6 wheels with only 2 powered wheels
 

we are thinking about doing a 6 wheel design with only the two centered wheels being powered. our outter 4 wheels would be the KOP FIRST wheels, and the 2 center wheels would be the 8" performance wheels from andymark. In our design we have made it so that if we decide to power 4/6 or even 6/6 wheels that would be possible. I just wanted to know if any teams have tried anything like this before.

Re: 6 wheels with only 2 powered wheels
 

Are you mounting the KOP wheels lower than the treads? You'd end up with a vertical offset of 1.25" between the middle and outer wheels, since the KOP wheels are 6". You'd get a lot of rock with that design.
Also, consider that all the weight supported by a non-driven wheel is pretty much wasted. It's analogous to driving a rear-wheel-drive vehicle in the snow. Without sandbags in the back, it's hard to gain traction.

Re: 6 wheels with only 2 powered wheels
 

you are going to be sacrificing power/torqu with only 2 drive wheels, but it should move well. I like the idea of being able to change your drive though.

Re: 6 wheels with only 2 powered wheels
 

It's an interesting concept, but I think you should consider your drivers before you follow through. While the 2/6 and 6/6 configurations would probably handle the same, the 4/6 is going to have quite different handling characteristics than the other two. If your driver has been training on the 2/6 and she has to switch to the 4/6 config, it's going to throw her off for a while until it becomes familiar. Just something to think about.

Re: 6 wheels with only 2 powered wheels
 

Why 8" and 6"? What prevents you from using all 6" or all 8"?

Re: 6 wheels with only 2 powered wheels
 

We are using 6" KOP on the middle with 6" omni's on the corners. All six will be powered. It turns great and has a lot of pull.

Re: 6 wheels with only 2 powered wheels
 

1519 has successfully used center wheel drive in the past. We used the old 12" pneumatic Skyways in the center with "omnis" at both ends - we put 1" flexible pool tubing over the 8"skyways to give them some lateral slip.

Some of the advantages of this drivetrain are:

- very simple to build
- EXTREMELY reliable (our 2006 bot went through 1 regional, nationals, and 5 offseason comps and all we had to do was check the tire pressure
- maneuverable

Of course, you have to consider some of the cons too:

- not as much traction as a drivetrain with more powered wheels (although it is still quite respectable)
- cannot handle a multilevel playing field

You can check out some videos of it at our site

Re: 6 wheels with only 2 powered wheels
 

We used a center aligned drive in Triple Play, and it worked very well for us in that game. (We went 7-2 with it at the championships and were the leading scorer for our side in all but one match.) It does not do well in a pushing match, but we found that this was more than compensated for in that game by the ability to just go around other robots. It was able to spin with a diameter only about 2 inches greater than the corner to corner diamter of the robot. We had sliders and whole thing was only about 1.5 cm off the ground. I wouldn't recommend this as the competition floors are not always completely even.

The one word of caution is that it takes a while to learn to drive well. Using sensors and software to help smooth out the ride was very helpful. As long as you get it done with enough time to practice and calibrate, it can be a good idea.

Sidenote: We are looking at this type of drive this year, as a backup in case our mecanum drive (first time our team has tried it) doesn't work like we hope it will. This also gives twice as many kids a chance to work on a drive train.

Re: 6 wheels with only 2 powered wheels
 

wow! thank you all for your quick feedback!
i like all the things you guys have pointed out, they have helped me and the team a lot in deciding what we are going to do.

one of the main reasons we went with the 8" wheel in the center is because we can get a little bit more speed out of it. This wheel will be raised 9/10", therefore making it 1/10" lower than the other 6" wheels.

I also forgot to mention that we will be using the andymark super shifter transmissions to power the two center wheels.

Re: 6 wheels with only 2 powered wheels
 

We're doing something similar this year:



8" wheels in the center, 6" omnis on the outside. The omnis are dropped down so that the chassis is on a 1/4" of rocker.

All wheels will be powered, even though only 4 wheels will be on the ground all the time. Also, we're using AM Toughboxes instead of the BaneBots transmissions.

Re: 6 wheels with only 2 powered wheels
 

One thing that I can see from a flexibility standpoint - if the center wheels are direct driven on 8" then that would work fine as long as you are only driving those 2 wheels. If you then attempt to drive 2 or 4 of the other wheels at 6" diameter (in addition to the center wheels), then you will need to be careful with your sprocket ratios to get the speeds to match (the smaller wheels will need to rotate faster to cover the same distance). Not that it's a big deal but something that you need to be aware of.

Re: 6 wheels with only 2 powered wheels
 

why dont you just adjust the height of the wheels by lets say half an inch or maybe even a quarter and using all 8" or maybe even all 6"

that may you wouldn't sway that much

but im not all too crazy about the whole six wheel drive in this years game

ill tell you from personal experience those things turn on a dime and go straight but its not gonna be the fastest way to get around the track

Re: 6 wheels with only 2 powered wheels
 

It looks like you guys are well along the way to a great design.

I think you should try this out on a test bed first... make up a plywood frame and put everything on.

I think you may find the use of the AM KOP wheels in the corners will limit your ability to turn somewhat.

You will find that this is exacerbated when you load your robot towards one side or the other .... say if you have an arm or lift extending out which changes your center of gravity.

In an ideal world... the four outside wheels would have little weight on them and then your turning would be easy.

Since FIRST is most definitely NOT an ideal world... when you put weight on them and try to make a turn they will stick to the carpet when you try to make them move sideways while turning... they stick more when there is more of the robot weight on them.

This is precisely why many of the designs above are using omniwheels in the corners.

I would suggest that if you have a lift or an arm on one side of the robot you consider at least putting omni wheels on that side.

Its a great start... a six wheel robot with the center wheels pivoting can be very powerful and also very agile if you make the right decisions on robot weight loading.

Also remember that if you are going to carry the ball... you may also have additional problems if it is not carried directly OVER the axis of rotation which is midway between the center wheels. This will also lever additional weight onto those outside wheels.

Good luck on your robot!!!

R

Re: 6 wheels with only 2 powered wheels
 

thank you again for all of your guys' help!
we are finishing up some CAD models today, maybe i can make a teaser or two for you guys!

Re: 6 wheels with only 2 powered wheels
 

If you would like to try making a prototype of this drive base you could make some cheap "omnis" like the ones we used on this prototype base. We just got cut a slit down a piece of some blue pool tubing (I think it's used as electrical conduit). Then, we just ziptied it around one of the KOP wheels. They aren't pretty, but we used them through at least 10 tournaments with zero problems. Plus they were way cheaper then buying real omnis and worked almost as well for our application.

http://img155.imageshack.us/my.php?image=wheelshq2.jpg