Best way to obtain/make metal sphere

[Numaholic]

Hi everyone.

I am part of a team were our aim is to fight off robots which we build for fun. Our design was a ball robot, which simply uses its mass (with high defense hopefully) to 'crush' opponents.

Anyway, the problem is I was looking for a metal sphere for our robot, or preferably two hemispheres which we can attach together with screws, however due to where I live I can't really find any. The only metal scrapyards that exists have stores where you buy sheets of metal or can ask for a custom shape, however I imagine that they are expensive.

I don't really have many tools available, mostly just a dremel, but I may have a friend who has some tools, but I doubt they do much. I was wondering of we could get a mold, buy a sheet of metal and hammer the thing into shape. I don't know if that would result poorly, or if we can find a mold strong enough to bash with a hammer. Also, the metal has to be fairly strong because other people will be using weapons like hammers against us, so there is a bit of a contradiction with trying to use a hammer to bang it into shape.

As you can see, our team is a bit stuck. I thought you guys might have a few ideas to help the problem. Thanks!

 

[Danger]

Nothing springs to mind, but I'll think about it. How big do you want it to be?

 

[huntoon]

Buy an old globe. Then armor it.

 

[Danger]

Great idea, Huntoon. I'd forgotten that they used to be made of metal. All of the new ones seem to be shellacked cardboard or maybe plastic.

 

[huntoon]

Maybe do something like this cut from sheet metal?
(from here: http://www.quadibloc.com/maps/mpo0501.htm)

 

[256bits]

Make your own sphere. Obtain 3 strips of flat metal, say an inch wide and thickness you desire and length approximate to the circumference of your sphere. Make 3 loops with the strips and apply each loop at 90 degrees to one another so that you have some semblance of a sphere. Rivet each loop to the others where they contact by passing over one another and voila you have yourself a sphere framework of desired size and strength. You have acces to the interior thru the spaces which you can cover up with some sheet metal or mesh and curve that if you wish. That should be certainly a lot more to the capabilities of a limited supply of tools. In addition you can put cross members across parts of the framework for extra strength and a place to put you internal drive mechanism and whatever else needs to be put in there. A lot cheeper and a lot less work than banging out a whole sphere from metal.

 

[Numaholic]

Thanks for he great ideas.

At the moment I'm not sure of the exact size, I've emailed the person making the rules. I think it was a cubed meter from memory.

The easiest idea might be the one 256 bits suggested. I looked up old world globes/metal globes on the internet briefly, but the problem is I'm in Australia and the cheapest ones seem to be from America. Of course shipping will be a lot for me, probably around $50. The ones I found on Australia (Ebay) were more expensive and had a far less range (some were more expensive than $200).

Huntoon's method I still have to cut, which I haven't had much experience in or may not have the tools, so it would be easier than to cut rounded metal strips. I can easily buy metal sheets where I am, so that should be good. I think then I'll place metal sheets in the inside as well of several layers of different shapes so it is fairly strong.

The problem with my layering idea that will get rid of access to the inside. The hemisphere idea might be good here. I could make the hemispheres separately, although my measuring will have to be absolutely precise to make sure I can fit them together. Then on one hemisphere I'll have almost a metal tab sticking out so i can just screw the two hemispheres together.

Does this sound all okay? Thanks everyone for the help, it is much appreciated.

 

[Danger]

There's another approach to this, but I don't know whether or not it fits the requirements. One simple question will solve that. Does it have to be metal?
It seems to me that some sort of polymer would be better suited to the whole idea. The mass that you want for crushing things can be internalized with a blob of tungsten or lead. (Maybe use lead-acid batteries to consolidate 2 purposes.) Any thin metal is likely to be more vulnerable to cutting/poking/drilling attacks than a suitable plastic is.

 

[huntoon]

here's a way to up your cool factor, maintain access to the inside, easy (ish) to construct, and still be round.

make a bucky ball / fullerene!

 

[Numaholic]

I do not need to use metal, it was just the first thing that came to mind that could take some force and be solid enough to roll. I don't know terribly much about the different properties of different polymers, so I'm happy to listen. It just has to be available where I am, and be practical in the sense of the amount of tools I have.

The bucky ball looks cool, I must admit, but it may not have a good defense. I imagine there will be other robots trying to destroy me with hammers and the like, so I will have to plate the stuff in the inside. That will then make it inaccessible unless I cut the thing.. it all gets a bit complex. However, I will keep it in mind, it is pretty fancy to look at.

Just for some more extra information which may be relevant to what you guys are thinking, here was the main design I was basing the robot off:

http://www.instructables.com/id/Remote-Controlled-Basket-Ball-Robot/

 

[Danger]

That's a mighty cool link, Numaholic. I think it provided me with a new way to tease my cat.
As for the type of plastic, I was thinking along the line of polyethylene about 80 mil or more in thickness. It's easily available from restaurants in the form of used cooking oil buckets. It's tough as nails, but still reasonably flexible.
Although you didn't mention it, I figure that you're also going to have to coat the thing with an outer textured material such as hockey tape to provide traction.

 

[rorix_bw]

There are a lot of television shows like this (combat vs radio controlled machines) which you may like to study for ideas.

A quick google found this, which, down the bottom, has links to the information pages of the winning machines. These machines are quite large: a meter in length and 100 kilograms in weight.

http://en.wikipedia.org/wiki/Robot_Wars_(TV_series)

Weapons seem to a wedge shaped robot with a flipper to turn others upside down, or various armoured boxes with rotating "hammer arms", plus Razer which has a piercing spike "jaw". Not all the designs have photographs in wikipedia, but they are not hard to find with further google image search.

 

[Aero51]

Are you sure this rolling robot idea will work at all? It seems like the ideas you have will be difficult to implement and may compromise the integrity of your final product.

 

[Numaholic]

I just got more details on the rules, no sharp objects are allowed (or flames, chemicals etc.) so drilling and cutting shouldn't be a problem.

If I made really thick layers of polyethylene that would be strong. The only problem is that the weapon of the ball is its mass, so adding mass inside might be complex. Also, the polyethylene being soft may make the design more difficult to implement and not stable enough to put the chassis and all of that in. Although it may a very nice layer for the outside on top of the metal for extra defense. I found this:

http://www.ehow.com/how_10029798_make-polyethylene.html

So I could hopefully get some chemicals to make this.

I was looking at those types of robots, but since blades and all of the main weapons can't really be used, it makes those designs have less strength. I also thought no one would expect a rolling ball to appear, and have no idea how to attack it. They would all be close range and when they have to come to attack, they will be bowled over. I was thinking of having a flipper, but I thought the ball design was so stupid no one could beat it.

Also, I just realized a problem with the plastic. It will be flexible and not hard, so it won't do much damage to the robots. However, inside padding may be good.

This competition is just meant to be a bit of fun, and I don't even know if others are using metal because they are not taking it seriously, so I don't have to make an evil robot which will take over the world.

The ideas may be difficult, however I have another 4 months or so. Our team is fast at working once we get the parts, it is just that we are having that problem now.

There is another added complexity with making two separate hemispheres, that is getting the metal to bend perfectly into shape. I'm thinking off making the sphere then just cutting it down the middle.

 

[chemisttree]

I'd just make a hermetically-sealed robot that sprayed graphite powder everywhere. My tires would be spikes for traction and theirs would be spinning and eventually shorted out by the electrically-conductive weapon of mass destruction...

 

[Danger]

I'd just make a hermetically-sealed robot that sprayed graphite powder everywhere. My tires would be spikes for traction and theirs would be spinning and eventually shorted out by the electrically-conductive weapon of mass destruction...

You are truly a nasty bastard! Good on ya, mate.

 

[rorix_bw]

I'd just make a hermetically-sealed robot that sprayed graphite powder everywhere. My tires would be spikes for traction and theirs would be spinning and eventually shorted out by the electrically-conductive weapon of mass destruction...

Unless the organisers are unprepared or nuts they will have a provision against dropped weapons (e.g. oil jets), non captive bolt ranged weapons (e.g. guns, sprays) and systems (e.g. spiked wheels) that damage the arena floor.

 

[Aero51]

The ideas may be difficult, however I have another 4 months or so. Our team is fast at working once we get the parts, it is just that we are having that problem now.

This is a dangerous mentality for a team design^^^. I was speaking from experience earlier. I was on an RC aircraft design team for four years and it is very easy to have things go south if just 1 part of a plan does not come together. Have a back-up plan and do not assume anything!

 

[rorix_bw]

I haven't seent he rules but I am skleptical about how a sphere will work.

How do you move it, how do you steer it, and how does it attack?

 

[Danger]

How do you move it, how do you steer it

By shifting the internal mass. Take a closer look at his link. The attack aspect is what worries me. He hopes to crush the opposition, which I doubt is possible.

 

[rorix_bw]

Looked at plans. I see that it won't have to worry about wedge shaped robots getting under it and then flipping it up with a flipper, assuming it is robust enough to suvive violent inversion.

My thought are that I don't see much traction or steering ability compared to e.g. a conventional 4 wheel chassis. It's going be even harder to control if anyone bumps into it, or continues to bump into it, since it the controls will change orientation each time.