As we wrap up another amazing season for FRC, I’d like for everybody to share their thoughts about how different drivetrains performed in Stronghold.
This year, my team opted for a 6-wheel pneumatic wheeled drivetrain and had great performances from it. We modified the AM14U3 chassis to accommodate the wheels and had no major failures throughout the three competitions we attended.
I’d love to hear about your team’s experience whether you used this setup, tank treads, a custom solution, or anything in between. I’ve seen some really creative and effective drivetrains this year. Is this the year of the Rhino tread, as some proclaimed it to be early in the build season, or the year of the pneumatic tire?
Team 5546 (ART) used 10in rubber pneumatic tiller style tires run using geared down simple boxes and 35 chain. As a driver I tried and failed many times in practice to get the bot stuck. We also didn’t have the ugly problem with the moat that several six wheel drivetrains had. Also “Hi Mom!!”
Our team used the 20 inch nanotube form andymark. We put chain in the rail and connected it to an vex pro 2 cim ball shifter. We attached 8 inch pneumatic wheels to it and riveted a plastic board to the bottom. It worked pretty well except that no a couple of occasions the rivets holding the board on broke and got stuck on defenses. Also we had to replace one of the sprockets in the nanotube because it became stripped from a loose chain.
We went with the WCD and where had no problems that were caused by the wheels being cantilevered out. We Chose the WCD because it was what we had experience working with. A complete description of our teams drive train is found in the previous post.
We used 6 7" pneumatic tires on independent double swing-arms with a spring-loaded adjustable suspension. A bit over-engineered? Probably. Cool? yes. Effective? Yes. Probably our most creative drivetrain yet, and something that will be remembered for 236’s 2016 robot.
Straight up WCD 6-wheel 8" pneumatic drivetrain. Center wheel was mounted in one of the Vex plastic bearing blocks, surrounded by two single speed clamping gearboxes. The gearbox axles had gears which drove another gear on the center wheel shaft for two reductions. Outer wheels were mounted on the WCP bearing blocks and driven by 9mm wide belts on 30 tooth Vex pulleys. Don’t remember our final gear ratio, it was around for top-speed around 13-14 fps.
I can definitively state that driving 8" wheels with 9mm belts on 30 tooth pulleys works but is pretty marginal. 30 tooth is the biggest you can get and still slide under the CIM on one of the clamping gearboxes, so you’re not going to get a lot of torque out of this drivetrain.
We used the metal bearing blocks for the outer wheels because we knew they’d get abuse. The plastic bearing block is the only one a documented C-C distance with the clamping gearbox, so we had to go with it in the middle. It was getting rather wobbly after 2 competitions of play.
8-wheel drive with 8" (7.65") dia pneumatic wheels, WCD-configuration using VersaChassis and WCP single speed transmissions (4 CIMs, 14t pinions, and 14:60 2nd stage option) and #35 chain/sprockets.
We played 58 official matches over 4 events (plus around 7-8 practice matches). We played defense in quite a few of those matches, so we put plenty of abuse on the robot. Had a few issues with gearbox damage (sheared gears, loose shafts, exploded bearings) and had to replace quite a few rivets (and a couple gussets) in our chassis over the season. No issues with popped/flat tires, bent axles, or thrown chains. Never got stuck on a defenses all season long.
6-wheel drive with 8"/7.65" AM pneumatic wheels 9.018" apart. Used #25 chain on 16 tooth sprockets direct C-C +0.018". Powered by a 4 CIM WCP SS gearbox at 15.4 fps. The design originally called for 13t pinions on the CIMs for 17fps instead and no center drop. The frame was basically a square with some cutouts, and was very robustly built excepting the use of 90* sharp gussets instead of triangles on the corners. Fortunately, they held all season. 5/32" rivets everywhere. However:
We experienced problems with the two mounting holes for the CIMs bleeding into each other enough that the 13t distance got way to close to the 12t distance, causing huge lockup of the gearbox until we swapped to 12t pinions. I think I sent an email to WCP about it; making the two different mounting holes actually separate from each other would have been really helpful on their part. We also had to add a 3/8" center drop later in the season. We didn’t break any chains, but we did throw one at SVR due to bad assembly of the chain run pre-match (badly misaligned).
Overall, it worked great, except we could beach on the moat. Making the the DT not beach in design is something we can practice in the future. :o
6WD, #25 chain-in-tube, AndyMark 8" pneumatic hubs with tires off Amazon due to supply constraints. We goofed and designed it for an odd number of chain links, which meant half links with all their issues (especially the ones with the little wire instead of the ones you can get off of McMaster). Next time, even number and the acquired-for-Orlando Dark Soul tool will fix this issue…but somehow we never got stranded on the field from chain. Clean living.
The frame was octagonal, so our corner wheels were flipped inboard. Easy to do it either way in the future. We supported the other ends of each axle, which was apparently not necessary (especially with our light weight) but we were being cautious because we knew it was a rough game. This design philosophy will be easy to adapt in future seasons to design needs.
The drive tubes were tied together by a riveted octagonal top pan. This was a mistake, as replacing the chains (which happened a lot early on–remember those half links?) called for faster removal than drilling out and replacing that many rivets. Not having the outboard chassis supports would make it a little easier to service without removing ev-er-y-thing, but a better method is necessary for future years.
We played with softer air pressure in the corner wheels to create more rock and be more compliant on the defenses. Only popped one tube in two regionals, on Friday in Orlando (our second). We drove at least two matches on it before replacing it due to time constraints and never had a problem.
All in all? I give this drivetrain a B. For as many new things as we tried, I’m satisfied.
This year really helped out with breaking us out of our losing routine of trying to deal with a stock chassis, as I got a 64", 4 road wheel, track system drawn up on CAD.
The only real issues we had with this chassis were tensioning problems.
At our first competition, week 1, the track came off several times throughout the competition, mostly when we pulled a hard turn.
But after fixing that in time for our second, week 6 competition, the chassis worked extremely well, getting a LOT of traction on the carpet, while still retaining it’s turning radius.
But if I could change one thing on that drive system, it would be adding active suspension to each road wheel. Making it possible to keep the chassis from bouncing around so much on the defenses, whilst stabilizing the central boulder launcher.
5940 Used the AMU14 Chassis with the 8 in. Pneumatic wheel upgrade kit. We were lucky to be able to get an upgrade kit before they sold out, and it worked like a dream. Four 6 inch pneu. wheels would probably be better, considering we sheared 4 gears, but the kit was super easy.
We used 6wd with a setup that mimicked the rocker bogie system on the Mars rovers, and could lock into a normal dropped center 6wd configuration. Vexpro ball shifters and 15mm wide belts, with 36 tooth pulleys, WCD setup with Versablocks.
Once the system was setup correctly and all of the belts tensioned properly, we had zero issues through Vegas and the championship. The drivetrain absorbed shock well and didn’t have any issues going over defenses.
If we were to do it all over again, we might just do the standard 6wd pneumatic setup that lots of teams used. It would have saved lots of time during build season.
We built a full Brecoflex base with the pulleys cantilevered WCD style before the team really inderstood how bad this idea was. We redesigned at the end of week four, with 10wd that looked slightly like the MCC robot, as it used the wcp wheels I had strategically purchased just in case. The four corners were fully independent suspension on coil springs with about 1 1/2" of travel. It ended up being the right choice to redo the bot that late in the season, but our students will not forget the lessons they learned about the design process for next year.
We decided to use 4 10" pneumatic balloon wheels, thus we needed a custom made frame (out of c-channel), custom belts (not too hard to find) and figure out a way to mount the hubs on them (this took us a whole Saturday because we had it right, then decided it was wrong and redid it, then found that that was wrong and reverted back to the original mount, which has worked perfectly), etc. The wheels helped us literally bounce over the defenses (we did have them slightly overinflated, the max psi they’re supposed to have is 2.5 psi, but it’s more fun with it bouncing ). I have only found one other team that used them, and they used 6 of them.