pic: Sheet Metal Chassis Prototype



This is a prototype chassis for the upcoming season, we always wanted to do a sheet metal chassis, and this year, it looks like we will!
Specs:
1/8" aluminum
1/8" bend radius
10 holes for assembly
alternating 10 and 1/4" holes for attachment points
Please comment and critique my design (PS we do not want to use rivets so we will be using bolts instead)

Is your gearbox plate integrated into the frame?

If so, nice stuff. You’ve got a great start here, better than most.

Start out by extending your flanges a little further at the end pieces

Any particular reasons why you don’t want to use rivets? I’m just curious.

Really nice job. I’m also wondering why you decided against rivets, and against dropping the center wheel.

Regardless of the reasons, this is an excellent chassis given those constraints. Nice job. How does the gear ratio look?

I too am wondering the same thing. It looks like a CIMple Box with that direct drives 8" wheels (custom hex output shaft?). If this is in fact the case, this robot likely will not have enough torque to initiate movement of a 150 pound robot (battery and bumpers included), or you will not be able to reach a max speed given the length of the field. Correct me if I’m wrong.

Edit: I realized that the Toughbox mini has a very similar look to the CIMple box, in which case the gearing (depending on which gears you chose) is probably reasonable for a FIRST robot. I’m still curious what the ratio is, and what speeds you expect.

Increase the flanges on the front and back to add more metal. Consider bending another return flange. Select the aluminum type: 1100, 3003, 6061-T0-T6 or 5052-H32 then check you minimum bend radius with the people who are going to bend your parts.

Needs a integrated belly pan to stiffen the chassis. Add some joggles on the length to make it stiff. Consider a separate electronics panel so you can preassemble your electronics

Don’t forget the mounting points for the manipulator.

Needs quick release bumper brackets and battery box

Add clearance through holes to tigthen the CIM on the transmission.

Loctite your nuts before competition.

Thanks for the feedback!
the gearbox is a toughbox mini with a 10.7:1 ratio built into the 1/8"" aluminum, this is a bit more reduction than we had last year and it worked great! by great, I mean we though it was the 2nd best drivetrain on the field! (2nd to 141 who had some crazy hyperspace swerve drive which after looking at for about 10 minutes, I still couldn’t comprehend! I will now work on the modifications making this a more feasible, and realistic design! For the belly-pan, would there be anything wrong with using 1/2" Birch Plywood? It would be lightened and might end up lighter than aluminum, I will find out!

also, how much larger should the flanges on the ends be, currently they are 3/4", wound 1" be acceptable?

Make the flanges on the front/back of the bot 1.5 - 2" long, and then take the edge and bend a 1/2" flange down from that.

Take another set of the plates that you are using to strengthen the drivetrain tube and put them on the bottom. This will help a lot with strength.

Birch will be fine. You can attach electronics to it quite nicely with some industrial grade double stick tape. The birch will keep your frame square and help prevent the front from bending in when you hit things.

I would suggest using 1/8th inch lexan for the belly pan. It’s lighter than wood and more flexible, so it has less of a chance of cracking if you get hit really hard or flip over (I hope that won’t happen :eek: ). Also, you can easily attach your components with zip ties (or screws, if you like). We went with 1/8th inch lexan last year, and were very satisfied with the results.

I believe the point IS rigidity. Without the rigid base would this still work as well? Was your bot a sheet metal bot?

No, our robot was not sheet metal, but since every almost every FIRST game required some sort of manipulator to be built on top of the drivetrain, those structures would act as a sort of crossbar than reinforced the drivetrain anyways. Since the lexan would save weight, crossbars could be installed on the drivetrain beforehand anyways, and it would still weigh less than with a wooden bellypan.

Silly me, we were next to each other in the Galileo pits. I should have remembered.

However, I think that the crossbeams tend to be a nuisance that can actually warp the frame instead of strengthening it, so be careful about that. This’ll also depend on the game and the OP’s design style. If you plan to design the manipulator beforehand (which you should), you can plan for rigidity from your crossbeams. If you plan to use the infamous rule of fudge and just do it on the spot, you should have a rigid base to build on.

we just built a prototype chassis for offseason (yes it was sheet-metal). And we used lexan in the middle for the electrical board. Lexan is a great way to strengthen the chassis (even though i dont think we needed it). I would recommend rivets, as we just used them for the first time and they seem to be very strong.

Why are you using an omni wheel? Is the center wheel lowered? How thick are the spaces between the lightening holes?

Cool Chassis though :smiley:

One of the cool things about sheet metal bots is that it is very easy to make multiple parts once the cutting/bending machine is setup. A second robot can be made in less time (minutes) than a tubular/extrusion based frame. Designed right the sheet metal frame tolerances are very high when compared to a cut, milled and welded frame. A sheet metal bot can use alignment pilot holes to locate brackets or use a tab and notch to locate parts during weld. I’m not saying sheet metal is better what I’m saying is it is a cost effective medium to make a robot out of if you have the right sponsors and mentors who can guide the students in the design.

A stiff frame is better than a flexible frame. The chain will stay aligned and taught. The manipulator will be more accurate and precise because it has a flat stiff base. Try shooting a ball into a basket on a trampoline. I’ve seen other robot drive trains just bend and break when ramming our drive base. We are building 120 lbs robots going 17’ /sec. That is a lot of force on impact. Aim to build your robot light, stiff and strong and you can’t go wrong.

I like 1/2" birch plywood, 95 has used it in robot frames for year. I would highly recommend it.