[Robotgroup] MOTORtHrEAD

Fri May 2 17:02:41 PDT 2008

Here's off the top of my head:

·      PWM (example: "… but you can drive 5A with PWM 80% duty cycle…")

> PWM is pulse width modulation, just a fancy way of saying turning things 
> on and off in quick succession so that the perceived output is somewhere 
> in between. Eg. A light switch; turn it on, its 100%, turn it off, it 0%, 
> now turn it on/off one time a second, other than a headache, you are going 
> to see a 50% duty cycle, half the time its on, half its off, BUT here the 
> kicker, do this really fast and you will perceive that the light is 50% 
> on, not just ON then OFF. Thus, the idea of PWM is really its a poor mans 
> digital to analog converter, with 1 line you output a pulse train, you 
> send it thru a low pass filter to "average" it then the pulses convert to 
> a voltage. The faster the pulse train has NOTHING to do with the average 
> value (but does how SMOOTH it is), that's the duty cycle, but faster the 
> speed the more constant the signal is when averaged and cleaner.

·      Transient currents

>>> Just means you have a circuit that runs under some normal conditions, 
>>> ok, fine ... now, you turn it off, and there are some lingering currents 
>>> these are transients. Also, the when you turn the circuit on, transients 
>>> occur. So transients in general in EE, simply mean the starting and 
>>> stopping electrical response seperate from the STEADY STATE of the 
>>> circuit. And transients take very complex math to figure out, and are 
>>> near impossible to calculate perfectly, SPICE etc. use iterative 
>>> algorithms to solve the "Transient" conditions in a circuit, about 
>>> 10,000,000 calcs are needed for a simple amplifier!

·      Overclock ("…you can run it at 6V and run it faster and
overclock it as well.")

>>>>>> Voltage is the "electric field" that is applied to a circuit, the 
>>>>>> field causes charge to move. By increasing the voltage, you increase 
>>>>>> the "pressure", and hence, the average kinetic velocity of electrons 
>>>>>> (and holes, the lack of charge), therefore, speeding up the 
>>>>>> circuitry. Or in a digital system ALLOWING it to run faster, for 
>>>>>> example. Take a CMOS part that runs at 5V and 10MHZ, push it to 15 
>>>>>> MHz it might start to fail, but increase the voltage to 6-7V and you 
>>>>>> will have more of a "noise margin", plus the field strength and rise 
>>>>>> times, fall times of all the dohickies inside are shorter since the 
>>>>>> field is stronger, thus it will work faster.

·      Locked rotor amp ("…you pretty much need to have a motor
controller rated for the locked motor amps of the motor you are going
to use." )

>>> When you talk about motors, you have things like stall current, start 
>>> current, lock current, these are boundary conditions of the motor that 
>>> gives you the envelop of operation at the extremes, so if you lock the 
>>> motor up, what kind of current will it draw with a particular voltage, 
>>> and what will the torque be etc. So you need to consider these things 
>>> for overloads, maintaining torque, etc.

To a 9 year old, I might use a real example, get a power screwdriver, put it 
on low torque and then have him try and stop the chuck, feel how it fights, 
it wants to turn, you want to stop it, while you hold it, its using power, 
and the battery has to be able to supply that power.

ANdre'

----- Original Message ----- 
From: "Robert Carter" <rcarter at ischool.utexas.edu>
To: "The Robot Group Mailing List" <robotgroup at puremagic.com>
Sent: Friday, May 02, 2008 6:02 PM
Subject: Re: [Robotgroup] MOTORtHrEAD

Hey y'all--

I feel kinda proud of myself that I was able to follow most of the
thread on RC motor controllers without being completely lost. While
reading, I started keeping a list of terms/phrases I didn't
understand. Here's the list; if anyone would like to fill in some of
the blanks for me, that'd be great.

·      PWM (example: "… but you can drive 5A with PWM 80% duty cycle…")
·      Transient currents
·      Overclock ("…you can run it at 6V and run it faster and
overclock it as well.")
·      Locked rotor amp ("…you pretty much need to have a motor
controller rated for the locked motor amps of the motor you are going
to use." )

That last one, I think I understand what it means from the context,
but when I tried to put it in my own words I couldn't come up with
anything that makes sense, so I'm curious to hear how someone might
explain it to an inquisitive 9-year old.

I've got more questions specific to what I'm trying to do with my
project, but let's start with these. BTW, has there ever been talk
about creating a glossary page on the wiki for stuff like this? Or
are there already a lot of good ones out there, that I just don't
know about?

Thanks--

Robert

On May 2, 2008, at 2:04 PM, brooksdesign wrote:

>
>  Allthough I think there are programs out there that I've heard of
> you just made public one of the parts of a new video game I've be
> contemplating. And in saying that and letting that cat out of the
> bag, any of you game programmer guys want to come out and talk
> about how to turn my scripts, cad files and ideas into something
> real that I won't leave sitting on the shelf because I can't get
> around to learning to write code? This project is waay more than a
> game.
> -brooks
> -----Original Message-----
>> From: Robert Carter <rcarter at ischool.utexas.edu>
>> Sent: May 2, 2008 2:24 PM
>> To: The Robot Group Mailing List <robotgroup at puremagic.com>
>> Subject: [Robotgroup] MOTORtHrEAD
>>
>> <clip>
>> The nice thing about electronics is that physics is the final
>> judge of
>> your choices.
>>
>> You can get people to "vote" for various approaches, but even if
>> all of
>> us voted for item "A" (placing a fuse in parallel with the motor
>> controller) that wouldn't make one whit of difference to the circuit.
>> </clip>
>>
>> Hell yeah, that's my way of learning: forge ahead with crazy ideas,
>> and learn from the consequences. If nothing else, you'll get some
>> good stories. Like when my brother and his best friends discovered
>> the formula for gunpowder and started a fireworks shop in the attic
>> over our garage. But, when it comes to electronics, I have to admit,
>> it gets expensive and time-consuming to have to keep running back to
>> the store or to the internet for replacement parts when something
>> explodes/melts/starts to smoke.
>>
>> I keep hoping that someone will invent an interactive website for
>> designing circuits, aimed for grade school students and/or middle-
>> aged project addicts with more enthusiasm than sense (like yours
>> truly). You could drag and drop motors of various amperage, LEDs,
>> transistors, capacitors, etc. onto a virtual breadboard to create a
>> circuit. If it works, you get the results in animation form: the
>> motor spins, the lights blink, etc. Or conversely, if you design it
>> badly, you can show the sparks and smoke as your components burn to a
>> crisp. Fun, inexpensive, and no one gets hurt.
>>
>> Usually when I think of something and it seems like a really good
>> idea, something like it already exists. Does anyone know?
>>
>>
>>
>> Robert Carter
>> Visual Resources Collection
>> School of Architecture
>> The University of Texas at Austin
>> rcarter at ischool.utexas.edu
>>
>>
>>
>> _______________________________________________
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>
>
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Robert Carter
Visual Resources Collection
School of Architecture
The University of Texas at Austin
rcarter at ischool.utexas.edu

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