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Southpaw 08-01-2017 15:03

2017 Drive Train
 
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 08-01-2017 15:11

Re: 2017 Drive Train
 
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 08-01-2017 16:48

Re: 2017 Drive Train
 
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 08-01-2017 20:25

Re: 2017 Drive Train
 
Quote:

Originally Posted by Southpaw (Post 1627263)
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 08-01-2017 22:22

Re: 2017 Drive Train
 
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 08-01-2017 22:24

Re: 2017 Drive Train
 
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 08-01-2017 22:27

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.

Agreed. Make it simple strong and compact

s-neff 08-01-2017 22:27

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?

In a pushing match, yes.

SamcFuchs 08-01-2017 22:46

Re: 2017 Drive Train
 
Everyone should read this before building anything but a tank drive:

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

Kevin Sevcik 08-01-2017 23:03

Re: 2017 Drive Train
 
Point to consider:
6-WD tank (preferably with a COTS shifter) is the fastest, easiest drivetrain to implement and program. Is a mecanum, H-drive, or swerve so much easier to line up that it outweighs the extra practice time you should have with the tank drive? Or the extra practice time with your practice bot because the tank drive is so much cheaper?

Also, a defensive tank bot is going to shove a mecanum or h-drive all over the place. Good luck scoring a gear while that's happening.

jee7s 08-01-2017 23:24

Re: 2017 Drive Train
 
Quote:

Originally Posted by Kevin Sevcik (Post 1627579)
Point to consider:
6-WD tank (preferably with a COTS shifter) is the fastest, easiest drivetrain to implement and program. Is a mecanum, H-drive, or swerve so much easier to line up that it outweighs the extra practice time you should have with the tank drive? Or the extra practice time with your practice bot because the tank drive is so much cheaper?

Also, a defensive tank bot is going to shove a mecanum or h-drive all over the place. Good luck scoring a gear while that's happening.

Aw man, if only I were still with Texplosion, that last part is a pure gem.

Yeah, don't overthink the drivetrain. You shouldn't need a vertical adjustment for anything. And, if you are off horizontally, build it into a mechanism rather than moving the whole robot. If you are placing a gear, have a way to rotate it or move it side-to-side. If you are a shooter, have a way to rotate your shooter to keep it on target. Put your code into things like that, not into complex drive.

GeeTwo 08-01-2017 23:44

Re: 2017 Drive Train
 
In 3946's experience, H-drive is harder than mecanum.

In 2013 Aerial Assault we decided to do mecanum (foolishly expecting a less defensive game), and it worked as well as expected, pretty much the first time around (OK, after fixing some wheel order issues), but we had it running two weeks after we made the decision on our prototype "Woody" (which meant ordering wheels and extra gearboxes before we could finish the build) and running like a champ on the competition robot "Buzz" before bag day. We used the WPI mecanumDrive class straight up, without encoders.

In 2015 Recycle Rush, we decided to do H-drive, and never got it working correctly all the way through CMP. It was only after the 2016 season that we got it working. If you do do H-drive, do not depend on a fixed-height strafe wheel - there is no height which provides the correct amount of load. The central wheel(s) must somehow have a controlled force against the carpet, whether passively through springs or actively through pneumatics or torque actuation, or perhaps some other ways you can come up with.

Another caveat which may or may not apply to you: H-drive requires a wheel near the CoG of your chassis (or one forward and one behind). This will interfere with the "chassis opening and combine" style gatherer that is likely to be commonly used by fuelbots this year.

RoboAlum 08-01-2017 23:45

Re: 2017 Drive Train
 
we are actually gonna use 610s DT from Ultimate Ascent but wooden mobility for us was not a big thing for us this year we want to just be a role player and focus on the gears but still win a pushing a match

Cothron Theiss 08-01-2017 23:59

Re: 2017 Drive Train
 
Quote:

Originally Posted by RoboAlum (Post 1627592)
we are actually gonna use 610s DT from Ultimate Ascent...

For those of us who aren't familiar with it, mind providing some details about what this is?

Jay O'Donnell 09-01-2017 00:10

Re: 2017 Drive Train
 
Quote:

Originally Posted by Cothron Theiss (Post 1627601)
For those of us who aren't familiar with it, mind providing some details about what this is?

Link to picture: https://goo.gl/images/pvbwyc

6 CIM, 6 Wheel Drive, single speed. I believe it was designed around acceleration, not a very high full speed.

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.

Koko Ed 09-01-2017 11:04

Re: 2017 Drive Train
 
Quote:

Originally Posted by pfreivald (Post 1627828)
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.

or the eventual ball pit the field will rapidly become...

Kevin Sevcik 09-01-2017 11:06

Re: 2017 Drive Train
 
Quote:

Originally Posted by pfreivald (Post 1627828)
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.

Ultimate Ascent is definitely a good game to reference. Shooting, cross-field cycling, hoovering scoring items, and two giant structures clogging everything up. The biggest difference is you can't expand the field by driving under the obstacles. 4 robot pile-ups next to one of the airships are going to be common. Being able to push around the side of that pile is going to be important.

daliberator 09-01-2017 11:10

Re: 2017 Drive Train
 
Based on the current stock Andymark has for Toughbox Micros, I think that a lot of teams are going for mecanum.:yikes:

mypie4050 09-01-2017 11:45

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.

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).

7keleher 09-01-2017 14:04

Re: 2017 Drive Train
 
We used h-drive in 2015 and got it working great. Mechanum is something we have never done because a) we haven't needed it and b) its more complicated than a tank or h-drive. For this year's game tank drive is probably best. For lining things up, just practice with the tank drive and build some mechanisms in for maneuvering game pieces within the bot.

chandrew 09-01-2017 21:42

Re: 2017 Drive Train
 
Quote:

Originally Posted by s-neff (Post 1627563)
In a pushing match, yes.

I would actually disagree with this. If you have a good gear ratio on a mecanum you can get a decent amount of force. Our team went mecanum in 2014 and we're actually able to push the more basic tank drives around.

messer5740 09-01-2017 21:57

Re: 2017 Drive Train
 
Basic question but couldnt find it anywhere else:
How fast does the andymark KOP chassis go?

slhs 09-01-2017 22:03

Re: 2017 Drive Train
 
1 Attachment(s)
Quote:

Originally Posted by messer5740 (Post 1628305)
Basic question but couldnt find it anywhere else:
How fast does the andymark KOP chassis go?

From user guide:

Jpatterson1710 10-01-2017 00:19

Re: 2017 Drive Train
 
Quote:

Originally Posted by Kevin Sevcik (Post 1627754)
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.

Quote:

Originally Posted by Cothron Theiss (Post 1627767)
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?

I totally agree, I just thought it was a fitting video to add to the conversation. Drivetrain R&D is not for build season.

Tom Line 10-01-2017 00:58

Re: 2017 Drive Train
 
Quote:

Originally Posted by Kevin Sevcik (Post 1627836)
Ultimate Ascent is definitely a good game to reference. Shooting, cross-field cycling, hoovering scoring items, and two giant structures clogging everything up. The biggest difference is you can't expand the field by driving under the obstacles. 4 robot pile-ups next to one of the airships are going to be common. Being able to push around the side of that pile is going to be important.

Not to let the cat out of the bag, but Ultimate ascent is the PERFECT game to benchmark against. Full field cycling ruled that year. Take a look at what the top 15 teams were running.

In fact, Ultimate ascent was easier than this game when it came to driving, because you could put yourself in safe zones when you shot. This year? Prepared to be pushed while putting the gear on or shooting into the goal.

Build a tank drive.

dardeshna 10-01-2017 02:21

Re: 2017 Drive Train
 
On a slightly different note, what motor / gearing / wheel size setup are you all using? Ideal feet per second I would imagine is relatively high. Shifting or no shifting? We are leaning towards 6 cim ~10-12 fps no shifting but I don't have great experience to tell if we got it in the right range or not for this game.

Jay O'Donnell 10-01-2017 03:13

Re: 2017 Drive Train
 
Quote:

Originally Posted by dardeshna (Post 1628405)
On a slightly different note, what motor / gearing / wheel size setup are you all using? Ideal feet per second I would imagine is relatively high. Shifting or no shifting? We are leaning towards 6 cim ~10-12 fps no shifting but I don't have great experience to tell if we got it in the right range or not for this game.

I've heard of plenty of teams thinking about doing exactly this actually. The benefit of that setup is a greater acceleration, so you can travel at that top speed for long straightaways across the field.

Personally I'm not a big shifting guy, I think it takes a very skilled driver to use it effectively.

TheMagicPenguin 10-01-2017 07:07

Re: 2017 Drive Train
 
Here on 1640 we plan to use our swerve drive again (big suprise). This year we are also going to introduce our CVT swerve to the field.

Darkseer54 10-01-2017 08:45

Re: 2017 Drive Train
 
Quote:

Originally Posted by Cothron Theiss (Post 1627767)
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?

How about 45lbs, with a functioning control system, working pneumatic system, a compressor too big for its own good, a metal tank, and a huge excess of wires and pneumatic tubing? Just because one 8 motor octocanum weighs 90 lbs doesn't mean all of them do.

https://www.youtube.com/watch?v=sf-mNuGsVhQ
Quote:

Originally Posted by Jpatterson1710 (Post 1627694)
Just Sayin.


JediSy 10-01-2017 11:45

Re: 2017 Drive Train
 
I personally think mechanum or Omni with tread-wheel hybrid. That's just an idea though. Problem is the amperage for mechanum.

Munchskull 10-01-2017 12:23

Re: 2017 Drive Train
 
Quote:

Originally Posted by JediSy (Post 1628578)
I personally think mechanum or Omni with tread-wheel hybrid. That's just an idea though. Problem is the amperage for mechanum.

How is amperage for the the mecanum wheels an issue? You will not be stalling them and thus you will not draw much current. Instead of stalling mecanums normally break the friction of the carpet and spin (if remember correctly).

Cothron Theiss 10-01-2017 15:06

Re: 2017 Drive Train
 
Quote:

Originally Posted by dardeshna (Post 1628405)
On a slightly different note, what motor / gearing / wheel size setup are you all using? Ideal feet per second I would imagine is relatively high. Shifting or no shifting? We are leaning towards 6 cim ~10-12 fps no shifting but I don't have great experience to tell if we got it in the right range or not for this game.

Wheel size: small as you can reasonably get them. I personally see no good reason to have drive wheels larger than 4". Lower ground clearance, less reduction, and less overall torque in the system is always a good thing. The only downside is that your wheels will wear more quickly. I imagine the <4" and 4" hex bore Colson wheels will be very popular this year.

Motors: my go-to combination is 4 CIMs & 2 MiniCIMs.

Gearing: I am usually an advocate for single speed gearboxes, and I still think you can't go wrong with them this year. My issues with shifters is that most teams are not able to fully realize the benefits of their shifting gearbox; whether that's because of poor design, a game that doesn't need two-speeds, insufficient driver practice or just mistakes in the engineering process, they're adding weight, cost and complexity and not getting much in return. However, this year is a good year for shifting gearboxes if you go that route. you have long open stretches of field you need to get across quickly and you have tight spaces where you need to push defenders out of the way. I have not done any of the math yet to really figure out sprint distances and distance to reach full speed, so I'm just guessing on the numbers themselves. But for this game, I'd say:

12 ft/s for a single speed gearbox
8 & 14 ft/s for a two-speed gearbox.

Cothron Theiss 10-01-2017 15:35

Re: 2017 Drive Train
 
Quote:

Originally Posted by TheMagicPenguin (Post 1628425)
Here on 1640 we plan to use our swerve drive again (big suprise). This year we are also going to introduce our CVT swerve to the field.

Do you have any of the source files for this CVT swerve design anywhere? I'd love to look at them.



Quote:

Originally Posted by Darkseer54 (Post 1628456)
How about 45lbs, with a functioning control system, working pneumatic system, a compressor too big for its own good, a metal tank, and a huge excess of wires and pneumatic tubing? Just because one 8 motor octocanum weighs 90 lbs doesn't mean all of them do.

https://www.youtube.com/watch?v=sf-mNuGsVhQ

That looks great! Mind if I ask what traction wheels you're using?

You're right, 45 lbs. is much more reasonable and your chassis looks both agile and powerful. I expect you'll see a lot of success on that that chassis.
But the reason I always will recommend a simple 6 or 8 wheel drop center chassis over the more complicated drive systems is that a well designed, well built, and well practiced tank drive will perform as well as something more complicated for most cases. Yes, there are situations in which it'd be really convenient to just move 6" to the left in a match. But those scenarios are not worth the time and effort that those more complicated drive systems require. And the robustness of a tank drive cannot be beaten.

In short, I think it's more important for teams to field the best robot and not the best drivetrain. Any time spent on a complicated drive system is time not spent developing other subsystems.

That329Guy 10-01-2017 19:32

Re: 2017 Drive Train
 
Speaking of drive train, we finally came up with the drive train we are going to use for this year. We were deciding between skid steer and mechanum and I was for skid steer. However, the main mentor already ordered the parts for mechanum. We're still deciding on our robot design, but at least we have a drive train. :)

dardeshna 10-01-2017 19:39

Re: 2017 Drive Train
 
Quote:

Originally Posted by Cothron Theiss (Post 1628741)
Wheel size: small as you can reasonably get them. I personally see no good reason to have drive wheels larger than 4". Lower ground clearance, less reduction, and less overall torque in the system is always a good thing. The only downside is that your wheels will wear more quickly. I imagine the <4" and 4" hex bore Colson wheels will be very popular this year.

Motors: my go-to combination is 4 CIMs & 2 MiniCIMs.

Gearing: I am usually an advocate for single speed gearboxes, and I still think you can't go wrong with them this year. My issues with shifters is that most teams are not able to fully realize the benefits of their shifting gearbox; whether that's because of poor design, a game that doesn't need two-speeds, insufficient driver practice or just mistakes in the engineering process, they're adding weight, cost and complexity and not getting much in return. However, this year is a good year for shifting gearboxes if you go that route. you have long open stretches of field you need to get across quickly and you have tight spaces where you need to push defenders out of the way. I have not done any of the math yet to really figure out sprint distances and distance to reach full speed, so I'm just guessing on the numbers themselves. But for this game, I'd say:

12 ft/s for a single speed gearbox
8 & 14 ft/s for a two-speed gearbox.

So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?

Darkseer54 10-01-2017 20:31

Re: 2017 Drive Train
 
Quote:

Originally Posted by Cothron Theiss (Post 1628760)
That looks great! Mind if I ask what traction wheels you're using?

That uses 2" Colson wheels which were hex broached. From what I've heard from members of the team, they may be planning to diamond cut them this year. The idea behind using such small wheels is by making the wheels smaller, the overall size of the module is less so you save weight.

Kevin Sevcik 10-01-2017 20:40

Re: 2017 Drive Train
 
Quote:

Originally Posted by dardeshna (Post 1628919)
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?

Less amperage per motor, which means you're more likely to traction limit before tripping breakers or overloading a speed controller. Less amps also means less voltage drop in your wires to/from the motors, which means you're spending more watt-hours on pushing and less on heating up wires. It's a small thing, but I suspect every little thing you can do to minimize unnecessary battery drain matters, even if you're using a fresh battery for every match.

Nbot 10-01-2017 20:48

Re: 2017 Drive Train
 
Quote:

Originally Posted by dardeshna (Post 1628919)
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?

Additionally, having 6 cims would allow the robot to accelerate faster than a setup with fewer cims.

Cothron Theiss 10-01-2017 21:10

Re: 2017 Drive Train
 
Quote:

Originally Posted by dardeshna (Post 1628919)
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?

Here's a really great paper looking at 4 CIMs vs 6 CIMs. Were you referring to the advantages of 6 CIMs over 4 CIMs or 4 CIMs & 2 Minis?

dardeshna 10-01-2017 22:00

Re: 2017 Drive Train
 
Quote:

Originally Posted by Cothron Theiss (Post 1628957)
Here's a really great paper looking at 4 CIMs vs 6 CIMs. Were you referring to the advantages of 6 CIMs over 4 CIMs or 4 CIMs & 2 Minis?

Great, thanks for linking the paper. I was originally referring to the difference between 6 CIMs and 4 CIMs, although I presume the same concept applies.

rlance 12-01-2017 16:34

Re: 2017 Drive Train
 
Our team is building both an omni and the KOP drivetrain this year and making them the same dimensions with the same opening location for ball retrieval. The plan is to use the omni, but with the backup option of the KOP DT.

Are we allowed to switch out drive trains at the competition if the need arises? If so, would both drivetrains need to be included in our 120 lbs? Do we need to come to the competition with the second drive train un-assembled?

Southpaw 17-01-2017 20:05

Re: 2017 Drive Train
 
Bumping the thread to ask, "Our team was driving and finding alignment time issues with the feeder station and gear deployment station, we are using the AM14U2 chassis in the 6 wheel configuration. Is H-drive worth is to overcome the drive practice required to become efficient at loading?" Our team has not built it before, and I am curious as to how difficult it is with the standard chassis.

Cothron Theiss 17-01-2017 20:27

Re: 2017 Drive Train
 
Quote:

Originally Posted by Southpaw (Post 1632662)
Bumping the thread to ask, "Our team was driving and finding alignment time issues with the feeder station and gear deployment station, we are using the AM14U2 chassis in the 6 wheel configuration. Is H-drive worth is to overcome the drive practice required to become efficient at loading?" Our team has not built it before, and I am curious as to how difficult it is with the standard chassis.

Your team is driving and prototyping already? Awesome!! You are exactly where you want to be. Switching to a completely different drive system that you don't have experience with and requires MORE driver training than a standard tank drive seems like a fool's errand at this point.

Ginger Power 17-01-2017 20:42

Re: 2017 Drive Train
 
Quote:

Originally Posted by Southpaw (Post 1632662)
Bumping the thread to ask, "Our team was driving and finding alignment time issues with the feeder station and gear deployment station, we are using the AM14U2 chassis in the 6 wheel configuration. Is H-drive worth is to overcome the drive practice required to become efficient at loading?" Our team has not built it before, and I am curious as to how difficult it is with the standard chassis.

Definitely stick with your current drivetrain. It's not worth the time to add strafing. Focus on getting good at lining up with your current drivetrain!

On another note: I'm very happy that 4607 built a Butterslide drive with 4" omnis and 2" custom traction wheels. We're essentially duplicating that drivetrain with some useful improvements. Being able to strafe while also having the ability to resist pushing while scoring is going to be so useful. If we hadn't built that drivetrain in the offseason there's no way we could've done it during the build season!

pHolmgren 18-01-2017 00:54

Re: 2017 Drive Train
 
Our team decided to go with a 6 wheel tank drive this year, with a sort of modified west coast style. We have a frame CAD model attached and would love to hear what you think.https://drive.google.com/file/d/0BzJ...ew?usp=sharing

Zebra_Fact_Man 18-01-2017 01:23

Re: 2017 Drive Train
 
Quote:

Originally Posted by pHolmgren (Post 1632784)
Our team decided to go with a 6 wheel tank drive this year, with a sort of modified west coast style. We have a frame CAD model attached and would love to hear what you think.https://drive.google.com/file/d/0BzJ...ew?usp=sharing

Please make sure that the gaps in you bumper supports are indeed less than 7", or that you run a second support bar across the side of the frame. Otherwise you will be in violation of R31.

Otherwise, great work. My team is also doing 6wd DS WCD. So serviceable and utilitarian.

Michael 4499 18-01-2017 01:40

Re: 2017 Drive Train
 
Quote:

Originally Posted by Zebra_Fact_Man (Post 1632790)
Please make sure that the gaps in you bumper supports are indeed less than 7", or that you run a second support bar across the side of the frame. Otherwise you will be in violation of R31.

Otherwise, great work. My team is also doing 6wd DS WCD. So serviceable and utilitarian.

Is this correct? From my understanding of R31 it sounds like it is more the definition of a supported bumper. In the chassis displayed, they aren't trying to count that as a supported area but instead just not putting bumpers there. As long as they have 6 in. of support on each side, they should be fine.

Please correct me if I have a misunderstanding of this.

Cothron Theiss 18-01-2017 02:21

Re: 2017 Drive Train
 
Quote:

Originally Posted by Michael 4499 (Post 1632793)
Is this correct? From my understanding of R31 it sounds like it is more the definition of a supported bumper. In the chassis displayed, they aren't trying to count that as a supported area but instead just not putting bumpers there. As long as they have 6 in. of support on each side, they should be fine.

Please correct me if I have a misunderstanding of this.

Solomon isn't referring to the cutout in the front, he's referring to the bumper mounts on the sides of the robot between the drive wheels. That gap around the middle wheel looks like it's close to being in violation.

Cothron Theiss 18-01-2017 02:26

Re: 2017 Drive Train
 
Quote:

Originally Posted by pHolmgren (Post 1632784)
Our team decided to go with a 6 wheel tank drive this year, with a sort of modified west coast style. We have a frame CAD model attached and would love to hear what you think.https://drive.google.com/file/d/0BzJ...ew?usp=sharing

Looks good! Any reason you are going with the AndyMark DuraOmnis over the Vex Omnis? And what is the purpose of the center rail running from the back of the cutout to the front of the back rail?

mypie4050 18-01-2017 09:24

Re: 2017 Drive Train
 
I know that thread has been open for awhile now, but I'll just throw in my two sense. Our team has officially decided to go with a custom-build mecanum drivetrain. I know most teams have decided by this point, but our reasoning was as follows:

1. Agility/maneuverability will be key for auto/gear placement
2. Defensive situations can be avoided by "running away" - it is harder to trap a mecanum robot
3. Possibility of a "ground-engage" mechanism for staying in one spot (perhaps for shooting)
4. Sacrifice torc for speed - i.e. with a mecanum drivetrain we have little reason for torc, so can therefore throw torc to the wind, and go for as much speed as possible in our drivetrain.

I know some have said that mecanum is not the way to go this year, but we think there's plenty of use to be had there.

JesseK 18-01-2017 09:28

Re: 2017 Drive Train
 
Quote:

Originally Posted by pHolmgren (Post 1632784)
Our team decided to go with a 6 wheel tank drive this year, with a sort of modified west coast style. We have a frame CAD model attached and would love to hear what you think.https://drive.google.com/file/d/0BzJ...ew?usp=sharing

Consider what happens if you need to take a wheel off in this setup. Do the plates in the corners prevent it? If so, you should adjust the plating to make sure you can do any maintenance you need to do on this drive train.

Ari423 18-01-2017 10:14

Re: 2017 Drive Train
 
Quote:

Originally Posted by mypie4050 (Post 1632852)
I know that thread has been open for awhile now, but I'll just throw in my two sense. Our team has officially decided to go with a custom-build mecanum drivetrain. I know most teams have decided by this point, but our reasoning was as follows:

1. Agility/maneuverability will be key for auto/gear placement
2. Defensive situations can be avoided by "running away" - it is harder to trap a mecanum robot
3. Possibility of a "ground-engage" mechanism for staying in one spot (perhaps for shooting)
4. Sacrifice torc for speed - i.e. with a mecanum drivetrain we have little reason for torc, so can therefore throw torc to the wind, and go for as much speed as possible in our drivetrain.

I know some have said that mecanum is not the way to go this year, but we think there's plenty of use to be had there.

While most of your points are true in a general sense, be careful about over-extrapolating.
  1. Maneuverability will be important for placing gears, but in order to take advantage of a mecanum drive's maneuverability, the driver needs a lot of practice with the robot in different situations. This means that you need to either build a practice robot or have your robot finished by week 5 at the latest so your drivers can get a lot of practice before they start competing. Often drivers end up driving mecanum as if it were a tank drive (ignoring strafing). This is especially true if you are not using field-centric driving.
  2. While mecanum drives have the ability to be more maneuverable and can "run away" from a pushing match, often drivers get caught up in pushing matches anyway. If the pushing match occurs in a tight space or a place on the field where visibility is limited, drivers tend to try to push through the defender instead of running away. Large amounts of driver practice can correct these tendencies, but you will need practice 2-on-1 defense in very limited visibility areas in order to fully practice getting out of these situations. Also, running away usually means you will have to take a longer route, which takes more time.
  3. Just make sure that your "ground engage" mechanism keeps the robot balanced even when it is being pushed. A single plate in the middle of the robot leaves the robot susceptable to tippping if a defending robot tries to push it. Also, if you get knocked out of alignment, you will need to retract the grounding mechanism, re-align, and redeploy it, which takes a lot of time. And make sure to cover your mechanism in tread to avoid breaking R05. At this point, you're getting pretty close to an octocanum drive.
  4. Assuming you mean torque, the mechanical influence, not torc, a necklace worn by the ancient Gauls, you are correct to a degree. Mecanum wheels have a forward CoF of about 0.7, compared to around 1 for traction wheels. This means you can gear your robot faster and not draw as much current. This does not, however, mean that you can completely disregard torque. You still need to make sure you have enough torque to accelerate your robot from a standstill and change directions quickly.

I'm not expecting to change your design; you made an engineering decision and you should follow through that. I just want to set the record straight for other teams who may be looking to this thread for ideas.

My team, to my chagrin, has run mecanum drives 4 of the 5 years I was a member (not including this year). I was a driver for 2 of those 4 years. So I have a lot of experience with the benefits and drawbacks of mecanum drives. In general, I think there are very few cases (practically none) where a decent mecanum drive is better than a good WCD. Even in 2015, I still would have preferred that my team would have stuck with a WCD.

Ether 18-01-2017 10:22

Re: 2017 Drive Train
 
Quote:

Originally Posted by Ari423 (Post 1632877)
Mecanum wheels have a forward CoF of about 0.7, compared to around 1 for traction wheels. This means you can gear your robot faster and not draw as much current.

Would you please provide a more detailed explanation what you meant by this? i.e. How do you get from the first sentence to the second one?



Kevin Sevcik 18-01-2017 10:58

Re: 2017 Drive Train
 
Quote:

Originally Posted by Ether (Post 1632884)
Would you please provide a more detailed explanation what you meant by this? i.e. How do you get from the first sentence to the second one?

You're traction limited at a lower torque, so if you're trying to spin wheels at 40-50A (so as not to blow a breaker) you can have a higher gear ratio on a mecanum vs a 6WD.

Ari423 18-01-2017 11:06

Re: 2017 Drive Train
 
Quote:

Originally Posted by Ether (Post 1632884)
Would you please provide a more detailed explanation what you meant by this? i.e. How do you get from the first sentence to the second one?



The way I understand it, if you keep the gear ratio constant and lower the wheel's CoF, you lower the friction load placed on the motor (when pushing) and therefore lower the current the motor draws. If you are limiting your speed to keep the pushing current at or around 40A, gearing that would bring a traction robot to 40A should only bring a mecanum robot to around 28A. That means that you can gear the robot to go faster (i.e. draw more current for the same load) by about 140% to bring the current back to around 40A.

Ether 18-01-2017 11:53

Re: 2017 Drive Train
 
Quote:

Originally Posted by Kevin Sevcik (Post 1632907)
You're traction limited at a lower torque, so if you're trying to spin wheels at 40-50A (so as not to blow a breaker) you can have a higher gear ratio on a mecanum vs a 6WD.

That's much clearer.

Better to ask than to assume.



pfreivald 21-01-2017 18:57

Re: 2017 Drive Train
 
Quote:

Originally Posted by Ari423 (Post 1632877)
Maneuverability will be important for placing gears, but in order to take advantage of a mecanum drive's maneuverability, the driver needs a lot of practice with the robot in different situations.

I have never found this to be true. A mecanum drive controls *exactly* like a first-person shooter on any given game console--once told that, I have yet to have a student who can't drive it pretty well the moment they're handed the controls, and it doesn't take much time to get really good at it.

Quote:

Originally Posted by Ari423 (Post 1632877)
While mecanum drives have the ability to be more maneuverable and can "run away" from a pushing match, often drivers get caught up in pushing matches anyway.

This is the reason that I, coach of a team that's used mecanum four times and octocanum another four, agree that mecanum is definitely the wrong drivetrain for this year. My prediction is that monstrous defense (especially in the tournament) with criss-crossing robots and the restricted driving space around the airships is going to make most mecanum teams rue their choice.

Quote:

Originally Posted by Ari423 (Post 1632877)
Assuming you mean torque, the mechanical influence, not torc, a necklace worn by the ancient Gauls, you are correct to a degree. Mecanum wheels have a forward CoF of about 0.7, compared to around 1 for traction wheels. This means you can gear your robot faster and not draw as much current. This does not, however, mean that you can completely disregard torque. You still need to make sure you have enough torque to accelerate your robot from a standstill and change directions quickly.

Specifically, too many teams gear their drivetrain so fast that they lose too much acceleration on the low end, and ultimately traverse the field more slowly than if they'd have geared lower.

Quote:

Originally Posted by Ari423 (Post 1632877)
In general, I think there are very few cases (practically none) where a decent mecanum drive is better than a good WCD.

I agree, though I'm a huge proponent of octocanum. It's highly competitive, impresses sponsors, and is psychotically easier (and cheaper) to implement than swerve. I highly recommend any team looking to branch out into other drive systems to give octocanum an off-season try.

ZMarks 23-01-2017 13:54

Re: 2017 Drive Train
 
When people say "Tank Drive" I get all warm and fuzzy thinking back to my first FIRST experience.
FRC 971's 2004 Half Track


COTS Snowblower tracks, mounted at an angle, with the previous year robot's spare wheels

Robosparks2926 23-01-2017 14:03

Re: 2017 Drive Train
 
Are the CIM bag motor (217-3351) and the vex mini CIM (217-3371) considered CIM motors as described in rule R32?

jnicho15 23-01-2017 14:08

Re: 2017 Drive Train
 
Quote:

Originally Posted by Robosparks2926 (Post 1635166)
Are the CIM bag motor (217-3351) and the vex mini CIM (217-3371) considered CIM motors as described in rule R32?

Only (full size) CIMs are CIMs. Other things with CIM in the name or that look like CIMs are NOT CIMs. MiniCIMs are MiniCIMs and so on. Also, the numbers you list are explicitly mentioned next to their respective names with unlimited quantity.
https://frc-qa.firstinspires.org/manual/R32


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