Dual Mecanum

[drwisley]

Has anyone tried stacking mecanum wheels? I'm curious to see if it improves strafing control. We have a few years of experience with mecanum and haven't been able to strafe quickly without drifting one way or the other.

[Joe Johnson]

As far as I know there is nothing preventing Mecanum wheels from working in pairs.

For example you could have a 8WD with the front two sets acting as a traditional Mecanum set and the back pair acting as a Mecanum set. In this set up you would have two X's (from the top side -- see this thread)

\.../
/...\
\.../
/...\

The first and 3rd wheels should be driven together and the 2nd and 4th wheels should be driven together.

A problem will be do you lower any of them? I suppose that if you do, you'd lower the 1st and 4th rows otherwise you'd effectively have the middle pair on the ground forming an O from the top. Which is bad because you won't be able to spin effectivley (again see this thread)

Another alternative is to have this config:
\\.//
.....
.....
//.\\


BUT... The more I think about it, the more I believe the question is the wrong question.

Wrong question: "Has anyone tried stacking Mecanum wheels?"

Right question: "How can I go sideways with Mecanum wheels more effectively (= fast and straight)?"

The answer to that I think is two fold.

#1 keep your CG in the middle of the machine (as much as you can) and
#2 feedback loop using an angular rate sensor*

With these two steps I believe you can get what you want without having to resort to dual Mecanums.

Cheers,

Joe J.

*often called a "gyro" for historic reasons involving the means that angular rate sensors were implemented prior to MEMs electronics. Like the confusion between "power" and torque, I wish the world were otherwise, but I will just add it to the list for the time being and move on...

[drwisley]

Thanks for the quick and thorough response Joe.

We have always focused on suggestion #2, angular rate feedback, and have never made a conscious effort to balance the normal force between each wheel. I have rarely had the luxury to, in the past I'm always trying to remove weight where ever possible.

Intuitively, I figured decreasing the vibration amplitude in half and consequently doubling the frequency by using dualies would improve strafing drift. I'll definitely try out tip #1 first.

Thanks again,

Dave

[EricH]

I'd have to agree with Tip #1 from Joe. Back in 2005, 330 tried mecanum on an experimental basis. One of the tests was how well we could go sideways with a tetra [8lbs] about 2' from the robot on a pole. Let's just say that the robot did a nice sideways arc.