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From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Reducing contact resistance for low volt use?
Date: Tue, 07 Jan 2003 03:39:15 GMT
Organization: MindSpring Enterprises
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X-Server-Date: 7 Jan 2003 03:41:06 GMT
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>>>>>>With 20-30 cells in series powering that motor, that's a lot more than
>>>>>>100A, even with wire and connection resistance.
>>> You keep getting this ass backwards. Series batteries do NOT
>>>produce ANY more current than does any one single cell in the pack.
You keep confusing the configuration of the battery packs used in the
machines we're discussing and the configuration of the cells tested
with the discharger I'm building.
If one cell won't deliver the current I need through the discharger
(with the MOSFET full on), then I can add a second cell (or more) in
series. This higher voltage will cause more current to flow. I can
then measure the voltage across one cell to determine its performance
at that, now higher, discharge current level.
>>> Nice embellishment, but quite meaningless. Instead of operating
>>>outside the levels of design for the batteries AND the motors, you
>>>should select a motor that does the same job at the PROPER voltage.
There are almost no components run at their rated values inside a
If we had the weight allowances to do so, we might just do something
like that...but I doubt it. Someone would very quickly up the voltage
to the motor and gear it down more for more torque and acceleration.
Especially since they know that the motor will still last WAY beyond
the point they need it to.
>>> Juicing up a motor over its spec is a step backward as they go DOWN
>>>in efficiency as you go up in voltage, regardless of the observed
That's a great theoretical spec but it doesn't affect most builders as
they'll just increase the voltage further to make up for the
inefficiencies. I don't care if the motor draws 120% more current at
double the voltage due to decreased efficiency. I get a LOT more
torque and speed anyway. It doesn't matter to builders that they
can't get the theoretical maximum efficiency as they can't fir the
batteries and motors need to do so in the robot.
>>>There are plenty of high torque motors that can
>>>perform at the same (better) levels as your overtweaked motors do.
I invite you to find one that can perform better than the ones
currently in use. Hundreds of people have been searching for motors
for these applications for years and hundreds of motors have been
tested....by folks who know a lot more about motors than you and I do.
Any of us can find a high-torque motor that operates more efficiently
at the voltages we have available. Finding one that has a machined
(not cast) mount that can survive a high-G smash or being flipped 6ft.
into the air is another matter. How about surviving a stall-condition
because my frame and motor mounts got smashed by a 27-lb tool steel
bar spinning at 2000RPM? Many high-torque motors burn out in seconds
when stalled. How much would your motor cost? If I have to replace
one every event, it better be inexpensive. How about not being larger
than the wheel diameter of my robot (down to 2.5")? Does it have a
shaft that I can attach my gears or sprockets to? I don't have room
for a brushless motor controller, better be PMDC. Does it have
terminals that I can use? Most motors have terminals sized for their
"typical" applications, not near-stall conditions. Does the motor
weigh more than the ones we're using? I can't use the extra torque if
I don't have the weight budget for it.
Several motors are currently used by the different weight classes in
combat robotics and R/C plane and car users have their own set of
motors (with some crossover between the two). Lots of research has
gone into these motors...*especially* the plane/car motors. But, new
ones are found occasionally and you'd have lots of friends in the
combat robot or R/C communities if you showed up with all these motors
you say you can find. I look forward to reading about these motors
that you'll soon recommend...especially in the R/C and BattleBot
>>> You are shooting yourselves in the head, much less the foot.
I feel like doing just that after answering all these separate posts.
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