12-08-2011 16:51

AdamHeard

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

The Engagement of the drivechain is pretty low on the module near the gearbox, I'd be worried about that slipping.

Also, the outward flanges will make dealing with bumpers difficult, and are somewhat exposed and vulnerable. Try flipping them to the inside.

The pocketing is not symetrical, which bothers me, but clearly isn't a functional issue.

If your electronics hump attached to the siderails of the chassis, it would greatly increase the strength and rigidity.

Do you already have a sheetmetal sponsor lined up and good to go, that's key to this design obviously.

Can you post just the module? Curious to see how it's changed.

12-08-2011 17:32

Hawiian Cadder

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

in your current configuration it will be impossible to turn. I looked at swerve a while back and i think that having the steering chained in an X was what I was using. as is you cannot orient the modules into a circle, and you cannot turn in a "short tank" style. the only way that this will turn is in "long tank" style, and because it only has 4 wheels, that may be very difficult.

12-08-2011 17:48

PAR_WIG1350

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

Not impossible, but inconvenient, steering usually links the front wheels together and the back wheels together which allows for double ackerman-like (car-like) steering. The X configuration eliminates that possibility but allows for easier pivoting and as such is ideal for crab drive (translation and rotation in place only, 3 degrees of freedom)

12-08-2011 18:23

Colin P

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

Any reason for the chamfered corners? Does that help stability or anything when working with sheet metal or are you just going for style points?

13-08-2011 12:21

ggoldman

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

I was hoping to comment on the Sheet metal fabrication of your chassis.

I have found that ribs on the outside edges of the part aren't always enough to hold the loads you need. I have used "rib forming tools" in real part applications in the field (outside of first) to add extra structure. Any sheet metal fabricator should be familiar with these.

http://www.colemanmachinery.com/ribforming.shtml

(Above link shows some examples)

Also, when using sheet metal, you should look into using PEM style nuts so that you can use fasteners into your sheet metal. PEM style nuts are pressed into the sheet metal. They have internal threads so that you can fasten things to them.

Good luck with the designing!

Best,

Gabriel Goldman
Sr. Research Engineer - NREC

14-08-2011 16:32

msimon785

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

Thanks for the comments. I will take your advice and add flanges to rivet the hump to the side-rail. The idea for using the hump to house electronics is one that I am somewhat conflicted about. It makes accessing the electronics very convenient, but it takes far too much space up. I am looking into other options.
What do you mean by pocketing? I definitely support symmetry, but I can't picture what you mean.
I can definitely move the flanges to the inside. I had them facing outwards for convience's sake, because I did not want to spend time chamfering all the flanges.
Also, we have not secured a sponsorship yet, but I'm working hard on that and making it a priority.
Last, I will post the module right now, and you should see it sometime late this afternoon.

The chamfered corners were just something I wanted to test out in terms of aesthetics. I doubt you'll see them on our actual robot. So far, I have not found a great way to make bumpers for a design like this.

14-08-2011 18:54

AustinSchuh

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

I'd say that the flanges that you have on the frame are not nearly large enough. The should be at least 1" long, and probably closer to 1.5".

I'd also recommend switching the pairings of power and steering so that the two wheels on the short side are ganged together. This lets you car steer when driving with the long side forwards (when it is hard to skid steer), and skid steer when you are driving with the wide side forwards.

Also, think through what you are going to do for sensors very carefully, and draw them in. You don't drive a swerve without lots of sensors and control loops.

14-08-2011 21:00

PAR_WIG1350

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

There is no reason that two wheels that are steered together should be driven together, in fact the opposite is true. If power/drive were to be kept as it is, the steering should be switched to the short side. If steering is kept as it is, then power/drive should be switched to the short side. Both of these options will allow for crab and car style steering, but the former in the long configuration and the latter in the wide configuration. Also, if the wide configuration is used, then skid steer can be used as a backup.

14-08-2011 21:05

AdamHeard

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

Austin and his team have made a pretty solid crab drive, and then programmed it using much superior controls than most teams use on theirs. I trust him

14-08-2011 21:19

Jeffy

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

I would worry about those CIMple gearbox mounts flexing and throwing a chain. There is a reason the KoP chassis has braces for the gearboxes.

15-08-2011 02:37

msimon785

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

Thank you. I will take that into consideration and add supports and braces for the CIMple gearboxes.

15-08-2011 18:46

PAR_WIG1350

Re: pic: 3rd Iteration of Sheet-Metal Chassis- Swerve

I'm not sure he and I are in disagreement, His post could be interpreted to describe at least 3 different crab variants.