What teams have desgined a 6 wheel drive system?

[Rich Kressly]

Originally Posted by Pit Bull 1126

wow, i wasn't expecting all this information!

thanks, is there any pictures of thier drive systems of any of the drive systems?

or possibly inventor files.. thanks!

I'm not sure if Team 25 has Inventor files, but they graciously shared their 2003 Evil Machine design with Team 103 who used it on their 2004 bot Monkey Business. Team 103 used only four wheels, but adding the additional two is no problem at all (In fact 103 had two more wheels on just two weeks before shipping). The Team 103 version of the Team 25 drive system is well documented in the 2004 Inventor Website found here:
http://inventor.cybersonics.org

[Salik Syed]

6 wheels are awesome.... i would use them on ANY robot even 6" wheels and definitely 6 wheels are necessary for anything over 8" / pneumatic otherwise turning sucks.... the main thing is that the center wheel MUST be lower than the other two wheels otherwise its pretty pointless.... i guess you get more traction (and less turning) but with the center wheel our robot w/ 12" pneumatic tires, turned about 20 times better than our 2003 bot which had 4 wheels and 8" rubber tires

[Andrew]

Team 356 has used a six wheeled drive system (with suspension) in 2003 and in 2004. In 2003 we had chips and drills driving separate wheels (with the front wheels being chain driven from the center wheels powered by the drills). In 2004, all six wheels were independently driven (chips, drills, fps).

In 2003, the front suspension helped us keep all six wheels on the ramp and top of the platform when we were attempting to take the hill.

In 2004, the suspension helped us climb onto the two platforms. We generally had 4-6 wheels in contact with a surface at all times.

2003, the Velvet Fog (http://www.chiefdelphi.com/forums/sh...light=team+356)
(http://www.chiefdelphi.com/forums/sh...threadid=17799)

2004, Wolfgang (http://www.chiefdelphi.com/forums/sh...ad.php?t=25833)

[DougHogg]

Team 980 learned about the 6-wheel drive system (with middle wheels 3/16" lower) from Team 254 and Team 60. They in turn credited Team 25 with the idea.

This idea was a breakthrough for us. Previously we had to keep gearing down our robot so that we could turn without blowing fuses (especially turning in place). This last season, using 6 wheels, our robot could spin like a top. We used programming to implement a reduced turning speed (with a button to over ride the programming if we had to turn really fast). We used gyros during autonomous, but not when our drivers took over.

In conjunction with Team 716's two-motor gear boxes (non shifting design
using drill and black motors from the Chief Delphi White Papers), our robot
was fast and maneuverable this year.

As it turned out, we also had some luck that the six wheel design
contributed to. Originally we hadn't planned on going up onto the platform
to hang, but then it turned out to be really hard to grab the bar from the
floor. One of our students discovered that we could do a wheelie (by backing up and then quickly going forward) and climb onto the platform which made it possible for us to hang quickly.

We had wanted to direct drive the middle wheels from the gear box, but we
couldn't fit the gearboxes (with drill motors, transmissions and gear boxes) side by side, so we wound up driving all six wheels with chains. It turned out to be very reliable using 1/4" chain. Basically the drill/black motor combination drove all three wheels on each side, so we got full traction although only four wheels were on the ground at any one time.

Sorry I don't have any drive train pictures, but you can see our robot on
our web site at team980.com.

Thank you Teams 254, 60, 716 and 25 (and many other teams who have
helped us) for sharing your ideas. They were a big help!!!

[JVN]

Originally Posted by DougHogg

Team 980 learned about the 6-wheel drive system (with middle wheels 3/16" lower)

This last season, using 6 wheels, our robot could spin like a top.

Doug has gotten to the heart of the matter here.

The 6-wheel drive with the lowered middle wheel GREATLY increases the turning of the robot. I know MANY teams who implemented such a system.

My main question is...
What distance do you drop your middle wheel?

I spoke to Steve from 254 and he told me they use 3/16" (as Doug mentioned above). I spoke to others who said they use a full 1/2".

What does everyone else use?

Lately, in all my pre-season design efforts I've used 3/16. I don't really have any good reason for it; other than Steve said it works for them. (And I LOVE their robot in action...)

Anyone?

John

[Alex Cormier]

Originally Posted by JVN

Doug has gotten to the heart of the matter here.

The 6-wheel drive with the lowered middle wheel GREATLY increases the turning of the robot. I know MANY teams who implemented such a system.

My main question is...
What distance do you drop your middle wheel?

I spoke to Steve from 254 and he told me they use 3/16" (as Doug mentioned above). I spoke to others who said they use a full 1/2".

What does everyone else use?

Lately, in all my pre-season design efforts I've used 3/16. I don't really have any good reason for it; other than Steve said it works for them. (And I LOVE their robot in action...)

Anyone?

John

i've also heard 1/8"

[Wayne C.]

Originally Posted by Rich Kressly

I'm not sure if Team 25 has Inventor files, but they graciously shared their 2003 Evil Machine design with Team 103 who used it on their 2004 bot Monkey Business. Team 103 used only four wheels, but adding the additional two is no problem at all (In fact 103 had two more wheels on just two weeks before shipping). The Team 103 version of the Team 25 drive system is well documented in the 2004 Inventor Website found here:
http://inventor.cybersonics.org

Here are some pics of the drive system of the team 25 recent six wheeled modular monsters. The whole robot pic is the 2002 robot Silver Scorpion- that made it to the final 4 in Nats. The modular drive pic is from Evil Machine 1- the 2003 finalist. As we've learned we have made the drives modular so they can be detached as a unit and replaced quickly. The kids strip them down and reassemble them like a soldier does with a rifle. The drives have never failed- never. They are now obsolete and the next generation will be a little faster and a little more powerful, at least according to prototypes. We have some new ideas up our sleeves. ; )
WC

[Wayne C.]

Originally Posted by JVN

Doug has gotten to the heart of the matter here.

The 6-wheel drive with the lowered middle wheel GREATLY increases the turning of the robot. I know MANY teams who implemented such a system.

My main question is...
What distance do you drop your middle wheel?

I spoke to Steve from 254 and he told me they use 3/16" (as Doug mentioned above). I spoke to others who said they use a full 1/2".

What does everyone else use?

Lately, in all my pre-season design efforts I've used 3/16. I don't really have any good reason for it; other than Steve said it works for them. (And I LOVE their robot in action...)

Anyone?

John

John-
Although it seems to make sense and would make design interesting we have never moved any of the center wheels from our machines out of line from the rest. We want the deep grab traction for the motors and pushing power. And I think any who play us will agree that the machines are speedy and maneuverable. We use two joystick tank drive on the machines and they can spin in place with no problem at all.

Perhaps the answer to this is the fact that we have such wide wheels (custom made from Skyway wheels) and a gearbox with great power. We are probably horsing the machine around so much when we turn that the coefficient of friction on the center wheel is negligible. We usually give the machines the "Big Mike" test- if they can shove him away they are strong enough. If we lowered the center wheel we negate the traction we are looking for back to 4 wheel drive.

WC

[RogerR]

Originally Posted by JVN

My main question is...
What distance do you drop your middle wheel?

we dropped our middle wheels just .1", and it worked fine for us.

[Madison]

I've always imagined and wanted the opportunity to design and build, for anyone who's interesested (hint, hint, nudge, nudge), a six-wheel drivetrain that keeps them all at a single height, but uses omniwheels on the four corners. It seems like that's a simple solution for enhancing traction in the robot's direction of travel while minimizing additional friction in turning.

I'd be surprised if another team has not yet tried this method, though nothing springs to mind.

[Paul Copioli]

We lowered ours 3mm (close to 1/8") and we could spin like a top.

To the point of traction: if all the motors are geared together per side and then run to the wheels, the lowered center wheel does not reduce your tractive effort (pushing ability). A six wheel drive concept is like using powered castors. The design is such that the center wheels take most of the load and the outside wheels balance load when the CG is moved on either side of center. If the drive is designed correctly, you pushing ability is not reduced as long as all the items touching the floor are powered.

[JVN]

Originally Posted by M. Krass

I've always imagined and wanted the opportunity to design and build, for anyone who's interesested (hint, hint, nudge, nudge), a six-wheel drivetrain that keeps them all at a single height, but uses omniwheels on the four corners. It seems like that's a simple solution for enhancing traction in the robot's direction of travel while minimizing additional friction in turning.

I'd be surprised if another team has not yet tried this method, though nothing springs to mind.

Team 40 used that method this year.
I seem to remember them turning pretty well.

Now for some editorializing:
In order to push competitively in this competition, one needs as much tractive force available as possible.

Tractive Force = Wheel Coeff. x Normal Force

Normal Force is limited to the weight of the robot (and whatever the robot is able to pick up. In order to maximize Tractive Force, we want our wheels/treads/whatever to have the MAXIMUM coefficient of friction possible. (Many teams use high traction belting, or pneumatic tires).

Here is the kicker -- I have NEVER seen an omni wheel that can compete with straight up, high traction wheels when it comes to coefficient of friction. So... if you use omni-wheels on your robot, you are "wasting" normal force. You have weight sitting on "low" traction wheels, and have decreased your tractive force.

The GREAT thing about the 6WD configuration, is that it allows the robot to turn like crazy, but ALL the robot's normal force is sitting on driven, high traction wheels. It's the best of both worlds! Turning + Pushing!

Note: Casters pose the same problem. If you have weight resting on "non-driven wheels" you're shooting yourself in the foot again, when it comes to pushing matches.

For more information about WHY the 6WD, lowered middle wheel configuration turns better... check out Chris Hibner's turning whitepaper. He's got GOLD in there: http://www.chiefdelphi.com/forums/pa...le&paperid=222

It's physics,
John

[JVN]

Originally Posted by Wayne C.

John-
Although it seems to make sense and would make design interesting we have never moved any of the center wheels from our machines out of line from the rest. We want the deep grab traction for the motors and pushing power. And I think any who play us will agree that the machines are speedy and maneuverable. We use two joystick tank drive on the machines and they can spin in place with no problem at all.

Perhaps the answer to this is the fact that we have such wide wheels (custom made from Skyway wheels) and a gearbox with great power. We are probably horsing the machine around so much when we turn that the coefficient of friction on the center wheel is negligible. We usually give the machines the "Big Mike" test- if they can shove him away they are strong enough. If we lowered the center wheel we negate the traction we are looking for back to 4 wheel drive.

WC

Wayne,
First off, I'd like to say I'm a huge fan of your team's machines. You guys are great.

The amazing turning ability of your machines is DEFINITELY linked to your "wide" wheel configuration. It's all physics (you can see it in Chris Hibner's whitepaper, I linked in my previous post).

I disagree with you on one point:
I would argue that your 6WD configuration isn't helping you get more traction. For the most part, surface area isn't a factor in tractive force. (F = mu x N) <-- No "A"

For our applications (rubber on carpet) these are NOT perfect surfaces, and cannot be expressed perfectly with the above equation. They are intertwining meshes. This would help explain getting "more" traction using 6WD.

However, I would argue that you're not getting very much more.
Is there any chance you'd be willing to help with a little experiment?
It is for the mutual sharing of knowledge to benefit the entire communitty.

Wayne, do a straight up pull test with one of your robots. Record some values for it's maximum linear force. THEN, have one of your kids remove the 2 middle wheels from your drive modules (put them on top of the robot somewhere, so the normal force doesn't change). Now try the pull test again.

I hypothesize that your second test will be within 10 lbs of the first test (if not closer).

If you participate in this little experiment, I know I'd be (along with many others) very interested in the results.

Thanks,
John

PS - Your gearbox isn't any more over-powered than the rest of ours! 2 Drills + 2 Chips = 1552W = 2.08 Hp. How you guys manage to gear it so fast, yet still push so hard is beyond me. Up here on 229, we're genuinely convinced you guys are defying physics somehow. Are you sure you don't have 2 extra drills tucked inside that thing somewhere?

[Cory]

Originally Posted by JVN

PS - Your gearbox isn't any more over-powered than the rest of ours! 2 Drills + 2 Chips = 1552W = 2.08 Hp. How you guys manage to gear it so fast, yet still push so hard is beyond me. Up here on 229, we're genuinely convinced you guys are defying physics somehow. Are you sure you don't have 2 extra drills tucked inside that thing somewhere?

Running into something at 15-18 fps probably helps explain that to some degree

[JVN]

Originally Posted by Cory

Running into something at 15-18 fps probably helps explain that to some degree

Momentum is one explanation but...
I watched them (From a standstill) win pushing matches against teams they shouldn't have! It was incredible...