02-02-2015 22:44

asid61

Re: pic: 4004 drive base teaser

I forsee weight distribution mecanum problems in the future if your robot works like I think it does.

02-02-2015 22:46

Gregor

Re: pic: 4004 drive base teaser

How much experience do you have with off-center weight on a mecanum drive?

02-02-2015 23:02

asid61

Re: pic: 4004 drive base teaser

http://www.chiefdelphi.com/forums/sh...=133500&page=2
If you plan for it, you might be okay depending on how far into the chassis the totes are.
We prefer to prototype things that we know are going to have less problems. Which is exactly why we don't build off-center mecanum drives.

02-02-2015 23:49

Gregor

Re: pic: 4004 drive base teaser

That's a great way to limit yourself.

We're building an off-center mecanum. Absolutely love the mecanums for this game.

03-02-2015 00:31

GeeTwo

Re: pic: 4004 drive base teaser

Last year, we had a mecanum drive. Our prototype was off-center on both axes, but the drivers learned to compensate. That said, we went with H-drive this year because we felt that tank drive was an 80-90% solution, and we'd just use strafe for that last bit of alignment.

03-02-2015 00:38

GeeTwo

Re: pic: 4004 drive base teaser

With all the extra holes in the side panel, my first thought was that you'd turned a KOP chassis "inside out", but that supposition doesn't survive closer observation. There also aren't enough holes to save much weight, at least compared to a number of designs which look like dinosaur or bird bones. What design criteria led to all those extra, unused holes?

03-02-2015 00:46

asid61

Re: pic: 4004 drive base teaser

I'm pretty sure we're not limiting ourselves by ensuring that we have a working robot.

I'm not saying it won't work to have an off-center mecanum. However, you will have you compensate for drift in code or with suspension, which takes time.
We wanted to go mecanum, but found that our play style would limit their effectiveness. I like mecanum. I'm just saying that putting the center of mass so far forward could invite problems.

03-02-2015 06:32

pribusin

Re: pic: 4004 drive base teaser

The 'extra' holes are mirrored holes so that we have one side panel tat can be used for either side of the robot. Since this is our first year using CAD to get custom drive base parts made for us, we wanted to keep it simple for both us and the fab shop.

03-02-2015 06:56

MrBasse

Re: pic: 4004 drive base teaser

Looks pretty good guys! Who did you use? Versatile or someone else? We'll have to talk about cost sometime for some of our offseason projects.

03-02-2015 07:48

pribusin

Re: pic: 4004 drive base teaser

We used Total Quality Machining. The dad of two of our new team members runs that shop - fortunate find!

03-02-2015 19:15

Chris is me

Re: pic: 4004 drive base teaser

I think you're missing Gregor's point completely. His point wasn't to say that your team made bad design decisions, not at all. His point is that you're giving firm, absolute-sounding advice to other posters without having any experience with the mechanism yourself.

When you say things so definitively and firmly like that, it implies a level of confidence in your knowledge that goes beyond you having read someone else say something like that somewhere else on Chief Delphi once. It's disingenuous, and it is VERY easy to post like that, give bad advice by mistake, and hurt teams who listen as a result. Trust me, I've been there, it's not fun.

His other point was that by deciding an idea has no merit (won't "actually work") without any prototyping, you're limiting your options based on preconception rather than evidence. His follow up post is indicating that perhaps his own team has had experience with mecanum drive that makes him confident in his own design choice.

If you aren't precisely sure of what you're saying, don't say it like you are. One of these days someone just might listen.

03-02-2015 22:18

asid61

Re: pic: 4004 drive base teaser

Are you saying that Ether is wrong when he says an off-center mecanum will require compensation for in code/ driver? When Ether says or corroborates something, I consider that more than just a random bystander saying something offhand. I'm not just throwing stuff out there randomly, I am providing a direct link to the information which is directly supported by Ether.
Because of that, I consider the compensation a problem, and for that reason I avoid off-center mecanum; it's extra work that my team just doesn't want to do. I am 99% certain that an off-center mecanum in this game's context will be extra work compared to just slapping a set of mecs on there if you stack off-center. The remaining 1% is just to account for designs that stack off-center but keep the weight centered. If teams want to deal with that, go ahead. However, if the OP was not aware of this at all, then I thought it could be helpful to warn them beforehand.

If the OP thinks they've got it, they can go ahead go ahead. Of course if they've already done it there should be no problem. I am simply pointing out that there are things that need extra work in an off-center mecanum, either in code or in driver (or mechanism, I guess, if you go with suspensions).

EDIT: That link you provided doesn't say anything about drivetrain in it as far as I can tell... am I just missing it?

03-02-2015 22:24

Snowfire

Re: pic: 4004 drive base teaser

We are making almost the same chassis and drive train. We have a tower for the totes to up and down on. We chose to have the center of gravity to be slightly behind the center-to-center distance of the two drive axles by changing the location of our tower. That way when we are loaded we have our weight more forward, but too much. This does mean sacrificing strafing capabilities unloaded. Hope this helps!

Edit: I noticed that you are using VEXpro gears outside your frame. I would definitely be careful with these; Team 1986 Titanium had issues with their gearbox being outside their frame. These gears need to be lubricated properly or else you will have a lot friction in your drivetrain. You probably also want a shield beneath your gears to protect them from carpet and other robot parts

03-02-2015 23:04

Deke

Re: pic: 4004 drive base teaser

That chassis looks awesome! I can't wait to check it out at west Michigan. Very clean, nice work!

I'm sure the rest of the robot will require some gawking at too.

03-02-2015 23:07

bkahl

Re: pic: 4004 drive base teaser

I think these videos will substantiate Chris's link

https://www.youtube.com/watch?v=pRc0LtIe5VI

https://www.youtube.com/watch?v=lXPJt4mrx0o

https://www.youtube.com/watch?v=IC7JSvYqnrk