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Jolt & friends - Team Overkill - NSW
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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There wasn't much visible damage, probably due to all that cement backing up the shell. The corner that was hit is a bit crumpled so that the top cover will never fit on again. I can just pour in more cement to replace the stuff that fractured and fell out, then the test bot is good to go again.
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Post Sun Sep 14, 2014 7:14 pm 
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haz



Joined: 15 Aug 2011
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Hi Nick.

You said you had to buy a full roll of Z type belting. Do you reckon it would be possible to buy a few meters off you and maybes a welding jig as well? Postage and stuff would probably be a pain in the hole but I'm not sure if I can get short lengths of the same stuff in the UK or Europe.

No problems if not Smile
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Post Tue Sep 16, 2014 6:27 pm 
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Nick
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You could easily make a welding jig, I just threw some random bits together to make mine. I will post some detailed pictures.

I'd be happy to send you of the belt at cost price, just let me know how much you need and I will work out the cost with postage. Sea mail is fairly cheap but take 2 months, air mail might be reasonable if I can fit the belt in a smaller padded envelope.
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Post Tue Sep 16, 2014 6:38 pm 
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Nick
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I found enough material to make a jig, so I will knock one up later tonight.
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Post Tue Sep 16, 2014 7:25 pm 
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Nick
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The jig turned out better than the first one I made:



I will get that sent off in the next couple of days.
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Post Thu Sep 18, 2014 6:11 pm 
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Nick
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Something for almost nothing

While trying to increase Mr Mangle's battery capacity, I took a gamble on a new Turnigy A-spec 3.7AH, 6S, 65C pack. I was using two separate 3.2 AH, 3S packs and Hobbyking listed the larger pack at almost the same weight.

When the new pack arrived today, it was only 17 grams heavier than the two smaller packs, while having and extra 500 mAH of energy - definitely something for almost nothing! All I need to do is open up the wrapping, add a centre tap wire and replace the wrapping Smile



This is the business end of the pack with most of the kapton tape removed. Two centre-tap wires have been added; they only power one drive ESC each so I can get away with 14g wire. The A-spec pack construction looks just as good as the name brands, very similar to TP and Hyperion; if the performance matches the packaging I will be very happy.

With the pack all wrapped up again, it now weighs an extra 50 grams, which isn't surprising as I added extra Kapton tape, two layers of foam, a UMHW tape layer over the foam and extra thick heatshrink over that.

Given that the original battery I used in the UK only had a 2.7AH capacity, adding an extra 1 AH or 37% will deliver larger hits for longer.
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Post Thu Sep 18, 2014 10:55 pm 
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Jaemus
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Joined: 01 Apr 2009
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Just watched your beater test video again and noted the following

- That thing moves an incredible amount of air, there is shit blowing everywhere

- Mr Mangle eats a bit of that palm tree frond that's laying in front of it before it gets to the target drone, and disintegrates half of it as though it never existed Razz

- I make your spin up time bang on 3.5 seconds, was that full throttle with the correct battery pack for the design?

- Kill spectators?!

Very nice btw, now buy a slow motion camera and film it again Very Happy
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<Patrician|Away> what does your robot do, sam
<bovril> it collects data about the surrounding environment, then discards it and drives into walls

Post Fri Sep 19, 2014 10:48 am 
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Nick
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Thanks for the analysis! All that air movement must be the reason why the current draw is so high - beaters are obviously very inefficient at high RPM. If I can find a good drum design, Mr Mangle could probably go quite a bit faster - I just hate the usual drum design with a heavy axle that does not contribute any kinetic energy.

The weapon can probably spin up a bit faster; the radio channel is set to 90% and the servo travel speed is set way down. The ESC may also be set to soft start, so if I turn off all those safety measures, the spin-up might come down to 2.5 seconds. The larger capacity battery pack might help shave a few milliseconds off if the voltage sags less. I can always stick in an 8S pack for a demo but its too heavy for the competition.

Kill spectators? There are some ant nests in the joints of the driveway but I don't want to be that sadistic kid with a magnifying glass Laughing

Watch out for another vid on the weekend with the the Exilim camera at 240 fps video.
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Post Fri Sep 19, 2014 11:33 am 
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Jaemus
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Excelllllent, very much looking forward to slow-mo precision destruction

Would it help to machine the beater's trailing edges to a more aerodynamic profile?
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<Patrician|Away> what does your robot do, sam
<bovril> it collects data about the surrounding environment, then discards it and drives into walls

Post Fri Sep 19, 2014 11:58 am 
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Valen
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Joined: 07 Jul 2004
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Try a block of foam in the core of the beater, might reduce the flow somewhat.

If you were keen you could totally encapsulate the beater in foam so its totally smooth on the outside then just let it explode away as it hits things.

(a super light open cell foam is what I'm thinking, so it'll just crumble before it gets in the way of anything)

Also you get to bring a broom to events ;->
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Post Fri Sep 19, 2014 12:02 pm 
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Nick
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I have some very light and still cellulose packing foam, but I am worried that when it breaks up, it will get wedged between the beater and the frame. The foam might just vaporise or it might be strong enough to cause motor or belt damage. Perhaps a slow speed test is in order.
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Post Fri Sep 19, 2014 12:11 pm 
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miles&Jules
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The foam idea might also be classed as damage to your robot…but don't let me stop you he he
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Post Fri Sep 19, 2014 5:10 pm 
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Nick
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This is the foam sheet, its very light and reasonably hard:



Two or three layers could be glued together and then shaped with the bandsaw; even a rough drum should dramatically reduce the turbulence. I think the foam is made of cellulose - any ideas on a glue that works best on that?
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Post Fri Sep 19, 2014 6:01 pm 
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Valen
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cellulose is the fiber in wood, so I'm going to suggest wood glue ;->

That looks a whole bunch like some packing foam we have, its *super* tough stuff.
it cuts easy but won't tear for crap.

I'd be after something like a PVC foam in the lowest density you can find like H35 or whatever, its tough but if you crush it it won't spring back at all. The 35 you can crush in your fingers and it weighs 35kg per cubic meter ;->

but giving it a try with that foam would tell you if its worth doing.
I wonder if a grinder on the lathe would give you a nicer "round" than the bandsaw?
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Post Fri Sep 19, 2014 7:23 pm 
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maddox



Joined: 21 Dec 2006
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We use a bench grinder mounted on the lathe to finish the cast polyurethane wheels.
LARP foam weapons we sometimes grinded down with a powerfile before latexing.

So yes, it's very well possible that foam reacts well to that kind of machining.

Post Fri Sep 19, 2014 10:07 pm 
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