Most Effective Drivetrain?

FIRST General Forum
1

Last year was clearly dominated by pneumatic wheels. Some teams stuck with that, and I disagree there. What does Chief Delphi think the most effective drivetrains are?

Of course, it’s a little late. But now that we all have seen a competition, what does everyone think? I personally think that 6 4-6" Plaction (AM Treaded) wheels are the best. It boasts ridiculous traction and if you use all 6 CIM’s there, ridiculous pushing power too. I’m not good with the gearing, but our team (with a similar drivetrain to what’s described) is quite snappy, and hopefully we can put it head to head against the 2016 bot (a complete tank). EDIT: Worth asking which tread is the best. We stuck with green, but they don’t last much longer than the softer tan. I think red/tan is the way to go, depending on your weight class. What is CD’s opinion?

I’ve seen teams pull off Mecanum quite well though. It helps when you know you won’t face defense, and is great for gears (especially bots with a ground intake). It would be interesting to see a team with a “modular” system to switch between Mecanum and 8" pneumatic, but there are issues like inspection, accidentally selecting the wrong code, and the long wheel base from Mecanum not allowing the pneumatics to turn.

I personally see no reason for Swerve this year. It always is a cool idea, but I think many teams who use Swerve are pushing the CAW (New BOM) to $4000. I think people invest too much in it, and for what payout? A little more pushing power, but not as much as pure tank. It’s also difficult to maintain.

I think we can all accept that Holonomic and H (Butterfly, U, whatever) are out of the question. Too little pushing power on only slippery omni’s. Yes, cheaper than Mecanum, but so is Tank.

Rhino is also not worth it IMO, since you don’t need the pushing power. It was perfect for Stronghold, but it will drive on top of fuel (possible fouls) and defense doesn’t need to be as invested as last year’s.

Pneumatic wheels, I can see the appeal. I expect many second-year teams will take that as the norm now, since they mostly saw pneumatic wheels last year. I love those wheels, but I don’t think they are perfect. They are large, they need to be inflated evenly, and they require a very short wheelbase. This short wheelbase makes tipping easier, since the wheels need to be close, and have a wide radius. They also cause brownouts.

Drop center tank is worth a shot if it’s convenient, but it needs to be very slight. Last year, drop center bots were constantly tipping, often causing them to miss. If you did drop center, I hope it was almost unnoticeable. Like, a layer of gaff tape under your treads. Just barely enough to relax the force on your front or back wheels, shortening your wheelbase without compromising stability.

2

1322 uses 4 cim 8 wheel drive, the way we have our gearbox set up, it boasts incredible torque.

3

To your point about drop centers, I would say about 95% of 6wd or 8wd drivetrains have some sort of drop center between 1/16" and 1/8".

4

We used 6 pneumatic knobby tires for Stronghold, and it was fantastic for navigating the ground defenses. However, we also made our robot skinny enough to drive up half the ramparts without getting caught on the opposite ramp, and a skinny long skid-steer with grippy knobby tires is about the worst of all possible worlds. That robot ate through batteries like you wouldn’t believe.

This year if you’re shuttling gears you definitely need to think about defense, as you’re very exposed in the neutral zone and a good defender will also be bumping you around as you’re trying to align with the gear peg.

5

3620 is running 6 CIM 8WD on 4" Colsons, using AndyMark EVO two-speed gearboxes. Very zippy. We use an active gear placement mechanism with transverse position control to avoid re-aligning the whole robot at the elevator.

I think good swerve drives will be very effective this year for retrieval/elevator alignment, FUEL collection and shooter aim, and spinning past defenders. For example, watch 2767 in our playoff matches with them. The key to good swerve is experience with its complexities – in the code, in the pits, and behind the lexan.

6

It seems to me that what is most effective drive train depends on your strategy of game play. We are using swerve and I think it is the right call for us as our #1 focus is on gear placement, climbing and we have a floor gear pickup. It is fast (17 FPS) and very maneuverable to cross a crowded field to get a gear and in placing a gear on the peg or picking up a gear from the floor.

Having said that, it is expensive, hard to program, relies on a lot on gyro and encoders, more complex than most and takes some getting used to for the driver. If we hadn’t had some guidance from an experience swerve drive team (2767), collaborating with another team (5162) using the same modular design swerve modules and been working with it in the off season it would have been a bad choice.

7

A lot of team use swerve drives because they are more maneuverable than a standard tank drive while still maintaining enough traction to no get pushed around as much as a mecanum or h drive. Yes they do usually cost alot more than other drivetrain options but for some teams who have the resources to properly pull off a swerve it makes sense this year with the flat field and lots of tight spaces where having high maneuverability makes sense. There are other reasons to choose a drivetrain than for pushing power and added defense ability.

8

2054’s swerve drive is absolutely disgusting. I think they are running traction wheels and they were knocking us up and down the field pretty well.

Our mecanum is actually working pretty well for us, it is just taking some getting used to as far as what to do in certain scenarios

9

I think it depends a bit on what you are trying to do from a strategy this year.
If you are gear running, you need to be fast as it is a long field with sprints on the order of 40 feet. In most FRC games, Sprints have been either half field side to side (approximately 12 feet), or half field (due to feeders and scoring positions) which is about 30 feet.

If you are just gear running and climbing, in theory you probably want to go as light as possible with the robot, and therefore may be OK with a very fast single speed. As the loading zone is protected, then holding ground is less essential other than when scoring gears.

If you plan to shoot and unload volleys of balls from a fixed position, you probably want to be able to hold your ground or push through others. You will also likely have fewer and shorter sprints (but not much). I would think these modes naturally fit calling for a shifter set-up and high traction wheels. I could see teams making an argument for pneumatic tires for this case.

While you can make an argument for mecanum to help align gear loading and gear placing, like most years you are simply trying to justify a desire to use mecs IMO. They tend to have a slower top speed and lesser pushing power. That beig said, a light and incredibly agile version could be effective in this years game provided the driver was extremely skilled.

With Flat floor, Pick and place games, teams can really justify almost any drivetrain decision with enough rationalizing. I would personally recommend traditional skid steer 8WD as they tend to have a good balance of maneuverability, traction, and stability. 6WD can be a bit pitchy, especially with higher “drop” values which may be OK for gear runners ,but would might be detrimental towards shooter.

Overall though, like most years, architecture has less to do with performance than driver skill and robustness. Finishing early and getting practice will improve even the most skilled drivers. It will also help find in early failure bugs in the system which will improve fielded robustness.

10

Ike nailed it.

Because of the defenses, last year pneumatic tires, tank treads, and 8+ wheel with high-drop centers were popular.

Strategy always determines best drive train, but this year has greater variation in strategies than many.

We’re doing “just gears” and climbing, so we went light, fast, easy to build, and easy to maintain. We designed for 100 lb with bumpers and battery, and will play closer to 75. We did this by cutting off the front half of a 2014 kit chassis and going 4 2015/16 kit wheels and 4 CIMS: 12.8 fps design speed. We thought about getting grippier wheels but thought it might backfire by landing the robot on its back.

11

Depends on your point of view, I suppose. :rolleyes:

If you can’t catch’em, pick’em. And then of course, there’s this.

12

I think this year we are slowly starting to see swerve drives become more dominant than other years (both offense and defense-wise). One thing that comes to mind is this match, in which 1741 (1st year of swerve) starts pushing 461 (8-wheel tank): https://tbatv-prod-hrd.appspot.com/match/2017inwla_qf3m2

13

To expand a bit here, our mecanum drive has been amazing for quick maneuverability. We’ve been able to avoid defense on multiple occasions by out maneuvering our opponent. However, when we do get caught by a powerful drive train, we get absolutely destroyed. I have to compliment 2054 on their drive train (and their robot in general). They dominated the floor at St. Joseph and I look forward to competing with them at West Michigan.

14

Knowing what 2054 is running under that robot. A swerve drive on defense can be a frightening experience. A strong driver should be able to out position the opponent and depending on what the other team has, may be able to out push them. Swerve drive comes with its headaches, done well though, it can be a thing of beauty to watch.

15

While my team is using a two speed 6WD with 4" colson wheels, I personally believe that the 2+2 drive may be one of the strongest this year (and really in any year with a flat field). For those who may not be familiar with the term, the 2+2 drive comprises of a 4 wheel drive with 2 traction wheels in the back and 2 omni wheels in the front. While driver skill is a big component of how effective a drivetrain is for a team, the mobility of the 2+2 drive allows the driver to do more advanced evasive maneuvers (J turns, jukes, etc) more easily and with more defense around. I’ve seen some nasty maneuvers pulled by teams driving with a 2+2 that can’t be pulled off with other drive trains.

16

We picked octocanum this year, geared for 18 f/s in tank, 13 f/s in mecanum. The whole system was incredibly difficult to get working, especially the eight drive chains, which kept falling off or breaking, but when we finally got the whole thing locked in, it was totally worth it.
We can shoot across the field in a second and a half in tank, and then the robot pops up and sort of floats around like a hovercraft in mecanum. By far the most fun robot I have ever driven.

17

My team this year decided to go with a 6WD, West Coast Drive with roughly a 1/8" drop center. We used 4" Colsons, but 2" wide on the center and 1.5" on the ends so turning is easier but we still maintain quite a bit of traction. Since with a 6WD usually pivots on the center wheels, we don’t really drain more battery by having the larger center wheels. We are a single speed robot but we geared roughly 5.7:1 which gets us about 13 to 14 feet per second, making gears fairly quick. We put a twist on a typical West Coast Drive and used solid 2 x 1 aluminum for our drive rails that are pocketed out in non essential locations. This makes our drivetrain very sturdy, without adding too much weight. Besides some issues with snap rings Thursday night at practice, and some bearings coming loose during Semi Finals 2, we never had issues at FIM St Joe. The bearings were noticed a few events before so we added some loctite around the bearing hole (on the gearbox bearing), but it must have not had time to sit and really work. I believe it was an aggressive hit we took to the side (Semi Finals) since the bearings were forced out of the drive train rail also. We had issues momentarily with driving on that side but it was shortly regained and we finished the match just like normal.
I highly recommend using a West Coast Drive to anybody who wants a quick, simple and reliable drive train.

18

Blue Nitrile is the way to go. In my opinion, it gives the best balance of grip and durability of the tread options. Plus, nothing beats that smell.

I personally see no reason for Swerve this year. It always is a cool idea, but I think many teams who use Swerve are pushing the CAW (New BOM) to $4000.

Do you have any data to back this up? Because I’d almost argue the opposite. If teams are making custom swerve modules, they’re probably not buying COTS gearboxes, which is often one of the most expensive parts of a drivetrain. But either way, the actual cost is not in any way the most expensive part of swerve.

I think people invest too much in it, and for what payout? A little more pushing power, but not as much as pure tank. It’s also difficult to maintain.

Why do you say swerve doesn’t offer as much pushing power as a tank drive? I think this year is a great year for swerve.

I think we can all accept that Holonomic and H (Butterfly, U, whatever) are out of the question. Too little pushing power on only slippery omni’s. Yes, cheaper than Mecanum, but so is Tank.

Not at all. I’ve really only seen evidence of a few teams doing this, but I’m still hoping for teams that run holonomic drives (whether kiwi or Killough) and follow 33’s policy in 2014 of going around defense in every direction. A fast, light gear-runner with a holonomic drive, a small wheelbase, and very good drivers could dominate the field by going around any and all defense.

Drop center tank is worth a shot if it’s convenient, but it needs to be very slight. Last year, drop center bots were constantly tipping, often causing them to miss. If you did drop center, I hope it was almost unnoticeable. Like, a layer of gaff tape under your treads. Just barely enough to relax the force on your front or back wheels, shortening your wheelbase without compromising stability.

Teams needed higher center drops last year to make it over defenses and to compensate for the often higher turning scrub seen in pneumatic tires last year. I agree that center drops should usually be less than last year, but the amount of drop depends on the geometry of the wheel base, the type of wheel, the gearing, and the general power consumption. For some teams, very slight drops will work. But for many teams, a layer of gaffer’s tape would not at all be sufficient. Plus, gaffer’s tape is neither as durable nor as grippy as most treads or wheels.
Plus, tipping is only an issue if you’re running an odd number of wheels per side. 8-wheel WCDs are my personal favorite for their mix of stability, simplicity, and reliability. Other than that, I think Ike pretty well nailed it.

19

Swerve is the most effective drivetrain for most years IMO (2016 is one exception). Whether it’s worth the effort or not is up to each team.
1323 looked really good at CVR this year with their swerve, and we’re only in week 2.

20

6WD, 6CIM 2-speed with 3.75 custom-shaved colsons. Adjusted, 8.4ft/s low & 15.5ft/s high. Theoretical, 10.1 low & 19.4 high. We should have actual speeds from the encoders after our next event.

We spent 4 hours tuning spacing and finding/fixing manufacturing defects in the gearboxes until our current monitoring setup gave us a low of a current as possible with just the gearboxes. We then made sure the gearboxes matched current draw in order to work out any ‘pull’ to one side.

We spent hours playing with control options until we settled on ‘Halo’ style. We spent hours of simulation and voltage ramp tuning before we settled on an acceptable balance of low-voltage protection vs response during acceleration/deacceleration.

It was simple enough to allow us to get lots of driver practice before bag day. It was just enough complexity to ensure we’d out-perform our opponents. It’s probably one of the coolest ‘simple’ drive trains we’ve designed. Hopefully the dog gear assembly holds up through the increasingly kinetic collisions around the airship blind spots.