Frequently Asked Questions
Bob Aberle | <REDACTED>
What's the deal with digital servos?
Also included in this column:
- Plans reduction and enlargement
- An engine-cleaning solution
- SLK Electronics' LiPoDapter
THIS IS THE 19th monthly column in which I will try to give you the best possible answers to questions you have written or E-mailed to me. Each new inquiry has a sequential number for identification purposes.
Because publication space is limited, part of this month's material will be published here, and you can find the column in its entirety on the AMA Web site at www.modelaircraft.org/mag/faq/index.asp. All questions and answers are posted there.
You can access particular questions by subject matter or categories. This was done to help you retrieve data for certain subjects. When you call up a question, it reads "Answer ..." Double-click on that word, and that information, along with any related photos, will appear.
Let's start!
Q151: "I've seen references to digital servos. I gather that these new type of servos offer higher resolution. What's the real difference between our older-style
A151: More and more digital servos have been showing up on the RC market in the past couple years. I would guess that every popular RC manufacturer now offers one or more types of digital servos.
These digital units do offer higher resolution, which results in more precise control of your model. The 3-D-type RC competition fliers must all be using this type of servo for the various hovering maneuvers they have to perform.
Digital servos are generally larger in physical size, which makes them better suited for bigger and heavier aircraft. They offer much more power (output torque), and they consume more current than a standard analog servo. On top of all this, the digital servo costs more because of the higher parts count and more complexity.
Normally that would have been the end of this answer, except I just received two new digital servos for evaluation purposes from FMA Direct. They are identified as the model DS300. Item DS300BB has plastic gears with a ball-bearing-supported output shaft, and item DS300MBB has metal gears. What makes these so special is that you can program them with your fingers!
After installing the servo in your aircraft, place it in a “setup mode.” Program the servo by moving its output arm so that the control surface is first located in its center position. Move the arm to your control-limit positions (at each extreme), and then set its direction of rotation. The servo remembers these positions, providing “model memory” without having used a computer radio system.
These new servos can operate on 2.5–12.6 volts. That means you can power your RC system from one-, two-, or three-cell Li-Poly battery packs directly. Several FMA Direct receivers also operate on a wide voltage range, so, in effect, you can power a complete airborne RC pack (receiver and these digital servos) with Li-Poly batteries and not have to resort to a voltage-regulator circuit.
This isn’t the place for a full-blown RC-component review. If you find this new digital-servo concept interesting, look at further details on the FMA Direct Web site at https://www.fmadirect.com/site/fma.htm?body=Products&cat=8.
Q152: “I know that the AMA now has the John Pond plans up and running and that I can now purchase plans copies of some of my old favorite model aircraft from years back. Being a scratch builder I often reduce or enlarge plans to create a model size different from the original. I’ve heard of special plans-copying services but was wondering if you could steer me in the right direction.”
A152: The John Pond plans are now posted on the AMA Web site: www.modelaircraft.org. Click on “AMA Plans Service” on the front page. Once you are there, you have a choice of the John Pond Plan Collection or the Model Aviation Plans Service. You can look at a complete catalog on the Web site and print an order form off-line for your convenience.
I obtain many original (full-size) plans and then have them reduced so I can build tiny electric-powered models (parking lot size, typically weighing less than 10 ounces total). I have resorted to obtaining my reduced-size plans copies from my local Kinko’s copying store (which are located across the US).
The limit is 36 inches wide on the original (length is unimportant). The cost is roughly $1 per square foot of print and $1 setup charge to make the reduction (or enlargement within the confines of the 36-inch maximum width). I generally have two plans copies made: one to cut up for templates and the other for the actual building.
While setting up this new plans-copying facility at AMA Headquarters in Muncie, Indiana, recently, I learned that the equipment is capable of reducing and enlarging plans. I suspect it involves a scanning process prior to making the actual print.
I’ve asked headquarters personnel responsible for this service to look into the possibility of offering a custom plans-copying service. They may not be staffed for such extra work, but if it is possible, it would prove to be a boon to modelers who like to cut out and construct their models from scratch (basic raw materials!). If I get more information I will gladly pass it on.
Frequently Asked Questions
Bob Aberle
Q153: "What will remove the somewhat burned fuel residue stains on the cylinder head and mufflers of fueled engines? I've tried MEK [Methyl Ethyl Ketone], acetone, lacquer thinner, mineral spirits, and denatured alcohol without any luck."
A153: A few years ago I bought a chemical that was available in the detergent/cleaning-chemical aisle at most local supermarkets. As I recall, it was like a paste that was brushed on, typically on an engine's cylinder head. You left this chemical on for a while and then rinsed it off with water. The result was a bright and clean cylinder, making the engine look new.
I couldn't recall the product, so I turned to one of the most prominent engine experts in the US and Model Aviation Hall of Famer Dave Gierke to see if he had more details. You are in luck! He wrote:
"It just so happens that I developed and marketed such a product back in 1999. It's called 'Demon Clean' and it works just like you described. This product doesn't harm the engine's metal, rubber, or synthetic seals.
"Two years ago I sold the rights to this product to Brian Cooper of Cooper Custom Blended Fuel of Battle Creek, Michigan (E-mail at <REDACTED>). Brian is located at <REDACTED>. His phone number (after 5 p.m.) is <REDACTED>.
"Demon Clean will remove all stains as described within 45 minutes of application (rinse off with tap water). I believe this product now costs $21.95 (plus shipping) per 8 ounces, which can clean approximately 10 engines. You best check that price with Brian!"
That's what I call a detailed answer. Thanks, Dave!
Q154: "I heard you say many times that you can't use a peak detect charger (which is used for Ni-Cd and NiMH batteries) to charge Lithium Polymer batteries (Li-Poly). I own several good peak detect chargers and still wonder why I can't adapt these chargers to Li-Poly charging without having to purchase another dedicated charger?"
A154: I realize that I have preached "no peak detect" charger for Li-Poly batteries since they came onto the market. I would still say that right now, except that prominent modeler Sid Kauffman of SLK Electronics has come up with a new product he calls the "LiPoDapter." He also created the popular ElectriCalc computer program that helps you select the right motor, battery, propeller, and drive train for your particular electric-powered model.
I have used a prototype of his new LiPoDapter, and it does work. MA's battery columnist Red Scholefield had some details about this product in his September column, which I urge you to read.
Very basically the LiPoDapter is contained on a small PC board and has two pairs of cables. You insert this adapter between your peak-detect charger and the two- to six-cell Li-Poly battery pack. Set the charge current on your peak charger, and the LiPoDapter will safely cut off charge when the battery reaches roughly 90% of full capacity.
The adapter also senses and selects the proper number of cells in your Li-Poly battery pack and confirms that number by providing a flashing LED. The number of flashes represents the cell count.
The LiPoDapter is going to sell for approximately $40. So if you already have a peak-detect charger, it will only cost you $40 more to have the capability of charging Li-Poly batteries. If you are interested in this device, you can read the full instruction manual at www.slkelectronics.com/lipodapter/instructions.pdf. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
