8 wheel mecanum drive

[Lyler1]

Hi! this is my first post here!

I have a question regarding Mecanum drives. My team, 4096, built a mecanum drive last season, all in all good, but we felt that the torque on our wheels was being wasted because our wheels were slipping. This year, we want more traction on our wheels in order to achieve better acceleration. How feasible would it be to put 2 mecanum wheels side by side next on each corner. They would be fixed on the same drive shaft, so they would rotate in unison, almost like an extra wide wheel. At the moment, 6 inch VEX mecanum wheels are our top candidate.
Any advice is appreciated! Thanks!

[EricH]

I've never seen that on an FRC robot, but I have seen blocks of multiple mecanums working together.

However, I suspect that you won't see improved traction. Mecanum rollers don't really get down to microscale interactions like treaded wheels, so I suspect that while a doubled traction wheel will show an increase in traction due to "interesting" stuff happening where we can't see, a doubled mecanum probably won't.

If I might make a suggestion, search for "octocanum" here on Chief Delphi, and see if you think it will work. Octocanum pairs each mecanum wheel with a traction wheel and switches wheels depending on whether traction or maneuverability is desired.

[Lyler1]

Is it feasible to make a mecanum drive with two side by side wheels on each corner to add traction?

[Ether]

Originally Posted by Lyler1

Is it feasible to make a mecanum drive with two side by side wheels on each corner to add traction?

Doubling mec wheels will likely not add traction.

[Jared Russell]

I don't know about adding traction, but it sure does look cool.

[Ty Tremblay]

Doubling your wheels will double the surface area in contact with the floor. This reduces the force on each wheel, reducing each wheel's traction. In short, you'll see no significant improvement in traction by increasing the number of wheels you have.

Couple that with the fact that mecanum wheels must slip in order to work, and you're better off sticking with 1 mecanum wheel in each corner.

[thenomnivore]

Just as a general rule of thumb, mecanum drives are crap when it comes to being able to grip and just exceeds in slipping on surfaces. Honestly, the only advantage mecanums have to other drive trains is the strafing ability and mobility but is bad when it comes to speed and being able to push other robots. Other drive trains that are available are direct drive or the 6 wheel drop. But its up to you on what to use.

[Jay O'Donnell]

Originally Posted by thenomnivore

but is bad when it comes to speed.

I'm afraid I don't follow your logic here. Speed of a drivetrain is more dependent on motors and gear boxes than anything else. As far as I'm aware the wheels shouldn't have too big of an impact (except for size of the wheels, but a traction wheel of the same size won't be any different than a Mecanum wheel). You are correct in that pushing ability is greatly reduced by having mecanums, but speed is not.

[thenomnivore]

Originally Posted by Jay O'Donnell

I'm afraid I don't follow your logic here.

Sorry i forgot to correct myself on that part.

[Ether]

Originally Posted by Ty Tremblay

the fact that mecanum wheels must slip in order to work

Whenever someone says that, I always wonder what they mean.

[AndreaV]

I can't see double mecanums adding traction or speed, but I can defiantly see them adding weight!

[team222badbrad]

Originally Posted by Jared341

I don't know about adding traction, but it sure does look cool.

24 looks even cooler!

http://youtu.be/2O8Cj0XiRIM?t=3m47s

[MooreteP]

Originally Posted by Jared341

I don't know about adding traction, but it sure does look cool.

And it has a minibot!

[Ty Tremblay]

Originally Posted by Ether

Whenever someone says that, I always wonder what they mean.

Technically, the rollers on the mecanum wheels don't slip in an ideal design (there is no slip between the surface of the rollers and the carpet). Often, however, there isn't a 1-to-1 relation between the tangential speed of the wheel and forward velocity of the robot.

So, if you look at it from the perspective of the wheel, and you don't want to take the above paragraph (or more) to describe it, you say that the wheels are slipping.

It may not be technically correct, but I've come to use it as mecanum "slang" if you will. Unfortunately, I use it so much that I didn't think twice before using it here.