Stronghold Drivetrain Review

[daliberator]

Hey everybody,

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?

Thanks,
Henry O'C

[Crew Cox]

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!!"

[thinker&planner]

Before Stronghold was released, I really wanted to use something like the WCP bearing blocks for our drivetrain, but our team thought that cantilevered wheels was not a good idea this year.

We ended up going with 8" pneumatic wheels in an 8 wheel drive with 1/4" plate drive pods. No problems with any of it.

I'm wondering what damage teams who used cantilevered wheels sustained, and the thought process they went through in making that choice.

[arc25565]

Originally Posted by thinker&planner

Before Stronghold was released, I really wanted to use something like the WCP bearing blocks for our drivetrain, but our team thought that cantilevered wheels was not a good idea this year.

We ended up going with 8" pneumatic wheels in an 8 wheel drive with 1/4" plate drive pods. No problems with any of it.

I'm wondering what damage teams who used cantilevered wheels sustained, and the thought process they went through in making that choice.

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.

[SamcFuchs]

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.

[Kevin Sevcik]

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.

[MaGiC_PiKaChU]

8 WD 8" pneumatic wheels, drop down 1/8. Drive base 32x28. Each wheel powered independently trough a 775 pro and a versa planetary gearbox, 9ft/second.

Even if a motor or a chain stopped working, the robot could still move. The 8 motor drive allowed for some insane pushing power, as well as great traction to get over the outerworks.

[ollien]

Originally Posted by MaGiC_PiKaChU

8 WD 8" pneumatic wheels, drop down 1/8. Drive base 32x28. Each wheel powered independently trough a 775 pro and a versa planetary gearbox, 9ft/second.

What did you do to prevent burnout? Those little motors seem to be very good at it.

[MaGiC_PiKaChU]

Originally Posted by ollien

What did you do to prevent burnout? Those little motors seem to be very good at it.

8 of them. the motors had too much torque to stall, the wheels were just slipping on the carpet before they could get close to burning

[asid61]

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.

[Lil' Lavery]

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.

[Billfred]

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.

[maxnz]

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.

[daliberator]

Originally Posted by maxnz

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.

I saw your drivetrain at 10k and at the week 0. It looked awesome! Did you guys ever have trouble in pushing matches, with the wheels having no treads?

[maxnz]

Originally Posted by daliberator

I saw your drivetrain at 10k and at the week 0. It looked awesome! Did you guys ever have trouble in pushing matches, with the wheels having no treads?

We never actually got into any real pushing matches. I think that if we were to get into one, the belts would probably just skip.

On the topic of skipping, we only had major trouble with belts skipping at two points: when the gearboxes were loose, and when some of the c-channel between the frame and the c-channel holding the wheels collapsed in on itself (the second one at the week zero event, which is why we spent about 2-2.5 hours in your shop around lunch instead of competing). We found solutions for both, the first one being to tighten the bolts holding the gearboxes to the frame, and to add a churro shaft holding the gearboxes together so they didn't bounce around so much. The solution for the second one was to bend back the c-channel (using bolts with two nuts on them and tightening them in opposite directions) and to add a 1" piece of o-channel to the middle of the c-channel to prevent bending there.

Another thing we heard from a few people was "You put a boulder in there as a wheel? Oh, that's an actual wheel." They did look similar to a boulder, especially when they were new.

Those wheels were very fun to watch on the field. I'm currently putting together a montage of all of our bot's jumps over defenses. Not sure when it will be done, but hopefully before state (no promises though).