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-   -   pic: Chain and Wheel in Tube (http://www.chiefdelphi.com/forums/showthread.php?t=140676)

notmattlythgoe 28-12-2015 15:56

pic: Chain and Wheel in Tube
 

MichaelBick 28-12-2015 15:57

Re: pic: Chain and Wheel in Tube
 
It looks like you could make the outer wheels dead axles, which would make it easier to manufacture.

notmattlythgoe 28-12-2015 17:15

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by MichaelBick (Post 1515039)
It looks like you could make the outer wheels dead axles, which would make it easier to manufacture.

I'm curious, what makes a dead axle easier to machine?

cadandcookies 28-12-2015 17:22

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by notmattlythgoe (Post 1515055)
I'm curious, what makes a dead axle easier to machine?

Holes for bolts don't require the same tight tolerances that bearing holes do, would be the main thing I could think of. But if you're doing a full tube thing like this, it would seem to me to be quite likely you have some sort of CNC capability, which makes that less of a factor.

EricH 28-12-2015 17:22

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by notmattlythgoe (Post 1515055)
I'm curious, what makes a dead axle easier to machine?

Bolt sprocket to wheel. Stick big bolt through spacer, sprocket/wheel/bearing setup, apply locknut/jamnut/other locking fastener. Done. (Or, use a length of steel rod from McMaster, thread the ends with a die or drill for a cotterpin. Still a minimum-machining job.)

A live axle requires a keyway/hex feature and some sort of retention for the wheel/sprocket separate fro each other.

notmattlythgoe 28-12-2015 17:53

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by EricH (Post 1515059)
Bolt sprocket to wheel. Stick big bolt through spacer, sprocket/wheel/bearing setup, apply locknut/jamnut/other locking fastener. Done. (Or, use a length of steel rod from McMaster, thread the ends with a die or drill for a cotterpin. Still a minimum-machining job.)

A live axle requires a keyway/hex feature and some sort of retention for the wheel/sprocket separate fro each other.

Cool. Good to know. Do you not lose those advantages with this being exact C2C chain in tube though? I'd imagine you need those tolerances to be high still so going to a dead axle doesn't really help in this case does it?

I'm a Software Engineer not a Mechanical Engineer so these are serious questions.

EricH 28-12-2015 17:57

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by notmattlythgoe (Post 1515062)
Cool. Good to know. Do you not lose those advantages with this being exact C2C chain in tube though? I'd imagine you need those tolerances to be high still so going to a dead axle doesn't really help in this case does it?

The exact center-to-center can actually be easier--the main thing is that your precision work is all on the tube, and it's a smaller hole so it can be easier to get right. I'd be willing to bet that it's possible to place and drill a dead-axle hole by hand--and drill it straight, too, with the right tools!--or drill press by someone who knew what they were doing.

There's also the option of throwing a tensioner block into the system, probably an off-center mounted delrin cylinder, but that kind of defeats the purpose of "ease of maintenance".

GeeTwo 28-12-2015 18:20

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by notmattlythgoe (Post 1515062)
Cool. Good to know. Do you not lose those advantages with this being exact C2C chain in tube though? I'd imagine you need those tolerances to be high still so going to a dead axle doesn't really help in this case does it?

Quote:

Originally Posted by EricH (Post 1515066)
The exact center-to-center can actually be easier--the main thing is that your precision work is all on the tube, and it's a smaller hole so it can be easier to get right. I'd be willing to bet that it's possible to place and drill a dead-axle hole by hand--and drill it straight, too, with the right tools!--or drill press by someone who knew what they were doing.

There's also the option of throwing a tensioner block into the system, probably an off-center mounted delrin cylinder, but that kind of defeats the purpose of "ease of maintenance".

As the tube constrains the chain, there is a much greater tolerance for chain slack. You may get backlash, but if the tube fit is tight enough, the chain can't come off the sprocket unless it breaks.

Cash4587 28-12-2015 23:44

Re: pic: Chain and Wheel in Tube
 
To be quite honest, that doesn't make the machining any easier.. The way my team does it, which is not the best way to do it but is perfectly fine for FRC requires the same amount of machining. In 2014 we were able to do a c-c belt drive train on a manual mill with no issue. It used the same bearing setup as shown in this picture. Either way, it would be a bit on the mill properly spaced the correct distance from the last hole. We use a 1.125" mill bit to drill bearing holes and have had no issue with tolerance thus far, we do not us a CNC.

AustinSchuh 29-12-2015 02:47

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by Cash4587 (Post 1515122)
To be quite honest, that doesn't make the machining any easier.. The way my team does it, which is not the best way to do it but is perfectly fine for FRC requires the same amount of machining. In 2014 we were able to do a c-c belt drive train on a manual mill with no issue. It used the same bearing setup as shown in this picture. Either way, it would be a bit on the mill properly spaced the correct distance from the last hole. We use a 1.125" mill bit to drill bearing holes and have had no issue with tolerance thus far, we do not us a CNC.

Sounds like you have a pretty solid way to get the C-C. I'd suggest live axle in that case, since you'll constrain the bearings better. If you go with a dead axle, one of the design considerations is keeping the chain tight. If you tap the end of a shaft, your c-c won't be all that accurate because the clearance around the bolt in the frame adds a lot of play and potential for motion under impacts.

Cash4587 29-12-2015 02:58

Re: pic: Chain and Wheel in Tube
 
We have a mill with a digital read out it's pretty useful. I think the best thing about c-c drivetrains is the fact that you don't have to mill slots for bearing blocks. However, with all of the new vex/wcp parts now pretty widely available, adding tensioning cams to the drivetrain only requires one more hole drilled in the tube. the WCP bearing blocks are huge time savers.

asid61 29-12-2015 03:02

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by Cash4587 (Post 1515149)
We have a mill with a digital read out it's pretty useful. I think the best thing about c-c drivetrains is the fact that you don't have to mill slots for bearing blocks. However, with all of the new vex/wcp parts now pretty widely available, adding tensioning cams to the drivetrain only requires one more hole drilled in the tube. the WCP bearing blocks are huge time savers.

PREACH! The slots for a WCD are the worst part, and due to the inexperience of student machinist there are usually errors every year (except this one!) so going C-C also saves time in my opinion.

Nate Laverdure 29-12-2015 07:49

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by GeeTwo (Post 1515072)
As the tube constrains the chain, there is a much greater tolerance for chain slack. You may get backlash, but if the tube fit is tight enough, the chain can't come off the sprocket unless it breaks.

Inside a 2" tall x 1/8" wall extrusion, this kind of chain retention only happens when using 17t sprockets. 2363 uses 16t sprockets. There are different reasons why our chains don't come off the sprockets.

GeeTwo 29-12-2015 08:07

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by Nate Laverdure (Post 1515157)
Inside a 2" tall x 1/8" wall extrusion, this kind of chain retention only happens when using 17t sprockets. 2363 uses 16t sprockets. There are different reasons why our chains don't come off the sprockets.

My point was not that all chain-in-tube has close-fit sprockets (the one pictured in OP is not), but that this technique could be exploited with a dead axle to make even "tape measure and drill press" tolerances feasible.

Chris is me 29-12-2015 08:10

Re: pic: Chain and Wheel in Tube
 
Quote:

Originally Posted by GeeTwo (Post 1515158)
My point was not that all chain-in-tube has close-fit sprockets (the one pictured in OP is not), but that this technique could be exploited with a dead axle to make even "tape measure and drill press" tolerances feasible.

Nothing about a dead axle drivetrain lowers the position tolerance requirement for an exact-center drivetrain at all. I have no idea what you're talking about here. You need more precision than that regardless of whether or not your axle spins.


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