RC Electrics
Bob Kopski, <REDACTED>
THIS COLUMN OFFERS one Electric Connection Service and continues last month's Electronic Speed Control discussion.
Angelo "Sonny" Varisco, a former member of the high-powered Silent Electric Fliers of Long Island (SEFLI) group (that put on NEAT [the Northeast Electric Aircraft Technology fair]) is now resident at <REDACTED>, and he is eagerly seeking folks in that area to share E-joy with.
Sonny tells me his immediate area includes Northwest Broward County and South Palm Beach County, and so far he hasn't been able to hook up with E-fluters nearby.
We gotta fix this situation, so I'm asking E-aeromodellers in the area described to get in touch with Sonny. He can be reached at <REDACTED>.
I'm sure he can share many stories with you about E-flight Long Island style! And do be sure to tell 'im Bob sent ya!
Last month's column included some discussion about Electronic Speed Controls (ESCs) and, in particular, the Battery Eliminator Circuit (BEC) feature. At that time I indicated I'd have more to share about ESCs this month.
Although much of what follows is "old news" to most E-aeromodellers, many new readers have been asking related questions in recent months. It's clear that newcomers still need the same kind of basic information that everyone else did in his or her own E-beginner days.
What an ESC does
The primary and historic purpose of an ESC is to effect motor (rpm) control in our Electrics. One might picture the ESC as a valve in a pipe that can be adjusted to control water flow.
Basically, an ESC is inserted in the wiring between the motor battery and the motor, and is then used like a valve. It controls the effective voltage that reaches the motor from zero to essentially the full battery voltage.
An ESC smoothly controls motor voltage from full off to full on, but can be positioned anywhere in between. The varying voltage results in varying motor/propeller rpm.
Unlike a valve with a manually adjusted knob, the ESC is remotely controlled with the transmitter throttle stick. The typical ESC has a three-wire cable—just like a servo—that plugs into the receiver throttle channel output.
This throttle command from the transmitter winds up as an instruction to the ESC, just as it would to a servo. The stick position tells the ESC what percentage of the available battery voltage to allocate to the motor.
Types and sizes
The basic ESC idea has been around for approximately two decades, and now there are many kinds available from many suppliers. There are tiny ones and much larger ones, and there are ESCs for normal brushed motors as well as for brushless motors.
The physical size of an ESC is largely driven by its capability. Thus the smallest are suited for small motor/battery combinations, such as in park flyers, and the largest—with more electronic stuff inside—are for the largest of E-power systems.
The two most common considerations that drive ESC "size" are motor battery voltage (cell count) and motor current. And unlike motors, some contemporary ESCs actually have labeling that describes some of these specifications!
One might find some ESC label indicating use with "6–8 cells" and "5 amps max," while another describes much greater capability.
Programmable features
Throughout the years, the rudimentary ESC has been gradually embellished with numerous operational features. Nowadays these features are often programmable by the user.
- Some ESCs allow the off range to be (electrically) fitted to the physical throw of the throttle stick.
- Some can have an optional brake function invoked, and some of these even allow the "hardness" of the brake to be set.
- Others can be programmed to retard motor operation at a selectable battery voltage to prevent running the motor battery down too far.
There are other common and exclusive ESC features, depending on the manufacturer.
Battery Eliminator Circuit (BEC)
As described last month, it's now routine to find ESCs with a built-in Battery Eliminator Circuit (BEC). This is a hardware option feature that can be used or not. The BEC allows one to power the airborne radio gear from the motor battery. It "eliminates" the need for the normally used radio battery.
Right now I have 16 fully equipped, fully operational Electrics, and only one has a classic radio battery installed. It is really nice not to have to maintain the radio battery in all these (or any) airplanes, and I'm not alone with this preference.
Each time I charge the motor battery I've replenished the radio power source as well, and I can fly with total confidence.
I also know that like myself years ago, some people still do not feel comfortable using BEC. For those with this feeling, please take it from this reformed nonbeliever of old that contemporary BEC is very workable and very nice to fly with. (Early BECs had a bad reputation.) Follow the instructions that come with your ESC, and all should work fine.
Remember that connection of the ESC to the receiver throttle output mentioned above? It's this same wiring connection that allows the BEC function to power the airborne guidance gear.
Basically, since the ESC must be connected to the receiver to get its control instructions, everything else is in place for the receiver and servos to receive power from the ESC BEC. Thus that single three-wire cable carries voltage from the ESC to power the receiver and servos as it also carries throttle instructions from the receiver to the ESC. It's a two-way street.
There is one other variation of this approach, as you'll see later.
ESC wiring and installation notes
The typical ESC has three wire sets emerging from it:
- One two-wire set goes to the motor battery.
- A second two-wire set goes to the motor.
- A third three-wire set goes to the receiver.
And yes, the actual installation may include an arming switch, a fuse, and appropriate connectors, but that's another discussion. Note that it's critically important not to mix up the "battery in" and "motor out" wire sets!
All BECs have some limitations to "how much" radio gear they can power. They also have cell-count limitations on the motor battery they can be used with. These considerations are described on the ESC instruction sheets and must be honored, as follows.
The BEC is normally an integrated circuit (IC) regulator and a few other associated parts. These ICs regulate the (higher) motor-pack voltage down to approximately five volts for radio power.
The regulator ICs themselves have definite limitations on how much power they can dissipate before they overheat. This limit means that for a given motor battery cell count there is only so much average current that can be supplied to the radio gear while remaining below the dissipation limitation.
This is because the voltage difference between the motor battery voltage and the nominal five-volt output, when multiplied by the average current into the receiver and servos, is the power dissipated as heat in the BEC component.
Since almost all airborne radio-system current is taken by the servos, it is common to see ESC instructions describe how many or what kind of servos can be used safely for each ESC product and motor battery cell count.
It is important to honor these instructions because the consequence of not doing so can be a failed BEC function, which might mean loss of radio control — definitely a "no-no" in a radio-controlled aeromodel!
If this sounds complicated and scary, please accept that it is not. It's simply a matter of following the product instructions.
There are many ESCs on the market that have varying degrees of BEC capability, so nearly all applications can be accommodated—but not every one, as in the following example.
The largest cell count I recall seeing advertised for use with BEC is 12. Some of the smallest ESCs have lower cell-count limits. All this means is that for motor batteries exceeding the BEC cell-count limit, it's necessary to use a separate radio battery; i.e., to remain with a "normal" radio installation.
It's common to see an ESC description such as "for use with up to 12 cells with BEC and up to 18 cells w/o BEC." This means the ESC itself can be used with as many as 18 cells for motor-control purposes, but only with as many as 12 cells when BEC is used.
Since all ESCs connect to the throttle channel of the receiver, there is always some provision for selecting the radio power source. Because one cannot safely power the radio gear from a radio battery and from BEC at the same time, there is always a means provided to allow one or the other to be used.
This might take the form of a switch or a cable adapter, or some other modification that is used to disable the BEC operation when a normal receiver battery is used. Yet other ESCs have a fourth wire set as the exclusive power-supply cable for the radio.
All ESCs I know of are available with radio-connector options, so that the ESC can be used with all brands of radios. Some allow the user to make this selection after purchase, while others must be purchased with the correct radio connector installed.
Relatively few ESCs are supplied with motor and battery power connectors, so this aspect can be customized by the user to his or her preference. Therefore, some soldering is needed with many ESC installations.
This latter consideration can be intimidating to some aeromodelers, so some suppliers offer a connector-installation service. One is New Creations R/C.
Basically, if you order the ESC you want, then specify your preferred power connectors, your ESC will arrive ready to connect into your power system.
Of course, you can get your club expert to help with this soldering chore instead.
Throttle range mismatches
Some recent reader letters have described a problem wherein the throttle stick motion of some transmitters does not result in full off to full on motor control with a particular ESC. In effect, it's possible to have a "mismatch" between the signal range of a transmitter and the input signal-range needs of an ESC.
If this occurs with a nonprogrammable transmitter and/or a nonprogrammable ESC, there is little that can be done short of modifying the transmitter stick setup itself. This is certainly not a "nice" thing to have happen, and fortunately it seems that such problems are few and far between.
From what readers have written, such ESC/transmitter "misfits" take the form of too much stick throw at the low end and "not enough" stick throw at the high end. These readers indicate that too much of the stick throw is "used up" just to get the motor to come on, and that leaves "not enough" stick throw to reach the full on condition.
In principle, one should be able to reposition the throttle pot inside the transmitter to help accommodate this situation. Since various transmitters are made differently, it's not possible to describe the process in a "one size fits all" fashion.
Rather, if you can see a mechanical way to rotate the pot body or the pot shaft to "advance" the relative electrical position of the pot, you may be able to "center up" the electrical throw available and achieve full off to full on ESC operation.
Some have been successful with this approach, but it does alter the normal throttle-stick behavior for that transmitter. This means it may not work properly with servos or other ESCs.
The obvious option for all this is to find an ESC that does work with your transmitter. A programmable ESC that can match the stick range should do the trick.
Resources
Because of the huge variety of ESCs on the market, it's quite difficult for anyone to be familiar with them all. However, one person comes very close to this distinction: Bernard Crawley.
Bernard writes a (nearly) monthly column for the electronic E-aeromodelling magazine ezonemag.com, entitled "A Controlling Interest." Bernard discusses all sorts of things, including test and performance results for ESCs by name.
I strongly suggest that you access this reference and rummage through the archives of Bernard's work. To the best of my knowledge, there is no similar ESC info source that even comes close to what this resource offers!
So ends another column. Next month will include some more ESC discussion.
Please enclose an SASE with any correspondence for which you'd like a reply. And no, I do not ordinarily use E-mail for this purpose!
Many happy E-landings, everyone! M4
Transcribed from original scans by AI. Minor OCR errors may remain.
