RADIO CONTROL ELECTRICS - 2004/08

RADIO CONTROL ELECTRICS - 2004/08

Bob Kopski, 25 West End Dr., Lansdale PA 19446

Overview

This column includes:

• One meet announcement.
• One Electric Connection Service (ECS) request.
• A follow-up to the April/May "noise" topic (chokes and CIUs).
• Discussion about switches and their application.
• A closing item of note.

Cedar Rapids Sky Hawks Electric Fun Fly

Plenny Bates, a longtime reader from the early 1990s, sent information about the Cedar Rapids (Iowa) Sky Hawks Electric Fun Fly scheduled for August 7–8. Plenny is the meet CD.

Details: www.foxcoins.com/skyhawks/funfly/ If you don't have online access, call Plenny at (319) 362-2969. An AMA license is required to participate.

Electric Connection Service (ECS)

Bill Baker (1902 Peter Pan, Norman OK 73072), an established aeromodeling contributor and longtime reader from the late 1980s, asked if this column's ECS could assist him.

Bill and others in his area pursue E-powered sailplanes and are seeking others to join in this specialty. If interested, get in touch with Bill.

Follow-up: Power-system-induced radio noise (chokes and CIUs)

The April and May columns covered power-system electrical noise and how it can cause receiver glitching. One common noise path is the receiver–ESC cable, which interconnects the radio and power systems and can act as a "noise highway." The earlier columns suggested an easy test for noise problems.

There are generally two ways to reduce or eliminate this condition:

1. Use an ESC with an optoisolator input. This is likely the best solution but requires a different ESC and typically disallows the use of a BEC.
2. Use chokes in the receiver–ESC cable. This is often nearly as effective, can be applied to existing ESCs, and allows use of a BEC.

Both approaches break up the radio-frequency noise path between receiver and ESC while leaving the motor-control signal intact. I have used the choke method successfully for decades on six-meter and 72 MHz systems. It's easy, low cost, and safe.

Some modelers simply install chokes routinely, even if no noise is suspected.

Making Choke Insertion Units (CIUs)

CIUs allow you to insert chokes in-line between the ESC and receiver without cutting the ESC cable. They can be made for any connector type using a matching aileron extension (I usually use a 6-inch extension).

Parts and suppliers:

• Chokes: 10 µH units, Mouser Electronics catalog item 542-77F100 (approx. $0.60 each). Mouser: (800) 346-6873 or www.mouser.com.
• Heat-shrink tubing: small sizes (e.g., Du-Bro assortments available at hobby shops).
• Matching aileron extension cable (6-inch recommended).

Each CIU needs three chokes (one per wire). The only other materials are heat-shrink tubing and basic soldering supplies.

Assembly steps:

1. Cut the extension cable and separate the three individual wires of each cable half. Strip about 3/16 inch of insulation from each—take care not to cut wire strands. Twist and tin the exposed wire ends.
2. Slip a 1/4-inch length of 1/16-inch heat-shrink tubing (Du-Bro blue or equivalent) over each of the six wire ends. Slip a 1/4-inch length of 1/8-inch heat-shrink tubing (Du-Bro yellow or equivalent) on one of the cable ends to aid identification.
3. Trim the choke leads to roughly 3/16 inch. Tin the choke leads.
4. Lap-solder each wire end to a choke lead. Be sure to connect like-colored wires to each end of the same choke—do not mix them up.
5. Inspect all six solder joints carefully for quality.
6. Slide the smaller heat-shrink pieces over the solder joints and use a heat gun to shrink them.
7. Slide a 3/4-inch piece of heat-shrink tubing over the chokes and connections, center it, and shrink it with a heat gun. The CIU is finished.

The completed CIU is inserted in-line with the ESC/receiver cable. Re-run the noise tests from the April/May columns (or a flight-range test) first without the CIU and then with it installed. Many noise problems are eliminated or greatly reduced.

Notes:

• You can cut the ESC cable and install the chokes directly there, but the deployable CIU is preferable because it allows easy testing—sometimes the receiver–ESC cable is not the noise path.
• If the CIU solves the problem, you may leave it in place or install permanent chokes in the ESC cable. I prefer to carry a spare CIU in the car to help others at the flightline.

Switches and their application

A photo (referenced) showed various switches used in RC electrics. The toggle switches I use as arming switches in brushed power systems are heavy-duty units suitable for systems up to about 30 amps; I install them in series with the battery and ESC input.

Recommended switch:

• DPDT (Double Pole Double Throw): ITT Industries/C&K part 7201SYSXQE or Digi‑Key catalog item CKN1035‑ND. Digi‑Key: (800) 344‑4539 or www.digikey.com.

I use both poles in parallel, with a wire overlap soldered to both terminal sets. These switches are robust and time-proven; I do not recommend RadioShack switches.

Why small switches can work in higher-current systems:

• The switch is used only to arm the system when the throttle is off. With the throttle off, the ESC input is not switching "live" high currents, so flipping the arming switch does not create make/break arcing at the contacts. The ESC handles the live switching when active. In this "cold" condition the small switch contacts can close many times without damage. Once the ESC is activated, the closed contacts carry the higher current without the stress associated with switching it on.

Brushless caveat:

• I did experience one instantaneous failure of a quality toggle switch in a brushless application. Most brushless ESCs have large, low-ESR capacitors on their power input leads. These capacitors present a very low impedance at the moment of connection, effectively causing a short-circuit inrush that can cause intense sparking and arcing at the switch contacts, destroying them even if the throttle is off.
• Because of this, I no longer use toggle switches in brushless power systems. I prefer power-system connectors as switches for brushless setups, even though they still experience arcing on connection. Anderson Power Poles are a good choice: their initial contact occurs at the tips of the contacts, not the final mating surface farther back on the metal fingers, so the important contact surfaces avoid the initial arcing abuse.

Small slide switches:

• The small slide switch often found on ESCs is not a power switch. Its light-gauge wires are too small for motor currents. It only enables or disables the ESC electronics (arming/disarming) and does not remove battery power from the ESC entirely. The ESC electronics will continue to draw a small current from the battery with this switch off, which can allow packs to drain if left connected. If this is your only switch, be sure to disconnect the battery when finished flying.

Closing note

This is a special column. A few days after receiving my copy of the May issue of MA (and roughly a month after the April issue), I received 37 reader letters in reaction to the April discussion of an apparent design/manufacturing problem in the aging ACE Pro 810/RCD Platinum AM receivers. This brought in the largest, quickest reader reaction I've ever had. I'm gratified that so many found interest and help in a topic I reluctantly included.

So ends one more column and concludes 20 years of my association with MA and with you. Thank you all for giving me this great opportunity to "fly" with you! Ain't Electrics great?

Please include an SASE with any correspondence for which you'd like a reply. Everyone who does so gets one.

Many happy summertime E-landings, everyone.

MA

Transcribed from original scans by AI. Minor OCR errors may remain.