- Editor's Corner -
by Cecil Collum
The new year has arrived and with it a new Club President, Ron Roberts. Ron will be writing a "President's Corner"
in most of the newsletters this year. He has surrendered the newsletter position and I will attempt to present an
informative letter each month. Should you have an article you wish to share with the Club, please e-mail it to me
at redleg142@hotmail.com and it will be included.
This is your newsletter and your input is greatly appreciated. You don't need to be a professional writer
to place an article here, I certainly am not a professional! My plan is to send the letter to Ron a week prior to the
monthly meetings so he can put it on the web in a timely manner so, if you want to have an article included, please get it
to me during the last week each month.
I subscribe to an e-magazine from Great Britain and it has writers world-wide who contribute some very good articles,
among which is one from the November '09 issue entitled "Volts and Amps for Dummies" by John Wheater. I secured
permission to use it in our newsletter but because it takes six pages, it will be broken into three segments. This
article explains the electric side of our great hobby better than anything I have read and should benefit all of us.
I will also attempt to include interesting events in our area as well as regional events of which I am aware.
One of the first is the Kansas City RC Swap Meet scheduled for 16 January '10. Several of our members have made
this trek a couple of times and found it very interesting and the fellowship enjoyed during the trip makes the miles fly
by. The opportunity to purchase a plane, engine, or accessories at good prices makes the trip worthwhile.
Dwaine Mayhew purchased a 1/6 scale Cessna 182 and engine for $90 last January and a Quadra 35 cc engine for $50!
A food concession is available, serving hotdogs and hamburgers. There is a Denney's Restaurant a short distance
away should you prefer a different selection.
I also plan to include a synopsis of the monthly meetings in the newsletter for those who can't attend. I will
also run off a few hard copies for anyone who doesn't have a computer but I am aware of only one member at this time in
this category. If you know a member who doesn't have a computer, please e-mail me at the address above so I can add
him to the list.
Enough prattle, let's get to the good stuff! The article below is from modelflight, an English electronic magazine
(e-magazine www.modelflight.regheath.com) published free monthly by Reg Heath, who graciously granted us permission to use
it, and written by John Wheater. It is definitely worthwhile and will consume six pages of our newsletter. Keep
in mind it's English and they use a few different terms. Lets begin..........
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The Magic of Electric Flying
or
"Volts and Amps for Dummies"
By John Wheater
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IT SEEMS there are many who are confused with what goes where and why and what motor and prop should be used on what
battery and so on. When you find a web site that will explain volts and amps and watts it serves only to confuse
by analogies to water and taps and pressure and stuff like that which confuses me as well as the next man. My
father was an electronics engineer, he made a television from scratch in 1936 and received signals from Alexander Palace
in London but none of his knowledge, absolutely none, has rubbed off on to me. So, if I can fly electric successfully
without an in-depth knowledge so can you.
I shall describe only the "brushless" motor set up as that is the way of things these days and I am hoping to do it in
words of one syllable that even I can understand.
The Basics:
- The Brushless Motor is effectively a three phase AC motor. Current through any two connections will create a magnetic
field, making the rotor turn a partial revolution. It will not work without a "controller".
- The Controller, "ESC" which stands for Electronic Speed Control "commutates" a brushless motor by turning dc into ac
and switching the two wires which are being energized in a sequence using a DC source, i.e. a battery.
- What you NEED to know:
- MOTOR + ESC + FLIGHT BATTERY = MOTIVE POWER
- The speed of the motor is controlled by the ESC and to do this we need a radio receiver "Rx" which is controlled by
the radio transmitter "Tx".
- What you NEED to know:
- MOTOR + ESC + FLIGHT BATTERY + Rx (controlled by Tx) = CONTROLLABLE MOTIVE POWER
2. Choosing a motor - "Thumper"4250
- There are hundreds of them. How can you hope to choose which one you need to power your specific model?
Let's look at the data for a typical motor then take each aspect in turn in an attempt to assist our selection:
- "Thumper" 4250 ( This is an English brushless motor)
- 10.8v -25.9v
- 600 kv
- 7 winds
- 45amps max
- 720 watts max
- Total length 70mm, l w/o axle 50mm
- diameter 42.5mm
- shaft 5mm
- weight 210g
- Recommended props from 12 x 6
- Models up to 3kg
- Recommended controller 45amp constant
- The operating voltage. [Item "a."] I don't have to explain that the motor will go faster by increasing the voltage do I?
- The first item of motor data we need to consider is [Item "b."] Kv. This is the number of rpm per volt that the motor
will provide. Let's look at two in extremis:
- 600 Kv
- 4,500 Kv
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What you NEED to know:
- A low Kv motor will turn a larger propeller and provide more torque.
- A high Kv motor is more suited to small propellers and provides less torque.
The first thing to remember is that the published figures are only a guide as it is impossible for a manufacturer to
state what will be the Kv on your set up as they don't know what size prop you will be using. The stated Kv is,
therefore, the shaft speed without a load.
Basically, a larger propeller is more efficient than a small one and generally speaking the larger the model the
larger the prop required. A small propeller will turn faster on similar power because it offers less resistance
to the air so think of a smaller prop for faster models.
You will understand readily if I tell you that a large prop will need more power to turn it than a small one.
It therefore follows that the larger the prop the larger the motor required. Let's assume all the way from now
on that we are using a 3S Lithium Polymer Battery, the "Lipo". 3S is simply a way of stating that the battery has
three cells in Series (the number of cells we are concerned with). A single Lipo cell has 3.7 volts so a 3S has
11.1 volts ( 3 x 3.7v = 11.1v)
So back to our two motors, how fast are they going to turn on a 3S Lipo?
- 600 x 11.1 = 6,660 rpm
- 4,500 x 11.1 = 49,950 rpm
Don't forget these are NO LOAD figures.
Particularly if you have been a glow motor flier you will be able to accept 6,660 rpm but 49,950 rpm? The simple
answer is that ii) is suitable only for a high speed, small diameter fan in EDF (electric ducted fan) jet type models.
[Item "c."] is the number of winds on the motor's armature.
- What you NEED to know:
- The lower the number of winds the faster the motor will turn for a given voltage and the lower the torque.
[Item "d."] The motor's maximum current draw.
- What you NEED to know:
- The higher the number of amps the more power the motor will provide.
[Item "e."] The maximum rate of electrical power the motor will consume before it generates too much heat and lets
the smoke out. Don't panic, this is a very simple mathematical formula to determine how many watts an electrical
circuit can carry or how many watts an electrical device will require: Watts = Volts x Amps.
- What you NEED to know:
- The higher the wattage the higher the power the motor is capable of producing.
Incidentally, to give you some idea, 1 horsepower = 745.699872 watts
To be continued next month.
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FMAC Biographies
Since we seldom see every member at the
meetings or field, there
are many that I don't know other than by name, so I would
like to
run a series in which a brief biography of each member is featured.
Where you went to school, when you began flying RC, what type
models you prefer, military service, etc. |
Of course, one may opt out if he desires but I believe this will help us become better acquainted and make a
closer club.
To kick off this feature I will include a brief bio of myself.
I was born in June, 1941 at Sparks Hospital in Ft. Smith, graduated from Ft. Smith Senior High School in
January, 1959. As I had joined Company "C", 212th Signal Corps of the Arkansas Army National Guard in
June, 1958, I reported to Ft. Chaffee on 22 Mar 59 for Basic Military Training. Scoring highly
on the OQT, I was offered an appointment to West Point from Basic but declined.
Instead, I reported into the Southeastern Signal School at Fort Gordon, GA, for Pole Lineman/Field Wireman
School, from which I graduated and became a telephone lineman.
As I was processing out of my six months training, a Master Sergeant persuaded me to stay on active duty but to go to college,
so I returned to Ft. Smith and went to the 1959/1960 terms at Ft. Smith Junior College. I then transferred to the
University of Arkansas but was recalled to my unit during the spring 1961 semester due to some forgotten "crisis". I
served thirty-two years total, four enlisted and twenty-eight commissioned, retiring in May 1990 as a Lieutenant-Colonel,
Field Artillery.
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My retirement was officially suspended until 6Mar91 due to the Gulf crisis although they refused to recall me to
duty. I elected to remain in the Retired Reserve until 1Jun01, when I was officially retired and credited with
43 years, 11 months and 8 days of service to the US. Too bad all of that time didn't apply to pay! Most
of my time was spent in 8" howitzer battalions, most of which were nuclear capable. I also served on a General
Staff as Installation Transportation Officer, Procurement Officer and Personnel Officer and was guest instructor at
numerous NCO Academies and Officer Candidate Schools.
I purchased my first RC plane, a Hobby Lobby Telemaster .40, here in Ft. Smith from Duke Fox in 1982 while here on
leave. My thought at the time was that it would keep my son out of trouble but I ended up getting the bug.
Due to one transfer after another, I didn't solo until August 2000, after retirement from the Army. My son flies
RC helicopters when he can between assignments to remote Air Force stations. I have belonged to numerous RC clubs
in Indiana, Tennessee, Texas, Oklahoma and Arkansas and keep membership in my home club, the Mid Arkansas Radio Control
Society in Little Rock as well as Flightmasters.
I served MARCS as Secretary for three years, newsletter editor for two years and Vice-President for six months prior
to moving to Ft. Smith.
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Next Meeting:
Tuesday, 13 January 10
Time: 6:30 PM
Place: Western Sizzlin on Towson Avenue
Come join us!
It's time to pay our AMA and club dues! Pay before the February meeting and save $5.00!
2010 Officers:
President: Ron Roberts
Vice-President: Harold Wille
Secretary: Mike Beck
Treasurer: Bill Womble
Past President: Josh Price
Newsletter Editor: Cecil Collum
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