Best Drivetrain

[=Martin=Taylor=]

The Following is Fact:
The purpose of the drive train is to get the manipulator in position to score as many points as possible in the minimum amount of time.

That’s all you need to know. The best drive train is the one that accomplishes this task the best. Period.

It doesn't mater how many wheels, chains, motors, or gears you use. If 2WD will get the job done, use 2WD and use the time/money/resources saved to work on the manipulator.


The Following is my Opinion:

Historically, 6WD with the center wheel lowered has been the fastest system.

If you need to climb a ramp, 6WD is necessary to prevent bottoming-out.

But if the playing field is flat, why bother with 6WD at all? I mean, two of the wheels aren't even touching the ground. So why bother? If the playing field is flat, save yourself some weight and only use 4WD with the wheel axels spaced 12" apart and casters on the front.

Some will argue that swerve, mechanum, omni, and tank treads offer advantages over 6/4WD. But when you consider how many teams consistently win regionals and championships without these systems it becomes hard to see what the real benefit is.

As for the 25 vs 35 argument...

2006 Our team used #25 in 2006 with the kit frame and it was a COLLOSAL disaster. We couldn't keep the chains in line, or tensioned and they kept falling off.

2007 Deciding we would never use tensioners or #25 chains again we switched to #35 with movable axels for tensioning. This dive train was very robust, but also very heavy.

2008 Deciding that maybe we had been too rough on #25 we switched back, implementing the same movable-axel tensioning system we used in 2007. Worked great. Much lighter and we never lost a chain.

So it really comes down to tensioning. #25 needs to be really tight, so you need a good tensioning system. #35 can be much looser. Some teams like 766 and 330 have gotten away without using any tensioners.

[Lil' Lavery]

Originally Posted by Hachiban VIII

The Following is Fact:
The purpose of the drive train is to get the manipulator in position to score as many points as possible in the minimum amount of time.

That’s all you need to know. The best drive train is the one that accomplishes this task the best. Period.

It doesn't mater how many wheels, chains, motors, or gears you use. If 2WD will get the job done, use 2WD and use the time/money/resources saved to work on the manipulator.

What about defensive robots?

[=Martin=Taylor=]

Originally Posted by Lil' Lavery

What about defensive robots?

You can win playing defense. But you can't win without playing offense.

Defensive robots depend on offensive robots to win. Building a robot that can't score, or even one that isn't designed with scoring as the primary strategy, is risky.

[JVN]

Originally Posted by Hachiban VIII

But if the playing field is flat, why bother with 6WD at all? I mean, two of the wheels aren't even touching the ground. So why bother? If the playing field is flat, save yourself some weight and only use 4WD with the wheel axels spaced 12" apart and casters on the front.

Two Words:
Normal Force.

If you want to build a robot capable of pushing, you want every ounce of weight sitting on top of the highest traction drive wheels you can find. If you have weight sitting on non-driven wheels (like casters) you are reducing the amount of normal force available.

In some games or for some strategies pushing is not an important consideration. In these cases a 6WD may not be important.

Brief Aside:
In my opinion drivetrain design is very formulaic. "If you want to do X then you need to do Y." It is all about the functionality requirements your team has, and the design trade-offs you are willing to make (these trade-offs may involve things like weight & team resources, or things like pushing power & top speed.)

I should write a paper on this sort of thing.

-John