4 wheels v. 6 Wheels

[Joshua Sicz]

My team has done 6 wheels the past 4 years of the frc season. Last year we used 4 6'' treaded metal wheels with 2 6'' dual omni wheels. This year we are debating to only use 4 6'' treaded wheels instead of 6. We need more opinions on what are the benefits of each one are. Teams that have experience in both would help. Thanks!

[Ether]

Originally Posted by Joshua Sicz

We need more onions...

Portabella or Vidalia?

[Joshua Sicz]

Originally Posted by Ether

Portabella or Vidalia?

Haha funny. If anything Portabella.

[gpetilli]

Originally Posted by Ether

Portabella or Vidalia?

Mushroom OR Onion? I prefer AND.

http://www.tasteofhome.com/recipes/p...oom-onion-soup

not often that I get to poke at Ether.....

[CalTran]

Originally Posted by Joshua Sicz

My team has done 6 wheels the past 4 years of the frc season. Last year we used 4 6'' treaded metal wheels with 2 6'' dual omni wheels. This year we are debating to only use 4 6'' treaded wheels instead of 6. We need more onions on what are the benefits of each one are. Teams that have experience in both would help. Thanks!

Spelling mistakes aside, a little more information would be helpful.

Last year we used 4 6'' treaded metal wheels with 2 6'' dual omni wheels.

I assume your robot was set up something like:
t------t
|........|
o------o where t is a traction wheel and o is an omni?
|........|
t------t


What was the wheel setup?

This year we are debating to only use 4 6'' treaded wheels instead of 6.

Is that 4 6" wheels with tread instead of 6 identical wheels or instead of the 4 tread/ 2 omni configuration you had last year?

[Marc S.]

As far as number of wheels, 6 has been a very reliable number for many teams. The difference is that 6 allows the robot to turn a lot easier than 4. Just remember to add a .125" to .187" drop on the center wheel so that only 4 wheels are on the ground at once.

Many teams have also run 8 wheels, with the center 4 wheels dropped. In both scenarios all the wheels are traction.

[Joshua Sicz]

Originally Posted by Marc S.

As far as number of wheels, 6 has been a very reliable number for many teams. The difference is that 6 allows the robot to turn a lot easier than 4. Just remember to add a .125" to .187" drop on the center wheel so that only 4 wheels are on the ground at once.

Many teams have also run 8 wheels, with the center 4 wheels dropped. In both scenarios all the wheels are traction.

When we had all 6 wheels treaded and we did lower the center an 8th. So make the robot only on 4 wheels at one time.

[Mongai]

Originally Posted by Joshua Sicz

When we had all 6 wheels treaded and we did lower the center an 8th. So make the robot only on 4 wheels at one time.

This is a popular design choice for robots. Last year for the 2013 game, Team 935 had a wheel drop. I want to say the final drop height was less than 1/8" (I'll check when I go over today and subsequently edit this post).

I remember a lot of problems when our robot came to a sudden stop while testing with a 1/8" drop. It would rock to rest on the two front or back wheels, depending on which direction the robot was going when it stopped. This would cause the Frisbee launch angle to lower -- or rise -- causing us to incorporate an angle of launch error to our shooting calculations. Just something you should pay attention to. Not having a drop on a six wheel is counterproductive to its design intent however. Again, I'll update when I run in today.

[Ether]

Originally Posted by CalTran

I assume your robot was set up something like:
t------t
|........|
o------o where t is a traction wheel and o is an omni?
|........|
t------t

Why did you assume that?

[CalTran]

Originally Posted by Ether

Why did you assume that?

I have no idea why that made sense to me in my head. Changed my first post to just ask what the setup was.

[pmangels17]

Are you driving in a wide configuration or a narrow configuration? The wheel base distance bakes a huge difference in whether you can turn well with four wheels.

[Joshua Sicz]

Originally Posted by CalTran

Spelling mistakes aside, a little more information would be helpful.

Is that 4 6" wheels with tread instead of 6 identical wheels or instead of the 4 tread/ 2 omni configuration you had last year?

We are switching from 6 identical wheels, which is what we used last year, to 4 6" wheels with tread.

[Madison]

Originally Posted by Joshua Sicz

My team has done 6 wheels the past 4 years of the frc season. Last year we used 4 6'' treaded metal wheels with 2 6'' dual omni wheels. This year we are debating to only use 4 6'' treaded wheels instead of 6. We need more onions on what are the benefits of each one are. Teams that have experience in both would help. Thanks!

I'm presuming that your setup last year looked like this:

T - T - O
|--------|
T - T - O

If you'd dropped the center wheel sufficiently, the omniwheel did nothing for you. If you didn't drop the center wheel, the omniwheel made it possible for your robot to turn.

If you were to instead build a drive that looked like this:

T - - - T
|-------|
T - - - T

...you'll likely find that you're unable to turn effectively.

You should not make decisions based upon opinion. You should strive to understand the science that led to the prevalence of 6WD robots in FRC and extrapolate the answers to your questions from that.

In your case -- the important factors to consider are the wheelbase, the available torque at the wheels and the coefficient of friction between your wheels and the carpet. With that information, you can calculate whether or not the drive you're contemplating will work.

[Joshua Sicz]

Originally Posted by Madison

You should not make decisions based upon opinion. You should strive to understand the science that led to the prevalence of 6WD robots in FRC and extrapolate the answers to your questions from that.

Sorry for me putting opinion, but yes our team makes every decision based off how it will benefit us and what we are trying to achieve. We always go for making a robot that can push other robots out of the way if we need.

And also we are used to build 6 WD robots, and that's what we know how to do pretty well for the most part.

[Jeffy]

Originally Posted by Joshua Sicz

And also we are used to build 6 WD robots, and that's what we know how to do pretty well for the most part.

Do this then. The less time you spend on a drivetrain, the more time you spend on manipulators.