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Unread 31-12-2012, 00:58
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Re: pic: WCD

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Originally Posted by the.miler View Post
Alternatively, you could make your bearing block out of a single piece of 1.25" wide by 2" high at 1/8" thickness tube, available at onlinemetals:

http://www.onlinemetals.com/merchant...269&top_cat=60

I know it's 6063 aluminum; our drivetrain was made with the stuff last year, and it was just fine to machine.

Bore your bearing hole and a couple of screw holes, and then lop off the top of your tube to make a C-channel like piece. Slide it onto the robot, tighten down your screws, and you're good. Our team used the system on previous robots before we moved away from the cantilevered drivetrain design; while I cannot personally attest to its effectiveness, as it was before my time, our mentors recall the solution as doing a fantastic job. Since we intend to return to cantilevered drive this year, we have of course revamped the design; a screenshot is here:

https://plus.google.com/u/0/photos/1...06823682841202

All the advantages of imbedding your bearings in a single piece, without having to make three different bearing block pieces. I thought it was genius when I first saw it, and the material is readily available.
This is genius

One question, so how do you keep overzealous tightening of the two black bolts from crushing your bearing block? (or am I just missing something )
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Unread 31-12-2012, 01:05
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Re: pic: WCD

How about the idea of no bearing blocks at all?
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Unread 31-12-2012, 01:07
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Re: pic: WCD

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Originally Posted by rcmolloy View Post
How about the idea of no bearing blocks at all?
This is what we did with our off season robot. We used the correct Center to Center for 25 chain, the did loosen a bit but over 3 off season competitions but we never lost a chain.

We are looking into going to belts however for our new iteration of the drive.
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Last edited by Mk.32 : 31-12-2012 at 01:13.
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Unread 31-12-2012, 01:08
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Re: pic: WCD

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Originally Posted by rcmolloy View Post
How about the idea of no bearing blocks at all?
I, for one, think this is really the best solution, but it takes too much guts for me to try out. We didn't prototype a exact c-c drive in the offseason, and there's too much potential for failure for my comfort level. I would need to know that we had this design in the bag (like you guys do) to use it during the season.
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Unread 31-12-2012, 01:43
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Re: pic: WCD

Jose,

I clearly haven't searched McMaster closely enough. The rod ends seem like a great idea; I used the eyebolt mostly because it was the first thing that came to mind, and will work just fine, as I only need to pull on the bearing block to achieve correct chain tension. If the rod ends become necessary, I will be indebted to you for having brought them to my attention

Garrett,

Again, I was not a member of Team 846 when we first used this design, so I do not know what ferocious punishment was threatened upon those who tightened the bearing block too tight I imagine that if you put some sort of spacer inside (or stack a bunch of those cool little VEXPro washers inside), just a touch smaller than the width of the tube you are clamping with the bearing block, you would prevent the bearing block from ever being tightened tight enough to cause failure.

All you fixed C-C proponents:

Yes, I wish we could go fixed C-C . . . with belts! That would be amazing. I do not think we would ever go fixed C-C with chain, we've just had too many issues with sprockets wearing down and consequently changing the tension on the chain . . . never mind just the stretching with time. As we get a little more experience with using 7075 for our sprockets or even implementing our off-season belt drive design, we may reconsider that stance. If any of you guys try it out (or in 973's case, have), we'd love to hear how that went.
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Unread 31-12-2012, 02:11
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Re: pic: WCD

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Originally Posted by rcmolloy View Post
How about the idea of no bearing blocks at all?
I'd be scared with #25 chain and/or indirect drive.
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Unread 31-12-2012, 02:56
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Re: pic: WCD

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Originally Posted by MICHAELABICK View Post
I'd be scared with #25 chain and/or indirect drive.
All I am going to say we did it: http://www.chiefdelphi.com/media/photos/38147
Ran 3 off seasons, not a single chain lost.
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Unread 31-12-2012, 03:59
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Re: pic: WCD

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Originally Posted by Mk.32 View Post
All I am going to say we did it: http://www.chiefdelphi.com/media/photos/38147
Ran 3 off seasons, not a single chain lost.
If you really need to that would probably be fine(but only if you're direct driving your centers). I just see so limited downside in going without bearing blocks. If you have the resources to spend on completely custom gearboxes then it's not going to take very long to make 8-12 973/1323 bearing blocks. Especially now with the new WCP gearboxes you can shift the resources used to make the gearboxes over to making bearing blocks that improve your consistency and efficiency.
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Unread 31-12-2012, 11:57
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Re: pic: WCD

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Originally Posted by MICHAELABICK View Post
If you really need to that would probably be fine(but only if you're direct driving your centers). I just see so limited downside in going without bearing blocks. If you have the resources to spend on completely custom gearboxes then it's not going to take very long to make 8-12 973/1323 bearing blocks. Especially now with the new WCP gearboxes you can shift the resources used to make the gearboxes over to making bearing blocks that improve your consistency and efficiency.
But the point is that if you simply don't need them, don't bother with the weight, complexity, cost, or manufacturing time, and the resources you would have shifted from gearboxes to bearing blocks can now be focused on something more relevant to the challenge. The question is whether you need them, and there is some solid evidence coming forward that you don't (with the usual caveat: if you do it right).

And I'm not sure what, if anything, direct driving the center wheel would have to do with an exact c-c?

Last edited by Aren Siekmeier : 31-12-2012 at 12:04.
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Unread 31-12-2012, 13:11
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Re: pic: WCD

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Originally Posted by compwiztobe View Post

And I'm not sure what, if anything, direct driving the center wheel would have to do with an exact c-c?
He is concerned about losing mobility (chain popping off) when using #25 chain without bearing blocks.
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Unread 31-12-2012, 13:59
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Re: pic: WCD

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Originally Posted by Akash Rastogi View Post
He is concerned about losing mobility (chain popping off) when using #25 chain without bearing blocks.
I still see no difference between an indirect drive with bearing blocks and an indirect drive without, since maintaining tension on the chain from transmission to first driven wheel is as simple as a slotted transmission noun. That point of failure doesn't depend at all on an ability to move wheels to adjust tension. And beyond that, the system is identical to a direct driven WCD (w/ or w/o blocks). I see bearing blocks and direct drive as two completely independent design decisions, though if there are other details I have overlooked I would be glad to hear them.
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Unread 31-12-2012, 14:07
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Re: pic: WCD

With a direct drive live axle drivetrain (or any chain drive), you need a method to tension the chain. Since this isn't an indirect drive, moving the gearbox isn't an option. The most efficient way to do it is to move the wheels slightly outward or inward, hence bearing blocks.
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Unread 31-12-2012, 15:36
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Re: pic: WCD

We had an 8WD WCD last season. The siderails were 1" x 2" x .125" rectangular tubing, and we put the bearings right into the siderails, no bearing blocks. They were designed to use exact C-to-C for #25 chain. Our thinking is that if the chain ever stretched to the point of being a problem, we'd replace it with new un-stretched chain. This served us well through two regionals. We never replaced a chain. Looking back, I think I'd have the students replace the chain at the beginning of each regional just to be safe.

See here for CAD:
http://www.chiefdelphi.com/media/papers/2752
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Unread 01-01-2013, 13:34
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Re: pic: WCD

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Originally Posted by rcmolloy View Post
How about the idea of no bearing blocks at all?
This was our approach last year also. We did do a few things to help prevent the loss of a chain. First of all our chains were all internal, placed inside the 1.5 x 2 frame rails. We changed our chains before the start of our second regional, before Championship, and again before IRI. We have had the same chains on since IRI which includes MANY hours of demos, Beta testing, drive practice, and the Ruckus.
Overall we didn't see much wear on the sprockets but the chain does stretch quite a but. We have looked at adding a chain tensioner to the system. If the chains were external I would look into a system to tension the chains.
Cutting the frame rails with exact c-c and not worrying about additional machine time for bearing blocks is nice. It gives us time to work on other aspects of the robot.
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Unread 01-01-2013, 13:41
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Re: pic: WCD

There clearly isn't a correct bearing block design for all teams with all resource sets across the board.

I think the distinguishing factor is teams that know how to machine and commonly do it, and those that machine less or have a buddy, sponsor, etc... make stuff.

If a team has a manual mill in house and regularly uses it, the bearing block design we make is just as fast to make (or even faster the way we cut them) than most of the ideas presented in this thread that are less rigid and functional. Our blocks look big and to someone who isn't used to milling it might seem like a lot of material removal, but it really isn't. We could manufacture a season set within 2-4 hours (that's 20-40).

The most important aspect of a bearing block for a WCD is rigidity. When it is clamped to the tubing, there must be no slop or play.
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