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deltafief 09-01-2017 00:16

Re: 2017 Drive Train
 
Quote:

Originally Posted by Jay O'Donnell (Post 1627559)
If there was ever a game to not overthink your drivetrain and just build a really simple tank drive, this would probably be it.

Pretty much this if you go mecanum or h-drive you run the risk of getting pushed around a lot as you have to make lots of trips to get gears or fuel

Munchskull 09-01-2017 00:29

Re: 2017 Drive Train
 
Quote:

Originally Posted by Jay O'Donnell (Post 1627559)
If there was ever a game to not overthink your drivetrain and just build a really simple tank drive, this would probably be it.

There is a reason that no robot on Einstein has ever had mecanum drive. (2015 is excluded)

lgphoneeric 09-01-2017 03:04

Re: 2017 Drive Train
 
So just so some newer teams don't read this thread and think that mecanum wheels are completely useless at holding their own in a game like this, check out this video from 2014. https://www.thebluealliance.com/match/2014arc_qm29
The bright red and yellow robot (us) were running the new vexpro mecanums (before the metal casters oh how we wish they had the metal insert like they do now) and we easily could hold our own in a pushing contest. The key with mecanums is that the center of gravity needs to be as low and as perfectly centered as possible.
So, do a lot of mecanum drives get pushed around, yes. BUT, if they are optimized, can they hold their own against the most pushy of robots, absolutely!
Just something to think about before teams blindly throw it out because they are under the assumption they can be pushed around with minimal effort.

s-neff 09-01-2017 03:50

Re: 2017 Drive Train
 
Quote:

Originally Posted by lgphoneeric (Post 1627680)
So just so some newer teams don't read this thread and think that mecanum wheels are completely useless at holding their own in a game like this, check out this video from 2014. https://www.thebluealliance.com/match/2014arc_qm29
The bright red and yellow robot (us) were running the new vexpro mecanums (before the metal casters oh how we wish they had the metal insert like they do now) and we easily could hold our own in a pushing contest. The key with mecanums is that the center of gravity needs to be as low and as perfectly centered as possible.
So, do a lot of mecanum drives get pushed around, yes. BUT, if they are optimized, can they hold their own against the most pushy of robots, absolutely!
Just something to think about before teams blindly throw it out because they are under the assumption they can be pushed around with minimal effort.

Frankly, in that video I see your robot pushing around other mechanum/omni robots, and using its momentum well to get the occasional hits on the tank drive 'bots. Your driver is doing a great job, within the physical limitations of the system... those limitations are minimized by the low CG & good system engineering, but still definitely there.

lgphoneeric 09-01-2017 04:43

Re: 2017 Drive Train
 
Quote:

Originally Posted by s-neff (Post 1627688)
Frankly, in that video I see your robot pushing around other mechanum/omni robots, and using its momentum well to get the occasional hits on the tank drive 'bots. Your driver is doing a great job, within the physical limitations of the system... those limitations are minimized by the low CG & good system engineering, but still definitely there.

One was a swerve, one was a mecanum, and the third was a 6 wheel drive. But often times its more about how you drive the robot and how limitations are overcome such as using momentum. I wish I had video of it, but one of the matches during our first regional (which weirdly only a few matches were recorded) we ended up pushing an 8 wheel colson drive across the field from almost a stand still. Can mecanum drives push very often, not really, but should they be eliminated from decision discussion simply because there is a little defense, in my opinion I definitely do not think so because a good drive team with a slick drive train can do surprising things. So ultimately the point I guess I'm trying to get at is just because a drive train doesn't have as much physical grip as another doesn't mean it can't at times match or outperform a technically gripper drive train.

Koko Ed 09-01-2017 04:52

Re: 2017 Drive Train
 
Quote:

Originally Posted by C_4187 (Post 1627557)
Mecanum vs. Tank?

Mecanum has an obvious mobility advantage, but how much does it really give up in traction/strength? Is it completely outclassed in strength to a tank drive system?

Uness your driving around a football field Mecanums do not give you the agility that people assume you'll get due to congestion on the field. You'll just get caught and stoned by defense.

Jpatterson1710 09-01-2017 05:05

Re: 2017 Drive Train
 
Quote:

Originally Posted by C_4187 (Post 1627557)
Mecanum vs. Tank?

Mecanum has an obvious mobility advantage, but how much does it really give up in traction/strength? Is it completely outclassed in strength to a tank drive system?

https://www.youtube.com/watch?v=O_vvVU4OBT4

Just Sayin.

Kevin Sevcik 09-01-2017 09:20

Re: 2017 Drive Train
 
Quote:

Originally Posted by Jpatterson1710 (Post 1627694)

Butterfly drive, especially shifting butterfly drive, is probably only a good idea for teams that already know what it is and aren't cruising CD for suggestions on drivetrain decisions.

Cothron Theiss 09-01-2017 09:38

Re: 2017 Drive Train
 
Quote:

Originally Posted by Jpatterson1710 (Post 1627694)

I don't want this to turn into a mecanum vs tank drive thread or an articulated drive vs tank drive thread, but I think the reasoning behind selecting a simple tank drive is more applicable this year than just about any other. An articulated drive might perform better as a drivetrain than a dropped center tank drive. But is it worth investing 2/3 of your weight allowance and 2/3 of your build season getting a complicated drive system working? Or is it better to build something that is robust and reliable, and spend that time on your subsystems and practicing to improve performance?

Joe Johnson 09-01-2017 10:03

Re: 2017 Drive Train
 
In my view, if you haven't built a swerve drive or H drive or mecanuum drive and had your coders code it and your drivers drive it, you really need to stick to tank drive this year.

The practice time you will lose with your robot is just not going to be able to be overcome by the extra features you are imagining you will have.

Finish early. Give your coders coding time and your drivers practice time and your whole team time to iterate and improve your robot. THAT is the way to be playing after lunch on the last day of the tournament*.

Dr. Joe J.

*said the guy who designed his first Swerve Drive for Ladder Logic (1998 season). Chief Delphi won 3 blue banners with CD3. I KNOW that drive trains matter. But driver practice matters more. A LOT more.

Chris is me 09-01-2017 10:12

Re: 2017 Drive Train
 
Disclaimer: Build a tank drive. Please. Just do that. If you are the kind of person who listens to advice on CD to make drivetrain decisions, do that.

--

That said, there's a pretty reasonable argument for swerve or butterfly drive this year if it's compact. The bumper rules limit intakes since six inches of room on each side of the drive must be backed by bumper - leaving more space for various omnidirectional drives. Lining up at the peg, goals, or human loader could theoretically be faster using a strafing drivetrain. And the full field sprints lend themselves well to butterfly style drivetrains.

But I mean, if you haven't considered these drives and built prototypes long before reading this post, it's too late, and the possible small advantage they could give your team is more than offset by the development difficulty. We have a bunch of other tough tasks to do in this game, don't make it harder than it has to be.

pfreivald 09-01-2017 10:22

Re: 2017 Drive Train
 
Quote:

Originally Posted by Chris is me (Post 1627784)
Disclaimer: Build a tank drive. Please. Just do that. If you are the kind of person who listens to advice on CD to make drivetrain decisions, do that.

Exactly. We built a swerve off-season and they are a LOT of fiddly work to get them to function just as you want them. Ours looks fantastic, and performs great--and we may very well just go with a 6 CIM shifting tank-type (WCD) this year.

SamcFuchs 09-01-2017 10:23

Re: 2017 Drive Train
 
It seems to me that people are far overestimating how hard it will be to deliver the gear. The (horizontal) margin of error is 6 inches. That's (approximately) the width of the gear. Because the hook is spring loaded, you have even more leeway, not to mention that the place you have to deliver to is directly in front of your driver station. I'd argue it was harder to line up with the chute in 2015. If your driver really can't do it, just put a camera on the robot and use that to align, but don't build your drivetrain around this particular challenge.

efoote868 09-01-2017 10:48

Re: 2017 Drive Train
 
Quote:

Originally Posted by Southpaw (Post 1627263)
Our team has thrown around the idea of using h-drive as a less complicated mechanum system.

From a design and build perspective, H-drive is by far more complicated than mecanum drive.

Quote:

Originally Posted by Southpaw (Post 1627263)
The movement is near-identical to mechanum and debatably easier to build.

PLEASE read the advice posted by experienced Chief Delphi members. If your team has not yet designed and built a holonomic drive system, week 1 of build season is not an ideal time to start.


In my experience, a field-centric holonomic drive is the easiest robot to learn to drive. Mecanum provides a good trade-off between complexity (2 extra gearboxes, a bit of learning to program) for increased maneuverability. It's also the closest you'll get to a COTS solution. Any other drive really needs to be developed in the off-season.

pfreivald 09-01-2017 10:55

Re: 2017 Drive Train
 
Quote:

Originally Posted by efoote868 (Post 1627816)
From a design and build perspective, H-drive is by far more complicated than mecanum drive.

We did straight mecanum for two years, switched to octocanum for a few years, did mecanum again for Recycle Rush. I've never had a student programmer who couldn't fully program a mecanum drive exactly like a 3rd person shooter in at most an afternoon.

There's this myth that mecanum is hard to program. It just isn't. (It's also incredibly easy to build. Just direct-drive four wheels off of appropriate gearboxes, and voila.)

That said, straight-up mecanum will be a mistake this year. The parallels to Ultimate Ascent say defense will be *huge*, and mecanum drives don't do a good job powering through defense.


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