Chassis Connections

[Siri]

Originally Posted by JamesCH95

Clem1604[sic]: watch out, your 6061T6 is becoming 6061T0 around the welded areas!

That it is. Luckily, we're [same team] pretty good about design strength & redundant supports. We've yet to fail a critical weld in 2 years* (though we do bow some). Still, I look forward to the the day we win the lottery and can correctly age back to a better temper. ...Then again, I look forward to that winning ticket for other reasons too. Like TIG welding!


*knock on...wood.

[rcmolloy]

For the past 3 years, our team has had our chassis fabricated out of 3/16" aluminum. The sides are bent at 90 degree angles for us to mount our bearings for the gearboxes. Also, this year we had two machined pieces of aluminum as well as custom brackets for our piston system. These have been helpful for more low to the ground games and our strategies. Here is a picture of the actual chassis alone without electrical wiring and all pnuematic tubing.



I know arial views don't simply do justice but I believe you can get the picture from here. If anything, I will take a picture of the chassis we have hanging around at the school from 2 years ago. Let me know!

[AdamHeard]

Originally Posted by JamesCH95

They look good. If you've got access to the CAD file would you mind switching the material to 4130 steel and making the wall thickness either 0.035 or 0.045? If that's easy to do I would be curious about the weight.

Prototype Frame for 2011.

Aluminum (6061-T6) 6.1 Lbs

4130 .045" wall 9.3 Lbs

4130 .035" wall 6.7 lbs

I'd like to point out that a substantial amount of the "weight saved" was in changing the .125" wall 6061 for our siderails to the .045/.035, which would be very impractical for us to do without a redesign of our bearing block system (which would just be more work for a net gain in weight). It's convenient to have that .125 wall. For reference, this is generally our only use of .125 wall on the robot.

I'd also like to point out that for our particular team, switching to a welded 4130 frame would take a significantly longer time to machine and then weld, along with costing us more (in the short term, as we don't stock steel or any filler rod, etc...).

Also, I hear it mentioned all the time that welded reduces the temper of metal. This is true, I do not disagree one bit. I just want to throw a counterpoint out for the inexperienced people reading who might otherwise assume "Welding aluminum is AWFUL! it turns to butter!" (I know I did a few years ago). The weakened material will be in your welded joints obviously, and with a good frame design these won't be loaded to failure. We've never broken a weld in a driveframe before.

I encourage everyone reading who is re-evaluating their frames for steel, to also do so for aluminum; I'm not saying one is better than the other, but if you analyze the steel and fail to do the same effort into aluminum, you aren't really proving anything. For some teams one will be better, and for others, the other; do the math, evaluate your resources, and make a decision.

[Brandon Holley]

Originally Posted by AdamHeard

I encourage everyone reading who is re-evaluating their frames for steel, to also do so for aluminum; I'm not saying one is better than the other, but if you analyze the steel and fail to do the same effort into aluminum, you aren't really proving anything. For some teams one will be better, and for others, the other; do the math, evaluate your resources, and make a decision.

I couldn't agree more with this statement.

Often when we're making engineering decisions, we end up choosing between 2 or 3 options and weigh the benefits. Sometimes when making these decisions we all have a tendency to declare one a "safe" bet or automatically declare it as valid, while trying to prove an alternative as feasible. While this is sometimes a good way to explore your options, its important to keep an open mind. Keep all of doors open, and gradually close them one at a time. Closing each door can be based on a variety of circumstances, just make sure you're choosing what works best for your particular situation.

-Brando

[JamesCH95]

Thanks for the response Adam.

I would add that although steel is harder to machine, the thinner wall thicknesses mean that there is less material to remove, so the machining/cutting times tend to balance out. Using abrasive tools might even expedite cutting time.

I agree that every option should be explored when a team is making a design decision. I remember when I thought "steel? that's too heavy" and dismissed it, oh how wrong I was.

[ttldomination]

Sorry for reviving this thread, but I was wondering if there was a major difference between the 6063 Al and 6061 Al tubing? Especially in regards to welding?

[cooker52]

Sorry I can't answer that question seeing how I have little experience in welding (which the most experience I've gotten is Acetylene and Oxygen).

But speaking for 1501 we use aluminum sheet metal and rivets to make most every robot using an engineering style known as monocoque (used in airplanes, vehicles, spacecraft, race cars). A simple effective style requiring primarily hand tools and few larger pieces of equipment such as a bench press.

Originally Posted by Andrew Schreiber

If I recall correctly Kettering's Formula Zero team (hydrogen powered car) is using a similar chassis. Ours is a little smaller due to race restrictions though. Something tells me 1501 used welded 4130 in 2007 for their chassis.

In 2007 AND 2008 both used welded 4130 Chrome molly. 2008 we used the Chrome Molly as a track for our "slingshot" launching method. We welded tabs on the Chrome Molly frame to attach our monocoque pieces on those 2 robots.

[JamesCH95]

Originally Posted by ttldomination

Sorry for reviving this thread, but I was wondering if there was a major difference between the 6063 Al and 6061 Al tubing? Especially in regards to welding?

There isn't an appreciable difference in the welding process for 6063 as compared to 6061, use your 4043 wire, 50Ar/50He shielding gas, and lanthanated tungsten, and you'll be fine. There also isn't much difference in the as-welded strengths of 6063 and 6061. I believe the main difference between the two alloys is that 6063 does not gain as much strength through heat-treatment, but is more resistant to corrosion.

Originally Posted by cooker52

In 2007 AND 2008 both used welded 4130 Chrome molly.

It's chro-moly (sounds like: "crow+molly") abbreviations of the two main alloying elements: chromium and molybdenum. Just a pet peeve don't take it personally

[cooker52]

I did a double check online last night and that was how they were calling it. I prefer to stick with calling it Chromium Molybdenum. No offense taken.