Odd 8 Wheel Tank Drivetrain Idea

We saw some tank drives get pushed around from the side quite a lot this year, especially in the 27v67 MSC finals. Our driver generally avoided getting t-boned, but our robot (8 roughtop wheel tank) was still susceptible to it and had issues getting out of it. What if, on a rockered 8 wheel tank drive, the middle 4 wheels were omnis and the outer 4 were very high traction? As long as the chassis was stiff enough, and maybe with a slightly larger than normal rocker, wouldn’t this give very high turning ability while still having rather good traction while pushing or accelerating? What if the middle 4 wheels were mecanum (4 different gearboxes)? Would that allow for omnidirectional drive while still having pushing power? I think we’ll try these ideas out sometime this summer, but have they been tried before and do any of you have any other ideas or suggestions? Would anyone near us (SE Michigan) like to collaborate on the testing?

This sound very similar to the octacanum drive, but the traction wheels are switched it. search for the dragonfly on YouTube, I forget which team made it. Search for “dragonfly octacanum” or something like that.

https://www.youtube.com/watch?v=O_vvVU4OBT4 I think this is what you were looking for. 4265 prototyped this drivetrain in the offseason, and successfully used it to win the Smoky Mountains regional this year.

Yeah, that’s it.

Maybe and Maybe, i can’t be sure, but i believe that it would be no for the traction wheels with the omni ones inside because the traction wheels would have to travel a greater distance creating friction with the carpet, therefore making your turning worse than it’d be if you had the 4 traction wheels inside and the 4 omni wheels outside, and this second would have about the same effect against being pushed by the side as the first one. I suggest you have a look at 971’s robot, they have a diamond shaped frame and a low friction bumper material, that is pretty good to avoid being pushed by the sides. Regarding the mecanum wheels with traction wheels, i believe it would give you omni directional movement, but it would be so bad your drivers wouldn’t even use it, the traction wheels would be holding your robot so it didn’t move sideways while you tried to move sideways. if you want mecanum wheels with traction you should try an octanum drivetrain, where the traction wheels can touch, or not, the floor, and you control that with pistons

Close, this drivetrain would be a combination of omnis and mecanums, however it would not use a pneumatic cylinder to shift modules up and down. Instead, the wheels would all be fixed and as the robot rocked from high acceleration or torque it would hit the traction wheels and gain traction. If the rocking worked consistently, this would result in similar performance to a butterfly or octocanum, minus bulky drive modules, pneumatics, and complexity.

The idea is that when turning, the traction wheels are high enough off of the ground that they don’t interfere. They would only engage when rocking from high acceleration or torque. I don’t really want omnidirectional movement, the mecanums would just be an interesting experiment. 971’s chassis and bumpers are very interesting and things that I’ll also look into, however, we like having a standard chassis that will work with all games so we can create the same one quickly after kick off. The diamond shape may be an option next year, however it may also not be one.

Interesting, i got what you want to to, it’s pretty much like a drop center wheel and it’d probably work in the situation you described above, but since the traction wheels would only be touching the ground at high speeds or high torque
your wheels wouldn’t touch the ground if someone got you from the sides, i believe it’s very important to consider that when deciding to use or not this idea, personally i believe that the agility you get from that won’t overcome the bullying you’ll suffer at the field, but that’s up to your team. Also, here is a good way to increase your agility without any major modifications to your drivetrain design http://www.chiefdelphi.com/forums/showthread.php?threadid=129276

We used a setup similar to what you’re describing. We had an 8WD West Coast Drive with 4 Colsons on the outside wheels and 4 omni wheels on the center, Depending on your drop, center of gravity, and gearing for acceleration speed, you may or may not drop back onto the traction wheels when accelerating, or in a pushing match. For this reason, you would need to actuate at least one end to ensure the traction wheels are touching the ground.

Now that I think about it, that’s exactly what we experimented with this year.

Have you guys tested your drivetrain without the actuation? Or did you start out with it? Your drivetrain actually was what gave me the idea and what I’m trying to get is the same result in the lightest, simplest form possible.

Yes we’ve tested it, and it really depends on how likely your robot is ever to recline onto the back wheels. You generally want a low CoG, so if it’s low enough you will never have the back wheels touch the ground while accelerating. You could definitely experiment with the drop though and may find different results. We found it works best to actuate one side, and it was still pretty light, at about less than or equal to 30 lbs.

How much use did your strafe wheel see? How much power did it have? I’ve been pursuing this more for turning ability than stafeing, but in a game like 2011 it could be very helpful for sure. How helpful was it in this game?

We used it in autonomous to get the second hot goal. During tele-op, we mainly used it to get out of t-bones; we could easily spin out of a perpendicular friction pin. For actual maneuverability on the field, it never saw too much use other than maybe adjusting for shots near the one point goal.

If I would change something about what we did this year, it would probably be to not use the center wheel and instead go for a 6 CIM single reduction with the same setup of omnis and traction wheels. We ran 4 CIMS this year because two were being used on the center wheel.

In a game like 2011, it could definitely be useful, and I believe 148 had originally planned to use a nonadrive again that year, but then left it off and went with what became known as butterfly, or now “Tex-Coast Drive.” Why they chose not to use it I’m not sure, maybe someone from 148 can expand on that.

If we ever get around to it, something I would like to see is putting the traction wheels in the center and omnis on the outside; the idea being you can still turn on a dime even when in traction for more controlled turns.