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#16
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Re: Swerve vs. Butterfly Drivetrain
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I can say from experience however that the code for a swerve drive does in fact scale rather well. It took me possibly 3 days to port the code over to java, 20 minutes to tune the PID, and another 3 days to make it look pretty so we could debug things, (and likely 4 to deal with the nasty issue of analog counters in the wpilib). The rest of the issues the system had stemmed from the unbelievable complexity of designing and building the darn thing (of which, to the credit of those who worked on designing and building it that year, there were very few.) Quote:
It took 3 days to build the mockup. It did not take 6 weeks to build the whole drive. The base was working by the end of week 4 that season. The first I directly stated, and I believe you should have noticed, the second is rather easy to infer, which I assume you also did. 3 days does seem a bit short though. I would expect a team with fewer vex related components on hand to take more time due to the process of procurement. Quote:
I would argue that a team with the means to build an effective swerve drive is almost guaranteed to have at least one programmer with the experience and talent to figure it out rather quickly, but such an argument would be based entirely in conjecture since I have experience only with two teams. It would stand to reason that I had not considered teams with a greater imbalance of resources between the programming and mechanical teams. Right, seems a component of my post is missing. I was sure I had typed it but voila, as I was going back to look for it it was gone. There was a bug in the wpilibraries. It caused the configuration to not work. What I had failed to mention (but which it would reason isn't too difficult to infer) is that the bug was indeed fixed (good god would I have had a rant to put up here if it wasn't.) in, if memory serves me well, approximately a snappy four days. The configuration itself was fine, and worked, again, if memory serves me well, flawlessly. Last edited by AlexanderTheOK : 11-07-2016 at 05:47 PM. Reason: fancier words |
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#17
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Re: Swerve vs. Butterfly Drivetrain
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#18
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Re: Swerve vs. Butterfly Drivetrain
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. |
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#19
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Re: Swerve vs. Butterfly Drivetrain
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? |
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#20
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Re: Swerve vs. Butterfly Drivetrain
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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! |
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#21
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Re: Swerve vs. Butterfly Drivetrain
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#22
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Re: Swerve vs. Butterfly Drivetrain
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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?) |
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#23
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Re: Swerve vs. Butterfly Drivetrain
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. Last edited by Taylor : 11-08-2016 at 09:25 AM. |
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#24
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Re: Swerve vs. Butterfly Drivetrain
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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. |
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#25
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Re: Swerve vs. Butterfly Drivetrain
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! |
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#26
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Re: Swerve vs. Butterfly Drivetrain
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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. |
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#27
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Re: Swerve vs. Butterfly Drivetrain
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#28
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Re: Swerve vs. Butterfly Drivetrain
I'm not sure if I'm misunderstanding something, but we had an 8 wheel tank this past season. The last time we did anything other than tank drive was in 2009 with our single module "swerve". (closer to a giant turret with bumpers)
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#29
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Re: Swerve vs. Butterfly Drivetrain
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The only previous times 330 had a non-traditional tank drive, either they never made the field ('05 mecanum) or they were just an added feature (1999's rotating drivetrain could roll front wheel modules and rear wheel modules independently--handy for dropping down to snag floppies or raising up to slide onto the puck). 330 has never attempted a swerve, other than that '09 robot (which... well, it was a well-camouflaged tank drive). Unless they've tried something in the last couple offseasons, which I doubt. |
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#30
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Re: Swerve vs. Butterfly Drivetrain
Especially for 3rd/4th robot, a butterfly drive will likely be viewed as a negative while a swerve will likely be viewed as a positive when it comes to alliance selection.
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