Electronics

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Primate
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Re: Electronics

Post by Primate » January 13th, 2010, 5:06 pm

I know this is kind of a different direction, but it still ties in to the electronics discussion. Basically, we're having trouble finding items light enough to be blown by wind power and levitated by electromagnets that are also strong enough to make electrical connections.

For example, we're blowing a rather light metal cylinder onto two terminals, but for some reason or another it refuses to complete the circuit. Do you guys have any suggestions for making these little gizmos work?
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Re: Electronics

Post by cypressfalls Robert » January 13th, 2010, 5:11 pm

Primate wrote:I know this is kind of a different direction, but it still ties in to the electronics discussion. Basically, we're having trouble finding items light enough to be blown by wind power and levitated by electromagnets that are also strong enough to make electrical connections.

For example, we're blowing a rather light metal cylinder onto two terminals, but for some reason or another it refuses to complete the circuit. Do you guys have any suggestions for making these little gizmos work?
for the wind , just make a sail---wright stuff type

and for the electromagnet a steel BB or ball bearing works

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Re: Electronics

Post by Dark Sabre » January 13th, 2010, 5:49 pm

Primate wrote:items light enough to be...levitated by electromagnets that are also strong enough to make electrical connections.
It depends on what you are using for power (how many amps can be sourced), but you can wind a pretty powerful electromagnet.

I wouldn't "levitate" anything. I would just wind the wire around a nail and have a ball bearing stick to one end. When the electromagnet is turned off, the ball bearing drops onto a see-saw or a switch, neither of which take a large mass to actuate.

This was mine:
519|30/DarkSabreMission 2005 (5).jpg
The ball is in the bucket there and you would use a microswitch instead of a light gate, but the basic premise is the same.

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Re: Electronics

Post by Primate » January 14th, 2010, 9:04 pm

Ah, that makes sense. Well, the problem is the electromagnet is extremely temperamental; it seems to work initially, but after repeated use without rest it just dies. I wonder if I'm pumping too much voltage through it. It's currently hooked up to a nine-volt battery.
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Re: Electronics

Post by Dark Sabre » January 14th, 2010, 11:00 pm

If it is dying, then you are probably pushing more power through it than it can dissipate through heat. The heat builds up, melts the coatings (enamel stuff on magnet wire or the plastic/PVC coating of normal wire) on the wire wrappings, and then you have shorts between wraps. That's what I would guess is happening. If the electromagnet is very hot to the touch, that's the problem.

Unless you have very, very few wraps, it seems strange that you would have that problem with a 9-volt battery. The little 9-volts are notorious for sourcing almost no current.

In 2003 Mission I had trouble with my electromagnet overheating. Sometimes it would melt the hotglue that held it in place.
You can barely see it in the bottom right in this picture:
439|28/DarkSabreMission 2003 (4).jpg

In 2004 and 2005, I switched from telephone wire for the electromagnet to the enameled wire you can buy from RadioShack as "magnet wire". That let me get a lot more wraps in and seemed to help with the heating problem.
One thing you could definitely do is install a switch in the electromagnet circuit so that you only ever have it on right when you finish setting up a run.
You may not be able to do this second thing, if you have already done a lot of your mission, but I made my electromagnet the first transfer after the machine was triggered. Since I switched it on just prior to starting the run and it got switched off a few seconds in, it didn't even have a chance to get warm. The little cardboard hoop hotglued to the front left is actually where I kept the ball bearing to remind me to activate it.
You can see the light switches I used as my "masters" in the center of the machine. One of those was a manual shutoff of the electromagnet. You can also see the #1 written on tape on the electromagnet (top left, second thing down), signifying that it was the first normal transfer.
528|30/DarkSabreMission 2005 (58).JPG

So if you add more wraps to the electromagnet, it will have greater resistance. Voltage is constant here, since the electromagnet is presumably the only thing running off the 9V battery, so V=IR tells us that the current will go down with the increased resistance. The electromagnet has to dissipated heat ~equal to V*I, so more wraps = lower current = less heat...I hope :P
Too many wraps and nothing will stick to the electromagnet, so you have to find a happy medium you can work with.

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Re: Electronics

Post by gh » January 15th, 2010, 2:31 pm

Actually, your battery is probably just dying. Nine-volt batteries are not notorious for their unexpected amazingly low capacity, but they should be. There's really only about 200mAh or so in one, IIRC. If you're using one for something that's constant and one-shot with a big demand in terms of current, like an always-on electromagnet, even less of that capacity is usable because of the way batteries work.

I expect you probably need a better source of power, unless like DS said, you just have few wraps and it's overheating.
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Re: Electronics

Post by Primate » January 17th, 2010, 12:15 pm

Thanks guys, I appreciate it. I did manage to get my hands on some of that magnet wire you talked about, Dark Sabre, so hopefully that works out a little better. I'll also probably try to switch over to a D cell or something, less current with the same resistance and hopefully it'll last much longer.

I like the idea of having it as the very first task, though. I'm gonna entirely rework the design, I think. It utterly failed at invitationals. One group managed to get freaking 59.88 seconds. I think they had a timer IC hidden in there somewhere to change how long the motor ran for. One of the things they had that I really liked was a breadboard which connected all of the circuits. Now, maybe a breadboard's a really bad idea, since you pull one wire out and you're screwed, but a central control panel would be nice. We'll see; I'm gonna measure twice and cut once this time.
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Re: Electronics

Post by gh » January 18th, 2010, 9:35 pm

Breadboards are terrible to have in a device during competition. At some point, you just have to stop making improvements and freeze it into a stripboard or something, because breadboards are absolutely unpredictable. They have weak frictional mechanical joints, introduce resistance and capacitance to your circuits, and will melt/rust/dirty with use (and abuse) over time.
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Re: Electronics

Post by Dark Sabre » January 19th, 2010, 12:14 am

My old team's EV completely failed to operate at nationals because a wire on their breadboard came loose and they didn't have a diagram to fix it. Should have been preventable in a number of ways, but :roll:

You will also run into more current limitations on a breadboard than with normal wire connections. I wouldn't recommend running nichrome wire or washer fluid pump size currents through your average breadboard, for example.

So I would second gh on that.

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Re: Electronics

Post by Uncle Fester » January 20th, 2010, 7:19 pm

ABSOLUTELY DO NOT run nichrome wire-type currents through a breadboard. The tiny phosphor-bronze coatings will burn up inside the breadboard and you will have a very hard time finding the location.

Looking at a breadboard which has six of 144 contact holes burned out as I type this.
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