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Unread 28-06-2016, 13:03
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Re: pic: Another Belt-In-Tube Drivetrain

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Originally Posted by Ty Tremblay View Post
Thanks. I'm a little bit concerned about the lack of flanges on the pulleys, but with less than .035" of space on either side I just couldn't fit them in. That said, the .035" is small enough to let the tube wall be the "flange" if anything goes wrong and the belt tries to walk.
I'm also concerned about not having rotating flanges on at least the center pulley. My old team used the Vex belt upgrade on the AM14U chassis in 2014. It worked for the season, but the belts showed some pretty hairy wear, as the sides of the two belts rubbed past each other on the common, center pulley.
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Unread 28-06-2016, 13:17
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Re: pic: Another Belt-In-Tube Drivetrain

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Originally Posted by Ty Tremblay View Post
Sorry about that. I had realized that my belt model wasn't thick enough so I changed it and then realized that I had about .003" of space between the belt and the "roof" of the tube. I found 23T GT3 pulley stock on SDP/SI and decided to make that change since it gives me enough roof clearance (.043") and still gives me room for the bearing counterbore.
You have nothing to worry about with flangeless pulleys. 2791 has never had flanges on the pulleys and has never had a problem at all. This is one of the benefits of belt-in-tube.

As for GT vs HTD belts - the biggest thing to keep in mind is availability of particular belt lengths. Sourcing GT2 and GT3 belts can be difficult, but it is extremely easy to get HTD belting. I have heard that the HTD's deeper tooth profile is supposed to be better for reversing loads / ratcheting prevention as well, but I have no data to back this up.

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Originally Posted by nuclearnerd View Post
I'm also concerned about not having rotating flanges on at least the center pulley. My old team used the Vex belt upgrade on the AM14U chassis in 2014. It worked for the season, but the belts showed some pretty hairy wear, as the sides of the two belts rubbed past each other on the common, center pulley.
If belts are properly aligned and tensioned, this just shouldn't happen. When the belts are on the pulley, they aren't moving relative to each other at all. I've never run into significant problems with a setup like this.
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Unread 28-06-2016, 19:25
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Re: pic: Another Belt-In-Tube Drivetrain

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Originally Posted by Chris is me View Post
You have nothing to worry about with flangeless pulleys. 2791 has never had flanges on the pulleys and has never had a problem at all. This is one of the benefits of belt-in-tube.

As for GT vs HTD belts - the biggest thing to keep in mind is availability of particular belt lengths. Sourcing GT2 and GT3 belts can be difficult, but it is extremely easy to get HTD belting. I have heard that the HTD's deeper tooth profile is supposed to be better for reversing loads / ratcheting prevention as well, but I have no data to back this up.



If belts are properly aligned and tensioned, this just shouldn't happen. When the belts are on the pulley, they aren't moving relative to each other at all. I've never run into significant problems with a setup like this.
Does 2791 add any additional spacing between centers in their drivetrains?
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Unread 28-06-2016, 19:43
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Re: pic: Another Belt-In-Tube Drivetrain

Quote:
Originally Posted by Chris is me View Post
If belts are properly aligned and tensioned, this just shouldn't happen. When the belts are on the pulley, they aren't moving relative to each other at all. I've never run into significant problems with a setup like this.
This looks to be like a quite tight definition of "properly". If the holes aren't bored a lot closer to square than many teams can probably manage, the belts on the drive shaft will migrate one way or the other, and shall end up rubbing on the bearings (not TOO bad, but not optimal), or each other (as described), or both (one goes to a bearing, the other is jammed against the first belt, with the same results). The 'both' case actually seems rather likely as I work through the variations.
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Unread 29-06-2016, 10:31
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Re: pic: Another Belt-In-Tube Drivetrain

Quote:
Originally Posted by GeeTwo View Post
This looks to be like a quite tight definition of "properly". If the holes aren't bored a lot closer to square than many teams can probably manage, the belts on the drive shaft will migrate one way or the other, and shall end up rubbing on the bearings (not TOO bad, but not optimal), or each other (as described), or both (one goes to a bearing, the other is jammed against the first belt, with the same results). The 'both' case actually seems rather likely as I work through the variations.
A quality live axle drivetrain should be striving to get those bearing holes as concentric as possible for maximum efficiency and best performance anyway. This is significantly easier in a tube drivetrain, where both "sides" of the drive are actually the same piece, than it is in a drivetrain with multiple side plates. These efficiency gains are one of the subtle benefits of a "west coast" tube style drivetrain, and it absolutely isn't out of reach of teams who have some access to machining resources and put an emphasis on quality.

Quote:
Originally Posted by Ty Tremblay View Post
Does 2791 add any additional spacing between centers in their drivetrains?
I've heard adding .005-.010 can help, but 2791 has always run them exact center with no additional length. The belts initially seem a little looser than a brand new chain, but that's just how belts like to run. One of the pitfalls of manually tensioning belts is that it is somewhat easy to over-tension a belt, weakening the whole system, because it seems like belts should be tighter than they actually need to be.
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Last edited by Chris is me : 29-06-2016 at 10:34.
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