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From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Reducing contact resistance for low volt use?
Date: Tue, 07 Jan 2003 02:34:34 GMT
Organization: MindSpring Enterprises
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X-Server-Date: 7 Jan 2003 02:36:25 GMT
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>>>>>>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.
Yes!!! >>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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