The Frame thread

[Grim Tuesday]

So, every year, my team makes the same exact frame, just modified for the years game. It weighs too much, and doesn't do a particularly good job of anything. Since I will have a leadership position on the team next year, I've made it one of my major goals to change this. One of my friends came up with this quote:

"The frame should be build to hold the robot; the robot should not be built to put in the frame"

This leaves me with a dilemma: We need the frame done early (that has been one of our biggest shortcomings in years past, not getting the frame welded until the end of week 2). On the other hand, I agree with my friend, which means we can't begin designing the frame until the design is done at the end of week 1.

According to Inventor, the frame weighs a whooping 35 lbs, not counting the supershifters, or the treads. Add those in, and your at 50 or so.

The problem is, we have used the same frame/style of frame for so many years now, our team has pretty much forgotten how to do anything different. So, I thought to myself, this is FIRST, teams like to share information, right? And people like to show off their designs, right? People like to critique designs, right?

I would be very grateful if other teams could show me pictures, or CAD of how they do their frames/drive trains. In return, I will show you and tell you a bit about ours!

We build a lower frame out of 1x1 aluminium T-slot. Very strong, very durable. Very heavy. We sandwich treads between two pieces of those T-slots. The treads are made from fan belts turned inside out and driven with a sproket from the supershifters (last year we used toughboxes). We build an upper frame out of 1/16 aluminum to support various mechanisms. The whole assembly is welded together, and we use T-slot sliders to put many things into the system.


Thanks in advance for other teams' help!

[,4lex S.]

When I look at a FIRST challenge with whatever team I am involved with, I like to have my options open, which is why I am a big fan of a super simple drive type that can be built off of. The T-slots and the extra attachment points seem to make the design you built very modular though, which I like.

Let me get to the point, T-slot is heavy. Switching to a gusseted or welded tube frame will get you to a happy place. If you have sheetmetal options, you can go with that. I also became a fan of the kit frame working with 2702, we built a very solid, and reasonably light drive with it alone (much lighter than what you have quoted). I am sure you can find plenty of pics of the structural tubing design, whether it is a WCD Derivative or something else, they all seem to work pretty well.

I shall provide my take on the tubing frame as well, I have posted this before, but I challenged myself to make a warp resistant (keep welds away from the drive components) gusseted frame that was relatively light. Heavy 254 influence below. This has never been built, but it sums up a lot of peoples ideas.



Probably the big thing I tried to improve with this frame was robot torsional stiffness. By that I mean the frames ability to keep the two drive component rails parallel. The stringers between the drive component rails really help if you don't put a top box on the frame like you have on your design. That is the advantage you have at the expense of weight, nice torsional stiffness.

Look into Team 221 LLC's bearing block tensioning system as well as 254's. They are both good ways of going about things if you choose to go live axel.

[akoscielski3]

Originally Posted by ,4lex S.

When I look at a FIRST challenge with whatever team I am involved with, I like to have my options open, which is why I am a big fan of a super simple drive type that can be built off of. The T-slots and the extra attachment points seem to make the design you built very modular though, which I like.

Let me get to the point, T-slot is heavy. Switching to a gusseted or welded tube frame will get you to a happy place. If you have sheetmetal options, you can go with that. I also became a fan of the kit frame working with 2702, we built a very solid, and reasonably light drive with it alone (much lighter than what you have quoted). I am sure you can find plenty of pics of the structural tubing design, whether it is a WCD Derivative or something else, they all seem to work pretty well.

I shall provide my take on the tubing frame as well, I have posted this before, but I challenged myself to make a warp resistant (keep welds away from the drive components) gusseted frame that was relatively light. Heavy 254 influence below. This has never been built, but it sums up a lot of peoples ideas.



Probably the big thing I tried to improve with this frame was robot torsional stiffness. By that I mean the frames ability to keep the two drive component rails parallel. The stringers between the drive component rails really help if you don't put a top box on the frame like you have on your design. That is the advantage you have at the expense of weight, nice torsional stiffness.

Look into Team 221 LLC's bearing block tensioning system as well as 254's. They are both good ways of going about things if you choose to go live axel.

why is one of the transmissions rotated 90 degrees, would it be in the way of something or is it just something you haven't noticed yet ?

[HighLife]

Kit Chassis and transmissions.

We usually play around with wheel configuration and drive ratios, but our record with the kit chassis speaks for itself.

2 Quality Awards
5 Finalist Awards
4 Championships
1 Trip to Einstein

[akoscielski3]

the things you should think about while building/designing a frame is

- torque (push through robots playing defence)
- speed (get around the field quickly
- Light frame (don't waist all your wieght on the frame)
- Strong frame (haveing to fix somthing on it or bending it back in place, can cost you the regional if you can't do it fast enough)
- Easy to repair ( ^ )
- easy access points to put frame together ( including wireing, attaching parts, fixing. You don't want to spend a lot of your days during build season building the chassis
- Easy to make ( ^ )
- simple to design the rest of the robot mechanisms on top of it (useing only a few new holes and bolts to attach the mechanism ontop of the chassis, or inside the chassis)

These are things that i have learned over the years that must be thought of while designing a chassis.

[BrendanB]

Originally Posted by akoscielski3

why is one of the transmissions rotated 90 degrees, would it be in the way of something or is it just something you haven't noticed yet ?

If it is the same type of tranny as the AM supershifters then by rotating one 90 degrees puts the output shafts at the same level.

[akoscielski3]

Originally Posted by BrendanB

If it is the same type of tranny as the AM supershifters then by rotating one 90 degrees puts the output shafts at the same level.

Not if they are using Gen2 Andy mark transmissions, the output shaft is not in the middle, but lowered. making the output shaft moved to the side and up higher. unless he is using a different transmission though.

[Chris is me]

Originally Posted by akoscielski3

Not if they are using Gen2 Andy mark transmissions, the outdut shaft is not in the middle, but lowered. making the output shaft moved to the side and up higher. unless he is using a different transmission though.

He's using the AM Supershifter, which doesn't have a centered output shaft.

Originally Posted by Marc S.

http://www.simbotics.org/media/videos/presentations

If nothing else, you can build a super easy drivetrain like the one above, that is also "better than 90-95% of teams". Certainly better than the tank drive and very simple.

This is an amazing video and should be required viewing for all rookie teams.

[akoscielski3]

Originally Posted by Chris is me

He's using the AM Supershifter, which doesn't have a centered output shaft.

I see now, i've never really seen these or even looked at them to use on a chassis. Does anyone know if they are better than Gen 2's??

[JesseK]

The major flaw I saw at champ's with design that Alex posted is with the side rails -- the ones that are supposed to back the bumpers. 973, 254, 968, and 1868 all used the same exact drive train with minor differences. Their bumper-backing side rails were made out of 1/2" box tubing.

On 3 out of the 4, that 1/2" box tubing was warped or bowed inward by 1/8" to 1/4" -- somewhat negating its effectiveness and being technically illegal to the most pedantic of bumper rule interpretations. To be honest, 99% of 2-level welded frames I saw are in violation, even ours. It's simply too difficult to get that thing 100% straight if it's not perfectly flat on a welding table

1" box tubing could possibly make the 2x1" vertical frame members torsion/warp rather than simply the side rail, which would then stress the side rails that hold the wheels. I'd consult with a welder before giving that concern any weight though. Perhaps Cory will chime in if he sees this.

It's easy to prevent warping during welding on a 2D frame (just the 2x1 rails). Yet things can get very tricky when moving to a level that isn't clamped directly to the welding table. It's one of the many reasons why WCD has been a very successful drive train for so many years -- its function:simplicity "ratio" is unsurpassed, thus it mitigates many of the issues that more complex frames have. Compliance with bumper rules in recent years has been the root cause of the extra necessary complexity of side rails.

[AdamHeard]

Originally Posted by JesseK

The major flaw I saw at champ's with design that Alex posted is with the side rails -- the ones that are supposed to back the bumpers. 973, 254, 968, and 1868 all used the same exact drive train with minor differences. Their bumper-backing side rails were made out of 1/2" box tubing.

On 3 out of the 4, that 1/2" box tubing was warped or bowed inward by 1/8" to 1/4" -- somewhat negating its effectiveness and being technically illegal to the most pedantic of bumper rule interpretations. To be honest, 99% of 2-level welded frames I saw are in violation, even ours. It's simply too difficult to get that thing 100% straight if it's not perfectly flat on a welding table

1" box tubing could possibly make the 2x1" vertical frame members torsion/warp rather than simply the side rail, which would then stress the side rails that hold the wheels. I'd consult with a welder before giving that concern any weight though. Perhaps Cory will chime in if he sees this.

It's easy to prevent warping during welding on a 2D frame (just the 2x1 rails). Yet things can get very tricky when moving to a level that isn't clamped directly to the welding table. It's one of the many reasons why WCD has been a very successful drive train for so many years -- its function:simplicity "ratio" is unsurpassed, thus it mitigates many of the issues that more complex frames have. Compliance with bumper rules in recent years has been the root cause of the extra necessary complexity of side rails.

We actually didn't have the same style bumper support, we just had some "cheater plates" (as we called them) that came out and touched the bumper (1x~3.5"x.125" plates riveted on) every 8" or so. The actual load of the bumper was really only supported by the two bumper mounts that were 1" diameter aluminum round sitting flush against our siderails.

[JackS]

Originally Posted by JesseK

The major flaw I saw at champ's with design that Alex posted is with the side rails -- the ones that are supposed to back the bumpers.

We found an cool way around having to deal with welding that super structure. The bumper mounts are pictured below and were relatively easy to use, although next year we may update the design a bit.



That is our drive base from this year fresh from the welder. (You can see the welds aren't even ground down.) 3"x1.5" tubing that is 1/8" thick doesn't require bearing blocks, and internal belts are easy to change with the window above the center wheel. This DT is REALLY simple and it doesn't even require CNC milling (although it is nice). Virtually no maintenance was required and our 9mm wide belts held up fine for 2 regionals.



Above is a concept drive based on our "WCD" from this year. Custom 3" wheels only require a single 12:56 reduction in the gearbox to go 12 fps. (The 56 tooth gear is ~2.8" in diameter so there is little ground clearance, but it is right behind the wheel anyways. The tubing is also only 2"x1") It weighs somewhere in the low 30s with CIMs and w/o the shown arm superstructure. I'm working on getting a similar sheet version out soon. Basically this is a lighter and simpler version of our robot this year (which weighed a whopping 98 lbs.)

Feel free to contact me for any CAD.

[Chris is me]

I like how we're trying to save weight when we came in at 95 pounds. Continuous improvement!

[thefro526]

816 experimented with a "Drive train in a tube" style frame this year, similar to Team 221 LLC's "Rockbox". Either side of the drive was put into a 4x4x1/8" Aluminum Tube, and the two tubes were welded to some 1x1x1/8" Cross tubes to make the frame. The Bare frame weighed 15lbs without any pocketing. If we were to have done some modest pocketing we probably could've pulled out a pound or two but we didn't see the need to.

Here's a picture of the frame with all drive components and electronics installed:



In retrospect, the frame was easy to build and plenty strong for a game with bumpers and moderately light weight. If you've got welding and some basic machining abilities, it's not a bad way to build a frame, though there are better options out there.

[roystur44]

Take a look at our galleries of previous builds. We use sheet metal and rivets for almost all the parts on the robots we build.

laser cut .090 5052 alum
student designed using SolidWorks



https://picasaweb.google.com/971.FIRST/2011Build#