2017 Drive Train

[Southpaw]

There's obviously a lot of debate surrounding which drive trains can serve what purposes. This thread is created to centralize this discussion to provide easier access to all teams.

One of the more uncommon drive systems which still proves useful is the h-drive. This system has omnis on all corners, with a central omni to provide lateral movement. Our team has thrown around the idea of using h-drive as a less complicated mechanum system. The movement is near-identical to mechanum and debatably easier to build. This of course being in contrast to using tank drive (reliable and simple). Can we get some insight?

[Bkeeneykid]

I'm not sure how a h-drive is simpler to build. With mecanums, you simply just mount wheels on each corner. The stock AM14U3 chassis even has support for it with Toughbox Micros. Meanwhile, with a h-drive you have to add a cross member and have a whole different drive wheel and gearbox in the middle. With H-drive you can have three gearboxes (you can tie the two side wheels together), but you need at least 5 motors. Mecanum has four gearboxes but four motors needed. Both offer challenges, but a mecanum drive is a lot simpler to mount to some versa chassis quickly (or c-channel as my team uses) and get started.

[Chak]

This year might be more of a swerve drive game than previous years. More control of the drivetrain can help place gears, and there's a wide open field for swerve to dance around defense in. It combines the advantages of omni or mecanums (and more) without giving up resistance towards defensive robots.

Too bad I'm not confident in my team's ability to do swerve properly.

[evanperryg]

Originally Posted by Southpaw

There's obviously a lot of debate surrounding which drive trains can serve what purposes. This thread is created to centralize this discussion to provide easier access to all teams.

One of the more uncommon drive systems which still proves useful is the h-drive. This system has omnis on all corners, with a central omni to provide lateral movement. Our team has thrown around the idea of using h-drive as a less complicated mechanum system. The movement is near-identical to mechanum and debatably easier to build. This of course being in contrast to using tank drive (reliable and simple). Can we get some insight?

Mechanically, H-drive is harder to make because you need the center wheel, but programming-wise, assuming you're writing your code from the ground up, H-drive is a breeze compared to Mecanum.

[C_4187]

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?

[Jay O'Donnell]

If there was ever a game to not overthink your drivetrain and just build a really simple tank drive, this would probably be it.

[Munchskull]

Originally Posted by Jay O'Donnell

If there was ever a game to not overthink your drivetrain and just build a really simple tank drive, this would probably be it.

Agreed. Make it simple strong and compact

[deltafief]

Originally Posted by Jay O'Donnell

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]

Originally Posted by Jay O'Donnell

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]

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]

Originally Posted by lgphoneeric

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]

Originally Posted by s-neff

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.

[mypie4050]

Originally Posted by Jay O'Donnell

If there was ever a game to not overthink your drivetrain and just build a really simple tank drive, this would probably be it.

This is very good advice. Any robot with a mecanum or omin train will likely be very easy to push around and be highly ineffective at both shooting and gearing (my proposed term for scoring gears).

[s-neff]

Originally Posted by C_4187

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?

In a pushing match, yes.

[SamcFuchs]

Everyone should read this before building anything but a tank drive:

http://www.simbotics.org/resources/m...rain-selection