Sheet Metal Chassis

I am currently designing a sheet metal chassis for next years competition, and would like some help. I have a couple of questions:
1: What thickness of sheet metal should i use? I currently have .060", but I am not sure what thickness would be the optimum balance between lightness and strength.
2: Should I use a round or cross hatch style lightening pattern?
Thanks so much :slight_smile:
http://https://m.facebook.com/?refsrc=http%3A%2F%2Fwww.facebook.com%2F&_rdr#!/photo.php?fbid=537651836285195&id=100001211502651&set=o.141923939241066&relevant_count=1&ref=bookmark&__user=100001211502651<<that is a photo of my current iteration

We originally designed a 3/32" sheet metal frame with the intention of holding it together with holes tapped for 10-32’s but then our sheet metal fab backed out on us…we scrambled to re-design for something we could build in-house with the tools and machines we had and settled on 1/16th" aluminum supported by 1/8" & 1/16" sq tubing, and it has worked out rather nicely for us…we play primarily defense and our robot has gotten and given quite a bit of punishment this year, and is still holding strong.

For the 3/32" design, I think we had triangles for the lightening pattern, if you’d like to see the design, let me know, and I’ll get a screenshot from the kid that designed it. We actually had two designs…one for a 6-wheel belt drivetrain and one for a four wheel drivetrain.

Hey there,

33 used .050 this year. Your 0.060 should work fine so long as its properly designed. Lightning pattern is up to you; I like circles. My only recomendation is that you leave some holes large enough to get a hand through. You’ll thank yourself later when you have to fix something.

Good Luck!
Regards, Bryan

I prefer .090, but .060 should serve you well. I’m 99% sure that 67 uses that thickness of sheet on all of their bases, and 33 uses even thinner sheet on theirs (.050). Much of the strength of a bent sheet metal part comes from the amount and location of bends made. If necessary, extra structural members run through the middle of the base can make the frame even more rigid.

The lightening pattern is a matter of personal preference. I have seen both triangle based and circle based patterns done effectively; however, with .060 I don’t see it necessary to do much lightening.

Also, I recommend using 3/16" rivets throughout the drivetrain, as they can be swapped with a 10-32 screw if you ever deem that necessary. 1/4" rivets are a bit overkill.

@others, If i’m wrong about anything I’ve posted here, please let me know :smiley:

We used 0.063 sheet with 3/16 pop rivets. We had conservative lightening on the side rails, and no lightning on the bellypan, and the bare frame weighed 9lbs.

Love it, and would do it again.

If you plan on using sheet, do yourself a favour and get a pneumatic riviter, it will save you a lot of time and effort.





What are you using to make your lightening holes? Do those flanges around the holes add any rigidity to the chassis?

Thanks

I know a lot of experienced sheet metal teams use very thin sheet(.060" thick) for their drives. However, if this is your first experience with sheet I would recommend using something thicker(like .090" sheet). A pocketed sheet drive is going to be plenty light already, and you don’t want to risk a drive breaking in the middle of competition. Once you have more experience you can use thinner sheet. If you have a sponsor with a punch making the parts a circle lightening pattern is going to be preferable. It will make for less time machining and happier sponsors.

We have typically used .090" with a circle based pattern to help decrease the time spent from our sheet metal sponsor. With this age of bumpers I’m sure you could get away with using a thinner material, but nightmares of straightening frames from 2003 still haunt me…

What alloy do you all use and what radius do you bend the angles? Looks like a large radius in the pic.
Thanks

Glenn,

.090" 5052 is a good place to start. .060" thick works also if designed properly with folds and gussets to strengthen the part.

.125" thk works good if you want weight down low to keep a low COG.

So it all depends on what you are trying to accomplish with your design. Pick the material that will compliment your design.

For your lightening pattern I would ask what the sponsor has in terms of equipment.

NC punching the parts I would stick to a round staggered perf pattern
NC Laser or Water Jett go with the diamond or round
NC router I would go with a light guage material and skip the lightening.

Keep costs in mind. Make it simple and clean. That is what I always tell my kids. Try to keep the part count down. It makes them think of better ways to design if they have a limited of the number of parts/time they can use to build a robot.

Here is a tip to help you get the correct flat pattern out of Solidworks

Use:
.100 for your bend deduction BD for .060 " material
.195 for .125"
.145 for .090"
use .035 for the bend radius on 5052

<3 Sheet Metal Chassis <3

Well I prefer to use 1/8" aluminum for the bigger, longer outside frames. Reason is that these are your main frames for your chassis, you don’t want to lack of any strength in it.

I used 1/16 for smaller parts in my chassis that weren’t going to be big enough to worry about too much strength, so you can feel free to use a mixture of any sizes.

I prefer to use Triangles as lightening patterns. They keep your chassis strong while easily

Here are two examples of my chassis’ using 1/8th material and triangles. The first chassis was actually built as an of season project, and was a very good and strong chassis.

Something additional that we did to that chassis was get the corners of each flange welded shut, that way it was harder for them to come apart and they were very strong.

Also another thing I have learned is that reversing the outside plates flanges, to go outwards rather then inwards. It makes it easier to assemble (because you don’t add flanges on the side of the front/back plates), and becomes slightly lighter (again because of the flanges you remove).
Here is an example of that

Have fun with your chassis design and make sure to post your results!

Somewhat on topic-ish.

Did you guys buy your own dimple die set or did a sponsor do them?

The sheet metal is all cut on a laser cutter. The “flanges” are dimples made from a dimple die. They add enormous strength to the overall chassis.

The metal is all 2024 T-3 aluminium. Our sponsor said that a 0.25 bend radius should be used for that alloy and thickness. We would stick to 5052 in the future, there were cracks at almost every bend point. The metal was very brittle.

Everything was done at the sponsor’s shop, laser cutting, bending, and dimpling.

Could you do all this with a normal sheet metal brake or do you need a press brake?

Not sure what you mean, but ours was done on a CNC break.

sorry I meant a manual break like this

versus a hydraulic press break(V shaped Die)

Correct…all our drive bases since 2008 have been made out of 0.060" 5052 AL.

Other than some bashed in corners, we’ve had no issues with strength or flex. Well, except for when we fell off the top of the tower with our practice bot…directly onto the front of the frame. One side was 0.5" shorter than the other.

All our panels are designed with a 1" flanged on top and bottom. Then we design in a “mid-plate” somewhere (depending on packaging) in the chassis to help tie the right and left side together. We usually cut our some additional gusset plates for any corner that didn’t have one designed in.

We typically tie in the other subsystems (shooter, lift, arm, etc…) of the robot into the frame with 1", 1.5", or 2" - 1/16" wall AL tubing so that it’s all rigidly assembled into the frame.

-Adam