12-06-2011 22:09

Thermal

Re: pic: 2338 6wd CAD practice

I can't say for sure but I believe ~.09" is the thinnest I have ever seen for sheet aluminum drivetrains.

13-06-2011 00:33

Colin P

Re: pic: 2338 6wd CAD practice

If you're referring to the plastic IGUS parts, I'd recommend you keep them away from the drivetrain. You can find steel ones that will hold up a lot better at smallparts.com, or at least pillow blocks.

13-06-2011 00:41

Marc S.

Re: pic: 2338 6wd CAD practice

Looks very nice. You have some skills. How about trying a West Coast Drive.

13-06-2011 08:02

jwfoss

Re: pic: 2338 6wd CAD practice

Looks like a pretty clean start. It's always good to do some design work in the "offseason".

Question: Does your team already have a sponsor capable and willing to do this type of work for you? If so I strongly suggest sitting down with them and having the go over what they can and cannot do. We had to redesign a couple of our parts this year after talking with our sponsor.

- It looks like you are supporting the toughbox output shaft with a third bearing, note that in general you only want a shaft supported by two bearings.

- Most teams for chassis stick with 0.090" or 0.125" 5052 Aluminum

- The hole spacing around the top looks good, and makes mounting thing alot easier, however the spacing on the front face looks too close together consider your hardware choices for that location.

- I strongly suggest adding spacers between the drive plates, or a piece of sheet metal bent into a "U" shape between the each pair of wheels.

- Avoid Igus bearings in the drivetrain, look into making custom bearing blocks or just another layer of sheetmetal as a shim.

13-06-2011 08:25

sgreco

Re: pic: 2338 6wd CAD practice

Most teams perceive .09 to the desired thickness for a sheetmetal drivetrain. I think this is primarily because it's what 148 uses. I'm sure 148 has valid reasoning behind choosing this thickness, but it seems like a lot of other people just recommend it because they know it's what 148 uses, and not based on any experience.

I don't really have any good quantitative information to share, but my team used all 1/16 aluminum this year, and we had no problems related to the strength of thickness of the drivetrain metal.

I see no reason to thicken the metal on that drive train, 1/16 is plenty strong enough. If you go up to .09 that is reasonable (but more than you need), but .125 is WAY too thick. If you use .125 you really don't need the flange for strength, and I would use 6061.

I wouldn't use the igus bearings. They are kind of flimsy. My team broke them on our intake roller in 2010, and that drivetrain will have a lot more stress on it.

13-06-2011 09:20

apalrd

Re: pic: 2338 6wd CAD practice

We've used .050 without lightening it in the past (why? It was easier for us to manufacture a thinner chassis without less holes than a thicker one with lightening, to get about the same overall strength.)

We made that chassis (Actually, four of them, 2006-2008 plus a crab-drive variant in 2009) almost entirely by hand. While we can access a waterjet if we plan ahead, we have little access any sheet metal forming equipment, so we bend all of it on our brake in our shop. At the thickness we used, we added small circles to support the (dead) axles, and riveted them into the main side in four places (so, a little part with five holes). The first two chassisess (2006 and 2007) had one and two sides with bumpers, and neither was damaged by other robots.


About the two-bearings-per-shaft rule - This is mostly because misalignment in the shaft will cause extra friction in the system, something you don't want. However, with the precision of waterjets and lasers (common sheet metal cutting tools), and assuming you assemble the chassis with this in mind, you can get away with three (or four) bearings on a shaft, as long as you carefully check for mis-alignment and file out the bearing holes as necessary so everything fits nicely. With the way your chassis is designed, you certainly need that bearing on the outside to support the loads, so I would keep it.

Also - I noticed you have an adapter plate to support the toughbox, and leave the outer plate of the toughbox. Why not make the adapter plate a little bit thicker and use it as the outer plate of the toughbox, and remove the "box" of the toughbox while you're at it? You'll save weight there (and not just a little bit of weight)

For bearings, you can use FR8ZZ (1/2") bearings from AM, here, or FR6ZZ (3/8") here. They would be held in by their flange, with the flange on the inside of the chassis and spacers on the shaft keeping them from moving inwards. They would probably sit in one of the small circular parts I was telling you about earlier. The outer wheels can be live or dead, it just changes where the bearings go and the shaft material.

It does look good.

13-06-2011 21:47

rcmolloy

Re: pic: 2338 6wd CAD practice

1/16 should be good without patterns. However, I would just be safe and stick with .090 because you have those patterns on there.

The drawing looks really good and clean.

14-06-2011 09:37

sgreco

Re: pic: 2338 6wd CAD practice

It shouldn't matter structurally if you have a cut-out pattern or not. The point of the cut-outs is to reduce weight by taking out metal that is structurally insignificant. If the cut-outs are made correctly, you shouldn't have to thicken the metal the accommodate the cut-outs.

14-06-2011 10:37

avanboekel

Re: pic: 2338 6wd CAD practice

If that is the case, then with the cutouts I have, Should 1/16 aluminum be alright?

14-06-2011 10:58

sgreco

Re: pic: 2338 6wd CAD practice

Yeah, you should be fine. I would add in some cross supports between the outer and inner frame rails on each side. It'll help keep the metal from bending over time, and add some rigidity for only a small addition of weight, but it does look like the belly pan is serving this purpose, so you might fine.

The drawing looks, definitely a great start.

20-07-2011 23:00

avanboekel

Re: pic: 2338 6wd CAD practice

http://oswegofirst.org/forum_2011/do...=351&mode=view

Here is an update

21-07-2011 11:15

chris31

Re: pic: 2338 6wd CAD practice

I get an error saying "The selected attachment does not exist anymore."

21-07-2011 15:29

roystur44

Re: pic: 2338 6wd CAD practice

During assembly one problem you will encounter is the problem of alignment of the wheels. By having 4 panels that join together guided by the front and rear panels you have introduced a possibility of alignment errors. One way to help out is to make the inside side panel a C shape weldment and the outside side panel will fit into it. A properly designed belly pan will keep the left and right sides aligned.

Another problem is access to the wheels, chain and sprocket. If you want to drop the wheels out of the chassis during competition you need to design in a method. Our team uses sliding bearing plates that attach to the chassis and screws into a bracket that holds the wheel. I can provide pictures if you don't get the idea.

Using .060 alum is okay here are some stats:

Weight per sq ft aluminum

.060 .907 lbs
.090 1.30 lbs using .090" can save up to 27% from .125"
.100 1.44 lbs
.125 1.80 lbs

We use .090 5052-H32 because it is a trade off between strength, weight and cost to process. We process all the robot parts on one sheet of material on a laser cutter.

One last tip is to think about using hexed bearings and hexed axles. Once you figure out how to broach your drive train will be much improved and your assembly will be simplified.

Also try adding in a electronics board that you can pre assemble your PDB, speed controllers and spikes then mount into the chassis. Saves time during assembly.