Stronghold Drivetrain Review

[mrnoble]

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.

[Oblarg]

We sheared all the teeth off of the 14t gear in the WCP 3-CIM SS. Did some naive load analysis, found that using that gearbox with 8'' wheels is really pushing the strength of the gears. Replaced the 14t gears with steel ones, did not see any more failures.

The WCP gearboxes seem to be designed primarily for 4''/6'' wheels, and using them with larger wheels is marginal. Definitely something to keep in mind for future years.

We originally had 9mm belts, and found that those ratcheted with wheels this big (FRC drive trains usually run them slightly out-of-spec even with 4'' wheels, though the specs given by Gates are for designed lifespans much longer than what anyone expects out of an FRC robot). Swapped to 35 chain, no problems there. WCP cams work like a charm.

[3072Cap]

Team 3072 went with pneumatic tires in the center, with omnis on the corners in a 6wd configuration. We also used Bimba pistons and custom designed plates to give our omni wheels suspension. We can raise and lower the wheels to give us better angles at things, and to help with shooting. We decided that this would give our robot an advantage, considering how high the RW is, not getting stuck in the moat, and helping absorb impact when ramming into things.

[Eric Scheuing]

6 pneumatic wheel (AndyMark tires and hubs), drop center, dead axle, #35 chain driven.

Our biggest issue this year is that we went wide instead of long. It made navigating the defenses more difficult than it needed to be. We thought we were being clever by designing our drivetrain so that the wheels would be closer together, but what we didn't factor into our design in our engineer lizardbrains is that we'd be hitting the defenses at high speed. Having some span between the wheels wouldn't have hurt us TOO much and we would have had an easier time of driving quickly. Good thing our driver is pretty flexible

https://drive.google.com/open?id=0B4...TgwWEl5ZzlFZ28
Early picture.

EDIT: Definitely used way too many bearings per axle. Next time, not so many.

[dmorewood]

Custom designed Nanotube Modeled off of the Andymark one. 6 9.5" Harbor Freight Wheels. All the wheels were independently driven by a CIM. We never stalled out and we rarely ever got stuck on the moat. It was a rugged and reliable drivetrain and one that we may end using again in the future.

[jodge1706]

I'm almost scared to say it but.......swerve

We did swerve, because our strategy was not to focus on crossing defences, although the drive train did work well against most in practice. Our strategy was to cycle through the low bar and shoot boulders in the high goal and be quick and efficient with that.

Our drive train had 4 in diameter wheels (custom made), with a 2 speed transmission reaching very fast speeds in high gear. It worked well for our strategy, it helped deter defenders, and in eliminations at Rocket City, helped play defense like no other. We tried to prove that, in objection to popular opinion, swerve would work great for this game, which it did. I can post pictures and designs if there's interest

[Jrizo]

We used a West Coast Drive. 6 andymark Pneumatic wheels, 3 stage WCP ball shifter with 4 cims , 1/8 inch drop center with WCP bearing blocks on each end, 35 chain with 12 tooth sprockets. The only problem we ever had was getting stuck on the moat but I think that was a battery issue since it only happened twice during all of our matches.Normally we would just power out if we were hung up. I would have to go back to watch the video to make sure that that was the issue

[Ryan Dognaux]

We tried to be as COTS as possible this year and it worked great for us. We went with the AndyMark KOP chassis, ran WCP 14:60 single speed gearboxes direct driving the center wheel and used 8" pneumatic tires in a 6WD configuration. #35 chain powered the outer wheels. Our acceleration was fantastic and our top speed was controllable. The drive easily handled every static defense and could push people around as needed. We didn't throw a chain all year and didn't have any chain tensioners.

The only problem we really ran into was maintenance on the drive gearboxes. We killed an 14T aluminum gear at Midwest and spent an hour taking off our drive side and removing the gearbox. It was definitely not designed for maintenance and we are going to take that into account for next year. Usually we wouldn't use 8" wheels in a game though so the bolts used to face mount the gearbox would normally be accessible.

[lorykzarr]

We used the AM14U3 KoP chassis with 12.7:1 2 CIM gearboxes. For wheels, we ended up getting tires from Princess Auto (Canadian Harbour Freight). We 3d printed a set of 2 piece inner wheels that the inner tube sat on. We then used aluminum plates that sandwiched the tire together after we had problems with breakages on the lamination lines of the 3d printed parts after pressurizing the tires (think of a beadlock tire/wheel). It probably would have been easier to cut down the stems on the steel rims that came with the wheels and then drill a bolt pattern to hold on the hex hubs and pulleys.

[cadandcookies]

I really want to see someone from 2220 post here-- their drive train was one of a few that I hadn't seen before this year.

As for 2667, we were terribly vanilla. We did pretty much what the OP did, but got wider wheels from Fleet Farm and used some 3D-printed parts to hold the pulleys to the wheels. Surprisingly we had zero failures at our regional and on our practice bot, even though we were using PLA at like 40% fill.

[GCarnes]

Originally Posted by jodge1706

I'm almost scared to say it but.......swerve

...I can post pictures and designs if there's interest

Yes please do. Im very interested to see how you guys designed you swerve drive to fit this year's game.

[JesseK]

Basic:

• West Coast Drive, 6 tires
• WCP DS - 2 CIM - 14:60 & 24:50 reductions
• Random Amazon tires, 4.15" from middle axle center to floor @ 35 PSI with full robot weight (8.3" diameter wheel for calculations)
• VP Aluminum clamping bearing blocks
• 6WD Drop Center, using the WCP offsets to raise outer/front and lower middle - total drop = 1/8"
• VP Aluminum Hex shaft for wheel axles

Advanced:

• Tire pressures (F/M/R) were 30/35/35
• On the floor, the wheel raise is more like 3/16" due to the tire pressures
• Track Width = 24"
• Wheel Base = 10.5"
• Extra 18T -> 38T sprocket reduction after the gearbox, iirc maximum theoretical speed was 14 ft/s
• Eventually settled on VEX Pro #25 HD chain with VP HD master links (don't use normal master links!), and once we got them everywhere we had no chains come off

Control:

• Standard tank-steering with 2 joysticks
• Optional "Drive Straight" arcade mode, legacy carryover from 2012
• Talon SRX "Speed PID" mapped joystick input to a speed, where maximum joystick input = maximum speed limit set via a constant. Set limit to 9 ft/s early in the season, incrementally raised to 12.5 ft/s by the end of WCMPs.
• Not sure if the kids put in a conversion of ticks/s -> ft/s, or if the SRX has it. Nice feature though.
• Testing showed peak of 12.1 ft/s as read by the SRX's. (Who needs a simulator any more? )
• NavX to detect defense crossing - though rough terrain didn't register too well...

Maintenance:

• Check tire pressures 2x a day
• Turns out the middle wheel blocks were 'floating' on one side and therefore would put excess tension on the chain leading to the front wheels. This wasn't a problem once we switched everything to VP HD chain. Probably should have gone #35 in design though.
• There was no metal fatigue on any of the sprockets, but some of the black anodization came off of each sprocket
• Bent one of the rear axles, but since it's WCD it was crazy-easy to replace
• Had a CIM wobble loose at WCMPs. Found it during one of our half-day full robot inspections, so it didn't cause much wear on the gearbox.
• Lightly re-grease gearboxes at start of event and at start of elims

[daliberator]

Originally Posted by JesseK

Maintenance:

• Check tire pressures 2x a day

We used Andymark pneumatic tires and didn't have any problems with air pressure. In fact, I'm pretty sure I can count on one hand the number of times we checked them throughout the season. Did you guys have to top yours off frequently?

[abbymarie]

We used 8 inch pneumatic wheel in a 6 wheel drive train, using the belts from the Kit of Parts. It worked amazing for breaching the defenses, we never got stuck on anything! Tire pressure was never a problem, we maybe checked it once or twice.

[daliberator]

Originally Posted by abbymarie

We used 8 inch pneumatic wheel in a 6 wheel drive train, using the belts from the Kit of Parts. It worked amazing for breaching the defenses, we never got stuck on anything! Tire pressure was never a problem, we maybe checked it once or twice.

What did you use for a chassis? Did you use AM wheels? The KoP belts worked very nice for us as well.