2x1x1/8 in vs 2x1x1/16 vs 1x1x1/16 in 6061 rectangle tube for main robot frame (square config w/ swerve modules on corners.)

Hi all, so my team is getting a head start on a revised version of our SDS swerve module based drivetrain during out offseason, and so I have a question about aluminum tube sizing for the main frame of our robot. The frame will be a 28in square made of 2x1in rectangle tube with modules in each corner. In the past we have use 1/8in wall for this, but in the interest of saving on weight I am wondering if 1/16in wall would do the job equally well. as a secondary question, how well do you think 1x1x1/16in would work in this application? Any thoughts are appreciated! thanks for reading!

I don’t know of any teams that use 1/8” for their swerve frames. Hell, even for most skid steer frames, 1/16” is more than enough. Honestly not really many applications where you’d need 1/8” wall tubing. We keep some on hand just in case, but I don’t think we’ll end up using it any time soon. Design things properly, and for the most part (read: buddy climbs and the like excluded), you can get away with 1/16”.

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Drive frames would need to be 1/8", if we were running full-contact without bumpers.

From long experience, if we were running non-bumper with the kind of drive power available nowadays, 1/16" would be destroyed. 1/8" tended to have a hard enough time as it was.

That said, bumpers do change that equation tremendously.

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True. With bumpers plenty of teams have managed to get away with 1/16”. 254’s 2019 bot is a good example, and IIRC they only ran 1/8” on their drive rails in 2018 to help handle the loads from their buddy climb.

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We use the 2x1x0.1 versatube in our drives. It gives us more strength than a 1/16th and is slightly lighter than 1/8th. The pre-drilled holes are nice too.

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We use 1/8”. One issue with 1/16” is it doesn’t work very well to put threads in it which means you need to design for a nut. A #10-32 will only have 2 threads in 1/16” which won’t hold much. And if you end up needing to put the nut all the way on the other side of the tube, you’ve got to be careful to avoid crushing the tube when tightening (esp on the 2” side).

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Our preferred aluminum frame perimeter, 1x1x1/16 VEX stacked 2 high. This makes a 1x2 with a beam in the middle of it. It is a good idea to incorporate the belly pan into the perimeter (unibody construction). We have also used a single 1x1 when tied to a belly pan.

Now our preferred frame material is 1/2x1/2 chrome moly,

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We like to use 1/16" wall on our WCDs with clamping bearing blocks, but we use 1/8" wall for the front and back of the frame since those areas can take some big impacts in competition. Cuts down the weight a lot, and with bearing blocks the chassis is plenty strong.

166 Currently uses 1/8" on our drivetrain (we hit hard in NE) but we will most likely be switching to 1/16" this year.

what wall thickness?

IIR the thinnest available, which is .035". 2020 was the first year of using it on a comp bot and so far we’re very happy. The 1/2" square is normally used in conjunction with other structural parts (unibody style). Stand alone parts (arms struts etc.) are typically made of 1/2 x 1"

You kinda need to be a welding team to use it however it is a breeze to weld.

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for us, we used a 2x1x1 1/8in frame for our swerve bot this year and with running without bumpers we dented the frame more than once but we also have gotten away with using 1/16 in for our frames in the past.

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Our choice: 2x1 1/8"

Giving your chassis more weight is sometimes needed!

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Great point! We use 0.0625 wall but use riv-nuts when we need to mount swerve modules to the frame.

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Are you referring to the .1" wall VEXpro framing or the .04" wall? I haven’t seen them offer 0.063 wall tubing. The double stack technique is interesting and sounds like it might have some advantages over 0.063 2"x1" in certain applications.

Lots of other places sell aluminum tube. Schupan has a local outlet we get a lot of aluminum from, McMaster has it as well. We do a lot of welding on 2767, so we do not make use of the Versaframe holes as much as some other teams.

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Sorry about that miss…

We have used both the thinner VEX stuff and the regular VEX stuff. Mainly the thinner. The Schupan stock is used to build the practice bot since it’s cheaper and right next door.

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How do you attach these together? Weld?

Belly pan is still aluminum right? I assume you rivet it on? Have you had any issues with tube strength after putting holes in it? Why the switch? I suppose the thinner tube let’s you run a wider wheel base without giving up much strength and it may give a bit more in the way of customization options. Pretty hard for a team that’s not set up to weld though.

1" stitch weld every so often (6-12"). NOT THE WHOLE LENGTH.

The belly pan is still aluminum and riveted on, typically with tabs vs. a hole in the moly. The swerve rails are also aluminum and mounted on tabs. We put holes in the 1/2’ moly for bumper mounts but they are in strategic areas that minimize a strength issue.

The main reason was to get a frame that was more resilient to yielding. 2017 frame would yield when flexed to 1.125" from flat. We had to flex the 2020 frame to 3" before it would yield.

I’m not sure how to work with Moly without a welder. If you’re a team that is good with rivets then maybe but I don’t count us in that camp. On a positive note, it is a good material to start with if you want to try to weld (vs. aluminum). You can use a cheaper welder (MIG) and it doesn’t require nearly as much skill.

If our welding resources up and disappeared, I predict we would use VEX tubing and rivets/bolts with an integrated belly pan.

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1323 is definitely onto something with the 2x2x1/16. I don’t thing it makes much sense when you isolate the drive train, but after looking closely at how they integrate their superstructure it makes more sense.

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