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Cognisant



Joined: 20 May 2012
Posts: 24
Location: Brisbane


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Back again.

Got a water cooled air conditioner for way below cost price and I've taken it apart, from it I scored three motors, two identical DC motors with their tolerances written on them (can't go wrong there?) which have an rpm of 4, but for $12 I wasn't expecting the world, heck they're a bonus when I was only expecting to find the main fan motor, and now here's my problem. This one's about the size of my fist, eh a little bigger, it says on it "YSY single-phase AC Fan Motor" and I have no idea what to do with an AC motor, also there's a ground wire, one that would have gone back into the wall socket, that's a little concerning.

Anyone have any experience with this sort of thing, this is my first time cannibalising parts so I don't really know what I'm doing.

I work in Officeworks so I can get discounts on various items like printers and shredders and catch them when they're on clearance (like the previously $75 air conditioner I just mentioned) so I'm keen to find out how to reuse their motors, or even if their motors are worth using, shredders should be good I think, printers not so much.

The AC motor has a capacitor wired to it, of that helps any.

Post Fri Jun 08, 2012 4:23 am 
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Nick
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Sorry, That motor is only ever going to run off 240V mains, not batteries. AC (alternating current) is what you get from a power point, while what you need is a DC (direct current) motor. One good local source for motors is Oatley Electronics http://secure.oatleyelectronics.com//index.php?cPath=53&osCsid=4b18cc11fc97a751a48f6f4e6c0e90a4 The 100W scooter motors are pretty popular and reliable.

Post Fri Jun 08, 2012 7:35 am 
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Cognisant



Joined: 20 May 2012
Posts: 24
Location: Brisbane


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This is obviously too dangerous to actually do, but with an inverter and about twenty or so 12v batteries in series I could run the motor at 220v (which the sticker says it can do) at... Well it says 0.25A which I assume means amps per hour, although that's a much smaller number than I'm accustomed to.

Is that the trade off, are motors much more efficient at high voltages?

But considering the weight of the batteries (even if I only need small ones) plus the wight of the inverter (the smallest I could find was 2kg) and the undeniable likelihood that so many batteries in series will simply catch fire, it's probably not worth it, even if it wasn't likely to kill me if I tried.

Meh, this has been an educational failure and it only cost me $12.

Post Fri Jun 08, 2012 9:26 am 
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Cognisant



Joined: 20 May 2012
Posts: 24
Location: Brisbane


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Btw thanks for the link Very Happy

Post Fri Jun 08, 2012 9:27 am 
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dyrodium
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Joined: 24 Aug 2004
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There's actually rules limiting the voltage in robots and 240vAC would be way too much... Plus those motors are notoriously hard to control proportionately (if at all).

You're quite right, motors designed for those higher voltages are much more efficient.

One of the more useful electronics calculations is P=IV where P = Power (Watts) I = Current (Amps) and V = Voltage.

Very Happy Scooter motors are near bullet proof too.

PS Don't be tempted to buy the "150W 12VDC MOTOR" from oately, it's got a plastic housing and is completely useless for our applications... Sad

Post Fri Jun 08, 2012 12:45 pm 
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Cognisant



Joined: 20 May 2012
Posts: 24
Location: Brisbane


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Okay so how about gears, shafts, bearings, and so forth?

I know where to get a dremel and mounting that'll let me drill holes to specific depths, I figure I can drill a few of these holes in some HDPE, put the shafts in the holes, the gears on the shafts and another bit of drilled HDPE on the shaft's other end to keep it all together, or something like that

But how should I be doing this?

Post Sat Jun 16, 2012 3:18 pm 
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marto
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Are you looking at featherweights still? And what motors, gears, wheels are you looking at using.

By far the easiest way to start is http://www.robowars.org/guides/guides-drill-hacking.html

Steve
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Post Sun Jun 17, 2012 2:03 am 
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Cognisant



Joined: 20 May 2012
Posts: 24
Location: Brisbane


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Thanks for the link, I think I've got that figured out now.

I'm currently working out the details for a hexapod design with an internal flywheel powered weapon, either a thrusting spike coming out between the legs (I know, shut up Laughing) or a top mounted axe (well more like a horseman's pick) and I'm most concerned about two things, how much having the armour made will cost (titanium itself doesn't seem to cost too much, having 7mm plate bent and drilled may be expensive though) and if a rubber wheel being pressed onto the flywheel will be enough to transfer it's energy to the weapon.

With about 26kg to work with I can afford to have this thing armoured up, mainly on the legs, presenting effectively a wall of titanium bars to the enemy (with torsion spring shock absorbers, which should make landing a decent hit damn difficult) while the body hides high (not very high, but y'know high enough) in this protective caged, with it's own mix of titanium and HDPE armour.

Concerning the weapons I think the axe will give me more reach, but it'll be slow and easy to avoid, whereas a blade that sticks out from underneath (oh right, both ideas are meant to be able to turret around) should be much harder to dodge and will definitely discourage anyone trying to get in between the legs. Probably the biggest things I'll have to worry about is getting flipped, which will leave the belly open to attack while flipping back over, or a high powered spinner catching on something and ripping a leg off.

Tactically there's the concern that I'll be defeated by someone doing light hit and run, it doesn't matter if they don't do any damage as long as they're getting points and I'm not my bot may as well just be sitting there. So I've considered making the spike a tethered projectile, the mechanism that moves it is already uncannily like a tennis ball launcher in design, but I'm still figuring out how I could retrieve and reload it.

Post Mon Jun 25, 2012 2:20 am 
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marto
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This is not going to end well.

The complexity which you are attempting with no prior experience really means this is going to fail. Sorry but thats just the way it is.

Build something which can at least drive, maybe then add a spinning weapon or a spike but keep it simple. Don't even think about walking, and don't think that walking will give you more weight to make your robot better armoured. All the extra weight allowance is used up in the walking mechanism usually resulting in less or no armour.

Steve
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Post Tue Jun 26, 2012 10:32 am 
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Knightrous
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This is what happens to walkers.


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Post Tue Jun 26, 2012 10:53 am 
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Cognisant



Joined: 20 May 2012
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Location: Brisbane


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Wow, that was interesting.

But yes I get your point Knightrous, the weight was all up far too high and those impressively spiked legs didn't give it any traction, in effect that's a fancy looking beach ball, especially considering how powerful most robot drivetrains are. So if mine is going to stand it's ground at all it either needs to be fast enough not to get pushed around, which is unlikely, or I need to design it with legs that'll give it traction and sloped armour so anyone trying to push it will push it down and themselves up.


quote:
The complexity which you are attempting with no prior experience really means this is going to fail. Sorry but thats just the way it is.

Okay, I wouldn't learn anything if everything went smoothly Wink
The stigma of failure should never stop one from trying.


quote:
All the extra weight allowance is used up in the walking mechanism usually resulting in less or no armour.

The servos themselves aren't all that heavy, most are only about 100g and I'll be using three per leg, practically bolting them to the back of the armour, if each leg weighs 3kg and if only 1kg of that is the servos, wires, shafts, bearings, mountings and springs then that means there can be 2kg of armour. Assuming I'm way off on my estimates and I only end up with 1kg of armour that still seems okay, the figure I have for titanium is that it's 4.506 grams per centimetre cube, 3.154 grams per 7mm thick centimetre square, meaning 1kg gives me about 317 square centimetres, which is roughly a 17x17cm sheet, and I don't plan on this thing being any bigger than it absolutely needs to be.

Will it be quick? No.
Will it be able to lift/flip an opponent? No.
Will it be able to push the opponent around? Perhaps, in a pathetically slow way.
Will it be able to climb? Slightly better than the other bots, but still terrible.

What it should be good at is:
1. Being hard to move (six rubbery contact points, flat ended)
2. Being hard to damage
3. Having a +5kg weapon system (leaving 3kg for batteries, frame, receiver)

Post Wed Jun 27, 2012 1:02 am 
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Knightrous
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Go down to Bunnings and buy a few sheets of 6mm MDF and build a prototype. Bring it to an event and have a play with one of the nicer pushy / wedge bots and gauge your expectations from there. You might save your self $2000 in Titanium and learn some things in the build process Smile
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Post Wed Jun 27, 2012 1:16 am 
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marto
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quote:

Okay, I wouldn't learn anything if everything went smoothly
The stigma of failure should never stop one from trying.

"Good advice is always certain to be ignored, but that’s no reason not to give it."

I am not saying that it is impossible just that your way out of your depth. C'mon 4 posts ago we were using AC motors... its all good to try and learn new things but I am still pretty sure you are going to learn quite a lot from building a box with wheels. And it might actually get to compete.


quote:

The servos themselves aren't all that heavy, most are only about 100g and I'll be using three per leg


On a 3kg leg.... really... The servo we used for our pit door was 160g and there is no way that would be robust enough to put in a feather leg. Not to mention the price of big servos and needing 18 of them. (You have just spent over $1000 right there) Even if it is strong enough the first impact it takes your very likely to strip all the gears. Build a prototype leg out of MDF then maybe you will understand.

My goal is not to dissuade you from building something or something interesting at that but at least do yourself a favour and try to learn to crawl first, what you are attempting is like trying to fly ... from the top of a cliff ... a very high cliff.
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Post Wed Jun 27, 2012 1:47 am 
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Cognisant



Joined: 20 May 2012
Posts: 24
Location: Brisbane


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The Hitec HS-5995TG stalls at 30kg with 7.4v and ServoCity sells sprockets and gears that will mount directly to the servo head giving it a mechanical advantage of two maybe three depending upon the size of the other gear/sprocket (obviously at a proportional loss of speed) and that will be transferring power to the shaft via a torsion spring, which will act as a really super heavy duty servo saver, although the leg itself may add leverage to any incoming impact... Ehhhh.

There are stronger servos, but they're disproportionately more expensive, I don't really know how big a torsion spring I can get away with yet, and there's the simple pain-in-the-ass problem that I haven't found accurate schematics of the servos yet and everything is built around them so I can't start designing in earnest until I've actually bought the damn things and measured them myself.

*sigh* Really want to be working with microcontrollers, my sort of thing y'know, I live in an apartment so needless to say I don't have a tool shed, I have a single tool box under my bed, so nearly everything I need I'm really going to need to have made for me and once it's made that's it, I'm stuck with it, no welding shit on and cutting shit off, so y'see if I'm going to be spending money at all I feel like the best investment would be something I can fiddle with (software) and reuse parts for other projects (the servos) if not the entire mobile platform (a hexapod) for other non-combat tasks (like following me around work with a big nerf gun on top).

I understand it must be frustrating to see me stubbornly pursue things that may well be beyond my immediate reach, but what drives me to do so is a longstanding passion for AI and by necessity robotics, a passion so strong that every day that goes by where I'm not a step closer to my somewhat Asimovian vision of the future makes me feel like some small part of me has died, so y'see the hexapod isn't just a means to an end, a tool to play some game, it's a chance for me to tear through the mundanity of the present and seize a part, if only a small part, of the future that I dream about.

In some totally insane way being told it can't be done just encourages me, and I have to fight that because you guys have raised some really good points and it is clearly to my benefit to listen to them.

I've got some little hobby servos from Jaycar, I'll build a trial leg with them and abuse the hell out of it, test some other shock absorption ideas, see what breaks and where, that'll be fun, I've also got some 0.016 aluminium plate around so I'll work on an ant/beetle weights in between other stuff and focus purely on it if I start running out of time.


quote:
You might save your self $2000 in Titanium and learn some things in the build process
A&E metal merchants don't charge quite that much, so I guess you're including the cost of machining it, or you're not and it's even more expensive, eh okay well trial leg first, then I'll look into other armour options, I kind of wonder how easily gouged HDPE is, deep gouging would be bad points wise but it would certainly absorb some of the impact forces and as long as it's suitably protective I can always upgrade to titanium later.

Btw I've been watching some of Scarlet's fights, that is one vicious little bot Shocked

Post Fri Jun 29, 2012 2:32 am 
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Knightrous
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quote:
Originally posted by Cognisant:

Btw I've been watching some of Scarlet's fights, that is one vicious little bot Shocked


Scarlet is a simple 150g antweight, built mostly on my kitchen table (except a small run on the milling machine in the garage). It has about $100 worth of parts in it total. Get yourself into the sport by building an antweight Smile
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Post Fri Jun 29, 2012 8:20 am 
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