Best Drivetrain options

[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 ?

[Kevin Sevcik]

Originally Posted by Lil' Lavery

How is it less complex than mecanum?

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.

[Ether]

Originally Posted by lynca

holonomic or tank drive ?

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

[Ether]

Originally Posted by Kevin Sevcik

Working out which PWM was for which wheel was somewhat frustrating for about 30 minutes or so.

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.

[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).

[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.

[Ginger Power]

Originally Posted by Donut

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.

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.

[jeremylee]

Originally Posted by JorgeReyes

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

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

[lamk]

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.