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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Here's a handy site for getting the energy in as flywheel:

http://www.calculatoredge.com/mech/flywheel.htm

Energy is dependent on mass and rpm. A 12V 4Ah battery (for argument sake) has 48 watt hrs = 170,000 watt seconds or joules.

If 90% of that went to drive and 10% to weapon that still leaves 17,000 joules of weapon energy. A flywheel would have to be heavier than the robot itself.

Sure there are losses, but you get the picture.
Correct me if I'm wrong.

Post Thu May 12, 2011 8:33 am 
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Fish_in_a_Barrel



Joined: 30 Sep 2006
Posts: 673
Location: Perth, Western Australia


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That calculator fails to take the shape of the flywheel into account. There is a robot calc around that nick has used which accepts the dimensions of the disc and will give more accurate results, plus spinup times iirc.
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Post Thu May 12, 2011 9:50 am 
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Knightrous
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Joined: 15 Jun 2004
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http://teamcosmos.com/ke/ke.shtml - has a good kinetic energy calculator
http://robots.freehostia.com/Spinningdisks/Disks.html - has all the old school maths and crap for calculating it manually.
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Post Thu May 12, 2011 11:48 am 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Those two sites are excellent, I go back to them all the time. Don't let me talk you out of a spring, but if you think of a vertical spinner like Demon as using a flywheel, they can have a very effective punch and adding a hammer to that would give you almost as much energy but in a downwards direction. One thing that might be hard with a flywheel is resetting the axe.

With a spring, you not only need it to store the energy, you need it to release the energy in the shortest possible time to accelerate the hammer. I recall seeing several epic fails of spring-powered weapons on Junkyard wars, where the springs had too slow release and travel to be effective.

The other classic axe mechanism is compressed gas; that has a whole different set of advantages and drawbacks

Post Thu May 12, 2011 12:38 pm 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Good points all.

Forgive the obvious, some visualizations on what joules are:
10kg dropped from 1 meter is 100 joules (typical spinning weapon, I think?)
100kg dropped from 1 meter is 1 kJ

I'm whizzed up from seeing Thor and the much smiting with hammers. Totally cool and I'm so down with it that I wanna try it.
But, we could kick flywheels around ad infinitum, ad absurdum, ad nauseum, but onto loftier matters:

There's an ethical question about sophisticated weaponry. Does it defeat the spirit of robot warfare? For that reason cutting lasers and untethered projectiles are banned. When does it become about the weapon, relegating the robot to a mere platform?
Which bring me to the next point.
I hope to employ another feature to hopefully compensate for the lack of armor. I want to use "plays". Whilst fully autonomous robotics is still largely out of reach, brief bursts of autonomy are very doable. Short duck-and-weave routines that are faster than human reaction time can be programmed which would give a machine attributes more like a true robot and less like a remote manipulator.

Post Thu May 12, 2011 1:02 pm 
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dyrodium
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Joined: 24 Aug 2004
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Semi-autonomy is very much encouraged, however the main point remains, you have to make sure it's disabled right up until a fight kicks off. Mostly just safety. For that matter, you can have your weapon fire when it detects another robot autonomously, that is all perfectly in the rules and would allow you to eliminate operator lag. Smile

I seem to view the rule set as a mix between safety and entertainment, lasers and bullets would probably do nothing to most robots but would kill.blind us fairly quickly! Most high damage potential robots are exactly that, a weapon and the rest of the bot is simply a weapon delivery device.
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Post Thu May 12, 2011 1:13 pm 
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marto
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Joined: 08 Jul 2004
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Cutting lasers I don't really know if they are banned but in any case would have 0 effect on a robot. Things can barely cut a few mm of plastic and could not be powered by batteries.

Untethered projectiles are banned as someone would put a gun or equivalent on a robot and end up killing someone which would be bad for our safety. Also in australia we have gun laws which could get in the way, in the US not so much.
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Post Thu May 12, 2011 1:19 pm 
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Fish_in_a_Barrel



Joined: 30 Sep 2006
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Location: Perth, Western Australia


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The lasers and projectiles are rules about spectator safety. The the tether is supposed to prevent the projectile from hitting or going through the arena wall.

The laser would have to be proven not to damage the arena wall and be safe in the case that someone looked directly at it. It is highly unlikely for any cutting laser to be safe in that regard.
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Post Thu May 12, 2011 2:05 pm 
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Knightrous
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quote:
Originally posted by frogbiscuit:
Forgive the obvious, some visualizations on what joules are:
10kg dropped from 1 meter is 100 joules (typical spinning weapon, I think?)
100kg dropped from 1 meter is 1 kJ


A simple 24" long, 2" wide, 0.4" thick steel bar (5.45lbs/2.47kg) spun at 3000rpm produces 3.8kJ. That is the specs for an average spinner, when you start looking at robots like Demon where they have optimised discs to have significant amounts of MOI on the extremities of the disc and backed by a high powered, high speed brushless pushing the weapon to over 5000rpm you soon see the energy go much higher. The forementioned 2.47kg steel bar spun at 5000rpm is 10.5kJ of kinetic energy.

Consider some armor Smile
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Post Thu May 12, 2011 3:35 pm 
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Nick
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True, 100 J would be OK for a beetleweight nowadays. I haven't calculated it recently, but Scissorhands weapon bar used to develop around 4.3 KJ and its heavier now.

Post Thu May 12, 2011 4:10 pm 
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Valen
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Joined: 07 Jul 2004
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Location: Sydney


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I really don't mean to rain on your parade but if i might make a suggestion.
make a MK0 bot first, a plank of wood with 2 motors and a battery, get it driving around

Swing by a comp and get a feel for things, see the wall of shame/pain ;->
The impacts are a lot harder in real life than they look on the videos.

leaping for the uber bot first time out normally seems to get disappointment.
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Post Thu May 12, 2011 4:51 pm 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Ok, you guys know your stuff. Mothballin' the monster and gettin me a piece of plywood.

To Jaemus:
In answer to your question, the bogie motors weren't end-to-end but angled with U-joints to they'd fit on 12" carousels.

Post Fri May 13, 2011 8:10 pm 
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marto
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Joined: 08 Jul 2004
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Location: Brisbane, QLD


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Nice. I would still like to see it built even if just for the awesome factor but I don't think it would be feasible to make straight up.

I was thinking ..... why not ditch all the fancy control and make it a cluster bot with 3 separate bots which sort of sit in..... once the top/weapon gets knocked off they could continue to menace the opponent. Of course weapon would be somewhat disposable but might be cool.
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Post Fri May 13, 2011 10:08 pm 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Haha, sick. You are one twisted puppy. I like it! A cluster.

Hey, gotta ask you. You said:
"...QLD or VIC you might get away with 0 armour. NSW no way..."
That's saying something, that the most badass state is not your own.

I've sorta already done the motor-on-wooden-blosk thing. Existing robot has 2 of the lamo J-motors mounted and the other 2 bogies are locked in place. In that config it still hauls its sorry ass around the room.

Having trouble with the I2C at the moment anyway, All that master-slave stuff for mutltiprocessor systems. Neural nets do have their attractions.

Just wondering, wonder if there's a way to keep australian expertise in australia?

Don't think I mentioned, the automatons speak to me in tones loving and unheard, and entreat me not to take refuge in the harbor of the tranquil.

Arg, I may regret that 4th whiskey in the morning...

Post Fri May 13, 2011 10:46 pm 
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marto
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Location: Brisbane, QLD


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QLD well Vic not so much any robots anymore seem to have a lot more interesting robots with less emphasis on the spinners and bricks. NSW seems to have a bit more of a spinner/wedge going on.
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Post Fri May 13, 2011 11:07 pm 
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