What kind of belts do you guys use to manipulate balls (like conveyor Belts for lack of a better word)? It seems like most teams use timing belts, urethane flat or round belting. My team is not very experienced and we havent worked much with belts, so we’re not sure which kind we should use this year. What are the pros/cons of each, or why does your team use the type of belts that you use? Also, is tensioning an issue using timing belts?
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If you use a belt/pulley calculator you can get exact center to center distance, assuming you can machine it accurately.
Any type of urethane belting will create drag. It takes a little skill to weld belt, but it allows flexibility in length if you aren’t great at machining.
Round urethane belt has a tendency to get off center and can “derail”, but using extra deep pulleys can help. It’s much harder for flat belt to get off path because it self centers on any high points. Using the thinnest flat belt possible reduces the extra drag it creates.
It many cases teams opt for wheels or rollers and jus try to avoid any lengthy game piece translations in the robot.
How precisely would we have to machine everything for the timing belts considering they’d be under minimal load? We don’t have an operational CNC.
If you don’t have a mill or can’t precision machine, then getting accurate center to center distances isn’t likely. Unless you use a sliding bearing block, your motor can be pivoted to tension the belt, or you add a tensioner on belt run. Center to center distance on belts is measured in thousandths. like 3.061 inches.
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We are using a Vex flat belt on some 3d printed convex rollers and it seems to work well. You do not have to be too precise as you can overlap it for adjustability. We have tried round “belts” in the past but game elements tended to make them jump off their pulleys.
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for infinite recharge we used a number of kit chassis (gates htd timing) belts as our elevator/indexing system. they worked great. we used the vexpro clamping bearing blocks with oval slot holes to allow for tensioning. ideally we would have added the eccentric cams to lock the tension placement in, but just the friction alone seemed to keep through at least a full day of use if not more, and it takes only a minute or so to retighten and tension
This year, we are using flat urethene belts. 2020, we used HDT timing belts, which were something of a Pain because of the need to get distances correct and ended up ordering some odd-sized belts just to deal with that.
We’ve used round urethane belts twice…they worked OK in 2012, but not too well in 2020, mainly because we had a lousy design. We also use timing belts in our drivetrain, and they work great, because AndyMark puts the axle holes in the right places.
Other than that, we find some other way to transmit motion, or move game pieces.
In most cases, IMO flat belting > round belting because it is easier to get an acceptable belt weld and has a more reliable method of not detracking (crowned roller). If you don’t have access to 3D printing, you can pull off the crowned roller with 2in wheels sandwiching a 2.25in wheel
Flat belting can be purchased from Vex (black) or McMaster-Carr (orange)
Of course, you can avoid a lot of this work, use less space, and possibly have a lighter system by using timing belts, but this also relies on a reliable center-to-center distance (several teams I’ve been on in the past couldn’t guarantee this).
No need to 3D print anything or stack up different sized wheels, Colson wheels have the perfect amount of crown as-is.
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For low-load timing belt situations, they will work fine with 1/32" to 1/16" of slack in many situations, so I wouldn’t feel too bad about doing them with relatively low precision equipment. That equation changes for things where having the right c-c is very important (drivetrains, arms, climbers).
We have used the flat urethane belts in 2019 and 2020. They’re super easy to weld to any desired length and also easy to have ride on a 3D printed crown wheel, a colson wheel, or a tube with a raised ring of electrical tape.
That said, I’m hearing that the urethane belts don’t grip the 2022 Cargo very well, so we’re considering using HTD belts instead. I would love to hear confirmation that HTD belts are that much grippier (because we haven’t had access to the shop to experiment, and it would be a shame to abandon the flat belts).
Oh I hadn’t thought about the belts not gripping the cargo. Can anyone confirm whether or not urethane belts grip the cargo sufficiently? Also, would it be possible to texture the urethane belts so that they’d grip better?
Ah ok. So a tensioner wouldn’t be necessary for something like this? I’m just worried about belt stretch.
I’ll be at 2481’s shop in a couple hours, we have round urethane belting, will check and post a video
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My experience is that timing belts don’t really experience a meaningful amount of stretch. We used a lot of timing belts in our 2020 robot without tensioning as part of the ball intake and conveyor system and didn’t have any issues with skipping or stretching through the two years that robot has been in service.
That robot for reference:
https://cad.onshape.com/documents/6361b8a456b7a79de029adec/w/e0f0cde97a4c4fc822418839/e/4d907d248345cbd0b251fd98
Thanks! That would be amazing.
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Interesting. So it sounds like timing belts and flat belting are about equally difficult and equally effective, assuming the flat belting has sufficient grip?
For us, timing belts are way easier on the design and manufacture side… print some pulleys, order belts from vbeltguys, no hassle, just a shipping+printing delay. Not to mention how cheap it is. YMMV though, especially if you aren’t heavy on CAD and don’t have a CNC.
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