I would recommend the kit bot frame. It isn’t as adjustable as 80/20 or ITEM or anything like that but it is adjustable enough and you can modify it pretty easily too. No welding required, just some bolts and some bolts and Loctite.
Our team used to use 80-20 but switched off of it for weight issues. We now use one-inch extruded aluminum (I don’t know a specific maker) for most of our robot. Several high strength needs still use 80-20, but extruded forms almost all exterior parts of our robot. It has been very strong despite being hollow on the inside (we don’t fill it).
Edit: We do use kitbot frame for the core of our robot. It has been proven strong, and allows us to have a working frame first week.
We’ve had a lot of success the past two years using standard 3/4 in wide, 1/16th in wall aluminum tubing. It’s certainly not adjustable without making your own holes, but it is very light, very strong, and very easy to work with. You can use hacksaws and hand drills to build the robot if you want to.
In 2007 Mark Johnson, one of our mentors, did the welding, while in this past year we used screws for initial construction, and then replaced as much of the screws as possible with glue and rivets. (though much of the robot is still held together by screws, for lack of time).
We’ve used 80/20 in the past, and the problems we had with it were weight and at least I personally never felt like the bolts and sliders held together quite as well as a good bolt and locknut or even screws. However this is just based on feeling, we didn’t really have an issue with that. It’s very nice for areas that need a lot of adjustment, so don’t rule it out altogether.
The kitbot frame is also pretty decent for the most part. You can easily make a very successful robot out of it.
80/20’s main advantage is that it requires little effort to make many different designs with it. It is not a very efficient shape as far as it’s strength/weight ratio.
If you want to spend more time designing, you should look into using many other sections of aluminum, as well as other metals and non-metals. Steel can be very effective (look at 1501’s 2007 robot), sheet aluminum is also used by them to make strong, light structures. We’ve used fiberglass pultrusions for our frame, and 842 uses it for their entire robot! Some teams use plywood, you could use spruce, or other woods, which take some effort to design but are relatively easy to work with and can be very strong and light (think of the early airplanes, which were made almost entirely of spruce). For aluminum, look into tubing, both round and square, and angle and sheets. Our robot used sheet and angle aluminum this year.
Also look at the various ways you can connect the parts. Rivets are great, they are light, strong, and quick to replace if needed. Bolts and nuts are a bit heavy and cumbersome, but can be removed and replaced many times. Glues are a bit tricky to apply and hard to repair joints made with them, but for some joints they are the best way to go. Welding is great for thicker alumimum parts, and for thinwall steel tubing (such as 1501 has used).
What kind of glue and on what parts/materials were you using it?
It was a polyurethane based glue I’m pretty sure, but I don’t know exactly what kind or brand of glue. I’ll be in the shop Wednesday and if we still have the container of it I’ll post back with more detail. We used it on 3/4 inch extruded aluminum tubing held together by flat plates. Before we did any gluing we roughed the surface up with a pneumatic disc grinder to create a surface for the glue to actually stick to.
We never had any of our glued pieces fail, and when we just glued two test pieces together and tried to break the joint we bent the metal before we did anything to the glue itself. We could easily have gotten away with not using the rivets, but we just used them to hold the pieces together till the glue could set.
Of course, don’t get it on your hands… or clothes. The other problem I could see is if it is in a high stress location and the part it’s holding on is damaged it would be a real pain to fix.
Nah, just the access is blocked. Without the Balrog, it’s wide open.
Mithril may, however, fall under the metal type Unobtanium.
Kit frame, or if you like custom, 1" by 1"-2" by 1/8" wall tubing is pretty good for a drive frame. Higher up, 1/16" wall works well. Thing about the drive base is, it takes a beating even with the bumpers, so 1/16" wall might not be the best option. (Then again, properly braced and with a decent material on top, 1/16" can support a robot climbing on top of it, so…)
I believe we only used 1/8th wall thickness in four pieces of the base frame, those being the four blocks that the axle( a dead axle) for the wheels go through. We did have one incident at Western where we hit the wall and bent our entire frame, but we fixed it, and then glued a solid piece of diamond plate at the weak point to give it a little more structure, without too much weight increase. If we had just incorporated a few triangles into the base in the first place it probably wouldn’t have been an issue at all.
3/4"x3/4"x.035" Chromoly Steel (Available at Aircraft Spruce) is wonderful if you can weld (not as tricky as aluminum i don’t think).
You can use 1/2"x1/2"x.035" as well for areas under less stress. The stuff is super light, (about the same as aluminum), more compact than 1"x1"x1/8" box aluminum, and three times as strong. Cost is the only downfall but it isn’t anything too unrealistic. Teams 269 and 1501 tend to work with this stuff and both come out with VERY solid frames.
ITEM is a similar solution to 80-20. Don’t have a source but I’ve heard it is stronger than 80-20 as well.
Other than that, on 171, we use Kit of Parts frame and 1"x1"x1/8" or 1"x2"x1/8".
We on 33 have been doing a folded sheet metal chassis for the last few years. Once you learn how to work with sheet, it is pretty easy, very light and very effective. You do need to learn rivet techniques and how to bend metal accurately an effectivele. We use heat treated 6061 T6. Before everyone tells me you can’t bend it, that is not true. Heat treated (T6) means you need to be very careful bending it and use an ample radius.
For the big structures we have generally been going with space frame welded aluminum tubing both square and round. I have a lot of race car chassis construction experience so it helps. One of our students did most of the welding this year. While she is not a pro, she gets the job done.
What material you decide to use depends on budget, equipment, and skill sets. 80/20 or Star bar is very easy to use but extremely heavy (from a KB33 perspective). 1/16" is the beefy stuff on our machine and we often go down to 0.035" wall round tube.
If you do not have a skilled welder, I would recommend visiting the Team 1216’s website and check out their chassis. The pre-drill 1x1x1/16 box with a very specific hole pattern. This technique gives 90% of the strength of 1x1 box with the flexibility of Star-bar or the kit rails with a TON less weight. These guy are pretty modest and only went to 1 regional so you won’t see a lot of buzz about them. As a structures guy, I have a lot of repect for this technique as it has the 4-way threat of strong, lightweight, flexible design, and easy to use/manufacture.
Another good source are the 2 “Behind the Design” books. You can almost tell what line of work the sponsors are in by the construction of the robot. With aircraft companies you will see a lot of sheet metal. Nasa and Robotics related sponsor teams seem to have a lot of CNC. Big 3 teams seem to have a lot of welding.
As far as material sponsors to order from Aircraft Spruce has an awesome selection but can be a bit slow to certain areas. They have some truly amazing materials line a strut material that is 11oz. for 8 feet. Online metals is a good plae to order small quantities, but were extremely slow on their delivery for us (I did find a way to expedite future orders). Mcmaster Carr is fast but expensive.
Bleh, the less 80/20 that’s used on a bot the lower my blood pressure is. It leaves too much room for last-second decisions that haven’t been thought through.
We’ve used 1/16 wall 1x1" 6061 Aluminum tubing for our frame for 3 years now. It’s always been welded. We have students that practice welding on our prototype frames, then they assist the pros who do the welding of the actual frame during build season. From there the frame goes straight to powder-coating at the same sponsor, which also adds strength and rigidity to the frame.
Our drive base frame this year came out to 6.1lbs after powder coating, and had zero CNC work or cheese-holes added to it. In future years we will probably experiment with 1"x1/2" tubing that has a 1/16" wall and sturdy injection foam in order to produce a more compact frame.