rubber band chafing we zip tie the bands away from the axle. Might be worth a try.

1 Like

I’ve also seen teams use screws through the sprocket in the innermost ring of holes to keep rubber bands off the axle.

1 Like

They are the robosource ones and firm stretch.

Don’t they need to be non latex?

1 Like

If your top roller is really close to the goal, it could be because the rubber bands spread outward when the roller is spinning fast which would cause them to scrape against the goal rim, the underside of which is really sharp for no reason

3 Likes

Good question! The relevant rule here is <R6d>:

(emphasis mine)

“VEX brand rubber bands” are repackaged Alliance non-latex, so, reading things literally, no, rubber bands made from other materials would not be legal.

But, a Q&A entry from Nothing But Net ruled that rubber bands made from other materials were OK as long as they were “close in elasticity”.

But but, a more recent Q&A entry, this one from Turning Point, suggests that rubber bands do need to be made from the same material.

(Note that previous season’s Q&A rulings do not automatically carry over.)

But the real point here is that last sentence in <R6d>:

It is up to inspectors to determine whether a component is “identical” to an official VEX component.

If an inspector really wanted to, they could perform some sort of “elasticity testing” on your rubber bands, and if they determine that their elasticity is substantially different from the VEX bands, they could potentially fail your robot for that reason. But I’ve never heard of anyone doing anything like that, and think it’s pretty unlikely that anyone ever would. In pretty much all cases, the inspectors’ procedure for determining whether your rubber bands are “identical to legal VEX parts” (if they perform such a check at all) will consist only of checking their size.

So, two takeaways:

  1. Practically speaking, can you use rubber bands made from different materials than the VEX bands? Yes, teams do it all the time.
  2. If you’re at all worried about the material your rubber bands are made from, save yourself the trouble and buy a 1lb box of Alliance Non-Latex #64 rubber bands (less than $5 on Amazon for multiple seasons’ worth).
9 Likes

@holbrook - great info!

I’d only add that I assume the (albeit remote) possibility of being called out on rubber band material type as an issue likely increases with the size / status of the event. Probably little (to no) concern at regular local events, only a bit more at Regionals / States events, and the most at Signature Events / Worlds.

My recommended “test” - if a random-material rubber band is genuinely giving you enough benefit over a non-latex one that you feel it would be a huge detriment to the robot if you had to suddenly change to all Vex ones… then you should probably start considering that those replacement bands may not, in fact, be functionally identical and SHOULD fail inspection (whether they do or not).

1lb for multiple seasons worth?! WHAT?!! I’m going to have to go have a talk with those kids… [stomps off to ask team where all of the rubber bands have gone] :joy:

7 Likes

I’ve already used 1 lb this season.

Ha - maybe I should ask my team why they’re not using more rubber bands!

3 Likes

Here’s an image. Ignore the colors since we just happened to have different colors and I tried to make a pattern.image

That’s a rather small flywheel you got there.

1 Like

1600 rpm so the tangential speed isn’t too far off a larger flywheel at slower speeds

This is a pretty stupid question but what’s the formula for rpm in vex? The calculators I’ve found are all for engine rpm