I recently redesigned my team’s entire pit as we were in dire need of an upgrade after the last five or so years of using pre-bought tool chests. I started out by using 1x1 80/20 framing as the structural framework for the new pit cart and then added tote drawers on the bottom row, 3 8" deep drawers in the middle row, and Fastenal tool organizers on the top row. There are shelves up top and pegboard on the back (there is a whiteboard on the back of the other pit cart as we want to build two).
Recently, I got into a discussion with my team as whether or not to use 80/20 framing or welding 1x1 steel tubing. I’m not sure which option is better, as I am very worried about screws in the 80/20 framing coming loose in interior framing and having to deconstruct the pit to retighten them, but on the other hand, we would need to get welding sponsors / equipment to do welding. Weight wouldn’t be that big of an issue as the casters I’ve chosen can hold up 1600+ lbs. Which options is better in terms of cost, easy of construction, difficulty of acquiring material sponsors, and longevity (will we have to repair every year or will it last 5 years without breaking?)
Garnet Squadron’s pit table was a mixture of Bosch FMS extrusion, and those steel drawers were part of the system too. The table would lift off for transport. Three FRC seasons (and this FTC season), no issues. Using thread locker and other appropriate fasteners would be a very good idea here.
Welded Steel Advantages:
Lighter for comparable strength
Less expensive (significantly perhaps)
Few, if any, fasteners to come loose
8020 Advantages:
Reconfigurable
No ‘special’ tools needed to assemble
Overall I would go with a welded assembly. I am sure you can find a welding sponsor and/or a local team or VoTech center with welding capability. Having lived through the heyday of powered/complicated robot carts I tend to value ease of maintenance in my support equipment over anything else, combined with lower weight and lower cost that makes the welded steel frame a clear winner in my eyes.
I strongly disagree with your assessment that the added weight doesn’t matter. That’s more weight to push over every obstacle at an event, more weight to push/lift/carry into/out of venues and trailers, and the extra mass makes the cart less nimble to push around even on flat ground.
We made a fastener shelf using all 80/20 fancy stuff and in general, are disappointed with it. It gets all loose and wiggly, yuk. IMO if you can weld, do it that way. Its stronger and cheaper.
80/20 gets expensive fast. 80/20 does give substantial education discounts though. Use loctite & properer torque on the bolts, and you will not have loose bolts. You cart won’t be subjected to the same loads & vibration as your robot.
Flash (1319) has built their pit largely out of the Bosch equivalent of 80/20. They regularly win awards related to pit design.
If you don’t count labor, steel tube can be cheaper. Especially if you have local welding talent.
I don’t know how different this cart design is from what you previously had, but I’d recommend building the cart out of 80/20 first and testing it out for a few weeks/months to see how you like the design. It will be a lot easier to make changes to the 80/20 version than if it’s welded, especially if you don’t have in house welding capabilities. This will also allow you to see how well the 80/20 holds up. In the end, if you aren’t happy with it, you can make a welded version and you will have plenty of prototyping material for build season.
I know of 2 80/20 carts used by teams that likely have 10+ years on them, and probably 60+ competitions. You might want to use a little purple Loctite to ensure the bolts stay tight, but are removable.
Some good considerations, keep the cart less than 30" wide so it easily fits in doorways.
Having adjustable risers is a great idea. Wheel placement year to year can change and being able to tweak the risers can make a big difference. This is where material like 80/20 can be very very handy.
Yea, I would agree with your assessment on weight. Either route we go with 80/20 versus steel tubing, we will probably have to make some kind of ramp to get it into the trailer because right now we use two 2x4s as ramps and I don’t think they could hold like 800+ lbs of brand new workbench
I like this idea as it leaves the door open for both options, but the current idea right now is to have the entire new pit ready for Georgia’s offseason event, GRITS, which will be held sometime in mid-October, so I think right now the team wants to find a design and stick with it.
We built 1x1 steal, and it worked out great, but the design was not the best, or flexible, so over the years, we have migrated away from them, to the point where we don’t travel with them anymore. I think the combo of the technologies that Ike suggests, may be a good fit, build a steal super structure, caster platforms, and use 80-20 for reconfigurable storage within that structure. The steal really held up to moving into and out of the facilities and ratcheting down in the trailer. Get good casters, with good support to structure.
We did welded steel carts. They’re heavy as heck. Our battery cart is close to 100lbs without batteries and our parts bin cart comes to 550lbs loaded. But, they’re indestructible, and still two students can easily handle the largest heaviest one. They do not bend, they do not flex, there are no bolts to come loose. After shearing off the casters on multiple toolboxes and wooden carts going over driveway aprons and potholes, we figured it was time for a change. Be sure to spring for good 6" dia casters. They aren’t cheap. Also, be sure at least two of them have good brakes.
On this note, there is also benefit to adding better casters and a steel plate or steel bar to the bottom of most toolboxes, to stiffen it up and spread the load. Some toolboxes just have riv-nuts in sheet metal mounting the casters, which is pretty bad.
You do get a lot of vibration rolling over parking lot asphalt and whatnot. I wanted to build carts once and be done with it forever. That’s why we went welded. Also, cost is a factor. Steel box tubing is pretty cheap. Also, it’s quick and easy to MIG weld, and cutting it was a breeze with the Rage Evolution saw.
One thing to consider about steel box tube is that it is not square. The corners are quite rounded. When you join pieces at a right angle, there will be gaps to fill with weld. For this reason, we went with a slightly larger size on our horizontals compared to our verticals, and it worked out very well.
Source: built heavy AF steel robot cart sophomore year. Easy (when you have a welder and have been welding for 3+ years at the time) and cheap to make, terrible to move around because tubing wasn’t selected intelligently. That cart is now a toolcart. Replaced wheels at Worlds; just because that wheel says it’s rated for 600 lbs doesn’t mean it actually is, especially when it develops a flat and stops turning because it had bushings, not bearings.
We built a welded aluminum cart for robot cart. Much better decision because we can easily modify it with bolt-on assemblies. Because rigidity was more of a concern than strength, welded ally is fine.
If your primary concern with 80/20 is bolts/nuts coming loose, it’s worth noting that you can drill thru the 80/20 rather than purely relying on the clamping force of the t-nuts to support the load.
In my opinion, building the cart should be practice for building the robot. If you commonly use 80/20 to build your robot, it makes sense to make your cart out of it. If you use welded steel for your robot, use if for the cart. If you use riveted aluminum tubing with gussets, make your cart from that. If you use sheet metal, there you go. Et cetera et cetera et cetera.
The cart is built similarly to a robot chassis, and in the end it needs to meet similar specs (weight, stiffness, max load, etc). Just like the robot, there isn’t one right answer for the best way to build a cart. The best way for your team will be the way that teaches you the most that you can put towards building your robot when next season rolls around.
Team 1108 usually has welded steel tubing (1/2-box section) as structure on robots too, so yes, it was ‘practice.’
Mostly 1" box section tubing and 1-1/4 angle on our cart. If you want it to be lighter, use less wall thickness. The table-top is steel and serves as structure too. The shelves are supported by 1/2 angle. The empty cart really didn’t weigh that much ( i could easily lift the whole thing), but we have lots of stuff in it.
Our roll-around carries our tool box, all of our batteries and charging, fastener cabinets, power strip and telescoping overhead LED lights. We also have bins for our ‘no robot left behind’ parts storage.
It has two 12-volt wheelchair batteries to run a drive motor. Really quick for us to move into a pit, though it is heavy to get into a trailer and fastened down.
We really like it. If we were doing it again, not sure we’d change anything.
Weight is likely to matter when you are packing to go to an event. In past years, we used a wooden flat-deck cart that was fairly light weight. We were able to flip it upside down and slide it into the van so that it rested on top of a bunch of grey totes to save space.
Pit carts get heavy with just the tools and materials. The weight of our frame is a few hundred pounds, plus the table top plus the box. Total its over 400 lbs empty. We knew we would be going over thresholds, parking lot bumps, trailer door gaps etc and we didn’t want the stress of steering the cart with casters, but the biggest concern is safety. We put about 95% of our entire pit on this cart and it approaches 1400 lbs. when loaded. The wheel set we have has hydraulic disc brakes capable stopping 3 times what we have on it. Its a very good thing because we have rolled down parking lot grades of 20% + at VCU, Comcast Center, and trailer door unloading.