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electromagnets
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Glen
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Joined: 16 Jun 2004
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electromagnets

well in a bid to try something new and unoriginal every weekend im toying around with electromagnets this time round.

ive wound myself a big electromagnet out of a 5mm diameter piece of iron rod thats about 300mm long and uses 18g all over it. problem is i hooked it up, and the test box section leaped up into it!

BUT the battery started smoking, because dumbass me didnt realise that the electromagnet was basically a piece of wire shorting the battery leads together Crying or Very sad

question being, do i need a resistor in the line or what??

me and my dad have been scouring the internet in an effort to try make ourselfs an rail gun spike. concept and construction seems do-able, just trying to figure out wtf a compulsator is Shocked, anyone know?
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Post Sat Sep 04, 2004 1:13 pm 
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Knightrous
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Compulsators are used for big big rail gun projects, they cost thousands of dollars, so you'll have to give that a miss. Other amateur Railgunners use large Capacitors for there projects.

www.powerlabs.org is a good place to start, Sam Barros has made a fairly cool railgun and fired it a few times.

www.voltsamps.com is another great place, very similar to Sam Barros, but this is run by Slava Persian. Slava and Sam both appeared on Tech TV together with a demonstration on "Microwave Fun"
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Post Sat Sep 04, 2004 1:57 pm 
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Totaly_Recycled
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mm what size batery were you useing and what gauge wire were you useing
It sounds like you were useing not enough turns of way too thick wire for the voltage aplied to the winding .Although it usualy the wire that starts smokeing so you must ahve been pulling heaps of amps

Post Sat Sep 04, 2004 3:30 pm 
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Glen
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well its 18 gauge wire and i was using two 2.3ah slas in parallel.

so im guessing more turns of thinner wire?
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Post Sat Sep 04, 2004 3:47 pm 
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kkeerroo
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The thing to remember about electromagnets is that the strength of the magnetic field is proportional to the current. The more current, the greater the field. If you reduce the current you will reduce the effectivness of the coil.
The "guns" from the above websites use large capacitor banks to discharge the large currents needed to move the projectiles. As stated, these currents can be over 10kA at meny 100s of volts! Do not play with these things unless you know exactly what can happen.
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Post Sat Sep 04, 2004 3:47 pm 
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Totaly_Recycled
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To Answer your question Glen --its a little bit complicated ..but i wil try to be simple and iff im wrong some one more knowledgable can cut me down ..lol

If you are makeing an electro magnet - as you make coils each coil will produce lines of magnetig induction in the iron core it is wraped around.
This induction wil also couse a resistance in the wire carying the current so the more turns you put on the more lines of magnetic force are getting induced into the core this causes more resistance ...

So the longer the wire the less curent it will cary as the resistance causes voltage drop .
There are lots formula's for working it all out but it gets prety involved with maths .

The best way i have found if you are experimenting is to put on as many turns as posible . then drop off turns until you get a reasonable current draw that doesnt exceed the amperage limit of the wire or in your case the battery ..and stil give a strong magnet .

When makeing the coils try to keep them as tight togther and as neat as possible once you get to the end of the core with the first winding start winding on top of the first one with the second layer going back along the core to the start then put the next layer on top going towards the other end again again and so on.

With your magnet i would start with about 20 to 25 mtres or so of wire and try that at 12 volts if its reasonable but not going over about 8 amps try 24 volts .The more turns you put on the more voltge you will need to get the same amout of curent to flow through the wire but more turns also creates a stronger magnet..

What you need to get is a ballance between a strong magnetic fied and too much current draw. High curent s create heat in the wire carrying them so if the magnet is geting real hot prety quick then you need to add more coils or drop the voltage aplied .
I Hope this helps and mabee some one else can add more or clarify it further .. I was trying not to get too technical ...

Post Sat Sep 04, 2004 10:20 pm 
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Valen
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electromagnets arent that good for robot wars i dont think, the power consumption to get a decent magnetic field strength is pretty heavy.
i dont mean to disparage glen at all, i am all for the funky magnetic battles *w00t* we can use the star trek solution and reverse the polarity of some shit to solve our problems *bonus*
(ever heard the song by i think "3 dead trolls in a baggie"? main line is "thats the way we do things lad we're making shit up as we wish" dissing ST)

interesting idea would be the aluminium edy current magnet, (a magnet that works on alumium, nifteh eh?)
downside would be that its probbly against the rules on the grounds of RFI/radiated magnetic fields heh and you thaught you had RFI problems before.

some of the *big* neodinium magnets perhaps could be a fun play toy, anybody got ni-cad batteries around?

Post Sat Sep 04, 2004 11:43 pm 
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Maelstrom



Joined: 18 Jun 2004
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Well electromagnets are against the rules.
Compulsators are highly dangerous (a heavy flywheel at high RPM that can explode violently, military type experiments are still trying to make them "safe" but no success yet, most attempts fail catastrophically) and no amateur has succeeded in making one.
Railguns use 10's of kiloamps but usually into the 100's of kiloamps at usually 300-1000 volts = highly dangerous unless you absolutely know what you are doing. It will vapourise your arm or more of you. This would be an unrestrained projectile weapon and against the rules (there is no way to overcome this).
The aluminium eddy current idea does not attract but repells and requires at least 600 volts at hundreds of Amps for a really small effect (small piece of 10-20mm diameter copper pipe/aluminium tubing only mm in length), for the effect you want you are looking at at least 6000 volts (16000 works better) at 1000's of Amps or more using Pulse rated capacitors any other capacitors will explode violently.
http:/www.voltsamps.com has been shut down by Slava Persion due to asshats injuring themself and others with dissected microwaves and blaming him for it.
You will get RF interference when the electromagnet is switched on and off and seeing as it will be inside your bot it will probably kill your electronics or at least interfere with them far more than it will your competitors electronics, so forget it.


quote:
we can use the star trek solution and reverse the polarity of some shit to solve our problems *bonus*

Reversing the polarity won't achieve anything other than a magnetic field that is polarised the opposite to before.

I don't mean any offense but these ideas are bad for anyone that does not have a lot of experiencce with high voltage at high current let alone extremely high voltage at extremely high current.

Post Mon Sep 06, 2004 12:29 am 
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Valen
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electromagnets cant be against the rules, they are what makes the motors work?

a DC electromagnet should be under the same rules as a standard magnet shouldnt it? though i spose the pulse could cause emp style damage to another bot.

the point about reversing the polarity of a standard magnet was it would reverse the polarity of the field, that whole like repels and opposites attract etc.

hmmmm
/me looks at calling enemy robots IBC's radio inteference wepons in last ditch attempts at wheedling out of a loss;-P
(note this is a joke)

Post Mon Sep 06, 2004 1:14 am 
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prong
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I think you missed the point. Glen is experimenting with much lower amperage and voltage electro-magnets than you are talking about. As far as i can see from reading the rules his magnet is fine as long as it does not cause and sort of electronic interference with the other robot.

A compulsator does not have to be dangerous, people have succesfully built them and if you search around a bit on the net you will find instructions on how to rebuild electric motors to create one. Maybe the army will build a huge one that could potentially shatter and be dangerous but we are talking about a 12kg robot here, the compulsator Glen could possible use would be very small. That said there is almost no point in actually using one as far as i can see, ni-cd's or Lead Acid batteries will supply the current he needs.

As for the railgun being an unrestrained projectile, where did Glen say that? He talked about using a railgun spike, basically a large solenoid. There is no projectile, just a spike to attempt to puncture etc other robots.

I think the word railgun is the word that mislead you, but having a large electromagnet that used say 100amps or so that when turned on, created a magnetic field that repelled or attracted a shaft through its centre (same as a solenoid) you could get that spike moving quite quickly. Not sure how well it would work but maybe you could also use some strong magnets on the shaft to give the electromagent something better to attract or repel. The spike would come out of the robot, but like a gas powered spike weapon it would never leave the robot completely.

Another use for the electro magnet would be to try and get a hold on the other robots, but this could be tricky. I also agree with Valen, the power usage on the electromagent will be very high, bit still it is an interesting thing to experiment with.

As for RF interference it will be an issue, as will the high voltage spikes from the electromagnet when it is turned off but since Glen is only using fairly low voltages it should not be too hard to isolate satisfactorily.

I do not mean to sound rude Maelstrom but it bugs me when people discourage other peoples ideas when they have not even read the persons idea properly or even have a good understanding of what they are talking about. Next time read the posts properly and do a bit of a search around on the net so you are up to date with what you are talking about. Also not every comment on here is serious, its usually pretty easy to tell the little jokes apart...

Post Mon Sep 06, 2004 1:15 am 
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prong
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what Valen said too Very Happy

Post Mon Sep 06, 2004 1:18 am 
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chris



Joined: 18 Jun 2004
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I have learned not to play around withb electromagnets, I made an electromagnet my science project last year and hooked up a 7amp battery up to an 18 inch rod between 2 peices of wood. the ends of the wire that i wrapped around the rod had a peice of wire sticking out of the end of the insulation and it shorted, burnt my hand, burnt the wood and almost blew my battery.... thats foor for thought... just remember to make sure that all wire is insulated.
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Post Mon Sep 06, 2004 5:54 pm 
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kkeerroo
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Has anyone considered the weight of the wire. Iron cores and formers not to mention batteries that will be needed to make an effective electromagnet?
Also rail guns do not use electromagnetic coils, thats gauss cannons. rail guns have two rails (hence name) with the projectile between them and use Lorenz Forces to move the projectile.
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Post Mon Sep 06, 2004 7:06 pm 
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Totaly_Recycled
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Yes have thought of that Vertex's magnet is built into the fly wheel as part of the wheapons weight .. the intermiediate reduction pully is an alternator so the I/c motor can top the batteries up while running Very Happy

Post Mon Sep 06, 2004 10:20 pm 
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Maelstrom



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When you connect power to an electromagnet it will cause an RF spike, when you disconnect power it will cause an RF spike which means it will cause RF interference and that is why Robotwars, Battlebots etc have banned them!
Reversing the field of an electromagnet will NOT cause it to repel, iron is attracted to either polarity tha same amount, only NON FERROUS metals are repelled by a pulsed or moving magnetic field, a continuous field has ZERO effect on non ferrous metals, I suggest you try it for yourself!
Where are the links to websites with compulsators that actually function and can deliver any significant current as good as or better than a pulse capacitor, I personally know people who are trying this for railguns and other devices requiring high amperage pulses!
Even a small compulsator would explode violently if there is even a small amount of stress fracturing in the metal or other material!
Show me actual scientific experiments not pseudoscience (which there is a lot of on the net and is most likely what you have seen)!
That aside the weight required would mean you would have to go into the 100Kg class just to have the compulsator let alone the weapon powered by it!
Railguns only work with short projectiles, long ones would weld to the rails, even short ones do this sometimes (again I know people who experiment with them)!
Using an electromagnet to drive a spike like a solenoid might work but again the weight problem and RF interference make this useless and would require the use of pulse capacitors (I know as I have been researching coil guns and built a small one)!
I do have a good understanding of these technologies, as stated above I have been researching electromagnetics, most specifically pulsed magnetics (you obviousely do not Prong)!
Kkeroo is right about the weight, it will be too much once you take into account the iron core, wire and batteries!
I am not trying to stop people from building just trying to stop people from electrocuting themself or being injured by schrapnel!

Post Tue Sep 07, 2004 10:39 pm 
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