From what I’ve seen most teams (including ours) are either using yellow belt or polycord for an elevator from the ground to the shooter/ launching device. What is the worst thing that has happened with your teams cord whether its snapping or something else. I just curious if teams have problems with these things.
I’d say ours is the cords walking around on the rollers.
The worst thing that happened to our orange urethane belting is that students got this idea to cut and re-join it after almost every match “just in case”. :eek: sheesh.
Oh Don i never told u we only did it at the most twice a day
We’ve been using polycord since 2010, and honestly, no problems. As long as we follow the instructions and cut it 11% shorter than measured, it works beautifully. It doesn’t just work for applications like collecting balls; if you want to prevent a motor from stalling, use polycord on a pully designed for a toothed belt, and the polycord will start to slip before the motor stalls. You can change its tension to adjust how much force it takes to make it slip.
The belts on our grabber in 2011 would fall off every once in a while, but that was more a symptom of the design of the rollers than anything else. It wasn’t a problem, either; there were 4 belts on each side, and it only took 1 for the grabber to work. It was also the only part of the robot that worked at all that year, but at least it gave us something to be proud of, dog toys and all!
The poly belting is some of the most durable stuff I’ve ever seen and used. 470 used belting from our Lunacy bot (which has endured 3 FIM competitions and countless demonstrations) on this years robot, and have had no problems with it. We just cut it to dimension and and rejoin it and it keeps holding strong, in the 3 years of us using that robot it’s never snapped.
This is the problem we’ve had this year; we’ve tried to fix it by limiting the cord’s ability to walk.
We first used it this year, it’s been working fine for us, no problems. It did take us a little while to figure out how to keep it in place, we figured this out on our prototype and it’s been working fine on our robot.
We’re using a “comb” to keep the cords in place, at one end. They run on very simple ABS rollers. We used the connectors and hollow cord, and only about 3% stretch.
Do you have a photo of this comb? (We used 5% stretch, though our belts are welded.)
sure…I have pics of almost everything!
[STRIKE]Second the picture motion.[/STRIKE] Our polycord was coming off our pulleys/rollers as well, but decreasing the amount of ball compression helped a TON, and we still could increase the amount of stretch in the polycord.
Something we considered but haven’t done was switching over to rapid prototyping instead of pulleys.
-Duke
We love our poly cord, we don’t have a problem with walking, maybe once or twice at max (were using custom rollers with grooves cut in them) and the welds are strong as can be. We did a test weld to test its strength (put it in a vice and pulled on it) and it was amazing, after 3 students and a mentor pulled on it, all it did was stretch.
We are using Squirrel’s comb. Except we made it out of 1/16" plexi. Works great.
Here is a picture of our “comb” for the belting. It will walk a little if a ball goes through, but it then walks back.
We are using 3% stretch on solid “welded” polycord. All seems well. What do others see as the advantage of greater amounts of stretch?
Our robot used the hollow polycord, joined with a barb at first. The barbs would snap out over repeated use, and finally we decided to weld them together. They have not broken since, and we have already gone through a regional. I would definitely suggest welding them for anyone considering to put polycord on their robot.
Actually for us, we figured out that as long as 2 cords are touching the ball on our tower it doesn’t matter where on the roller they are. So as we may move them back into their specified grooves on our rollers, it isn’t a big concern if they move out of place during the match.
For teams with a lathe, cutting channels for the polycord works well. We used mcmaster #8749K17 PVC pipe along with andymark hubs for 1/2" keyed shaft (drive) and 1/2" ball bearing hubs (idler). The hub OD is 2.25, so it was a nice match for the 2.25 OD, 1.125 ID pvc pipe. We used clear 1/4" polycord and fused the ends.
If you have a mill, just use a 1/4" ball end mill to cut a 1/8" deep channel in two blocks of aluminum, then you can heat the ends resting in one channel, push them together, and then cap it with the other piece of aluminum so that the fuse is nice and round.
We used way more bands than are necessary, 1 or 2 would be plenty.
The other method is to use the flat urethane belting and just crown a pulley with tape to keep it centered. Urethane v-belt would also work fine, we used that to turn our turret.
We used solid poly cord in '09 it worked well. Welding it was a bit of pain so we decided to try hollow cord this year. It has been working great. We use 5% strech, it works fine. To keep it in place we simply drilled 2 .250 holes in our Aluminum pipe roller on either side of the cords. We cut a short length of cord and stuffed on end in one hole, wrapped it around the pipe and stuffed the other end in the other hole. It works great, the poly cord stays in place and the short lengths have not slipped out at all.
Forgive the image, the photo has a bag between the bot and camera 
After using flat urethane belting for the first time this year, we will probably never use round polycord again (except if we need a crossed belt somewhere).
Easy to weld (overlap, hit with a heat gun, and press with something flat to square the weld. Turn over and repeat). Doesn’t require grooves (just build up a crown out of tape and the belt self centers, see: http://www.lhup.edu/~dsimanek/scenario/crowning.htm).
Our rollers are just aluminum tubes with bearings pressed in each end.