RADIO CONTROL ELECTRICS - 2003/02
Author
Bob Kopski 25 West End Dr., Lansdale PA 19446
Introduction
This column follows up and expands on the "chokes" topic from the September 2002 column, offers two product notes, and suggests ways for inquiring readers can help me help you.
The September column gave information about the nature and use of chokes in E-RC (electric radio control). That discussion referenced the April 1995 column, which covered the topic in greater detail. Both references included photo information about "choke insertion units" (CIUs): simple, low-cost assemblies you can make to aid in tracking down and curing some common electrical "noise" problems associated with electric power. (Article reprints are available from AMA Headquarters.)
Shortly after the September column appeared, readers began reporting success using chokes for noise problems they had encountered—some for a very long time. No one reported failures. This matches my long-term experience: chokes nearly always solve such problems.
Field examples of CIU usefulness
At the NEAT (Northeast Electric Aircraft Technology) meet in mid-September, a modeler described a problem with his power system. As he advanced throttle, the motor became "sputtery" and would not run up further, even though this happened well below full throttle.
I invited him to try a CIU (which I always carry). He installed it in the ESC-to-receiver lead, and presto—he had full-range solid throttle control. The CIU allowed him to fly the airplane the next two meet days. He took the CIU with him and later mailed me a thank-you note and an order for three dozen chokes for himself and his friends. (Each CIU needs three chokes—one in each wire of the ESC-to-receiver cable.)
Not long after that, on my flightline, a local modeler with a new hand-launch E-aerobatic model had a puzzling problem. Ground-range checkout looked good; motor and control surfaces were fine. When we extended the transmitter antenna to launch, the motor would not come on and the control surfaces were inoperative. With the transmitter antenna collapsed the controls were fine; with it extended near the airplane they failed. If someone else launched the airplane from several feet away, all was well, but it was impossible for one person to hold the transmitter and launch the model. There was clearly some kind of signal overload or related effect.
On a long shot I offered my CIU and, once again, the problem was solved. This had nothing to do with classic noise trouble, so chokes may have more to offer than previously known. As I write this, that pilot has had my CIU in use and has ordered more chokes.
This brought to mind a similar experience years ago: with a hand-launch craft, the motor came on by itself when I held the model and the transmitter. That "non-noise" problem was also solved with a CIU.
Possible explanations
I don't know exactly what's going on in these examples, but I can suggest two possibilities:
- The power-system components connected to the receiver via the ESC/receiver cable effectively increase the receiver's "antenna." Nearby transmitter output can more easily overload the receiver.
- Conversely, the ESC—when connected to the onboard radio—can act as an extensive conductor or large "pickup." Nearby strong RF fields can travel into the ESC electronics and cause malfunctions, possibly affecting the BEC (Battery Eliminator Circuit) that powers the radio.
A CIU inserted into the ESC/receiver cable effectively "breaks up" the RF coupling between the two. Essentially the receiver and ESC are disconnected RF-wise, allowing normal operation. Although I'm unsure of the exact mechanisms, the chokes have worked in these cases.
I recognize that many hand-launch E-airplanes operate without such problems. But if one or two craft show these troubles, others likely do too. Symptoms might not always be as severe, but the choke idea is worth trying. If you have a model with unexplained control "funnies," chokes are worth a try.
Signal nulls and repeatable glitches
It's common for RCers to experience a glitch at the same place in the air on almost every flight—it's as though there are repeatable locations where the airplane always gets "hit." These spots can be quite close and range is usually not a factor. Often the problem is more pronounced during slower flight, and other fliers at the same location may not have the same experience. If the affected pilot moves a few steps, reorients the transmitter antenna, or changes channel, the problem may go away or relocate elsewhere in the sky.
Radio-signal nulls are normal and common. You may experience short fades in an auto FM radio as a car moves along a road—periodic locations of "lost signal" even in open spaces. Nulls result from many factors, including signal frequency and local propagation conditions.
When a receiver encounters a null, its automatic gain control (AGC) raises the gain to look for the lost signal. That increased gain makes the receiver more susceptible to electrical noise in the environment. In E-RC, the onboard power system is a nearby source of interfering noise. As the model flies through a null, onboard E-noise can get into the now-more-sensitive receiver, causing surfaces to twitch or the motor to sputter. This can be especially annoying with speed controls that shut down on signal loss and require a full "off" throttle command to restart.
Chokes help here. They impede the flow of high-frequency interference between the ESC and the receiver while permitting normal interconnect function. Thus power-system electrical noise has a much harder time getting into the receiver whether or not signal nulls are present.
If you have system behaviors like the preceding, give chokes a try. Check the September 2002 RC Electrics column for detailed parts and procurement info, and invest the few dollars and little time it takes to make one or more CIUs. You could become a hero on your flightline by helping someone try a choke assembly!
Product notes
#### Anderson Power Poles Anderson Power Poles are the connector of choice for most E-modelers I've met. John Sernos popularized them in this hobby with his Sernos Connectors—Anderson Power Poles with heavier contact plating—although the standard ones work quite well.
I recently found an excellent supplier of Power Poles at good prices. West Mountain Radio (see the October 2002 column) lists quantities of 25 pairs for $19.95 on its www.westmountainradio.com website. Larger quantities are available at lower prices, so check it out for your group or club.
#### Universal Slow Charger (USC) Early discussion is underway about the possibility that the popular Universal Slow Charger (published in the September, October, and November 2000 issues) might become a manufactured product by an established electronics company. If/when that happens, I'll let you know.
Many readers have built the USC, and many more wish they could but feel they lack the resources or skills. If this materializes, maybe everyone who wants one can have a USC.
How to get the best help from me
E-beginners' questions don't change much over time. Even though Electrics is in its third decade, the same newcomer questions appear in reader mail. I always reply to inquiries accompanied by a self-addressed, stamped envelope (SASE), and I do my best to help. If I don't have a good answer, I'll say so and/or suggest other sources.
Beginner questions often focus on a problem with specific products, but usually they involve electric fundamentals that don't change much with product or time. I can't buy and try everything, but I'm familiar with what makes electric systems tick and can often help.
To help me help you, include all relevant information you can:
- What products are involved (make/models).
- Finished-airplane details: size, weight, etc.
- Battery details: cell type, capacity, number of cells, etc.
- Charger and charging specifics.
- Any other details you think relevant.
Often I must reply asking for more information; be generous with detail and I'll sort out what seems relevant and do my best to help. For example, one innocent beginner letter read: "I had three packs charged according to instructions but none of them flew good." It turned out the packs had been charged more than two months earlier. Get the idea?
Please include an SASE with any inquiry for which you'd like a reply. Everyone who does so gets one.
Many happy and safe E-landings, everyone!
HW
Transcribed from original scans by AI. Minor OCR errors may remain.
