6 wheel holonomic drive feasibility

[Pault]

Originally Posted by ekapalka

I'm getting the feeling that you have something against mecanum wheels... well, to each his own We have plenty of drivetrains that work, and even more people who know how to use them. Teams that decide to use mecanum wheels have to start somewhere, right?

My opinion (and I think his opinion, and the opinion of many people on this forum) is that just because you can build a mechanum drive doesn't mean you should. Maybe your team thinks differently, and thats perfectly fine. But the point was that the resources you put into a mecanum drive would be better spent on improving either your tank drives (no tank drive is perfect, there is always room for improvement) or the other mechanisms on your robot. Again, thats an opinion, and like you said, to each his own.

If you have want your robot to have pushing power, mecanum is definitely a terrible choice (this is an opinion backed by a lot of evidence). The are drivetrains out there that can give you omnidirectional movement and pushing power (swerve, octocanum, and probably some other rare ones), but only the best teams (think IRI caliber) are able to make one without devoting nearly all their resources to it. Generally, unless your strategy to play a certain year's game revolves completely around omnidirectional movement with pushing power, you should just stick with tank drive (or mecanum if you really insist). (I'm addicted to parenthesis (like, really addicted)).

[Nate Laverdure]

Originally Posted by Pault

My opinion (and I think his opinion, and the opinion of many people on this forum) is that just because you can build a mechanum drive doesn't mean you should.

Now is the perfect time to build a mecanum drivetrain. Your experience may differ, but I couldn't understand mecanum's bad reputation until I built my own version and saw firsthand how the drivetrain's actual behavior differed from the way I'd imagined the system would behave. If you get it done in the next 4 months, you'll be able to carry all of your "lessons learned" into the 2014 build season.

[IndySam]

Originally Posted by ekapalka

I'm getting the feeling that you have something against mecanum wheels... well, to each his own We have plenty of drivetrains that work, and even more people who know how to use them. Teams that decide to use mecanum wheels have to start somewhere, right?

Mecanum wheels are a wonderful exercise and learning experience for a team. If you guys want to experiment with them I say go for it.

When it comes to winning matches however, remember that the game should decide what type of drive you use, a mecanum drive might not match the game. We have done it once with great results and I could see them being very helpful in one other season I have participated in, that's 2 out of 9 seasons for me.

[Nemo]

Originally Posted by IndySam

Mecanum wheels are a wonderful exercise and learning experience for a team. If you guys want to experiment with them I say go for it.

When it comes to winning matches however, remember that the game should decide what type of drive you use, a mecanum drive might not match the game. We have done it once with great results and I could see them being very helpful in one other season I have participated in, that's 2 out of 9 seasons for me.

Which two games? I assume 2011 is one of them.

[Ether]

Originally Posted by ekapalka

What I was wondering is how to control the center wheels so as to not conflict with the mecanum wheels while still providing pushing power.

You could do it with independent drive of all 6 wheels (i.e. 6 drive motors, one for each wheel). Control the mec wheel speeds as you normally would (i.e. based on standard mec inverse kinematics), and control the omni wheel speeds based on inverse kinematics of the FWD and ROT command components.

I doubt whether this will provide much (or even any) benefit compared to standard 4-wheel mec though.

[ekapalka]

Originally Posted by Ether

You could do it with independent drive of all 6 wheels (i.e. 6 drive motors, one for each wheel).

That's exactly what I was trying to say :) So you don't think encoders will be necessary? Why would it not add any pushing power?

[Ether]

Originally Posted by ekapalka

So you don't think encoders will be necessary?

I purposely worded it the way I did:

Control the mec wheel speeds as you normally would (i.e. based on standard mec inverse kinematics), and control the omni wheel speeds based on...

To control the wheel speeds properly requires an encoder on each wheel. But you could probably make it work somewhat using open-loop voltage control.

Why would it not add any pushing power?

If you custom-made the center omni wheels using high-traction treaded rollers there might be a small difference. Seems like an awful lot of time, expense, and effort when there are better ways to achieve increased pushing force.

[ekapalka]

Originally Posted by Ether

[...]

thanks

[Ether]

Originally Posted by ekapalka

my apologies

Just to be clear:

All caps is considered shouting.

Bold is not considered shouting. I bolded it for context only.

No offense was taken, and no apology required.

(I went back and edited the prior post to remove the bold, lest my intent be misunderstood)

[Racer26]

1114 has published a fantastic paper on the economics of drive-base selection for different teams.

Drivetrain Selection (or: Why every team should build a tank.)

[Ether]

Originally Posted by Racer26

1114 has published a fantastic paper on the economics of drive-base selection for different teams.

Drivetrain Selection (or: Why every team should build a tank.)

A good resource. The comments about programming mec and omni seem somewhat dated.