Swerve vs. Butterfly Drivetrain

[Ginger Power]

What are the pros and cons for each drivetrain? What types of game fields are conducive for each?

For Swerve: what are the advantages to 4 wheel swerve vs. 3 wheel swerve?

For Butterfly: Also consider nonadrives and decadrives (a butterfly drivetrain with a strafe wheel or 2).

I'm trying to figure out what I should spend my time working on as I'm procrastinating on my schoolwork. I just keep going back and forth on which drivetrain offers the most benefit. For this comparison, ignore ease of design, and cost. Assume that the team looking to manufacture either of these drivetrains has access to a simple mill and lathe (no CNC).

In my mind, a decadrive and a swerve are comparable in weight, maneuverability, and cost. How about other factors like manufacturability, driver learning curve, and durability?

I'd also be interested to hear about what drivetrain would perform better in a game like Aerial Assist where there is a wide open field, assuming equal driver ability.

[itsjustjon]

I mean, I'd hate to sound argumentative but all of these drives are far too complex of a solution to the FRC games given in the past five years, give or take.

You'd be better off 86'ing any of these and switching it for a WCD due to easy manufacturing. And, since all of these FRC games are designed with rookie teams in mind, you'd be hard-pressed to find a game where Swerve, Mecanum, Nona-whatevers are necessary for success.

[dmorewood]

Originally Posted by itsjustjon

I mean, I'd hate to sound argumentative but all of these drives are far too complex of a solution to the FRC games given in the past five years, give or take.

You'd be better off 86'ing any of these and switching it for a WCD due to easy manufacturing. And, since all of these FRC games are designed with rookie teams in mind, you'd be hard-pressed to find a game where Swerve, Mecanum, Nona-whatevers are necessary for success.

I actually think swerve was a very good solution for 2014 and we enjoyed having it in 2015. Back in 2014 it was a lot harder to play defense on a swerve bot with a good driver then it was to play defense on a WCD bot. This is best demonstrated by 1640, who ended up being Einstien Finalists with 1114. In 2015 we used swerve on our landfill bot and it was exceedingly useful for quickly maneuvering to intake totes and just being able to turn in place to score our tote stack made us less susceptible to losing the stack. Hope these examples help. Personally I will always advocate for swerve on a relatively flat field where heavy defense could potentially be an issue.

[Bryce2471]

As advice for January I have to recommend using a WCD or similar skid steer drive. So if your team has not explored these thoroughly, you should start there.

However, choosing between a butterfly and swerve drive as an off season project is a completely different matter. The swerve drive is by far the better option, for many of the same reasons that it should not be used in most FRC games. Swerve drives are expensive, difficult to design, difficult to machine, difficult to assemble, difficult to program, difficult to maintain, and difficult to drive well. But when you get it all right, Swerve drive is an amazing sight to behold. This means that when you get done building a good swerve platform, your team will have grown and learned in every way, and you'll have a killer demonstration bot.
(Just my two biased cents)

P.S. I am biased because a swerve drive robot sparked huge inspiration in me as a freshman.

[Ginger Power]

This thread has mostly felt like a referendum against swerve drives, which has been telling. Given my current situation and the feedback here, it definitely seems as though butterfly is a better option for our purposes.

Some have mentioned that both drivetrains are unnecessary/too complicated for FRC and that WCD/Kop drivetrain is the better option. The point was made that a simple tank drive will offer 95% of the performance for a fraction of the cost. While that may be true, why isn't it worth investing build season time to implement a more complex drivetrain that has been perfected in the offseason vs. a WCD or kop drivetrain?

[asid61]

Originally Posted by Ginger Power

This thread has mostly felt like a referendum against swerve drives, which has been telling. Given my current situation and the feedback here, it definitely seems as though butterfly is a better option for our purposes.

Some have mentioned that both drivetrains are unnecessary/too complicated for FRC and that WCD/Kop drivetrain is the better option. The point was made that a simple tank drive will offer 95% of the performance for a fraction of the cost. While that may be true, why isn't it worth investing build season time to implement a more complex drivetrain that has been perfected in the offseason vs. a WCD or kop drivetrain?

The biggest problems I think teams face in implementing butterfly or swerve drives in season is a lack of testing pre-season, poor design choices, and a lack of good machine tools. I think octocanum can be done fairly well with a manual mill, but the design has to be very similar to what was done in the offseason to have a driving robot within a few days. IMO well-designed swerve drives are very rare, and often times teams do not have the machines to make them well.
Butterfly + strafe wheel takes up space in the center of the chassis, which is rarely available as well.
If you have the machines, the design experience, and the pre-season testing, I see no reason why you can't do swerve or butterfly/octocanum. Just make sure it actually benefits your strategy and/or driver before doing it!

[Andrew Schreiber]

Originally Posted by Ginger Power

This thread has mostly felt like a referendum against swerve drives, which has been telling. Given my current situation and the feedback here, it definitely seems as though butterfly is a better option for our purposes.

Some have mentioned that both drivetrains are unnecessary/too complicated for FRC and that WCD/Kop drivetrain is the better option. The point was made that a simple tank drive will offer 95% of the performance for a fraction of the cost. While that may be true, why isn't it worth investing build season time to implement a more complex drivetrain that has been perfected in the offseason vs. a WCD or kop drivetrain?

It's a function of priorities for me. If my goal is to be as competitive as possible the goal is to be as simple as possible and get as much practice and iteration in as possible. But sometimes you just wanna build something that's MFD.

[Chris is me]

Originally Posted by Ginger Power

Some have mentioned that both drivetrains are unnecessary/too complicated for FRC and that WCD/Kop drivetrain is the better option. The point was made that a simple tank drive will offer 95% of the performance for a fraction of the cost. While that may be true, why isn't it worth investing build season time to implement a more complex drivetrain that has been perfected in the offseason vs. a WCD or kop drivetrain?

The big thing is, even when you know how to do swerve drive and you've perfected it in the offseason, it still takes more time, resources, and effort than tank drive. The drive still won't work better than tank without great code running consistently, and you are robbing efforts from your manipulator development, drive practice, etc. to do swerve.

Basically, you have to decide that swerve is such a competitive advantage that it is worth putting less polish into other systems of your robot. In most games, it just hasn't been. There hasn't been a game where optimized omnidirectional drivetrains (swerve, mecanum, or otherwise) are strictly better than tank drives, other than 2015. And in 2015, mecanum drive built and programmed well could achieve what swerve drives could without as much mechanical or software complexity.

(note for those following along at home: this is a post where I'm arguing mecanum drivetrains were the best choice for a particular game. Hell hasn't frozen over, has it?)

[Taylor]

Does a butterfly-style drive necessarily imply the use of pneumatics? For a robot design that does not otherwise incorporate pneumatics, it is certainly important to factor in the space, weight, wiring, and programming required for a pneumatic system to support the drivetrain.

-----

Also, it's important to consider levels of implementation. When I think swerve, I think 16, 71, 111, 118, 1640. Those aren't representative of the 'average' swerve drive robot.
If a butterfly drive succeeds, it's pretty nice. If BD fails, it's still a completely capable 4WD robot*. However, there hasn't really been a team that has used it consistently enough, and at a high level of success, to be the standard-bearer for that configuration.

*the same can be said for a failed SD, but mechanical locks may be needed to achieve that.

[Ari423]

Originally Posted by Taylor

Does a butterfly-style drive necessarily imply the use of pneumatics? For a robot design that does not otherwise incorporate pneumatics, it is certainly important to factor in the space, weight, wiring, and programming required for a pneumatic system to support the drivetrain.

-----

Also, it's important to consider levels of implementation. When I think swerve, I think 16, 71, 111, 118, 1640. Those aren't representative of the 'average' swerve drive robot.
If a butterfly drive succeeds, it's pretty nice. If BD fails, it's still a completely capable 4WD robot*. However, there hasn't really been a team that has used it consistently enough, and at a high level of success, to be the standard-bearer for that configuration.

*the same can be said for a failed SD, but mechanical locks may be needed to achieve that.

For butterfly drive you need to physically switch which wheels are touching the ground. This movement requires fairly quick actuation, a very large amount of force at stall (enough to support the whole robot), and only two positions. To me at least, those restrictions scream pneumatics. I guess theoretically you could use motors (big servos maybe?) but that would be way more complicated than with pneumatics where all you need is a cylinder pushing between the module and a hard attachment to the chassis.

IIRC 148 has used variants of butterfly drive in a number of games (I know they used it in 2010). They haven't used it every year like some of the team's above have used swerve, but if I had to pick a team to be the standard for butterfly drive, I would pick them.

[iyportne]

This thread contains many excellent perspectives. And yes, swerve is not easy to employ but worth the journey. We tend to look at swerve as our development infrastructure and learning bed. We are currently on version 4.0 and have successfully used swerve to our satisfaction in the last two seasons. Code is rock solid and and basically a library object so scalability is not an issue. We have a solid working encoder and have now figured out a robust position and mount to survive an entire competition. We use our technology to develop relationships with local machine shops off season so we have that covered (though the last two seasons we used the Team 221 Revolution Pro modules). We have working robots to practice with so driver training is also covered. I would suggest that if you are interested in any advanced drive train(s) that you make it a multi-season effort and manage your competition risk as you go. And also, you don't have to re-invent the wheel (ha-I just saw the pun there) since FIRST rules dictate that if any of us develop off-season hardware or logic, we must provide design and code to the FIRST community prior to kickoff in order for us to use it that season. We post links to our Swerve design models and JAVA code here on CD.

A few more benefits to swerve added to those already mentioned are:
1. You are no longer limited to a two sided functional robot (front-back). Programming wise any side can be designated as front, and can be switched on the fly.
2. You can easily switch between or mix field-centric and robot-centric movements with vector math.
3. Your center of rotation is now virtual rather than mechanical, so it can exist anywhere - even outside the robot perimeter - great for object acquisition or placement.
4. Sure we use 8 motors, but the entire robot is now a very predictable 360° continuous turret while static or in field-centric motion - that means you have a turret for object acquisition and launch/placement.
5. With a full 150 lbs. competition weight on 4 swerve wheels pointed to the center of the robot, you have a pretty awesome brake for resisting defense or for ramps and it remains active at power-off.
6. You have full 4-wheel positive traction 100% of the time (obviously on flat surfaces) during any movement and don't suffer the movement control loss when not all four wheel are in weighted contact with some surface.
7. Our current development has gotten the net drive train weight near or below the standard KOP drive train.
8. If the game requires obstacle negotiations, you don't have to abandon the benefits of swerve, think of other add-on motion devices like belts, cogs or tank treads...remember Swank Drive?

We should have our Strange Swerve 4.0 designs posted before kickoff. Good luck with the development path you choose!

[marshall]

Originally Posted by iyportne

This thread contains many excellent perspectives. And yes, swerve is not easy to employ but worth the journey. We tend to look at swerve as our development infrastructure and learning bed. We are currently on version 4.0 and have successfully used swerve to our satisfaction in the last two seasons. Code is rock solid and and basically a library object so scalability is not an issue. We have a solid working encoder and have now figured out a robust position and mount to survive an entire competition. We use our technology to develop relationships with local machine shops off season so we have that covered (though the last two seasons we used the Team 221 Revolution Pro modules). We have working robots to practice with so driver training is also covered. I would suggest that if you are interested in any advanced drive train(s) that you make it a multi-season effort and manage your competition risk as you go. And also, you don't have to re-invent the wheel (ha-I just saw the pun there) since FIRST rules dictate that if any of us develop off-season hardware or logic, we must provide design and code to the FIRST community prior to kickoff in order for us to use it that season. We post links to our Swerve design models and JAVA code here on CD.

A few more benefits to swerve added to those already mentioned are:
1. You are no longer limited to a two sided functional robot (front-back). Programming wise any side can be designated as front, and can be switched on the fly.
2. You can easily switch between or mix field-centric and robot-centric movements with vector math.
3. Your center of rotation is now virtual rather than mechanical, so it can exist anywhere - even outside the robot perimeter - great for object acquisition or placement.
4. Sure we use 8 motors, but the entire robot is now a very predictable 360° continuous turret while static or in field-centric motion - that means you have a turret for object acquisition and launch/placement.
5. With a full 150 lbs. competition weight on 4 swerve wheels pointed to the center of the robot, you have a pretty awesome brake for resisting defense or for ramps and it remains active at power-off.
6. You have full 4-wheel positive traction 100% of the time (obviously on flat surfaces) during any movement and don't suffer the movement control loss when not all four wheel are in weighted contact with some surface.
7. Our current development has gotten the net drive train weight near or below the standard KOP drive train.
8. If the game requires obstacle negotiations, you don't have to abandon the benefits of swerve, think of other add-on motion devices like belts, cogs or tank treads...remember Swank Drive?

We should have our Strange Swerve 4.0 designs posted before kickoff. Good luck with the development path you choose!

Having watched these guys develop their swerve system as well as borrowed their lessons learned as well as those from Anthony at 221, this is all really good info.

I'm not 100% convinced about mixing other drive types with swerve (swank) but these guys made it work and it was impressive to watch.

Swerve is hard to get right.

[ctt956]

Originally Posted by iyportne

[snip]
7. Our current development has gotten the net drive train weight near or below the standard KOP drive train.
8. If the game requires obstacle negotiations, you don't have to abandon the benefits of swerve, think of other add-on motion devices like belts, cogs or tank treads...remember Swank Drive?

We should have our Strange Swerve 4.0 designs posted before kickoff. Good luck with the development path you choose!

Originally Posted by marshall

Having watched these guys develop their swerve system as well as borrowed their lessons learned as well as those from Anthony at 221, this is all really good info.

I'm not 100% convinced about mixing other drive types with swerve (swank) but these guys made it work and it was impressive to watch.

1533's swank drive from 2016 was definitely impressive. That robot could do everything in the game, and it did it fast. I think the swerve part saved time because of the ability to move sideways/diagonally/faster than a tank drive could make the same movement, if it could do it at all. IMO, it was easily one of the best robots within the NC district for 2016, and still amazing outside of the district. I saw similar designs with other teams(330 is a notable example); not sure whose design inspired whose, or if several teams had the same ideas.

[asid61]

If you've only got a simple mill and lathe, it's difficult to make a "modern" swerve drive (that's low weight and size, or comparable to a WCD in both). Butterfly is alright, but I like octacanum more because you can keep things in only 4 modules where with butterfly/H-drive you need center wheel to strafe as well. The strafe wheel will also inevitably have less pushing/acceleration power than one in a swerve drive.

Apart from the balance issues, 3-wheel swerve is nice because you can run 3CIM + 3 miniCIM. However, at that point you are using up 6 motors for drive + 3 for turning, leaving only 7 for all manipulators. For many teams, that's ok, but for some motor-heavy users you might want 8 (2 for shooter, 2 for angler, 1 for intake, 2 for angling that, 1+ for climber?). I prefer using a 4-wheel swerve with 1 CIM each to leave you with 8 motors.

I would say that swerve is equal to or has an advantage over H-drives/butterfly/octocanum in most aspects unless you're 33 in 2014 and are ok with being pushed sideways/drifting when you move. The main disadvantage is losing more motors and taking a lot of manufacturing time and weight. For those reasons I would go octocanum in most situations if you really want the strafing.

On a side note, I think the biggest advantage that swerve or other holonomic drivetrains have over a traditional WCD is being easier to drive. If you start somebody off on a field-centric drivetrain, they'll have no problems getting the hang of it quickly. There can also be a space-saving aspect depending on your overall robot design and the game in question, but more often than not it's negligible.

[Ari423]

Let me start with I have never physically made either of these, but I have done a number of CAD designs for each.

Swerve:
Pros:

• High traction in any direction (i.e. can push going sideways)

Cons:

• Lot of parts to fail
• Requires more precise alignment (harder without CNC)
• Complicated to program (more sensors and processing required in order to drive straight)
• Uses 8 motors (6 for 3-wheel swerve)
• Heavy without CNC
• Takes longer to tune before driving (multiple feedback controllers necessary)

4-wheel swerve is more stable if pushing matches are a possibility while 3-wheel swerve is lighter.

Octocanum/Butterfly:
Pros:

• Inherently supports two-speeds without a ball or dog shifter
• Easier to use COTS gearboxes as part of design
• Easy to program (viable without any feedback controllers)

Cons:

• Easier to be pushed
• Doesn't like uneven terrain

That's just what I can think of off the top of my head, I'm sure other people will have more.