Sheet Metal vs Tube Drivetrain

[cadandcookies]

Originally Posted by Zebra_Fact_Man

If you don't plan to go WCD / cantilevered axle, sheet metal seems to be the way to go. That said, if you do want to go WCD / cantilevered axle, I imagine it would be pretty difficult to do so with sheet metal.

Bottom line is, go with a system you are familiar with during the build season. Experiment in the off-season to grow your team's knowledge-base.

Back when I was on 2220, we designed our drive trains primarily as closed tube/channels (tube on each side of the axle). They had some disadvantages, but man they were absolutely bulletproof, and were incredibly fast to design and build (I was able to design one in the style we did for 2014 in about 30 minutes with all the COTS parts downloaded).

It's been said before in this and other threads: go where your expertise is.

If you don't have existing expertise, pick a direction that complements your existing skills and go that way.

[Cash4587]

Originally Posted by TheModMaster8

Belt is better (IMO) it has vary little, too no slack at all. Making it precise. it doesn't stretch nor does it brake (Vex's Belts other brands will though)
Chain normally (in my experience) is a flipping nightmare, chains stretch, masterlinks brake, sprockets strip, etc,etc.
Here is a document found on vex's website "Belt vs. Chain Drive Evaluation" by FIRST Robotics Competition Team 234(credits to 234!)

Hope this has help in some way

I really don't understand why so many people are chiming in about chain being such a problem. Chain is a very, very powerful tool if used correctly. It is even more powerful if you DO NOT use master links. After becoming familiar with the dark soul chain tool, I have to say, it is the best thing ever made for chain. Pushing the pins back in, and using the correct number of links using a chain center to center calculator is about the best thing you can use when designing mechanisms/drivetrains with chain. If you use those two things alone correctly you will never have to worry about tensioning/stretching so long as you use large tooth count sprockets and the right chain pitch for the job. My team used #35 chain for our final reduction coming off our Drivetrain gearbox with fixed direct C-C and #25 chain going from wheel to wheel direct C-C with no tensioners on either and had ZERO issues. We love chain and will continue to use it because it is easier and does not require custom belt lengths for each year or each robot.

[cadandcookies]

Originally Posted by Cash4587

I really don't understand why so many people are chiming in about chain being such a problem. Chain is a very, very powerful tool if used correctly. It is even more powerful if you DO NOT use master links.

The bolded part. Many people don't get to the part where they actually know how to use chain correctly. Same thing applies to belts. This applies to many things in competitive robotics, but is particularly pronounced in drive trains due to their overall "mission-critical" importance. A single bad experience for a given method or technique can scare someone off of that for a long time, even if it was an easily correctable user error.

[asid61]

I didn't want to get sucked into another chain vs. belt debate, but:
-Belts are lighter than chains. But, Vexpro pulleys are not lighter than sprockets. A 15mm belt drivetrain weighs as much as a #25 chain drivetrain, generally speaking.
-Belts are quieter than chains, and more efficient. However, 234's paper only covers #25 chain and not #25, and used an 8020 chassis to do it, so the exact amount imo is unknown.
-When put together with a Dark Soul tool (for #25), chain is extremely strong. Plus, masterlinks are at least $1 per chain run.
-Chain can be assembled on the sprockets, while belt needs pulley removal to go on if you're not tensioning.
-Belts will slip before breaking gears (on arms and stuff, anyway) depending on tension, whereas chain will kill everything before it dies in a spectacular fashion (ask me how I know).

That's all I think I know right now. I like belts everywhere but the drivetrain, personally, but they require forethought.

[TheModMaster8]

Originally Posted by Cash4587

I really don't understand why so many people are chiming in about chain being such a problem. Chain is a very, very powerful tool if used correctly. It is even more powerful if you DO NOT use master links. After becoming familiar with the dark soul chain tool, I have to say, it is the best thing ever made for chain. Pushing the pins back in, and using the correct number of links using a chain center to center calculator is about the best thing you can use when designing mechanisms/drivetrains with chain. If you use those two things alone correctly you will never have to worry about tensioning/stretching so long as you use large tooth count sprockets and the right chain pitch for the job. My team used #35 chain for our final reduction coming off our Drivetrain gearbox with fixed direct C-C and #25 chain going from wheel to wheel direct C-C with no tensioners on either and had ZERO issues. We love chain and will continue to use it because it is easier and does not require custom belt lengths for each year or each robot.

While i can not attest to reconnecting chain, I can say with utmost confidence. that belt is by far the easier of the two. Chain stretches making it inconsistent in slop. Belt does not stretch and is more accurate, lighter, cheaper, stronger(depends what kind you get), cleaner , etc. that's one of the reasons it's used in engines (and the fact that it can run at much higher speed without oil) Don't get me wrong. chain does have it's purposes, but drive wheels without any shielding to the chain is not one. (IMO) It's wonderful when making a forklift!

[asid61]

Originally Posted by TheModMaster8

While i can not attest to reconnecting chain, I can say with utmost confidence. that belt is by far the easier of the two. Chain stretches making it inconsistent in slop. Belt does not stretch and is more accurate, lighter, cheaper, stronger(depends what kind you get), cleaner , etc. that's one of the reasons it's used in engines (and the fact that it can run at much higher speed without oil) Don't get me wrong. chain does have it's purposes, but drive wheels without any shielding to the chain is not one. (IMO) It's wonderful when making a forklift!

Chain is also used in engines, though. And teams have run center-to-center chain, most notably us this year. Seriously though, 118 ran (and might still, I can't recall what they did this year) chain-in-tube C-C for years.
Chain technically doesn't stretch, but it does wear, albeit slowly. For us, chain wear was far less of a problem than bearing blocks getting closer together due to hole clearances. Last year we ran on one tension of chain for the whole season without any problems. I would say chain is the easier of the two due to the sheer amount of forgiveness it has (and it's ability to replace 20 pitch gears, but that's for another time).
There also seems to be a rare recurring problem of belt picking up field tape, although I have no idea why.

[TheModMaster8]

Originally Posted by asid61

Chain is also used in engines, though. And teams have run center-to-center chain, most notably us this year. Seriously though, 118 ran (and might still, I can't recall what they did this year) chain-in-tube C-C for years.
Chain technically doesn't stretch, but it does wear, albeit slowly. For us, chain wear was far less of a problem than bearing blocks getting closer together due to hole clearances. Last year we ran on one tension of chain for the whole season without any problems. I would say chain is the easier of the two due to the sheer amount of forgiveness it has (and it's ability to replace 20 pitch gears, but that's for another time).
There also seems to be a rare recurring problem of belt picking up field tape, although I have no idea why.

That is weird lol, though you when chain get slack it has sideways play meaning if you run chain too close to a bolt or wheel, you'll run into some problems. Belt has not play, and it can take a hit and be fine, though it really just comes down to what works best for the individual

[Billfred]

Originally Posted by TheModMaster8

That is weird lol, though you when chain get slack it has sideways play meaning if you run chain too close to a bolt or wheel, you'll run into some problems. Belt has not play, and it can take a hit and be fine, though it really just comes down to what works best for the individual

Sometimes the chain is its own worst enemy; we had the bent-clip-to-hold-the-plate half-links in our #25 chain this year and it blew itself apart hitting the other half-link in the travel. Whoops. Switching to a Dark Soul tool and better half-links that don't have the pin made things much better. (The nice thing about a tube frame: it's pretty hard for your chain to take a hit, except from itself apparently!)

I would be open to a belt-in-tube frame, because I definitely see the upsides from running belts in the AM14U series, but the packaging just wasn't going to happen in this year's robot.

[ThaddeusMaximus]

You can make any design work with about any construction method... thought it may not be the best. So again, back to the resources.

Consider turnaround time. Tube construction? You can easily make new or modified tubes in house ifneedbe.

Sheetmetal construction? If it's complicated geometry, especially trussed, you've either gotta have the equipment in house or wait for your jet/laser sponsor.



Now, to those nitty gritty things... though sheet metal can be made to good standards, it's much, much, much easier to make decently accurate parts in stock than sheetmetal when you lack a jet. Luckily FRC isn't demanding of high tolerances... usually.

[Mike Schreiber]

Originally Posted by asid61

I think it depends highly on your bending equipment.
Personally I'm partial to sheet metal because it goes together very fast (put everything in place and pop in rivets), but if your bending tolerances are +/- 0.01", it wouldn't be suitable for bearings and shafts between bent walls.
Tubes are very easy to work with due to the integrated right angles and geometry and my team has used a lot of 2x1 and 1x1 (both 1/16" and 1/8" wall) everywhere. I don't know how much of an effect your waterjet's accuracy and taper will have, but if you want to be more careful you can purchase a 1.125" reamer and use that to finish all holes to a final size.
1.124" would let you do a light press fit, but those have to be bought custom to my knowledge.

We use a brake and bend our chassis every year. You just need to set up a fence and make all your flanges the same length. I doubt we have a +/- 0.010" tolerance on our bends. We bolt up the axles and use those to line up the outer walls of the chassis. Water jet rivet holes in one piece and then drill to match in the other once its all clamped up and square. Water jet has been accurate enough in my experience for bearing fits. You don't need fancy bending equipment just a pretty standard sheet metal brake.

[Drew_trak]

First of all, I recommend using 1x2 x .125 aluminum tube for your chassis. We use this every single year (With the exception of last year). It allows for simple connection of gearboxes. One issue may be getting the chassis square. Our team machines 90degree gusset plates and I dont know if you guys have access to a mill.

As far as Chain vs Belt: Belt Is the way to go

My team is only starting to work with belt. The problem with chain is it stretches. Make sure you have the ability to tension your chain. One year, we couldnt tension a .25 chain and it kept snapping whenever we had quick changes in direction. Again, I dont know if anything I said applies to belts. If your team has gotten belts down, Dont go back to chain. They are heavy
-Best of luck

[GeeTwo]

Originally Posted by Drew_trak

One issue may be getting the chassis square. Our team machines 90degree gusset plates and I dont know if you guys have access to a mill.

In 2014, for Aerial Assist, we had no mill, and a run-down (ok, vandalized) cheap drill press. Despite this, we had no problem keeping our c-channel and tube chassis square. We used steel COTS flat corner braces and tees, in the same width as the channel and tubing for gusset plates. It was heavy, but not so heavy that we had to remove any mechanisms or drill any "speed holes" to pass inspection. It would have been even easier if we had bought four 90 degree corner clamps (which we discovered the next summer).

Our chassis was not only square when we built it, but survived a regional of Aerial Assault with no noticeable issues, excluding only our manipulator which reached outside the frame perimeter to pick up balls (and which was NOT so well supported on the corners).

[AdamHeard]

So many firm statements in here without much evidence or reasoning behind it...

When it comes to winning matches and making reasonably reliable robots, for 99.9% of teams both methods are fine.

We've run both in drive, and have been happy with both.

More recently we've run chain because if you already have the sprockets and chain, there is no lead time for any arbitrary length run (whereas belts are length specific obviously).