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Unread 15-05-2015, 01:15
Abhishek R Abhishek R is offline
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Re: pic: Manually machinable one-speed gearbox

One thing I want to make clear is that with the Texas Tube approach, it is almost physically impossible for the chain to jump off the sprocket if assembled correctly, because of the constraints of the tube. For failure to occur, the chain would have to essentially break, the risk of which can be minimized by not using masterlinks. Even if the chain loosens and rubs against the tube after a lot of usage, it will still probably be safe (as the other teams have noted, all these robots have been through multiple regionals and championships, and in the case of 118 some very defense heavy games like 2013 and 2014).

Other benefits include:
-Low maintenance (basically assemble and never touch again for the rest of the season)
-More space and weight efficient
-Relatively simple, no special equipment besides a mill required
-Keeps things clean and out of harm's way (the number of times I saw noodles getting stuck in the chains of other teams was too much to count, because of Texas Tube, we had virtually no problems driving over and around the noodles).
-This has more applications than just the drive train!
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Unread 15-05-2015, 07:28
Dan Petrovic's Avatar
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Re: pic: Manually machinable one-speed gearbox

Quote:
Originally Posted by Abhishek R View Post
One thing I want to make clear is that with the Texas Tube approach, it is almost physically impossible for the chain to jump off the sprocket if assembled correctly, because of the constraints of the tube. For failure to occur, the chain would have to essentially break, the risk of which can be minimized by not using masterlinks.
Abhishek, I'm not doubting the effectiveness of Texas Tube using chain. The results speak for themselves. I'm merely exploring other options. My students expressed interest in trying out timing belts for the drive train, so I just wanted to see what experiences other teams had with it.

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Originally Posted by asid61 View Post
That's a lot of weight you're gaining though (~2-4lbs depending on drivetrain), and you would have to settle for 1/8" wall probably.
I don't understand. This thread talks about 2x1x.125 tube being used for Texas Tube. Why would we have to "settle" for 1/8" wall?
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Unread 15-05-2015, 08:26
BrendanB BrendanB is offline
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Re: pic: Manually machinable one-speed gearbox

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Originally Posted by Dan Petrovic View Post
I don't understand. This thread talks about 2x1x.125 tube being used for Texas Tube. Why would we have to "settle" for 1/8" wall?
If you designed to package your drive in a 2x1 tube you could use the .1" wall tubing from Vexpro to shave a little weight down. 2x2 doesn't come in .1 wall and it wouldn't be wise to press bearings into .0625" wall 2x2 in a drivebase.

Drawing a quick 36" tube in Inventor I had the following weights:

.1" wall 2x1 Versa Tube: 1.97lbs. (0.65lbs. per foot)
.125" wall 2x1 tube: 2.4lbs. (.8lbs. per foot)
.125" wall 2x2 tube: 3.3lbs. (1.1lbs. per foot)

It all depends on what you have planned and are building on top. We had 2x1 Versa tube uprights coming off of our setup so 2x2 tubing worked very well for us. With the extra space it also can make mounting off of the tube a little easier and you can lighten the tube to bring the weight down a little. My personal preference would be a lightened 2x2 tube but that's just me.

Last edited by BrendanB : 15-05-2015 at 08:28.
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Unread 15-05-2015, 10:01
Dan Petrovic's Avatar
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Re: pic: Manually machinable one-speed gearbox

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Originally Posted by BrendanB View Post
.1" wall 2x1 Versa Tube: 1.97lbs. (0.65lbs. per foot)
.125" wall 2x1 tube: 2.4lbs. (.8lbs. per foot)
.125" wall 2x2 tube: 3.3lbs. (1.1lbs. per foot)
Thanks for doing this. Honestly, I'm not overly concerned with the extra weight. You're likely to save a little weight by using belts instead of chain, so it may cancel itself out.

Quote:
Originally Posted by Abhishek R View Post
I know, I wasn't referring to the belt system. I just wanted to say that in case people who haven't seen the method are reading this thread, because when talking to people in the pits at competition, they ask if we are ever afraid of the chain failing inside the tube where we don't have easy access to it and if we should cut access holes.
Okay, it just seemed like you were on the defensive a little bit. Thank you for spelling out the benefits. I love the idea of Texas Tube just because I really like the efficient use of space, but there are always those on every team that question its ease of use.

I do have more questions though. How would you get a continuous loop of chain without a master link? My team has only ever used master links with our chain.
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The sign applause was definately one of the best moments I had ever witnessed at a FIRST event.
Who knew silence could be so loud?

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Last edited by Dan Petrovic : 15-05-2015 at 10:09.
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Unread 15-05-2015, 10:16
BrendanB BrendanB is offline
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Re: pic: Manually machinable one-speed gearbox

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Originally Posted by Dan Petrovic View Post
I do have more questions though. How would you get a continuous loop of chain without a master link? My team has only ever used master links with our chain.
Buy one of these for 25 chain (also available at bike shops if you google enough):
http://www.team221.com/viewproduct.php?id=70

Follow these steps:
http://www.billetboard.com/showthrea...oul-Chain-Tool

First year using one and it was one of the best things we purchased this year. We had 50+ feet of 25 chain on our robot and only had four master links where our elevator platform connected to the chains. Using lighter chain (25 over 35), no master links, and C-C distances has really make working with chains an easy process and eliminated a lot of my worries in the past two seasons in our mechanisms.

Last edited by BrendanB : 15-05-2015 at 10:19.
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Unread 15-05-2015, 10:42
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Re: pic: Manually machinable one-speed gearbox

We did #25 chain in 2x2x.125 tube on our drop-center 6WD this season and had a good experience. No maintenance all season. There was some chain slap against the tube initially (16T sprockets and long chain runs; not a real problem but noisy), so we slid in a strip of UHMW to dampen that and now you'd never know.

We used a 2x2 because the frame rails in our design had minimal cross bracing due to the large opening for acquiring game pieces.
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Unread 15-05-2015, 11:52
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Re: pic: Manually machinable one-speed gearbox

So it sounds like the consensus here is that to do a Texas Tube design, you must keep all of the axles horizontally inline, and just put smaller diameter wheels on the outside to create a "drop center." I've been throwing together designs in CAD for different drivetrain styles, and I wonder if someone can explain to me if this would or wouldn't work:


(sorry for the poor render quality)

Rather than dropping the center or raising the outsides, I did both. I lowered the middle 1/16" and raised the outsides by 1/16", to end up with a
"drop" of 1/8". From everything I can see and read, this would fit very snugly into a 1x2x.125 tube. It's completely COTS and would let you use 4", 6", or really any other size wheel anywhere on the drivetrain -- which is big for teams with few resources.

General specs:
2"x1"x.125" aluminum tube
AndyMark Toughbox-Mini gearbox (alum plate cut down slightly)
17t #25 Team 221 dual sprocket
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Unread 15-05-2015, 11:58
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Re: pic: Manually machinable one-speed gearbox

Quote:
Originally Posted by KeeganP View Post
So it sounds like the consensus here is that to do a Texas Tube design, you must ... Put smaller diameter wheels on the outside to create a "drop center."
You can also use omni wheels on the outside wheels, especially in a game with little or no pushing and defense like this year.
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Unread 15-05-2015, 12:17
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Re: pic: Manually machinable one-speed gearbox

Quote:
Originally Posted by KeeganP View Post
Rather than dropping the center or raising the outsides, I did both. I lowered the middle 1/16" and raised the outsides by 1/16", to end up with a "drop" of 1/8". From everything I can see and read, this would fit very snugly into a 1x2x.125 tube. It's completely COTS and would let you use 4", 6", or really any other size wheel anywhere on the drivetrain -- which is big for teams with few resources.

General specs:
2"x1"x.125" aluminum tube
AndyMark Toughbox-Mini gearbox (alum plate cut down slightly)
17t #25 Team 221 dual sprocket
Yes, we've done this. The 1/8" total drop is "shared" equally between the outside and inside axles.

In fact, our entire setup is very similar to this, with only a couple differences:
-- we used 2x1.5x.125 tube
-- we used VexPro 16t #25 sprockets
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Unread 15-05-2015, 13:21
Knufire Knufire is offline
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Re: pic: Manually machinable one-speed gearbox

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Originally Posted by Nate Laverdure View Post
Yes, we've done this. The 1/8" total drop is "shared" equally between the outside and inside axles.

In fact, our entire setup is very similar to this, with only a couple differences:
-- we used 2x1.5x.125 tube
-- we used VexPro 16t #25 sprockets
Did you have the issue that 118 mentioned earlier of the chain grinding on the outer bearing race?
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Unread 15-05-2015, 13:24
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Re: pic: Manually machinable one-speed gearbox

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Originally Posted by Knufire View Post
Did you have the issue that 118 mentioned earlier of the chain grinding on the outer bearing race?
No, in fact we deliberately chose the 2x1.5" tube to avoid this issue with the 16t sprockets.

Here is a technical drawing of (an early version of) our drive tube.

Last edited by Nate Laverdure : 15-05-2015 at 13:28.
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Unread 15-05-2015, 08:38
Abhishek R Abhishek R is offline
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Re: pic: Manually machinable one-speed gearbox

Quote:
Originally Posted by Dan Petrovic View Post
Abhishek, I'm not doubting the effectiveness of Texas Tube using chain. The results speak for themselves. I'm merely exploring other options. My students expressed interest in trying out timing belts for the drive train, so I just wanted to see what experiences other teams had with it.
I know, I wasn't referring to the belt system. I just wanted to say that in case people who haven't seen the method are reading this thread, because when talking to people in the pits at competition, they ask if we are ever afraid of the chain failing inside the tube where we don't have easy access to it and if we should cut access holes.
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