Radio Control: Electrics
Bob Kopski
25 West End Dr. Lansdale, PA 19446
Modified Astro DC/DC Super Charger — common problems and questions
The modified Astro DC/DC Super Charger (modification described in the Sept–Oct 1987 issues) continues to generate reader response. This month I’ll cover one common problem and one frequent question.
Common problem: charger works on HI but not LO
- Some readers found the charger works with the HI/LO switch set to HI but not at all in LO. This is usually due to the transistor being installed rotated 180°—the collector and emitter are interchanged while the base is connected correctly.
- Some transistor lead arrangements are easy to confuse, and a rotated transistor operates in an “inverted mode.” Some transistors will function a little in this mode, which explains the “almost right” behavior.
- If this sounds like your problem: recheck the transistor lead connections. If there’s any doubt, buy a new transistor and install it correctly. That should restore proper operation.
Question: can the Astro 102 Super Charger be powered from house current via an AC/DC charger?
- Short answer: NO, categorically—not for typical larger pack charging. There are very limited exceptions, but they’re generally not useful.
- Reasoning and example:
- Many AC/DC wall chargers are sized to charge six- to seven-cell packs. Example: charging a seven-cell, 1.2 Ah pack at 4.0–4.5 A gives roughly 7 cells × 1.6 V/cell (charging) × 4.5 A ≈ 50 W output.
- An eight-cell pack requires about 8 × 1.6 V × 4.5 A ≈ 58 W output.
- The DC/DC Super Charger has less than 100% efficiency. If you assume 80% efficiency, the input power needed for a 58 W output is 58 W ÷ 0.80 ≈ 72 W. That exceeds the output capability of many AC/DC chargers.
- Additional problem: many AC/DC chargers have high line-ripple (poor filtering) on their outputs. The Super Charger is designed for a pure DC input; unfiltered ripple may cause adverse behavior.
- If you want a line-operated supply for bench charging larger packs: look for a 12 V DC supply capable of supplying about 20 A continuously. These supplies tend to be large and expensive; I don’t know of an economical source. See my June 1987 column for related bench-motor discussion.
KRC Electric Fly (1987 coverage and reader interest)
My January 1988 column covered the 1987 KRC Electric Fly. That coverage has generated lots of reader questions about people, places, and the event itself.
- KRC = Keystone Radio Control Club, based in Hatfield, PA (about 35 miles north of Philadelphia).
- The Electric Fly is a two-day, fun-fly format usually held the third weekend of September at the Hatfield club field. Many consider it one of the largest club-sponsored annual electric meets in the world.
- The Ninth Annual KRC Electric Fly is scheduled for September 17–18, 1988. The meet will likely move to a nearby larger field because it has outgrown the historic site.
- For more information, send a SASE to: CD Bruce Fensterstamacher, 636 Schoolhouse Rd., Telford, PA 18969.
ElectriCub impressions and power-system suggestions
The Great Planes ElectriCub has appeared in reader mail and in this month’s photos. I’ve seen examples in the air—they’re attractive both on the ground and aloft. I haven’t flown one personally, but here are some observations and suggestions.
- General impression: the kit is heavier than necessary, which penalizes ROG takeoffs with the stock power system. The stock system is marginal—some Cubs can barely get off the ground, some can’t.
- Options to improve takeoff performance:
- Use lighter 800 mAh cells instead of 1.2 Ah cells.
- Consider using seven 800 mAh cells (instead of six 1.2 Ah) with the kit’s 8×4 Tornado prop.
- Bench-run data (Thrustmaster motor with 7 × 800 mAh, 8×4 prop): about 10,500 rpm average, ~19 A input, ~135 W total input. That’s about the maximum I’d expect the Thrustmaster to handle while still giving reasonable motor life.
- My preference: install a 15-size motor with a speed control. That will give significantly greater capability. ElectriCub is roughly what I call a “three-pound plane” (typically 2½–3¼ lb). A 15 system pushes toward the upper end of this weight range but yields much better ground handling and even some aerobatic capability. Many readers agree that a 15 is the “way to go.”
15-size motor versatility (cobalt and super-ferrite)
I’ve been promoting 15-size motors for their versatility. Examples and observations:
- Illustration: a cobalt 15 installed in an Amptique (a small .05-type plane). The installation pictured used a cobalt 15, seven 800 mAh cells, and an 8×6 prop. The power level is similar to many .05 geared systems, and the plane flies indistinguishably from them—except with greater propeller ground clearance.
- Why use a 15 in such a plane? In one case, George Poos of Fort Washington, PA installed a 15 because he was tired of bending gear shafts and was planning a future 15-sized hydro. The 15 served well temporarily in the Amptique and will serve later in a dedicated 15 project.
- Practical notes:
- The 15 cobalt is relatively light and small (about 7 oz), smaller than some .05 ferrites, and fits easily in many .05 planes.
- Seven cells require only an economy charger, so a 15 lets you enjoy Electrics now and have extra capability later when you move to larger packs.
- I’ve flown 15s on 7, 8, 9, 10, and 12 cells, and seen 14-cell flights. I use six of these motors—they’ve powered planes from about 38 oz to 56 oz, both direct-drive and geared.
- Comparison to a cobalt .05:
- A 15 on seven cells typically runs at about 90–100 W input static; a .05 cobalt on seven cells typically at about 60–70 W input static.
- For the same operating current, 12 cells on a 15 gives roughly 70% more power than an .05 cobalt.
- The 15 and the .05 cobalt are similar in size and weight, yet the 15 offers much greater overall capability.
- Both cobalt and super-ferrite 15s are versatile; the super-ferrite 15 is larger and heavier but functionally similar. (There is no .05 super-ferrite.)
The Electric Model Fliers (EMF) of Chicago
- EMF is an all-electric group in the Chicago metro area with about 16 members at this writing. They are a fun-fly-oriented organization with a monthly newsletter, The Current Flow.
- All this good info came from The Current Flow editor, Steve Moskal.
- Contact: Steve Moskal, 30 S. Kensington Ave., LaGrange, IL 60525. Phone: (312) 354-2803. Tell him Bob sent you.
Oh, woe and unbounded grief! Another column is ending — with so much left to pass along! More next month.
Happy silent landings, everyone!
Transcribed from original scans by AI. Minor OCR errors may remain.
