Some topics have been made discussing drivetrain construction. Wanted to get some more opinions and see the distribution of drivetrain types and construction materials.
What does your team generally use on drivetrains?
1/8" 2x1 Metal Tubing
1/16" 2x1 Metal Tubing
Other Thickness 2x1 Tubing
Non-2x1 Tubing (2x2, 1x1, etc.)
1/8" Sheet Metal
1/16" Sheet Metal
Other Thickness Sheet Metal
Other
0voters
Does your team use aluminum as it’s main drivetrain material?
Yes
No, other metal
No, we don’t use metal on our drivetrain
0voters
What style drivetrain does your team generally use (if it changes from year to year, what did you use this year) ?
Kit Bot
WCD
Mecanum
H-Drive
SDS Swerve (MK1, MK2, MK3, MK4, MK4i)
WCP Swerve (SS Swerve, Swerve X)
Andymark Swerve and Steer
REV MAXSwerve (Requirements: Must be a time traveller)
Thrifty Swerve
Custom Swerve
Other
0voters
This year, my team specifically used 1/8" 6061 T6 Aluminum Tubing with a 1/8" pocketed bellypan made out of 6061 T6 aluminum sheet. Since 2020, we have been running SDS MK2s and more recently SDS MK4is. We made the switch from kit chassis to swerve after extensive testing in the 2019 offseason. We may switch to 1/16" tubing in the 2023 season if weight is an issue, but would like to stick with 1/8" tubes if possible to keep a low CG and strong frame.
Would love to hear about any interesting drivetrain choices teams have made or if there are any teams that have made their own mechanical changes to COTS drivetrains. Also, I’d like to hear team’s thoughts on 1/8" vs 1/16" metal for drivetrain construction.
We were a linebacker team when it came to drivetrains. 1/8 inch wall 2x1 tube and plenty of power in tank style. Up through 2019.
Then we switched to swerve. Now our game plan is quickness, aimed at full-range offensive capabilities and a high score ceiling. We went to 1/16 inch wall tube for our chassis frame.
Early on we started building one piece bumpers with good quality plywood — sande or Baltic birch — and robust joinery. Often with fabric selected for advantages specific to that year’s game. But the main idea was strength. Strong bumpers mean you don’t need thick tube behind them.
This year during the main season, my team ran a WCD with 1/8 inch aluminum 2x1 tube, usually we would do 1/16 inch box tube, but we decided on thick wall because we wanted to gear it toward defense, and we had no problems with the box tube bending, by far the bigger issue was the rivets that held everything together loose. Then in the off-season, we ran an SDS MK.3 swerve with 1/16in 2x1 box tube and we had no problems even with quite heavy defense being played on us.
I read “drivetrain” as the main chassis. The structure that holds the parts of the drive train. Our chassis is a mix of 4130, 6160, 3003(4), and printed parts. So…
While not part of the original post, I’d also expand that to teams have unique bumper configurations due to a unique chassis.
My team specifically is looking to do a 2910 style bumper this season using thin walled 1x1 tubing flush with the top of the 5” wood segments, which connects to standoffs on the chassis (one on the corner of each MK4i module, and one on either side of each module) and secures in place using these Slide-Snap Draw Latches from McMaster Carr.
If you plan on falling from a height, I recommend not pocketing your 1/16th wall 2x1 aluminium chassis…
Actually, I don’t recommend it regardless of your dropping plans
Sometimes students don’t listen, but that’s ok, because then they learn from their mistakes, and learning is what it’s all about
I recommend against pocketing aluminum tube in all cases. It takes additional design, CAM, manufacturing, and post processing time, all for a result that nets you less weight savings than switching to a thinner wall tubing while also severely compromising the structural integrity of the tube.
There’s so many better ways to save weight in FRC.
We actually used .100" wall because the .060 wall tubing didn’t support the bearings enough in our opinion on our WCD chassis this year. We didn’t use versa blocks because we had access to the school’s old Bridgeport so we could make the spacing the correct distance apart. The only problem we found with not using versa blocks was we didn’t have a way to tension the belts. We did notice small variations in belt length, not a lot but you noticed the tension difference once the belts were installed. We are trying out swerve right now, mk4i so we are not sure what wall thickness we want to go with. But we decided that if we run WCD this year we will use versa blocks on the ends with a solid mount in the center. Versablocks are 1/16" offset from center and if you use in all 3 locations you end up with 1/8" drop but if we center the middle bearing we can achieve a better 1/16" drop
The competition bot had 1/4" 6061-T6 for all inner and outer plates, on our practice bot we tried playing with the outer plate being 1/4" polycarb, while it worked it was a pain to assemble with the flex in the plate.
2020 and 2022 are almost identical with some minor improvement and a few less wheels, and replaced a few round spacers and shifting pieces with markforged parts.
In 2019 we had great success running kitbot with corner omnis, until our season came to an abrupt stop on Carver in quarterfinals due to a shattered HiGrip wheel. For 2020, we switched to an 8wd 6" pneumatic WCD with custom bearing blocks to to give us a lower center drop, which allowed us to clear the rendezvous point easier. For 2022, We purchased SDS Mk4s with L4 gearing and loved the extra mobility a holonomic drivetrain gave us.
I think we’ve broken all 4(?) revisions of this hub since they were introduced in the early/mid 2000s. Do not let them become side loaded. With corner omnis, all the side load is going through 2 wheels instead of 4.
They’re great outside of FRC as well if you’re going for utility:weight.
2007, or thereabouts, for introduction. We broke at least 2 that year; I believe by our 2nd event (might have been first) our rear side was failing. Rear side, for us, was the “loaded” side of a 6WD drop center. (Center was pneumatic wheels, front was more of the AM hubs.)
Yeah. Don’t side load those. If you can’t avoid it, replace 'em going into each event, and inspect before playoffs start just in case.
Good to know my team isn’t the only one who’s tried an elaborate “geardrive”. I figured we had the record at 14 wheels, but 22 is pretty impressive.
Until this past year we’ve built a few chassis using 3/8" polycarbonate, and more recently 0.09" bent sheet metal. Polycarbonate can be a good option since it can take an impact and not deform, but the manufacturing process tends to take much longer than other options. Sheet metal is convenient for a number of reasons, especially if you have the resources (or sponsors) to bend it quickly it can make for a very rapid chassis build.
This year we built a drive system using the MK4i swerve modules, so that basically forced us into using 1x2" tubing. That said, we’ve been pretty happy with it so far, and we still use sheet metal for our belly pan.
Plywood used to make FRC bumpers will have to absorb shock loads, when robots collide with things like end walls, game elements, and other robots. Plywood with more plies is stronger. It also holds its straightness and flatness better, allowing for more precise fit to the chassis it is there to protect.
For a swerve drive train wether you’re using SDS modules, WCP modules or Custom Modules I recommend 1/16 Aluminum because any swerve modules are kinda heavy. For WCD I recommend 1/8 aluminum it’ll take a beating much better that 1/16 will. If you do want to use 1/8 for Swerve maybe consider pocketing your tubing or making the rest of your bot hella light
