Best Drivetrain options
 

What do you think is the best drivetrain option for this year. It appears that 6wd drop center drives might have some trouble on the scoring platform because the center wheel will be the only wheel on the platform.

Re: Best Drivetrain options
 

6 or 8wd with no drop and omnis on the front/back. It doesn't change drive characteristics with different weight/center of mass and has no wobble. It can also easily go over the scoring area and with colsons and vex omnis should grip really nicely.

Re: Best Drivetrain options
 

Make sure you power all wheels with this setup.

Re: Best Drivetrain options
 

definately

Re: Best Drivetrain options
 

Slide/H-drive looks very promising. Without defense their is no worry about being pushed around. For a team with limited resources and expertise, this drive train provides the advantages of horizontal motion without the complexity of swerve or mecanum.

Re: Best Drivetrain options
 

i disagree with this the hump is 2 inches with a 16 degree slope having a 6 wheel drop center should have no problem making it over this in fact it would be beneficial because you would be able to pivot and spin while on top very easily,
a 6 wheel drop center is in the conversation for our team

Re: Best Drivetrain options
 

6in 4 wheel west coast. Make it like a mullet, that is to say business in the front party in the back, or in this case traction in the front omni wheels in the back.

Re: Best Drivetrain options
 

Any drive with strafing has a huge advantage this year. Stacking those totes precisely is hard. Like, really, really hard. I speak from experience there.

Re: Best Drivetrain options
 

I believe that's the direction my team will take. Our designs have in-frame tote manipulation, and having a four-wheel setup with omnis in front reduces the racking effects of not having a support between the front wheels that would be prevalent with four "tractionful" wheels.

Re: Best Drivetrain options
 

I don't believe Slide/ H-Drive will be as good as everyone thinks it is, many people are relying on the fact that the horizontal motion will be incredibly helpful. In reality I believe teams will use it as a way of adjusting their precision when needing to stack and line up for totes, which is completely valid until your vision is blocked or you don't have enough room to strafe. It would be better to build tolerance into your loading mechanisms rather than into your drivetrain where the tote being in the proper orientation is everything. Some teams will attempt to do both (Slide and Any-Orientation intake), we will just have to wait and see in practice which proves to be more effective.

Re: Best Drivetrain options
 

As a team we have done mecanum drives for the past 2 years in FTC but we do not see the value in a mecanum drive or a similar option. To be able to fully utilize a drive train like that you must have a lot of time practicing with it. We are not known for finishing robots quickly so we decided to go with a simple 6WD drive train that we get a lot of practice time on rather than spending a bunch of time on building a completely new drive train.

Re: Best Drivetrain options
 

A. Mecanum robots drive exactly like a first-person shooter. In my experience drivers need maybe ten minutes to acclimate to it.

B. Good call--finishing early and getting good practice time is more important than an "ideal" drive train (whatever that is.)

Re: Best Drivetrain options
 

I agree; strafing would be hugely beneficial.
We pretty much unanimously decided on swerve drive, which is a system we already have experience with.

Re: Best Drivetrain options
 

How is it less complex than mecanum?

Re: Best Drivetrain options
 

Take a look at the 2010 game Breakaway. The bumps in that game were much larger and a lot of team made it over just fine.

Here is one of our videos. (Skip to 0:48)

Re: Best Drivetrain options
 

All questions teams should ask before for selecting a drivetrain:

holonomic or tank drive ?

what size wheels , ground clearance ?

what is the desired speed and torque ?

single speed or shifting gearbox ?

Re: Best Drivetrain options
 

I'm guessing most people think mecanum is complex because thinking about how it moves can hurt your brain initially. And maybe they're worried about getting the wheel configuration wrong. In reality the most complicated thing is making sure all your wheels hit the ground most of the time, and that weight is relatively evenly distributed (side to side, at the least).

Worst problem I ever had was when someone pulled the PWMs on a mecanum robot we'd misplaced the code for. Working out which PWM was for which wheel was somewhat frustrating for about 30 minutes or so.

Re: Best Drivetrain options
 

Or both (octocanum). Or neither (H slide).

Re: Best Drivetrain options
 

Here's a procedure that might speed things up a bit.

Put the bot up on blocks.

Command pure forward (FWD), then strafeRight (STR), then rotateClockwise (RCW)... and for each command, record which direction each wheel is turning.

Unplug the PWMs and reinstall them per the attached chart.

Re: Best Drivetrain options
 

This will be the first in quite a few years that we do not use octocanum.

Nor are we using the drop-center WCD-ish drive we prototyped over the summer/fall.

Re: Best Drivetrain options
 

I went through the following decision process:

What technologies do we have a comfortable level of experience with?
Tank - yes
Mecanum - yes
Shifting - yes
Single speed -yes
Slide/H/octanum - no
Swerve - no

Advantages synergistic with proposed play style?
Mecanum - translation, non-rocking base of support
Tank - non-rocking base of support, (arguably) lower weight
Shifting - none, divided field means acceleration in short runs will be most important feature
Single speed - lightness, simplicity, low cost, with so many motors available we can add power until we like the performance

Since mecanum's classic disadvantages aren't a serious issue with recent upgrades from mecanum wheel makers and the lack of robot-robot defensive play (at least in my humble opinion) mecanum, with single-speed transmissions, won out for us. YRMV given different team experiences or preferences.

We already have a prototype mecanum drive slapped together to get the programmers and drivers practicing!

Re: Best Drivetrain options
 

My team will actually not be using our octocanum, and instead are running mecanum with a very high ground clearance (3+ inches).

Re: Best Drivetrain options
 

What about a 4wd with the rear wheels being traction wheels and the front ones being omnis

Re: Best Drivetrain options
 

4607 has used this in the past - we call it 'Peanut Drive' as that is what our 2013 drive was. I am sure there is another name for it...

Re: Best Drivetrain options
 

What were your experiences with it? Did it drive well?

Re: Best Drivetrain options
 

Haven't used one myself, but I've seen them in action. They tend to pivot around the traction wheels, rather than the center of the robot as you might expect if you're used to 6WD drop-center, but otherwise they're generally smooth and nimble.

Re: Best Drivetrain options
 

This works well, but as Eric said get used to driving it like a shopping cart. My team did this in 07 and 08 and you're guaranteed not to have a problem turning.

Re: Best Drivetrain options
 

We didn't have any trouble turning, but our belts did tend to slip a lot more than with other drives we've ran. I want to say that has something to do with the non central center of turn. Just a guess though. Otherwise great drivetrain that a driver can good with quickly. I would be suprised if 4607 didn't run it again this year. Although slide is appealing too for reasons already covered in this thread.

Re: Best Drivetrain options
 

We did this drive for 2013. It drove smooth and turned really well. It does have a tendacy to overshoot the turn more though as you have more rotational inertia and very little scrub. We have been considering it again for this year.

Here's a video in action:
http://m.youtube.com/watch?v=QD04NZHPLmc

Re: Best Drivetrain options
 

We have been driving an off season 6WD square Versachassis with 2 speed gearbox, 4 inches wheel with drop center. Strapped a bunch of totes in various position to the chassis with some clamped on metal bar to see how it drives. The drive team did not like the way how a 6 tote stack lean back and forth. 3 tote stack on the chassis not a big deal.
We remove the center wheel and the turning wasn't too bad and obviously no more leaning back and forth.
We also drove the 4 wheel configuration over the scoring area, bottom out and gouge the brand new built scoring area.
6" traction and omni wheel is on it's way. We will try all omni wheel or 2 omni and 2 traction. We are leaning towards 2 front traction and 2 rear omni but will have to see.
Also one really need to find a way to grab all the totes stacked on your drive train if you wanna move around quickly. We have some really "entertaining" video of "flying totes" when our driver try to turn or accelerate /decelerate too fast. Can't defies the law of physics.

Re: Best Drivetrain options
 

IIRC, 1625 Winnovation used this system in 2014 (and I think in previous year(s) as well). It was one of my favorite robots; the spins were amazing, yet they still had all the versatility to be able to play effective defense as well as escape it.

Here's a video of them on Einstein. If you can't see the numbers, they are the primary scorer on the red alliance. https://www.youtube.com/watch?v=xWPjs8zn9FI

Re: Best Drivetrain options
 

We have reconfigured a couple off season projects to the needs of this game for testing, and here's what we know:

• mecanum 6" does really well over the bump, surprisingly so.
• 6" Colson in front, omni in back does great too. we think it drives a bit like street racing, so its currently "drift drive" for us, though "mullet drive" is gaining.
• we cant decide between the two yet, so we are building both and running them through drive practice. we will let the drivers and coach decide.

I'm sure swerve is awesome. Next year, we will make that our off-season project. We have no experience with "H" style slide, so it's off the table too.

Hope that info is helpful.

Re: Best Drivetrain options
 

H drive isn't holonomic? Sure, it's anisotropic, but it can go forward-reverse, left-right, spin, and any combination I can think of.

Re: Best Drivetrain options
 

Not if the front and rear wheels are chained together on each side.

Re: Best Drivetrain options
 

How about the reverse with omnis in the rear and traction wheels in the front? Is there any advantage for one over the other?

We converted an old kitbot over the weekend to this configuration. It seemed to pivot about the front inside wheel. We had several team members drive it and they didn't appear to have any issues controlling it.

Re: Best Drivetrain options
 

Going to have to go ahead and say strafing is a must but if you can't strafe you should at least make a chariot design with casters...

Re: Best Drivetrain options
 

"Must"s are exceedingly rare in FRC competitions.

Re: Best Drivetrain options
 

Yeah I should have phrased myself better. Depending upon level of your team and comfort if you have the ability to do omni-directional movement then it is very valuable. Not to say that the arguments against omni-directional are non existent.

Re: Best Drivetrain options
 

How do you define holonomic? I was going off the wikipedia page, admittedly far from authoritative, but it reads:
I will add that I never liked this definition - it does not require that those degrees of freedom all have at least orthogonal components. It also considers mecanum and killough not to be holonomic until you add the mechanism or software library to map three inputs to four outputs.