What type of flat belt should I use and how do I join them together?

This year, our team is deciding to modify our hopper system during the offseason since we have the time. We took inspiration off of other robots that were using a system of flat belts and a stopper right before the transition to the shooter. We want to do the same thing, but we’re running into an issue of what type of belt to use. We want to try to use a low-friction belt so that too much pressure wouldn’t harm our stopper causing it to bend, but finding such a belt seems to be a hard feat. From my research, polyurethane belts seem to have high friction, and that is why we aren’t using them. I’ve looked at neoprene belts on McMaster which have a description of low-friction, but I don’t know if they can be heat-welded together. If they can be welded together, that would be great, but if they can’t, is there any other type of belt that could fit these specifications?

First of all, welcome!

Urethane belts are pretty much standard in FRC applications because they’re cheap and easy to work with. This video from the FIRST Capital Ri3D crew explains the process for them well (we used these same steps for 2020): https://www.youtube.com/watch?v=BpNwOOOO6w0

I don’t know your particular setup, so I’m going to riff on some ideas here:

  • Does your stopper need to be a physical stopper, or could it be a break-beam sensor telling your robot there’s a ball ready to shoot?
  • Could your belt system read current draw from the PDP or (in the case of SPARK MAX, Talon SRX, and Talon FX) motor controller, then stop itself when the current draw reaches an experimentally-determined “oh it’s stuck there” level?
  • Could your stopper be made more robust to withstand overdriving of the belt system?

It’s been a while since I’ve touched a yellow ball, but Bill’s questions are bringing it all back, in my mind

:slight_smile:

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Our whole belt system is connected through one single motor. This means that if the conveyor stops because it reads that a ball is ready to shoot/" it’s stuck there," the whole conveyor will stop and limit other balls to proceed into our hopper to maximize the space. From what I just described, this is the reason we need a physical stopper and why we can’t just stop the conveyor. On the question about a robust stopper, I believe that would just need prototyping more than anything to figure out, but we have a versaroller (with a 1/2" axle inside) that’s acting as the stopper. I don’t know if that would actually be enough to withstand the overdrive or what we could do better to make it more robust.

Then, another question: Can a second degree of freedom be integrated into your conveyor? An UltraPlanetary with a NEO 550 (or maybe even just the HD Hex motor if your torque needs are low enough) can tuck into awful small spaces, and flat belt doesn’t use any sort of master link. So at worst, two more rollers in your system (one driven, one freewheeling).

We ran two VersaRoller drums tightly spaced on our two-ball-wide dumper–powered off, balls tended to jam up at the end of our conveyor (on purpose) and then they’d move on when the dams were spun up. I am not worried about VersaRoller in this application.

Don’t laugh, duct tape. It’s cheap, has a low friction on the surface (the back, not the sticky area), and is fully customizable. Ever made a duct tape wallet? It’s the same theory, using two pieces of tape with the adhesive sides inward so that no sticky is left! Additionally, this would be easily replaceable and customizable. That’s just one option though, I’m sure there are many others.

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Then, another question: Can a second degree of freedom be integrated into your conveyor? An UltraPlanetary with a NEO 550 (or maybe even just the HD Hex motor if your torque needs are low enough) can tuck into awful small spaces, and flat belt doesn’t use any sort of master link. So at worst, two more rollers in your system (one driven, one freewheeling).

We have absolutely zero space for more versarollers and we’ve never used a NEO before, and I doubt we would want to use one now. Also, what do you mean flat belt doesn’t use any sort of master link? Could you elaborate?

We ran two VersaRoller drums tightly spaced on our two-ball-wide dumper–powered off, balls tended to jam up at the end of our conveyor (on purpose) and then they’d move on when the dams were spun up. I am not worried about VersaRoller in this application.

What sort of belt did you use for this? More specifically, did the belt slip or did it grip the whole time? If the versaroller is able to withstand a lot of pressure and force, then I think we’re fine to use a grippy belt such as a polyurethane belt?

Fun fact, 1293 replaced a belt at Palmetto with a couple bands of gaffer tape. (One belt broke, and replacing it would’ve meant dismantling our entire upper belt assembly and that just…nah.) I think it actually helped the balls move around on the inside, but we didn’t get a chance to experiment further as our rebuild stopped with the rest of the world.

What rollers are the existing belts riding on? Since they have to be a smaller diameter than the belt run itself, I’m having a hard time visualizing how you don’t have room (particularly if the existing belt run is made shorter to accommodate the new second belt run).

Many chain runs have a master link, which is assembled to create one continuous loop. (There are ways around this, but whatever.) If you’re using a master link, you have to buy master links for the number of chain runs you’re using. Urethane belts are welded together with heat, creating a continuous loop. And there’s no master link to stock, meaning you can make as many belts as you please until you run out of belt.

The VersaRollers themselves were driven independently by NEO motors for packaging reasons (and we had them lying around after abandoning our shooter plans). Balls simply squished past the drums in our design; I wouldn’t put them that tightly together in a shooter feeder application. Our conveyor system was made out of PVC pipe with hex-broached end caps for cost reasons and proved to be okay enough, though it was a pain in the butt to assemble.

With the exception of the aforementioned tape-repair belt, our belts were urethane flat belts from McMaster, 6075K18 if I remember correctly.

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What rollers are the existing belts riding on? Since they have to be a smaller diameter than the belt run itself, I’m having a hard time visualizing how you don’t have room (particularly if the existing belt run is made shorter to accommodate the new second belt run).

I think to better visualize our belt system, you should check out BumbleB, 3339’s robot, ours is practically made with the same idea.

Ahhh, a short one. It appears that 3339 is running two flat belt runs, one along the bottom of the hopper space and one vertical one leading to the shooter itself. It doesn’t seem like they’re staggering the two belt runs to run together on the same shaft, so it honestly could be a case where the horizontal belt ends and the vertical belt is driven by itself. Add some break-beam sensors to know when a ball is chambered in the vertical belt and when a ball is at the end of the horizontal belt, and you should be able to get at least your first two or three balls going fast.

I’ve done quite a bit of searching to find the absolute best tool for welding urethane belts. I was prepared to spend several hundred dollars. After extensive searching, I bought this: https://www.harborfreight.com/130-watt-heavy-duty-hot-knife-60313.html

It works fantastic. With a proper jig, technique, and finishing, you can produce urethane flat belts that are almost indistinguishable from being continuous. I will say the jig has a lot to do with it. We machined ours from a couple blocks of aluminum. It clamps the belt on each side, and slides together on pins to keep everything aligned.

In 2020 we used a hair flattening iron to melt the ends of our belts together. Worked flawlessly and didn’t have any belts break.

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Not quite answering the original question, but I wanted to highlight that you can use sensors at the top and bottom of your conveyor to advance the conveyor one ball at a time, thus eliminating gaps between balls. My team does this and we don’t even have a stopper between the conveyor and shooter.

You can see this in action here.

Here’s a pic of the top senor:

Here’s the sensor we are using.

Credit goes to 4201 for turning us on to these, they are dirt cheap!

Edit: fixed senor link!

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We love belts! Our belt wizard (on the left) made a jig so that we get two square ends that can be clamped flat and adjacent and then melted to each other with a heating iron. Worked very well for us.

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