Recently my team has been trying to design some frames, so that when build season comes around we will not be completely lost. I have been doing alot of research online and on ChiefDelphi, and I have come up with alot of different materials that we have been designing with. Some of these include square tube (both welded and bolted), bosch frame, plates and 80/20. Through these searches there have been some disagreements about advantages/disadvantages of each. I am now trying to get a detailed comparison list together, however I would like some input and personal experiences from other teams.
Most of my questions are specifically tailored towards 80/20…
What is weight comparison between 80/20 and similar size square tube?
What is thoughts on the different 80/20 methods of connecting pieces together (last year we used the old school 90degrees and they were heavy…I have heard good things about new anchor mounts)?
How has 80/20 worked for you in the past?
Whats thoughts on weld vs. bolt?
228 has used 80/20 frames since 2003; here are pictures of our 2005 and 2006 frames stripped down of almost everything else except the 80/20 and drivetrain. (Note that in the 2005 picture, the vertical 80/20 members at the 10 degree angle were actually used as a linear bearing for our elevator, which worked quite well.)
Most of my questions are specifically tailored towards 80/20…
What is weight comparison between 80/20 and similar size square tube?
What is thoughts on the different 80/20 methods of connecting pieces together (last year we used the old school 90degrees and they were heavy…I have heard good things about new anchor mounts)?
How has 80/20 worked for you in the past?
Whats thoughts on weld vs. bolt?
I think our team’s mechanical engineer has already answered all of these questions.
If I can add anything, when considering whether to use a welded frame or a bolted 80/20, remember that welds are cannot be easily repaired at a competition if they fail. However, if you were to bolt everything together using 80/20 and the anchor mounts, even if you seriously bend a piece, you just loosen the anchor bolts, remove the piece, slide in a new one, and retighten the bolts. Done.
Your trade off for using bolts over welds is the increased weight (usually about 2 lbs). In the end you will have to decide if having an easily repairable and modifiable frame is more/less important for your needs than a permanently welded frame than saves about 2 pounds.
If I had to choose between a welded 1x1x0.125 aluminum box chassis or a 1010 80/20 (with anchor-mounts) chassis right now, I’d go with the 80/20. The reason? Modularity. The concept of a modular frame is amazing, especially when in week four of the build season if you’re hit with a genius idea on how to improve x mechanism, or how to rearrange the mounting of y mechanism to improve its stabilty or rigidity.
Modularity of frames - whether they are Kitbot or 80/20 - can save a lot of headaches in the final stretch of the build season.
**What is thoughts on the different 80/20 methods of connecting pieces together How has 80/20 worked for you in the past?
Whats thoughts on weld vs. bolt?
**
Last year we had a chassis constructed partly of 80/20 and partly of lexan and aluminum plates (I’ll try to post a few pictures). It was my job to install our gearshifter, which was basically a plate on which the gearboxes would go that was supposed to attach to the chassis and be able to shift back and forth. We didn’t plan for installation of the plate ahead of time, so when it was time for me to go to work, it took hours of squeezing into tight spaces just to attach or detach it. If something had broken with our drive train in the middle of a match, it would have been impossible to fix on time. Ultimately, we had to scrap the gearshifter altogether.
I suppose my warning has to be taken with a grain of salt, since we didn’t plan too far ahead with our design and you’re already trying to work it out. If your drive train is going to be as simply laid out as the ones in the pictures from the above post, sure, go for it! 80/20 is not ultraheavy and a great material to have on your robot in general. But I will say that the more complicated your robot’s “internal organs” get and the more stuff you try to squeeze in there, the more messy dealing with 80/20 might get.
If you decide to weld your 80/20 frame make sure you clean all the joints. If you don’t clean it the welds will be weak.
Some years ago our team did exactly that. Amazingly the frame survived the season but we were able to disassemble it with hammers :eek: We literally “pulled” it apart, it was that weak.
80/20 is also difficult to cut. I would not recommend using it unless you have access to a mill. Cutting 80/20 on a band-saw or with hack saws will leave rounded ends, making butt-joints impossible. Without secure joints your whole frame will warp.
I think 80/20 is a great and useful material, it allows for easy adjustability and prototyping, but I would not recommend building your entire robot out of it.
Last year we used 80/20 for our superstructure, and we found that a miter saw with a wood blade worked fine for straight cuts on a budget. (Aluminum seems to be soft enough not to cause trouble with the wood blade)
We also cut Item (a competitor of 80/20) with a miter saw, it works fine with a carbide blade and some care.
80/20 is perfect for places that might need adjustability, but awful for places subject to shock loads. For example, our entire frame was made of 80/20 (Item really, but for the sake of discussion they are the same), the top parts that held the shooter, conveyor and ball basket were great, we could move members around to tweak things. Our lower frame, however, was a problem with it constantly shifting and loosening, even with bumpers, because of the beating we took (and gave) on defense.
I would think that a kitbot frame below with 80/20 everywhere else would be a good choice. Just remember that 80/20 is heavy - not heavy for its strength, but the strength may be far in excess of what is needed for some applications. In other words, don’t be afraid to use some angle or U channel where it makes sense.
If you guys are interested in 80/20, I STRONGLY advise you to call the local 80/20 rep, have him come in and talk about it. These guys are experts, and can really help a lot - and they are very happy to do so. I know the guy for up here in bergen county, so if you need help finding the guy for your area, PM me.
One thing to keep in mind with 80/20 type materials is that they have terrible torsional stiffness compared to a box tube. We used mostly 80/20 for the stack attack game robot. That year the weight and constantly having to tighten the whole robot turned our team off to 80/20. We have used the left overs for fast prototyping since then. Now we use mostly angle and plate 6061t6 aluminum.
Please, general (unqualified) statements about the stiffness, or lack there of, of 8020 material should not be made in this thread. If you actually sit down and do the math, you will find that the 8020, and similar, extrusion profiles offer both lateral and torsional stiffness that is within 5% of 1/8" thick 1x1 box tubing.
Most teams blow it when using 8020 by NOT using the proper connections. The “double anchor” connection is ONLY connection that should be used with these types of extrusions. It offers both the strongest connection, and the lightest connection. It is also the cheapest and easiest of the connections to deal with. Try finding another combination of qualities like that! The joining plates are just the wrong way to go for our applications, as they do not offer the strength, or the weight advantages of the double anchor.
I will also state that 8020 should only be used where it is required. If you plan on building a 5’x38"x28" box, you will run into weight problems. You will find the same problem with 1" box tubing. Only use the extrusions where required, and mate that to a more weight friendly 1" angle for an upper structure.
All this negative talk about 8020 is just reminding me that I should write up that White paper about the proper uses of extruded profiles.
Another great thing about 80/20 is that it can be used as a sliding piece. like on 177’s retractible rollers. Using 80/20 slide brackets ( metal brackets with a plastic piece on the inside that allow the 80/20 to slide freely) was highly effective, and very strong.
I’ve used Item and 80/20 as well and have found that i like the Frame-World extrusions the best. They are a good value, and have a nice clean look to them (no grooving, available in several anodized colors). The T-Bolts for the frame world stuff are also very strong as well as inexpensive.
The structural strength of the various extrusions are very similar, so it seems to come down to price and availability of accessories.
80/20 is anodized (usually clear) if you don’t remove the coating it won’t weld properly. It actually makes a god-awful sound when some one tries to burn through the coating rather than grind it off. It’s not intended for welding and I don’t recomend doing so for most uses.
Also I cant recomend using extrusion enough. Even though we can make 1/16th welded box frames we still use it for many things when its the right part for the job.
One thing I noticed on the 80/20 site the other day is that they have a new (To me) extrusion HT series which is tubular framing with offset holes. Its more like a kitbot frame material than the usual 80/20 that we all know and love. I don’t know if I would use it for a frame due to its size (and therefore weight), but it could be good for a super structure. Here is the catalog:
It only comes in 1.5" square right now. Some of the pieces have flanges built in which could be useful. Due to the fact that we can make something lighter by welding 1/16" tubing I dint think it would be great for 177, but for a team with less manufacturing and/or engineering resources it could be an excellent solution.
