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From: Tom MacIntyre
Subject: Re: Reducing contact resistance for low volt use?
References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
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Date: Tue, 07 Jan 2003 03:27:29 GMT
NNTP-Posting-Date: Mon, 06 Jan 2003 23:27:29 AST
On Tue, 07 Jan 2003 02:34:34 GMT, jmuchow@SPAMMENOTcamlight.com (John
Sorry for the top post, but I would just like to point out that this
is one very good way for innovation and development to
happen...pushing the envelope, they sometimes call it. Someone finds a
simple solution to a small-scale problem, and the next thing we know,
it is saving megawatts at the macro level.
I am of course not the first to see this... :-)
>>>>>>>You have obviously not read the earlier discussion in the same thread.
>>>>>>>John is not trying to stay within specs, on the contrary, he is using
>>>>>>>these batteries like no battery manufacturer ever imagined they would
>>>> Which is all but stupid.
>Obviously, the sport of combat robotics is not for you. Why on earth
>would I want to stay within "spec"? It practically guarantees a lost
>fight and that could mean my 'bot is spread all over an arena. If I
>can draw a lot more current from my batteries, I can run faster, spin
>a weapon faster, and generally have a better chance to survive.
>Who cares if the cells don't survive?
>>>>>>>Maybe you could find and read the earlier messages in the thread, I
>>>>>>>think it would make you understand what this is all about.
>>>> I do understand. A person is using motors AND batteries in a manner
>>>>that is destructive. I am supposed to help?
>No, you're not supposed to help. It's your option to just read the
>post and not respond.
>This is COMBAT robotics and things get destroyed...all the time. I
>run my 12V drive motors at 24V and they work fine. Do they get hot,
>of course! But I know that and it isn't a problem for a 3 minute
>fight. I draw approximately 40-amps from each 24V string of 3000mAH
>cells (one per motor) and that's no where near "spec" for the
>batteries or the motors. And my bot isn't pushing the performance of
>its components nearly as much as many others are.
>Even the R/C car and airplane builders use their cells at very high
>discharge current levels
>>>>>>>These battle-robot builders regularly take out 30 A for 6 minutes from
>>>>>>>3000mAh cells, and 50A for short durations, and they are trying to
>>>>>push performance even further.
>>>> All they need to do is put more batteries in parallel with those
>>>>already in place. More current per pack, not more voltage.
>How? Most builders are within ounces of their weight limitations for
>their robots. And R/C plane and car builders certainly can't add
>another string of cells. Especially when the guy next to them is only
>running one string at very high current levels (way beyond "spec")
>because the cells will last the short time he needs them to.
>>>>>John is probably not counting on getting 100A out of a D cell, but he
>>>>>wants to have measuring equipment to try it, to see the difference
>>>>>between different cells.
>>>> They all act like they are about to explode at those levels, and
>>>>real data about what Mfgrs are better is probably not possible. ANY
>>>>Mfgr's battery may or may not fail.
>Perhaps. But, the only way to tell is to test them. Builders don't
>want to see discharge curves up to a certain manufacturer spec level
>(perhaps 8-10C amps?). That information is almost useless. They need
>to see the discharge curves for their application. And the curves
>need to be plotted *beyond* the current levels for what most builders
>will need. If I saw curves to 40A, then I'd know how my 'bot would
>respond. But, what if I wanted to increase the motor voltage, or
>change the drive reduction ratio (resulting in more current draw while
>running)? We need these curves. And we need to know if there is any
>difference between manufacturers.
>In addition, there are applications where the high current levels are
>needed for only a few seconds; spinner start-up, high-power solenoids
>for weapons activation (mine take over 100A each for 0.5 seconds),
>Whatever current levels I can get from the discharger, I'll be able to
>>>> Sounds like a kludged way of performing the work.
>>>>If the motors are
>>>>low voltage devices, then the batteries would do better to provide
>>>>more current *AT* the working, proper voltage. That would mean more
>>>>batteries in parallel, AT the right voltage. The when the demand goes
>>>>up, the voltage hangs on, and the motor can PERFORM the task the way
>>>>it was meant to. AND BETTER at that.
>A great theoretical idea...almost never achieved in our applications.
>Weight and budget restrictions are extreme and why use two battery
>packs if I can abuse one and still have sufficient performance. Now I
>have some money and weight for additional armor.
>>>> What we do NOT do is ask power supplies OR batteries to do more than
>>>>they are designed to do. It is simply like asking for trouble. If he
>>>>wants more output torque, he should step down the shaft speed with
>>>>gear reduction or chain and sprocket reduction. Motor stalls would
>>>>cease, and higher speed peaks would be possible when loaded down.
>The entire sport of combat robotics (and to a lesser degree, R/C plane
>and car builders) is based on exceeding the specifications for the
>components that are used.
>The entire sport of combat robotics is *based* on extraordinary levels
>of "trouble". We're only asking what components can be pushed beyond
>spec, and how far can they be pushed....the reason for my testing.
>All of these 'bots are already geared down one way or another to
>achieve maximum torque at the desired speed. Some are run direct, but
>they use the proper sized wheels to limit the speed and current draw.
>But, we want more torque without extra weight. The need for extreme
>performance from our batteries, motors, drive systems, etc., way
>beyond what the manufacturers think is "appropriate", is common. In
>fact, it's mandatory when designing a combat robot.
>>>> He could get just as much data in attempting to charge one up at
>>>>100A. The data would look very much the same. Heat up until BANG!
>But, don't need 100A charge currents...we usually limit it to 5A.
>We do need MUCH higher discharge current levels though.
>>>> It might sound silly, but so does hitting one that hard on the
>Silly? Tell that to all the combat robot builders and R/C plane and
>car builders/drivers who want to extract every last bit of performance
>out of their machines.
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