Drive Train Prototype

[Jared Russell]

Originally Posted by Ether

Where did you get those mecanum wheels? Never seen ones like that before.

~

I believe they are these.

[Alan Anderson]

Does it spin in place well? It looks like the mecanum wheels might need to be swapped.

[Ether]

Originally Posted by Jared341

I believe they are these.

Ah. Looks like they've been re-designed. The roller mounting tabs look a lot sturdier. It looks like the rollers still rub against the mounting tabs though. That's a bit disappointing.


~

[Chris is me]

Originally Posted by Ether

Ah. Looks like they've been re-designed. The roller mounting tabs look a lot sturdier. It looks like the rollers still rub against the mounting tabs though. That's a bit disappointing.


~

I think that's an intended feature of the wheel; you can tighten and loosen the rollers to get varying degrees of forwards versus sideways traction.

[Ether]

Originally Posted by Chris is me

I think that's an intended feature of the wheel; you can tighten and loosen the rollers to get varying degrees of forwards versus sideways traction.

So it's not a bug, it's a feature? :-)

Seriously though, even if you loosen the rollers, they are always end-loaded when the wheel is being driven. This creates substantial friction. Roller bearing friction increases traction in the fwd/rev direction, but decreases traction and force in the strafe direction. For many applications (like Breakaway?) this may be a good trade-off.

I like the look of the new steel end-plates. The mounting tabs look quite a bit more rugged. The aluminum tabs on the 8" AM mecs bend very easily - even to the point of locking up the roller.

~

[Alan Anderson]

Originally Posted by Ether

Seriously though, even if you loosen the rollers, they are always end-loaded when the wheel is being driven. This creates substantial friction.

I don't understand. Are you stating that as a deficiency of this specific wheel design, or of mecanum wheels in general?

[Andy Baker]

Way to go Nitesh and WBI - this is a cool design! I hope you bring this to IRI so we can check it out.

Originally Posted by Ether

I like the look of the new steel end-plates. The mounting tabs look quite a bit more rugged. The aluminum tabs on the 8" AM mecs bend very easily - even to the point of locking up the roller.



~

The bodies of these wheels are actually old and an inferior version of the current version. The plates used on this jump design are from 2008. These tabs were significantly less rugged, since the steel wall thickness was only 0.04" instead of the current thickness of 0.05".

I find that the 8" Mecanum tabs are quite sturdy.

Andy B.

[nitbaj]

Originally Posted by Hawiian Cadder

how much does that weigh?

I currently weighs around 90 pounds with everything on it. It's pretty ridiculous, but we didn't really worry about weight when designing it this time around. The frame members are pretty much all 80/20 and we didn't put lightening holes in any of the other plates, so I imagine the weight could drop quite a bit. Weight will probably be one of the next big considerations in this design.

Originally Posted by GarrettF2395

Is there a reason as to why you decided to have the mechanums on the outside instead of the inside?
Did you guys play around with any other configuration ideas, such as having all 8 of the wheels on the ground at once?

We put the mecanum wheels on the outside because we thought those would be the primary driving wheels, and then the traction wheels would be used in a pushing match or a similar situation. And if a robot with a relatively high center of gravity is moving quickly on mecanum and switching directions, it is much more stable to have the wheels on the outside.

We thought about different things you could do with all 8 wheels on the ground, but it seems like you don't gain a lot with that because you lose both your traction and maneuverability.

Originally Posted by Alan Anderson

Does it spin in place well? It looks like the mecanum wheels might need to be swapped.

We haven't had any problems with the mecanum drive spinning or strafing. I believe our wheels are on in the correct orientation. Unfortunately, we've already made the mistake of putting them in the wrong spot once this year, so we wouldn't want to mess up again .

Thanks for all the compliments, and if you have any other questions or comments, please post them.

[sdcantrell56]

Originally Posted by nitbaj

We haven't had any problems with the mecanum drive spinning or strafing. I believe our wheels are on in the correct orientation. Unfortunately, we've already made the mistake of putting them in the wrong spot once this year, so we wouldn't want to mess up again .

Thanks for all the compliments, and if you have any other questions or comments, please post them.

The wheels are definitely not in the correct orientation. When viewed from the top the rollers of the 4 wheels should form an X.

[Ether]

Originally Posted by sdcantrell56

The wheels are definitely not in the correct orientation. When viewed from the top or bottom the rollers of the 4 wheels should form an X.

When viewed from the top they should form an X.

When viewed from the bottom they should form an O.

see this post:
http://www.chiefdelphi.com/forums/sh...4&postcount=18


~

[Thelilpluck461]

Originally Posted by sdcantrell56

The wheels are definitely not in the correct orientation. When viewed from the top the rollers of the 4 wheels should form an X.

In the pictures on the website the wheels are on the wrong way. If you look at the video the wheels are on the correct way. If you look at the video vs. the pictures the pneumatic and wiring is different, the video is the most up to date version.

[Henry Williams]

Just a quick update for everyone interested, since the last post we have fixed the mecanums, we had actually done this a while ago but some of the media was not up to date. We also replaced all the electronics board material with pegboard and we added a shooter so we could use it as a demo/show bot. It is still made of nearly all 80/20 so with the shooter and hopper it probably weighs about the same as a normal FRC bot now (but we haven't weighed it since so thats just an estimate).

[Aren Siekmeier]

Originally Posted by nitbaj

We put the mecanum wheels on the outside because we thought those would be the primary driving wheels, and then the traction wheels would be used in a pushing match or a similar situation. And if a robot with a relatively high center of gravity is moving quickly on mecanum and switching directions, it is much more stable to have the wheels on the outside.

Also, tank turning with the traction wheels will be easier with a shorter wheel base because you will get less tread rub.

[Tom Ore]

We used these Mecanum's this year. They do look a lot sturdier, but the bolts and rather small and can bend easily. Our Breakaway robot had a similar drive, but without the moveable wheels. We used 4 Mecanums on the inside and 4 traction wheels on the outside, raised slightly. This allowed us to cross the bump easily - the traction wheels were geared down and pulled us over the bump. We could cross the bump easily at full robot speed but when the robot came down on the other side of the bump, the bounce would bend the small Mecanum wheel bolts. The electronics guys didn't like us crossing the bump that fast anyway...

[MattC9]

Just curious how did you interface the gearboxes to the pods, do you have any CAD files we could look at? Because I was playing around with this idea (like ever one else it seems like) and could not find a good stable way to inter face the transmissions (I was just using the tough box nano in it) also what gear box are you using on it?