Best Drivetrain options

[kitare102]

Originally Posted by Munchskull

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.

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.

[c.shu]

Originally Posted by JorgeReyes

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.

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)

[lynca]

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 ?

[Ether]

Originally Posted by lynca

holonomic or tank drive ?

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

[pfreivald]

Originally Posted by Ether

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

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.

[JamesCH95]

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!

[Electronica1]

Originally Posted by Ether

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

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

[GeeTwo]

Originally Posted by Ether

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

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.

[Ether]

Originally Posted by GeeTwo

H drive isn't holonomic?

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

[GeeTwo]

Originally Posted by Ether

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

How do you define holonomic? I was going off the wikipedia page, admittedly far from authoritative, but it reads:

A robot is holonomic if the controllable degrees of freedom are equal to the total degrees of freedom.

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.

[JorgeReyes]

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

[Chief Hedgehog]

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...

Originally Posted by JorgeReyes

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

[JorgeReyes]

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

[EricH]

Originally Posted by JorgeReyes

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

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.

[Donut]

Originally Posted by JorgeReyes

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

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.