Stronghold Drivetrain Review

[s_forbes]

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.

[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.

[mrnoble]

Originally Posted by s_forbes

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.

Your robot was so dope. I enjoyed seeing it in AZ. It was the dopest.

[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?

[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.

[sanddrag]

We did a 6WD WCD with 8" Pneumatic tires on custom hubs, Vex Pro 2-CIM ball-shifters, and Vex Pro 15mm belts. The ball-shifters performed flawlessly other than some wear on the 3rd stage pinion gear. I wasn't perfectly happy with the belts. We calculated, designed, and manufactured for perfect center to center distance and they were very loose, and needed significant tensioning. After tensioning, they still ratcheted quite a bit when going from forward to reverse, but we never broke, threw, or wore out one. Also, the robot drove very smooth and quiet with them, which I cannot necessarily say about chains.

We used thunderhex shaft and bearings, which both worked great, except for the thunderhex shaft needing some sanding down. We also made copious use of the Vex molded plastic hex spacers, which are perhaps one of my favorite products they offer entirely.

We used West Coast Products bearing blocks, which really can't be beat for the price. We could easily make ones, but we were not just buying bearing blocks, we were buying time. One thing about these bearing blocks that absolutely drives me nuts is that when used on a 1" wide tube, there is no screw that fits it perfect. The overall width when assembled is something like 1 5/16. As a result, you have to go with 1 3/8 screws, which stick out 1/16. Either the 3/16 thick block should be redesigned to 1/8 or the 1/8 thick block should be redesigned to be 3/16 thick. You just cannot easily get 1 5/16 flat head cap screws. It's an odd design.

[inkling17]

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.

This year was our first year modifying the KOP chassis and we did a combination of the square and long configurations. We also used 8" pneumatics, but only used 6 of them. We barely skated by with a perimeter of 119.5", what dimensions did you guys use? Do you have any pictures of your chassis? I would love to see the wheel spacing.

[Piequals3.14]

6WD with 8" pneumatic wheels. Black. Very cool.
2 3CIM WCP SS gearboxes running the 14/60 gears with 14 tooth pinions 24T sprockets running #35 chain, with an outer plate to hold the shafts in place.

Tensioned chain a couple times and topped off tire pressure. Nothing went wrong besides that, which was real nice. About 10 f/s with good pushing power, could even shove around our 2014 robot

[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.

[Valkonn]

Our unique butterfly module drivetrain really showed it's strength on the rock wall and ramparts compared to other robots in our tier. I really like it but feel like over-engineering our drive train left the rest of the bot really weak and it really showed when we got demolished in the Las Vegas playoffs.

Edit: Here is the max speed it could cross the rock wall: https://www.youtube.com/watch?v=ovvr1kig3ls

I'm a huge fan of 1671's drivetrain this year, that thing is a monster and comparable to 254's.

[topgun]

6 wheel center drop live axle custom sheet metal chassis (AL 5052 .090") with 10" pneumatic tires from Harbor Freight ($4.99 each). We had custom hubs turned by a sponsor. #35 chain with axles placed with specific c-c distance so we didn't need tensioners. AndyMark Cimple Gearbox with 4 Cims geared for a free speed of 8.8 ft/sec.

No issues doing defenses as we could easily go over defenses. No observed damage on the chassis. Even survived a 3 foot fall off of our robot cart at one competition.

We went with 10" pneumatics given our experience in 2012 with the 4" tall center divider. That year we used 8" pneumatics and essentially couldn't get over the center divider or could with extreme difficultly. I am surprised that most 8" wheels had no issues going over the rock wall. I think the ramps had something to do with that which is something we didn't have on the center divider in 2012.

The team initially decided to go with a track drive. Luckily everyone was sold out in the first few days. We have never done a track drive and I wasn't too keen on doing our first one during build season.

Overall, a very good choice for us. Got us our first trip to Champs.

- Tom

[z_beeblebrox]

Great thread! Some information on our drivetrain:

-6 wheel tank drivetrain, .25" center drop, 4 CIMs
-10" Harbor Freight pneumatic wheels on laser-cut plywood hubs (for reduced weight, integrated VersaKey pattern and bearing bore)
-32x23" to fit on a single batter segment but accommodate 6 10"wheels and electronics. A cutout at the front provides clearance for the shooter
-Removable panels compactly mount electronic components
-Integrated (but removable) 11:72 single-speed gearboxes with encoder mounts
-4.25" ground clearance, 6" high center of mass
-#35 Chain, 12:36 reduction from gearbox output to middle and front wheels, 30:30 chain between middle and back wheels. CNC-routed HDPE cam chain tensioners are adjusted by tightening screws on the top plate
-Dead axles made from 1/2" Vex tube stock, 1/4" 5052 axle supports laser-cut by sponsor
-Superstructure mounts to 1x1x1/16" square aluminum tubes and can easily be tilted up for access or removed.
-Drivetrain including all electronics except battery weighs ~50 lbs. Wood chassis weighs ~9 lbs

For the second year, the structure was made from 1/4" baltic birch plywood laser-cut in-house on our Trotec Speedy 300 laser. Several refinements were made to our design and manufacturing process, including bolting the plywood to a flat MDF table in the laser to eliminate warping and improve accuracy and using only square nuts pressed flush with one side of the plywood for easier assembly than the centered nuts in last year's robot. The biggest improvement was development of a workflow for production of parts of up to 29x34" on our 29x17" laser cutter by flipping and realigning the plywood. By engraving markers for alignment on the wood, we were able to maintain <~.01" offsets between the two rounds of cutting.

The drivetrain performed essentially flawlessly through the season, allowing quick maneuvering around the field and crossing of all the defenses. No damage was sustained through three events. The only maintenance required was occasional chain tensioner adjustment, chain lubrication and the addition of small aluminum plates to retain improperly installed bearings in the gearboxes.

Some more information can be found in our engineering journal.

[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.

[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).