Micro Electronics 314

    

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Great Technical Information on Electronics

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Radio Gear

The radio I purchased is the Futaba 2PCKA AM 2 Channel Pistol with S3003 Servo and MC230CR ESC.  I got the package deal from Tower Hobbies $99.00.   I picked this radio because of Futaba's reputation with R/C, I think they look the coolest, and for the money I think you get a lot of features.  You get full trim adjustments on throttle and steering as well as ATV adjustments.  With a little R/C like this, you need those features.  

The ESC can handle 5-7 cells (however I've been running 8 on it for a while now without any problems) and has reverse and brake.  It weighs in at 44 grams but I swear that half of that weight is due to the massive 16 gauge wire protruding from the top.  It has a very small footprint of only 1.0" by 1.30" and fits easily on the upper deck of my RS4.  I haven't heard of anyone blowing up their MC230 on a Micro car so that's good.  These little motors pull much less current than the big 540 style motors which the ESC was actually designed to handle.  The current capacity of the FET's is: 90 amps forward and 45 amps reverse.  Don't settle for less!  My ESC never gets hot even under demanding situations.  I see no reason to buy any other smaller and lighter ESC at the expense of being capable to deliver high amperage.  Just because it's a Micro R/C car, doesn't mean it has micro amps of current flow through its electronics.  This ESC is smooth as anything.  Acceleration is very controlled and I never feel like the car is getting away from me without my control.

The biggest heaviest thing about this package is the S3003 servo.  It's no big deal really, it's a $10 standard servo that can be used for just about anything.  It works fine for me for now and I probably won't change it out for something smaller and lighter for a few more months still.  I highly recommend this package from Tower Hobbies to anyone getting into R/C.

Rechargeable Batteries - Evolution of the Ni-cad

I've been reading up quite a bit on Ni-cad rechargeable batteries.  I wanted to get rid of the 10 years of myth I've been fed over the years on how to charge and not to charge these things.  I've found some really good information.  Most of it from Panasonic's web site.  From the data I have read, I've concluded a few things.  For starters, I made a spreadsheet.  The spreadsheet shows charge times and charge currents for my custom battery pack made out of Panasonic cells.  This chart is actually a fairly generic system for identifying charge time vs. charge current for any Ni-cad battery pack.  There are only three input options:

V = Voltage of battery pack = 7.2V
mA = mA rating of cells = 1000mA
Cells = Number of cells in pack = 6 cells

With these 3 variables we can conclude various charging timing given various charge currents.  Most importantly to note is the fast charge times and trickle charge times and their respective charge currents.  You may use this spreadsheet even if your batteries are 600mA or 1800mA 4 cells or 8 cells and everything in-between.  This is because it uses a simple formula most commonly referred to as C/10 or 0.1C which means charge your batteries at 1/10 their ampere rating for 15 hours.  Then it just goes up from there in current and charge times.  The relationship it non-linear but can be easily graphed for a good visual representation.

View the Charge Calculator Spreadsheet

I claim no responsibility for the use of this information.  If you burn up your pack, melt your car, and start your living room carpet on fire, it is your own fault.  Use these guidelines at your own risk!  For example, according to the chart, the pack I charged should have taken 6 hours but it only took 5, so it's not totally perfect.  Remember that.

My first pack I built out of Ni-cad AA cells I bought at my local electronics store.  All I knew when I bought them was they were yellow, had solder tabs, 1000mA capacity, and only cost $1.95 a piece.  Later I got on the Internet and found the data sheets for these batteries.  The data sheets told me everything I needed to know about how to charge and discharge these things.  Which is also where I got most of the information in that spreadsheet.   Later on I built a new 8 cell pack out of Nexcell 2/3A batteries I bought from Paul at www.gadgetnerd.com.  The 2/3A cells are the way to go.  Even though they are NiMH, I still charge them in basically the same manner as outlined in the spreadsheet.  I watch for the negative delta drop in voltage and then pull the plug.  I've got my 8 cell pack to peak consistently at 12.38 volts.  That's 1.547V per cell which isn't bad at all by even the most demanding RC standards.

   


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