6 wheels with only 2 powered wheels

[bhsrobotics1671]

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.

[Taylor]

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.

[DarkFlame145]

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.

[Kevin Sevcik]

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.

[GUI]

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

[roborat]

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.

[Tapoore]

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

[mathking]

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.

[bhsrobotics1671]

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.

[Justin M.]

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.

[JHSmentor]

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.

[Dominicano0519]

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