pic: Robot Concept CAD

[MikeBrock]

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[sgreco]

You're not going to want to waterjet that out of a single piece of Aluminum. That's going to be incredibly expensive.

That frame will be much easier made with aluminum square tubing.

[lemiant]

Very cool! However, as much as you think that's simple, it actually sounds pretty complex for a rookie bot. You might want to take a look some of the shooter prototypes people are posting on here and make sure you really want a catapult. Nice CAD btw

- Alex

[MikeBrock]

Originally Posted by sgreco

You're not going to want to waterjet that out of a single piece of Aluminum. That's going to be incredibly expensive.

That frame will be much easier made with aluminum square tubing.

This is very true. How about waterjetting 1/8" plates for the top and bottom to hold together 2x1 tubing?


I do no see why this would be more complicated than a shooter, Lemiant. Care to explain your thought process?

-MB

[Siri]

Originally Posted by MikeBrock

This is very true. How about waterjetting 1/8" plates for the top and bottom to hold together 2x1 tubing?

You could, but what are you gaining with that? (Besides weight) I think you may well find that welding/riveting/bolting the 2x1" together with corner gussets will save you significant money and waterjet time. You also might want to put some more thought into the drivetrain before committing to 1x1" instead. Certainly plenty of robots drive with great 1x1" frame members, but attaching your wheel axles directly through 1x1" profile doesn't leave a whole lot of metal around most axles.

In places where you decide you need aluminum in non-stock profiles (a taller frame or a wider baseplate, etc), you can definitely get really creative. Also remember that it doesn't have to by aluminum, though. Many a nice electrical panel was made of plywood, carbon fiber, and many things in between.

With reference to the shooter: First, please, please, do not cantilever that axle. But more systematically, "non-continuous" shooters (as opposed to easy-to-turn-on wheels, cam-arming shooters, etc) in which you have to execute separate actions to load, arm, fire, etc can often be more complicated, especially with such a huge moment arm. (They weren't uncommon in things like Breakaway, where the travel distance was usually minimal.) It leaves you things with a few more challenges than normal.
- Where and what is the cylinder? And how precisely do you plan to use it? Is it providing the actual launch power?
- Where is the roller/how do you store and pickup balls and get them in the cradle?
- How long will it take to reload, and what's the range? (adjustable?)
- Most importantly, what are your design requirements? Are you meeting them with this?

On a catapult specific level, how far are you planning to shoot? Without knowing the specifics (CG), I'd be a little surprised if your back wheels stayed on the ground when launching for considerable distance.

Also, are your mecanum wheels mounted correctly? In the iso view it looks like they don't form an "X" from the top. Not a big issue in CAD, but your robot won't like it much.

Still your CAD is quite solid and your idea (even if I disagree with it) has a nice conceptual start. I can't say I'd do it, but if you've got a valid strategy, strong design requirements, excellent testing data, and the wherewithal to overcome the non-continuous shooter challenges, don't let us push you down.

[poohbear]

This is a great idea, comrad!!!

[Sean Raia]

Originally Posted by poohbear

This is a great idea, comrad!!!

There is no way that poohbear just stumbled upon this. I smell a troll thread!

[MikeBrock]

Ah yes, I am aware of the wheel orientation. I was quickly making a CAD and just used the mirror component tool. And yes, I am well aware of the individual power to each wheel.

As for the cantilevered shaft on the arm, I totally missed that, my apologies. It should be constrained in the center.

As for recoil, we are not worried about that, we plan on taking very close shots with this design so one pneumatic piston will be enough for power. We may add some sort of spring and release mechanism. The roller on the cradle of the arm is not in the CAD, but you might be able to see the mounting holes for it. Once I fix the CAD you will be able to see how the arm can swing down with ease to suck a ball in.

The frame is now going to be welded. Thanks for that suggestion.

-MB

[Crawler]

personally i would go with the base design they gave you, and not go with mechenium wheels unless you have a very awesome team of mentors that have done FRC for a while. Aside from that good cad, and i would love to see a catapult somewhere, i think most are going with a base ball type shooter

[goldenglove002]

If you're trying to keep it simple, why not just use the kitbot frame that comes in the kit of parts? You won't have to pay for anything extra, it comes together very quickly, and it's been proven to work. There's a reason FIRST gives it to us.

[mdiradoorian]

I am hoping that your goal is NOT supposed to go over the barrier because your mechanum wheels may break and will spend a lot of time to be fixing it at the competition. Other than that the inventor model is good.

[MikeBrock]

Originally Posted by mdiradoorian

I am hoping that your goal is NOT supposed to go over the barrier because your mechanum wheels may break and will spend a lot of time to be fixing it at the competition. Other than that the inventor model is good.

We plan to go over the bridge, not the bump. Implying that we might plan to go over the bump is a bit insulting to our intelligence. However, what if we added some sort of high strength shims along the front and back of the wheels (like fenders) out of something like steel or titanium. I think it would work in theory.

Why would mentor experience have anything to do with using mecanum wheels? There are boatloads of teams who have published mecanum drive code.

I was thinking; everyone complains about being pushed around with mecanum wheels. What if we used the internals of a shifting gearbox (they seem pretty simple) to make each wheel have two speeds? Then, a curved plate with some high friction material (traction tread) could come down on the rollers of each wheel and act as a brake. It would solve those issues but still allow us to strafe and slide around.

As for using the kit base: we don't see the need.

[EricH]

Originally Posted by Sean Raia

There is no way that poohbear just stumbled upon this. I smell a troll thread!

Nah, this one might actually be viable. Unlike a certain 4-traction-wheel arrangement...

This one just needs some tweaking. I believe I saw a team's video of a catapult design for Lunacy. (They didn't go with it that year.)

[scottydoh]

Originally Posted by MikeBrock

This is very true. How about waterjetting 1/8" plates for the top and bottom to hold together 2x1 tubing?

I see to need for a plate on both the top and the bottom. 1/8th or 3/16th plate on top of 1x1 tubing would be plenty. Or better yet, why not just use the provided kit bot frame? For the past 3 years my team has been using the kit bot frame with a water jet cut top plate for mounting and to keep things square (mind you, prior to 2008 they insisted upon custom building an entire frame, bottom plate + 6 walls out of 3/16 water jet cut plate...so much excess weight and time wasted on design). With the kit bot frame, we can usually have the chassis set up within the first week.

EDIT: Also, just another thought, I don't know how familiar you are with the Mecanum system, but each wheel needs to be powered individually, that means each wheel gets its own motor and gearbox. And from the looks of your drawing (which by the way is indeed very nice) Your wheels are outside the frame perimeter and thus illegal, unless of course your frame was smaller than 28x38.