6wd tank with 2 omnis?

[nuclearnerd]

Does anyone have experience with 6wd tank style drive bases, using 2 omnis on the front (and 4 tractions on the other)? I'm thinking this could be a good configuration for defense heavy games. The benefit would be almost all of the traction of a conventiinal 6wd (especially in fwd), but with faster turning and no rocking from a drop center. The downside is unsymmetrical handling going forwards and reverse, and reduced traction when in reverse.

I'm tempted to build a test base in the pre-season, but would love to hear other's experience first.

[EmileH]

In 2014, 1625 used a 4wd with 2 omnis/2 traction wheels allowing them to spin quickly and fly around the field yet still push effectively.

[nuclearnerd]

We used the 2 omni, 2 traction setup this year (as did *many* others), but we didn't have to think too hard about pushing power in Recycle Rush. Thanks for that match video though - it seems like 1625 had no problem keeping up with a similar configuration in 2014.

[The other Gabe]

I haven't ever heard of a team doing this, although from experience, there is not much shake from a drop center wheel on tank drive (my team has only ever not done tank once). if that really worries you, just use 5 wheels per side, like 2046 did in 2012

[timytamy]

Originally Posted by The other Gabe

use 5 wheels per side, like 2046 did in 2012

Do you have some pics/more info? I'm curious.

[kitare102]

3042 used a 6w WCD this year, and were having enough problems with brownouts due to our long wheelbase that we decided to switch the two back wheels to omnis. This is obviously not the same as your suggestion, as going forward we didn't get the traction of 4 standard wheels, but I can speak to the stability and maneuverability of the 2 omni, 4 traction wheel concept as a whole. definitely helps turning ability when dealing with tight corners and cramped conditions, so I would be confident in this setup's viability for getting around defenders. That being said, nothing provides better evidence that real-world testing, so I might suggest trying our some omnis on an old 6w drivetrain if possible.

Attached is a good view of our 2015 drivetrain to show what our setup looks like.

[Everett33]

862 has done a 4x traction-wheel, 2x omni-wheel drive with no drop in 2012 and 2013. From what I have seen on the field and heard from the co-driver of those bots, it has worked out well for them.

[Knufire]

Originally Posted by Everett33

862 has done a 4x traction-wheel, 2x omni-wheel drive with no drop in 2012 and 2013. From what I have seen on the field and heard from the co-driver of those bots, it has worked out well for them.

Wide or long? 5188 did this with a 38" long frame. We the omni pair on the front and the back and both had trouble turning. We ended up going for center traction (Colsons) and 4 outside omnis.

Originally Posted by nuclearnerd

We used the 2 omni, 2 traction setup this year (as did *many* others), but we didn't have to think too hard about pushing power in Recycle Rush. Thanks for that match video though - it seems like 1625 had no problem keeping up with a similar configuration in 2014.

Make sure you get a lot of drive practice with this setup if you want to use it in a higher speed game with defense. If driven well, it is very useful for getting around defenders. However, with the few minutes of drive time I had on 469's 2012 robot (front ball casters, back pneumatic wheels), turning to a specific angle becomes difficult, you need to compensate for the robots momentum by applying a bit of power in the opposite direction to spin to a specific angle.

[The other Gabe]

Originally Posted by timytamy

Do you have some pics/more info? I'm curious.

ugh I dont think I have any pictures of it at this point :/ been too long. there's some old video here: http://www.thebluealliance.com/team/2046/2012 and you might be able to see it up close there.

As to why we did it; Story time!

So, way back in 2012, we decided one of the key things was going to be field mobility: getting over the bridge and bump easily. however, we also wanted our robot to be as wide as possible, both to give us the widest possible collection area, and to make balancing easier. having a wider drive base and having a lot of weight up high (due to turrets) makes a robot tend to tip when going over a bump. my former team was and is exceedingly neurotic about tipping, and wanted to avoid it at all costs. that meant keeping our weight as low as possible (hence our turret at the bottom of the shooter tower), and, more importantly to what I'm actually trying to tell you, having as long of a wheel base as physically possible.

with a larger wheel, there would have been a shorter distance between the front and back wheel, which would make it harder to get over the bump. so we wanted small wheels. but that would cause us to high center in the middle of the bump, so we needed them along the full length of the robot. we could have done treads, but we had no experience with them, and man are they hard to do properly. turns out we needed 5 wheels on each side to make that work properly.

tbh, the multitude of wheels we had is rarely necessary, unless there is some sort of field barrier. But, at least in my experience, having lots of small wheels makes the effects of the drop center less profound. now that being said, we didnt use tank this year (H-drive instead), so I dont know how it affects lifts.

Edit: found some pictures that kinda show it
https://www.facebook.com/washingtonf...e=1&permPage=1
https://scontent.fsnc1-1.fna.fbcdn.n...3d&oe=566793A3

[juju_beans]

We have two 10 in pneumatics in the front, 6 in colsons in the middle, and 8 in omnis in the back.

oops didnt realize i was browsing in search sorry for the bump haha

[tickspe15]

Originally Posted by EmileH

In 2014, 1625 used a 4wd with 2 omnis/2 traction wheels allowing them to spin quickly and fly around the field yet still push effectively.

While you are correct that 1625 was very successful with a similar drive setup the match you linked may be a little deceiving. The team they are pushing around, 33, had only omni wheels on their drive train so they were very easily pushed around by defense.

[I_AM_Clayton]

Originally Posted by nuclearnerd

The downside is unsymmetrical handling going forwards and reverse, and reduced traction when in reverse.
.

We tested this on our 2015 bot during build season with the same idea that it would cut our turn speed in half. It turned out to be a nuisance because our robot holds totes out in front resulting in the robot leaning forward because of the dropped center. The omni wheels in the front resulted in the inability to move as effectively as we could before with belt driven wheels.