pic: sheet metal 6WD
 

Re: pic: sheet metal 6WD
 

Looks familiar.

Any reason not to make the bottom a full belly pan for electronics, etc?

Re: pic: sheet metal 6WD
 

Is there any way to rotate the shifters so that the motors line up, for ascetics and very insignificant COG changes?

Re: pic: sheet metal 6WD
 

1. I would recommend a center divider on one side of the motors. It will add strength and also a place to mount an electronics tray (e.g. from the back to the middle with the front open, or something like that)

2. Electronics tray could be perforated aluminum. Just cut it to size, rivet it in, and zip tie the electronics. Nice and easy.

3. I like the chain tensioning method. Super simple. If you want, you could put a 1" tall by 1/4" thick block with a hole for the axle, then tap the end for a 10-24 (or 10-32 if you want) and just tighten the screw to tension it, then tighten the axle bolts to hold everything secure.

4. Are you using servos for the SS's? If you are using pneumatics elsewhere on the robot (or even if you aren't), pneumatics will shift easier then the servos. I do not know how much better they are, but they provide a lot more force to shift then the servo does. We always shift with pneumatics when using AM shifters.

5. Rivets. If you are waterjetting or otherwise CNC'ing the sheet metal plates, just add a few holes per connection and pop rivet it. Easier to assembly, and not much more work in CAD (this is especially true with a pneumatic riveter, those are great)

6. Have you done any math on the speed and gear ratios?

7. .125" seems really really thick. We use something around .050 in our chassis, with a plate around the axles (a little circle with an axle hole and 4 rivet holes, around 1.5" in diameter), or the above mentioned tensioning block with some reinforcement.

Re: pic: sheet metal 6WD
 

.125 sheet is way to thick, especially with flanges. You can easily go down to .09 (a fairly standard size) wihout too many design changes. Any thinner (.05) and I'd make larger flanges just to be on the safe side.

Is there any reason you're lightening with circles instead of triangles?

Is there any reason you rendered it as an illustration?

Re: pic: sheet metal 6WD
 

Depending on what manufacturing process they have available, circles are great to use.

Check out pictures of 228's recent robots.

Re: pic: sheet metal 6WD
 

True, I tend to forget about punches since we don't have access to one.

What about flipping the inner plate around so the flange is on the wheel side. It looks like the flange is small enough such that this wouldn't limit access too drastically, and having a flange along the entire length will be muh stronger.

Re: pic: sheet metal 6WD
 

If you have access to a punch, kajeevan, I would recommend checking out Art Dutra's white papers here on CD. He posted his CAD files and he has some awesome designs in there.

Re: pic: sheet metal 6WD
 

How much is "much"?

Re: pic: sheet metal 6WD
 

Thanks!

I'm sure sure of the rational behind their choice of sheet metal direction flanges, but since the flange profiles look identical to the ones on our 4WD/6WD sheet metal designs, here's the rationality behind ours. The black flanges are our chosen sheet metal flange profile.



By putting the flanges where they are to avoid geometry conflicts, the necessary space between two chassis rails is kept to a minimum. These aren't the most optimal flange configurations for chassis strength, but they work good enough for our applications.

Re: pic: sheet metal 6WD
 

Fair enough. I usually think of a flange's strength benefits instead of its mounting benefits. Although, with roughly 5 inches of pool noodle and 1.5 inches of plywood between colliding robots, the bottom flange may not even be necessary.

Re: pic: sheet metal 6WD
 

The moment of intertia of the cross section is directly related to it's stiffness.

If you google, you'll see for a rectangle, the moment of inertia is 1/12bh^3 (base and height). Base being the side parallel to the axis the beam is being bent around.

So, a 5" tall .050" thick plate has an I = 1/12(5in)(.050in)^3 ~ 5x10^-5.

The same beam with two 1" flanges is that I plus the I of the two flanges. I = 1/12(.050)(1)^3= .004

So the beam with the two flanges has a total I of .004+.004+5x10^-5 ~.084.

.084 / (5x10^-5) ~150:1.

Even if I made a mistake in the math somewhere, this demonstrates the difference flanges make in design. I could go on for pages elaborating this, but it'd better to google and look yourself (key terms being beam, cross section, moment of inertia, etc...). You'll also then understand why I-beams are shaped the way they are.

Re: pic: sheet metal 6WD
 

I meant how much of a strength difference does cutting part of the flange out for the gearbox make? A poster said that it would be much stronger, and I wanted to know how much.

Re: pic: sheet metal 6WD
 

I totally misread your question then.

Similar concepts apply, just inverse. The beam is substantially weaker due to that flange removal. Depending on how the gearbox is attached, the gearbox itself could add a lot of support to the beam where material is removed.

Re: pic: sheet metal 6WD
 

delete please.