Advantages and disadvantages of using (rectangle/square/round) Tube versus C-channel for elevator mechanisms

Hello all, I was wondering whether there any benefits of using tube stock over C-channel stock when it comes to building an elevator mechanism? I know a lot of good teams prefer C-Channel (118,930, etc) But also there are other good teams who prefer the round tube stock (148,1684, etc), also other teams who use Rectangular/square tube (254,1323,930). Is there a reason why teams like using one over another other? Is it due to the ease of build, rigidity, etc?

I prefer stock for its rigidity, not just in elevators but in general. To be honest I can’t recall a time either of my teams has ever used C-channel for anything; for a just a little bit more weight you get so much more rigidity. I’ll be interested to hear reasons others prefer C-channel.

While it is very rewarding being mentioned amongst teams like 254 and 118, 930 does not use c-channel. We use 2x1 tubing, just oriented differently than you typically see in tubing elevators. Our design would not work with c-channel without seriously rethinking our bearing-blocks.

And to answer your question, I’d say for the simplicity in design. Our bearing blocks are just uhmw blocks milled to look like an H. 2019 we made them on our CNC, but 2018 we just bought uhmw in 2 thicknesses and made each block out of 3 pieces bolted together.

The C-Channel elevators definitely are more compact, and quite possibly more rigid. But the h-blocks allow each stage to really grip the stage before it, so I’d say it makes this design very rigid as well.

Just to clarify we along with Poof’s/1678 etc… Use 2x1x.060 box tubing for elevators. 148 & others you mentioned I believe used or have used round tubing.

When we did the weight comparison the round tube came out a tad bit lighter but the box/rectangle tubing so 10x easier to deal with for us. Even allowed us to rig the rope inside the tube nicely.

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So of all the elevators my team has built in the last couple years, they have all been ridiculously simple c channel two stage elevators with UHMW sliders in them. Worked very well for us this year, although we, or at least I, plan on moving toward steel tube stock and bearings if they come up again this year. Smaller, harder to bend or twist, less binding, and in theory lighter.

I would say it has more to do with the level of complexity required to build than anything else, as tubes demand much higher build tolerances since bearings are usually involved. I’m not saying you don’t need bearings in a c channel design, we just found that we didn’t.

Thanks for the clarification! I always thought you guys used C-Channel. Do you guys have any public documentation I could take a look at regarding your elevator system to have a better understanding of the system?

I never knew that you guys used rectangle tube! Its funny cause our team took a look at your guy’s robot multiple times at the WI regional and at the generac demo (1259 Paradigm shift). Would you have any pictures of the H style bearing blocks or have the link to where you guys used to purchase them?

This thread has more info. Can ask for more info in this thread

Using the 2x1x1/16" rectangular tube has been great for us enabling for our elevator to be rigid and easy to manufacture. In fact, for the WI regional we ended up bringing in our spare elevator in withholding (including the 3x 775pro gearbox) as it weighed under 20lbs.

But for the UHMW bearing blocks, we have custom made them for the past two years. We’ve had great success with them as you get so much surface area on the tube (making the elevator stable) while preventing the traditional marring of the tube by bearings in addition to being simpler.

In 2018, we made the bearing blocks in three pieces that we bolted together so all that was required was cutting the pieces to size. 2018%20UHMW%20Bearing%20Block

This year, with access to CNC machining, we were able to make them all out of a single block of UHMW which allowed us to make the blocks a lot more precise and experiment with different tolerances.
2019%20UHMW%20Bearing%20Block

We purchased all of the UHMW for this from McMaster Carr (https://www.mcmaster.com/uhmw-polyethylene). I hope this was helpful and if you have any further questions about our elevator or any other part of our robot feel free to ask!

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Lots of teams use 2x1 tubing for elevators, since it’s very strong, rigid, and has a number of standard solutions for bearings (the Andymark kits, the UHMW mentioned above, etc.) and it works very well, especially for elevators that are going to have to lift significant weight (like the whole robot.) There are other solutions, however, that are lighter and just as structurally rigid. Last year, we used 1x1 square t-slot stock (we got ours from 80/20), which is as strong as 2x1 but lighter and thinner in profile. The bearing blocks are milled UHMW that fit the t-slot and are much smaller than external blocks, while keeping a very secure and rigid connection between stages.

We do use c-channel occasionally, but only for specific purposes. We did use 1.25x1.25x.125 c as the base frame for our elevator this year, since the 1x1 t-slot stock could be socketed into it without other brackets or gussets. We use very light c-channel for other things occasionally (like a camera mast that could have the cable run up the channel more conveniently than running it through a tube), but we never use it for large structural components unless (as with the elevator base above) it offers an advantage by having an open side. Otherwise, square tube or t-slot is much stronger for very little extra weight.

A tube extrusion is much stiffer in the torsional direction than a c-channel extrusion. Usually, an elevator made with tubes will flex less than one made with c-channels. You can do an easy experiment yourself: next time you use up a roll of paper towels or toilet paper, take the cardboard tube and see how stiff it is when you try to twist it. Then make a cut down the length of one side of the tube and try to twist it again.

Round tubes let you maximize the size of the cross section of the tube while using the least amount of material, so they tend to be the lightest and strongest shape. It is really hard to attach things to round tubes though, so rectangular tubes tend to work better for most applications.

The cross section of an 80/20 style of extrusion makes me depressed, because it’s the antithesis of a lightweight rigid shape. Many teams have used it successfully however.

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1x1 80/20 is actually a bit heavier than 2x1x0.06 tube. The 1x1 is about 0.504 lb/ft and the 2x1 is 0.44 lb/ft. It’s a small difference. Haven’t used 80/20 but I would assume if you are using teh T-Sltop then it requires less custom stuff to mount to. But also wouldn’t provide the smoothness of a bearing solution.

Not quite sure how you got that 1x1 8020 is stronger than 2x1x0.06 either. For elevator rails, we care most about the profile’s ability to resist bending loads/moments. The measure of that is called the Area Moment of Inertia (higher = less bending). According to the product page you linked to, the 1010-s profile you used has a MoI of 0.046 in^4. Compare that to a 2x1x0.06 rectangular tube that has a MoI of 0.06 in^4 in the short direction and 0.18 in^4 in the long direction (from this calculator).

So the 8020 is heavier, and it bends more in both directions under equivalent loads. This is part of the reason why a lot of people on here don’t recommend using 8020 to build your final robot. It’s great for prototyping, but if you have the ability to manufacture using rectangular tubes you’ll end up with a lighter and stronger robot.

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Actually, we went with a bearing solution on our 1x2 tube elevator for Power-up and it was much less smooth than what we achieved with the t-slot and UHMW bearing plates. We managed a 3-stage elevator that could extend and retract fully from the top rocket hatch position (from and to loading station height) in about 2 seconds and never had a glitch.

Anecdotally, our 3-stage 2x1 elevator goes from bottom to top in about .75s and also never had a glitch after 70 official matches. But that also has nothing to do with the difference between extrusion and tubing.

Build quality matters a lot with elevators, as you’ve seen. Small misalignments compound quickly. But extrusion isn’t the magic answer. If it works for you, that’s what matters. And just like 2x1 didn’t work for you, extrusion doesn’t work for many other teams, for reasons specified in the other responses.

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I think this is the most important advice. If you have identified something in the “right” way to build a mechanism that causes you poor performance, finding another way that works better for you is a great option. Don’t spend forever trying to make the “right” way work if you have a perfectly workable solution in front of you.

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As noted above, tubing (whether square or round) is going to be stiffer than channel for the same weight [and material]. There have to be rather specific gains to justify using channel over tubing. These might include lighter hardware, easier construction, better packaging, or cost savings. 3946’s 2015 and 2018 (both single stage) lifts used channel, but saved weight (and cost) by using Teflon sliding pads [we got large enough scraps free from NASA in 2015 and had enough leftover for 2018] rather than ball bearings. In both cases, channel was used for the fixed upright, and the carriage included a sandwich of aluminum and Teflon which rode on flanges of the channel. In 2018, we also used the space inside the channel for chain runs, which allowed the channel to serve as a chain/sprocket guard and also (in a just-before-bag redesign which never made it on the field) allow easy access to the chain for maintenance.

I was giving 2 seconds as complete cycle time (up and back) at maximum extension. We were driving it with one 775 and a 25:1 VersaPlanetary gearbox and a 3/32 cabled cascade. I agree that it’s build quality that makes the difference, but for those with less experience building elevators, the t-slot system is pretty fool-proof, where some of the more commonly used systems are less so. In my reply, I was specifically talking about the difference between using a traditional bearing plate system (like the Andymark Elevator Bearing) and using UHMW bearing plates, which both your system and our do.

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