Belts 9mm or 15mm?

[Knufire]

Originally Posted by Cothron Theiss

While the GT2/GT3 profile is superior to HTD in almost every way, including service life, backlash, vibration, and load-carrying capacity, HTD belts respond slightly better to reversing shock loads. GT2/GT3 are much better suited for most industrial uses, but reversing shock loads are so common in FRC, what's best for industry isn't the same as what's best for us. The people at AndyMark and Vex knew this and made the informed decision to sell HTD pulleys and belts instead of GT2/GT3 after discussing it with people from Gates and other industry vets.





Just to add on to what Eli is saying about Gates' stated torque ratings not always being applicable to FRC purposes, remember that all of those values are rounded averages of many tests.

On the sourcing belt front, you have to remember that the GT2 and GT3 profiles are still patented by Gates, whereas the patent on HTD ran out so there's many, many more suppliers of HTD.

On load ratings on the design manual, those also might be based on fatigue and not instantaneous loading.

[Cothron Theiss]

Originally Posted by Knufire

On the sourcing belt front, you have to remember that the GT2 and GT3 profiles are still patented by Gates, whereas the patent on HTD ran out so there's many, many more suppliers of HTD.

On load ratings on the design manual, those also might be based on fatigue and not instantaneous loading.

Though it's really more the name that's been patented at this point, and not the actual profile, right? Because there are several suppliers, WCP included, that sell a "GT2 compatible" profile. I don't know where the lines are drawn on how close other profiles can get before being in violation of the patents, but I'd say the "GT2 compatible" profiles are pretty close.

And yeah, none of Gates' load ratings are off of instantaneous loading or reversing loads.

[R.C.]

Originally Posted by Knufire

On the sourcing belt front, you have to remember that the GT2 and GT3 profiles are still patented by Gates, whereas the patent on HTD ran out so there's many, many more suppliers of HTD.

I believe patent on gt2 belts are up but gt3 belts are still protected (source: gates rep)

[Munchskull]

My biggest question when it comes to belts on drive teains is what am I gaining buy using two 15mm belt vs any chain. Weight savings is all I can find. I worry that the larger space taken up might not be worth it. That said belts are my go to choice for everything else, 3D printed pulleys anyone?

[asid61]

Originally Posted by Munchskull

My biggest question when it comes to belts on drive teains is what am I gaining buy using two 15mm belt vs any chain. Weight savings is all I can find. I worry that the larger space taken up might not be worth it. That said belts are my go to choice for everything else, 3D printed pulleys anyone?

Unfortunately, when you sum up the extra width of 15mm belts and the weight of pulleys, the theoretical weight savings compared to #25 chain are nulled. :\

[IndySam]

Originally Posted by Cothron Theiss

Just because I'm curious, why the switch from gear drives? I still remember seeing your 2013 bot at the Smoky Mountains Regional and being in absolute awe. I also remember yours being the best drivetrain at the Regional.

Thanks for the compliment.

We might not. Really going on a simplicity kick and gear drives are not simple. As usual everything depends on the game.

[Andrew Schreiber]

Originally Posted by Munchskull

My biggest question when it comes to belts on drive teains is what am I gaining buy using two 15mm belt vs any chain. Weight savings is all I can find. I worry that the larger space taken up might not be worth it. That said belts are my go to choice for everything else, 3D printed pulleys anyone?

I know in the most recent instance I've looked at replacing a chain with a belt I was looking to remove slop from the system and would be using GT2 profile belts and pulleys to do so.

[Sh1ine]

Originally Posted by Munchskull

My biggest question when it comes to belts on drive teains is what am I gaining buy using two 15mm belt vs any chain. Weight savings is all I can find. I worry that the larger space taken up might not be worth it. That said belts are my go to choice for everything else, 3D printed pulleys anyone?

Belt offers more advantages over chain than just weight savings. They are slightly more efficient, they are cleaner, they do not stretch, and they do not require maintenance. We have used 24 tooth pulleys with 15mm HDT belt on both 4" and 6" wheels with 3 CIM single speed gearboxes for 4 seasons. We have never broken a belt. If you size your pulley correctly for the wheel and use exact center to center, you should only have to touch your belts one time, I can not say the same for chain.

[AustinSchuh]

Originally Posted by Deke

This.

If you aren't direct driving a 6wd center wheel with a transmission, I would not recommended using 9mm wide belts. That is the only drive configuration that would make them manageable. If there are small pulleys driving large high traction wheels, the 9mm wide belts will still give you problems in the 6wd direct drive center wheel.

We ran 9mm wide, 5mm pitch belts in 2014, GT3 with a 3.5" diameter wheel and a 24 tooth pulley. The center wheel was direct driven, with belts to the front and back wheels. We carefully measured the tension, and worked hard to keep them properly tensioned to avoid ratcheting or over-tensioning. They all broke right after as the season ended.

We are going to go to 15 mm wide belts next year unless the game is something weird again. It's just not worth pushing the limits. If you read the spec sheets, we are well outside the rated range for the belts.