# Holonomic Plus / X Drive Help

Hiya,

Was just wondering about the use of a holonomic plus / X drive and how effective it would be in turning if it was set up like this:

[ATTACH]8409[/ATTACH]

I haven’t heard too much about wheels in this configuration and was wondering if it would work or not.

Someone will explain mathematically much better than I can, so I won’t bother with the physics. Practically, this is the equivalent of putting Mecanum wheels on incorrectly. The turning is not good at all in my experience.

In short this can’t turn at all, that’s why it isn’t used.

As far as going in different directions, you’ll get similar performance characteristics as a regular X (same power, same speed), except that again you can’t turn so you can’t correct for drift.

If you think turning is overrated, go for it.

Not trying to pick on you, BUT since people like to name anything whatever they want these days, I’m officially making this the Hipster drive. There, I named it. It’s done, can’t be undone.

It’s different and -some- people may think that it looks novel, but only an idiot would actually use one because in trying to look different and novel, it fundamentally defeats it’s own purpose.

Just like a hipster wearing sun glasses that A. don’t block the sun and B. have slits in them that prevent the user from being able to actually see through them.

FYI I thought of this and realized it’s issue in high school like 7 years ago, and someone else emailed me asking if this would work a few months ago. It’s not a new concept, it just doesn’t work.

-Cody

If someone tries to push you, you will spin in circles on the rollers of the omniwheels. You will end up in a random orientation, ans you won’t be able to correct yourself. Basically what cody said, just giving a situation where it will fail.

Thanks Cody and all for the replies (:

I wasn’t really intending to use this without finding out the pros / cons (hence this thread), as I couldn’t really find any info on it on the web and I had heard mixed opinions from team members.

Well there goes this idea…

[ATTACH]8410[/ATTACH]

But at least because of the way I built the sides, all I have to do is flip them for a proper X-drive! Yay for modules.

Thanks again everyone!

To turn an x drive you power one side forwards and the other side backwards. If you do that on this drive, each set of diagonally opposite wheels will oppose each other and the robot will go nowhere.

Here is how you calculate the turning speed and torque of an x drive for an arbitrary wheel angle:

The (free) rotational velocity is http://imgur.com/eZq5Vl2.png.
The robots turning torque is 4Fhttp://i.imgur.com/baGCXop.png where F is the force exerted by one wheel.

Theoretically speaking, this arrangement gives you undefined turning speed and zero torque. Practically speaking it just won’t work.

The formulas are discussed briefly in this document:

Cheers Oliver (:

I kinda did get that at the beginning, but one of the other members in my team was arguing that no it would work so I kinda just wanted to make sure that it wasn’t gonna work.

Thanks for the help everyone,

Drive is all sorted now

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Marco

I would suggest that you use some grease… although it is obvious. I like chains but hate the friction.

I would suggest using larger sprockets, if possible; I’m not sure why, but the smaller sprockets cause the drivetrain of our A team to lock up repeatedly until they replaced the 6-tooth gears with the 12-tooth ones. We speculated that the issue may lie with the sharp angle that the chain is bending at and the smaller contact area for the sprocket to push/pull the chain.

Correct me if I’m wrong, but the diametral pitch of 6-tooth sprockets is different from the larger sizes. Therefore they don’t work as well with the chain.

Since everyone else is giving their suggestions, I’ll add mine. I find powering the right side of your drive base can help a lot. Here you seem to have only powered the left half of the base. Your last base couldn’t turn, this base can only turn.

Actually it can also strafe with only two wheels powered, think about it, just power it like a normal x-drive and look at how the vectors add up

Yes, my bad. However, you get about 1.4 motors worth of torque (about .7 per motor * 2 motors = 1.4). Actually, less because of the friction on the chain.

A claw bot could push it (2 motor drive base).

WAIT a minute…

You could have a shifting X-to-Hipster drive that would allow you to climb over bumps diagonally easier!!!

Start going at the bump in hipster, once the front wheel climbs over, switch to X for the middle wheels, then back to hipster for the back wheel!!!

Really impractical, but it has a …very slight… advantage over regualar X drives!!!
:D:D:D:D

Heya,

The reason only one side is powered is basically it’s unfinished haha, I have school exams this week so built as much as I could right before my exam and then went to exams.

I’m planning on both sides being powered in the future I’ll post an update when done.

Sooo I went with a couple suggestions and changed the 6-tooth sprockets and I’ve also finally added my other side motors

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Bonus with cube for scale:

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Well, it just depends what type of lift and intake you want. The base, lift and intake are very interconnected, so be sure to know how everything is going to to fit together before settling on any one base configuration. Also, some support connecting the two bottom C-channels would be good. The tower needs to be held on by something more than that 1x5x1, too. Preferably the tower C-channel would directly screw on to the base C-channel.

One good way to reinforce a robot is to try bending and pushing it in every way you can. If it isn’t rigid enough, reconfigure it to be stronger, or add more material.

Thanks and don’t worry, I’ve got the design for lift and intake sorted and the towers are just for structural placement at the moment, I’ll be bracing and properly building the towers soon but would like to test it’s driving before that.

And I’m planning on going with a reverse double 4 bar, hence the tower built in the middle.