What wall thickness do you guys use for your base? My team used 1/8 in thick 1x2 without weight lightening cutouts because this was our first year with a custom WCD and we didn’t want to experiment too much. I have seen teams that stay with full 1/8 in wall, lightened 1/8 in wall, and full 1/16 in wall. I think for next season we are leaning toward lightened 1/8 in wall.
We have normally done full 1/8th wall. After seeing 254 and 33 this year, we’re looking at doing 1/16th wall with reinforcements around the bearings this off-season.
Over the course of my time in FRC, I have run 1"x1" x0.125" wall tubing, 1" 80/20, and 2"x1" x0.100" wall tubing on drivetrains. I am pretty darn comfortable with the 2x1 0.1" wall tubing at this point, and don’t think I’ll be pushing 1712 to change anytime soon. If we do change, it would presumably be in the event we opt to move away from aluminum extrusion as our drive base towards sheet metal. In that situation, it wouldn’t really be an apples-to-apples comparison for material thickness, and would be dependent on a number of different factors.
We’ve only run a WCD for the past two years. In 2018, we used exclusively 2"x1"x0.1" tubing on the drivetrain. This year we did what 254 and 33 did and used 1/4" bearing blocks on 1/16" wall tubing. We had no issues with the rigidity or strength of the drivetrain whatsoever.
For context, we jumped off of HAB L2 very frequently, but didn’t play defense much or have defense played against us.
I don’t think the weight reduction you see in halving the wall thickness is worth the reduction in strength. Lightening it is certainly not correct as it removes more strength and less weight than reducing the wall thickness. Spend your weight where it matters, if you will.
Two strength concerns:
In games with high speed ramming like 2014, you can see some bending and buckling at 16 wall - particularly on any open face without bumpers.
Bearing point loads, if the bearings are directly in the tube, can cause failure of the tube or bearing hole under shock.
How about getting a little bit of both worlds? 1/8 in thick tubing with 1/16 in deep pockets cnced into them to lighten the load in the same pattern as a cutting a weight lightening pattern. Similar to 2122’s elevator.
We have no concerns with durability of 1/8 in thick tubing. We are just looking to cut down on some weight because we felt our base was heavier than it should have been.
We did 1/8" with a hole pattern. I’d be nervous about 1/16", although maybe in a game with little to no defense it might be okay.
In general I agree with Chris_is_me, in my experience lightened 1/8" stock is both heavier and weaker than un-lightened 1/16".
I’ll just leave this here
Would WCP bearing blocks prevent this?
1076 has done WCD every year since 2016. In the prior 3 years we ran 2x1 with 1/8" wall to be safe, however this year we knew going in we’d be at the weight limit, so we elected to go with 0.05" thick versaframe 2x1. Never had a single drivetrain problem relating to the frame (we did have a few bent/twisted aluminum axles at worlds from jumping off Lv2 50+ matches throughout the season).
We also run versablocks, so that helps support at the major load-bearing areas. With this setup I’m confident going forward that 1/16" wall and less is fine, regardless the game.
This was our first official season using a WCD, however I did some prototyping of it during the off season.
We used 2x1 with 2mm wall thickness (between 1/16 and 1/8), along with M6 riv-nut weight-relieve / holes. However, the front and back were reinforced with 8mm aluminum sheets. The drive train was able to survive through the entire season without any repairs despite taking numerous hard hits and t-bones
The game definitely matters. Still, I don’t recall ever using anything thinner than 1/8" in a drive train, though I might go to 1/10" with tubing, especially if I didn’t expect it to be a heavy defense year. It just wasn’t worth the risk that this year’s game might prove to be more damaging than expected. Besides, weight down low helps stabilize the robot!
Back when I was a student, anybody doing <1/8" in their drivetrain would be looked at askance, much like their drivetrain would be two matches later. This can be chalked up to the fact that at the time, we didn’t have bumpers, or they were strictly optional. And the hits were hard and vicious when delivered, though nothing like some this year (or in 2014). Frames bent, welds cracked, robots took a beating and gave one too. There were a few exceptions, of course; the KOP frame starting in 2005 wasn’t 1/8" as I recall (but was a funny shape) and the various sheet-metal drivetrains were cunningly bent to gain strength.
Nowadays, especially with the bumpers, I’m a lot more relaxed when seeing a drive frame less than 1/8" wall thickness. While I wouldn’t say unequivocally that that’s the way to go, I would say that using down to 1/16" wall–with proper bumpers and internal structure–is quite acceptable; I’ve seen it be used with minimal shielding as a robot ramp, with success. But the thing with a drivetrain is: If it fails, you. are. done. So the question you really want to ask yourself is: Do you want to gamble on your drivetrain staying properly set up through the event, or do you want to play it safe? And how safe?
Personally, anything under .1" thick would be playing with fire in a facility with lots of aluminum dust and rust. Anything over 1/8" thick is likely overkill, given the bumpers.
Please note: This doesn’t factor in using non-aluminum materials for the drivetrain. Chromoly steel, anyone?
The drive rails are close to the floor, so they’re good weight in terms of keeping the center of mass low. Having a bit of extra weight in the side rail isn’t such a bad thing. My preference is to leave the more aggressive weight savings tactics for things that are further up the robot.
If I wanted to cut weight on frame rails, my first inclination would be to use thin wall on the end rails and keep 0.125" wall on the side rails. If you bend an end rail, you can hammer it back into the correct approximate shape and still function (probably…). The side rail has the potential to bend in ways that render your drive train inoperable. The side rails are also harder to replace. On our robots, anyway. Replacing one of those would be a significant repair that might take us out of our next match or two, depending on the situation.
Followup question for those who mention reinforcing 1/16" wall with 1/4" or 3/16" aluminum-- what does this design look like? I’m familiar with conventional WCD bearing blocks and VersaBlocks. Do you stick to something similar with these, rivet/bolt a plate directly to the tube, or something else?
1717 did Chromoly steel frames in its latter years, and 5818 did a couple years of the same thing. We ran .035" thick, 1x1.5" 4130 rectangular tube with drive train bearings mounted directly in the tubes with no issues. We switched to aluminum for speed and ease of modifications the last two season though.
We used carbon fiber this year and fell in love with it. Our entire elevator and intake system weighed in at under 13lbs. I know the perception is that it is super expensive but we were actually surprised by how much of a value it was. For 96in of 2x1 ID the .05 wall thickness is $241 or .075 wall thickness at $314. It can be cut easily with a tile saw and other than the added safety precautions necessary it was easy to work with. We did not use it on drive last year but I know several other teams used it did anyone use it on drives yet? We may use it for a drive in the future though.
We’re trying the 254 method, which was well described below:
So basically custom wcp bearing blocks?
Not quite, these are hard mounted into the tube with the aforementioned 10-32 screws. They do not slide, and therefore have a fixed C-C distance for the chain.
If they slide, they couldn’t use the tube to keep themselves concentric, and would need to directly to attach to each other, as the WCP block do. However, this would prevent you from running the chain-in-tube.