Omni Wheel Configuration
 

I did a quick search, and I couldn't find exactly what I need...
What all would you need to use omni wheels on a robot? Like, a list of everything we would need and how much we would need.
We've never used omni wheels before, so we don't exactly know where to go...

Re: Omni Wheel Configuration
 

Nobody can answer this question for you. There are too many things we don't know about your robot.

Instead, please tell us what you're trying to accomplish, what you've learned after the research you've done and what questions remain. We can't help you unless you demonstrate that you've done some work and you give us some information to work with.

-Madison

Re: Omni Wheel Configuration
 

There are two videos that explain one of the designs we've been working on.
The Main System
The Intake System

And we don't really have any questions, because we're not entirely sure where to go from our current position. We've done some research, but it's pretty basic. If you'd like to read what we've gathered, I'd be more than happy to post it, but it's really just common knowledge.

Re: Omni Wheel Configuration
 

Sure -- but specifically, what do you need the omniwheels for? Presumably, you'd like to use them in your drive?

Are you using the kitbot? Are you designing your own chassis and drive train?

What kind of axles are you using? Are they dead axles (the wheel spins around a stationary axle) or live axles (the axle and wheel spin together)?

What diameter wheels would you like to use?

What are you expecting to gain from using omniwheels? It is very unusual for teams to use ONLY omniwheels in their drive.

Re: Omni Wheel Configuration
 

Designing our own chassis.
Live axles.
8" diameter.
Lateral maneuverability and a new experience (for learning and advancement with our engineering concepts.)
We are only using omni wheels. Why is it unusual?

Re: Omni Wheel Configuration
 

It should be pretty straightforward to use omniwheels in that arrangement. Both VexPro and AndyMark sell 8" diameter omniwheels. Both of them also offer a variety of hubs that bolt onto the wheels and will give you a hex or keyed bore. You need one hub per wheel.


Driving omniwheels on a live axle is no different than driving traction wheels.

Re: Omni Wheel Configuration
 

Is that everything, or is there anything else that we would need? We found a diagram for a basic drive system, but we don't need some of it.

Re: Omni Wheel Configuration
 

Okay, generally --

You need a gearbox with appropriate gearing for 8" wheels. You probably want something in the 12:1 range.

You'll probably need form of power transmission between the gearbox output and your wheels. This is usually chain and sprockets or belt and pulleys. It could also be gears. The power transmission component that turns your wheel's axle will have to be bored appropriately.

In FRC, a live axle is either a hex shaft or a keyed round shaft in nearly all cases. If you're using a hex shaft, you just need a hex bore in your sprocket or pulley and a hex hub attached to your wheel. If you're using a keyed shaft, you'll need a keyed bore on the sprocket and a keyed hub for the wheel. You'll also need a machine key -- a square piece of steel that sits between the shaft and the hub and transmits the torque between the two of them.

You'll probably need shaft collars or some form of retaining rings to stop the wheel and sprocket/pulley/gear from sliding around on the shaft axially. You want to use spacers for this as well.

Folks don't usually use a drive made entirely from omniwheels because it offers almost no resistance to be pushed sideways by a defender. If your strategy relies upon constant mobility around the field, being susceptible to defense may not be a big tradeoff. If any function of your robot requires you to stop in place (to aim, to score, to collect, to catch), an omniwheel drive may be a large liability.

The upside, of course, is that you can swap in a pair of traction wheels for a pair of omniwheels pretty easily and that'll give you some additional resistance to being pushed, spun in place, etc.

Re: Omni Wheel Configuration
 

On the off chance you don't already know this, if you want to strafe with those omni wheels, you'll need to mount them at 45 degrees.

Re: Omni Wheel Configuration
 

Thank you both, very much. You have definitely helped a lot.

Re: Omni Wheel Configuration
 

OmniWhels are a great piece of hardware. They have so many uses, that it would be useless to name all the possible configurations!
If you want to use it as a holonomic drive, just put a wheel on every of the four sides on the bot. If you want to use OmniWheels to pivot easier and more efficiently, just do a tankdrive, with omni wheels as the far-edge wheels. If you want to be able to easily drift, just make a tankdrive, with nothing but omniwheels!

Re: Omni Wheel Configuration
 

Or at 120 degree intervals!

http://www.ludep.com/working-out-the...he-kiwi-drive/

Re: Omni Wheel Configuration
 

You're both wrong. Just make them not all point the same way.

Re: Omni Wheel Configuration
 

Note that this description isn't sufficient for describing a holonomic drivetrain based on omni wheels. For example, the attached design is not holonomic (source image).

Re: Omni Wheel Configuration
 

It's neither sufficient nor necessary.

Re: Omni Wheel Configuration
 

a couple of files from previous CD posts (credits are in the files) that I think you will find useful in your trade-off analysis.

Re: Omni Wheel Configuration
 

Wikipedia seems to disagree.

http://en.m.wikipedia.org/wiki/Holonomic_(robotics)

Re: Omni Wheel Configuration
 

There's no disagreement. With the design I posted, you'd be able to control only 2 of 3 DOFs.

Re: Omni Wheel Configuration
 

I see. The attached differs from the source.

Re: Omni Wheel Configuration
 

A pragmatic suggestion: seriously consider how reasonable it would be for your team to successfully execute a holonomic drivetrain, for what sounds like the first time ever, starting half-way through Week 3 of build. Your drivetrain is the single most important sub-system on your robot, thus I strongly encourage you to use a low-risk approach.