BEC
Oct 01, 1999, 12:00 AM
<blockquote>
<p> </p>
<p>I’d like to start out this month by thanking those of you who have contacted me so
far for the encouragement and suggestions. I expect to be taking you up on many of them
over the next couple of installments.</p>
<p>An update item: Last month I neglected to give a price for the Astro Flight 215D
controller. The list price is US$79.95, but Astro Flight sells it over the Internet for
$60. Tower Hobbies lists it at $47.99 for the Futaba connector version, but they are out
of stock as of this writing.</p>
<p>This month’s topic is the battery eliminator/motor cutoff function of ESCs –
a subject that is often a source of lively discussion on the Eflight mailing list. For our
mini-review, we will be looking at the JMP7 micro speed control, made in France by
Jean-Marie Piednoir, and sold by WES-Technik. </p>
<p> </p>
</blockquote>
<p><big>A BEC Q&A, and more</big></p>
<blockquote>
<p>Gordon Tarling wrote a great BEC question and answer article for the most recent issue
of the British Electric Flight Association’s magazine, Electric Flight U.K. It is the
best balanced look at this function of ESCs I have read, so I asked him if I could share
it with you, and he has graciously agreed. After Gordon’s article I’ll add a few
thoughts of my own, then we’ll get to the JMP7 review.</p>
<p>Now, over to Gordon. I’ve added a few comments in [square brackets].</p>
<div align="center"><center><table border="1" width="85%" bgcolor="#E6E6E6">
<tr>
<td width="100%" align="left"><p align="center"> </p>
<p align="center"><big><u><strong>BEC - Q&A</strong></u></big><br>
By Gordon Tarling</p>
<p>BEC systems are frequently the cause of much controversy and misunderstanding in
electric flight circles. There are those who swear by it, those who would never consider
using it and those who don’t really understand it, but just use it because it is
there. Hopefully, this article will help to answer some of those oft-asked questions and,
maybe, help you to understand it a little more.</p>
<p><strong>What is a BEC?</strong></p>
<p>The acronym ‘BEC’ stands for ‘Battery Eliminator Circuit’ and
refers to a method of deriving power for the receiver and servos from the flight, or
motor, battery. This enables the receiver battery to be dispensed with, thus saving some
weight and bulk. Technically, there is no such thing as ‘a BEC’. It should
rightfully be called a BEC system, for it should incorporate some safety devices as well
as a means of deriving the required voltage. </p>
<p><strong>Where can I buy a BEC?</strong></p>
<p>Normally, you just can’t go out and buy ‘a BEC’. A BEC system is
normally incorporated into some models of speed control and will form an integral part of
that controller. There are certain safety functions which must be present in a BEC system
for aircraft - the power to the motor must be reduced or cut if the battery voltage gets
low, for instance - and these functions must be designed in as part of the speed control.</p>
<p><strong>How does a BEC system work?</strong></p>
<p>The flight battery voltage is normally higher than that required for supply directly to
the receiver and servos, so it must be reduced in some way. As well as being reduced, it
must also be maintained within certain limits. The lowest cost and most compact way of
achieving this is to use a device known as a linear regulator. The flight battery voltage
is applied to the input side of the regulator and it will normally give us a constant five
volts output.</p>
<p>Note that the regulator is only able to give a constant output of five volts while its
input voltage exceeds five volts by some margin. This margin varies between regulator
types, but is typically around 0.8 Volts for those normally used. Thus, as soon as the
flight battery voltage drops below 5.8 volts, the regulator will no longer be able to
maintain the five volts output which we need and it is said to have ‘dropped
out’. This situation must not normally be permitted to occur, or we should endanger
our valuable radio link, so it is arranged for the power to the motor to be reduced or cut
completely as soon as the battery voltage nears this level.</p>
<p>Apart from the linear regulator, there are other methods of obtaining the required five
volts, but they are not normally used because they are either more complicated and bulky,
less reliable, or will create more radio ‘noise’ to interfere with our
receivers. </p>
<p>The linear regulators which are used for our BEC systems are normally very reliable as
they are designed for use in other pieces of electronic equipment, not exclusively for our
speed controls. Because of this fact, they also have their limitations, of which we must
be aware.</p>
<p><strong>What are the limitations of a BEC system?</strong></p>
<p>As mentioned above, we are ‘borrowing’ regulators for our own purposes which
are normally designed for other applications. Because of this, most of the regulators have
some protective functions built in which will prevent these regulators from destroying
themselves under fault conditions. It is these very protective functions which can cause
us problems. In no particular order of priority, they are:-</p>
<blockquote>
<p><strong>a) Reverse polarity protection</strong> - no real problem here, this function
can actually do us a favour, for I have seen several burnt-out speed controls where the
regulator was the only major component to have survived!</p>
<p><strong>b) Overvoltage protection</strong> - again, no real problem here, you are never
likely to encounter this function as long as you are only using commercial speed controls
and stick to the recommended number of cells.</p>
<p><strong>c) Overcurrent protection</strong> - this is one of the two major protective
functions which is quite capable of giving us a problem. Every regulator has a maximum
output current specified by the manufacturer - exceed this limit and the regulator shuts
down in order to protect itself from burning out. When the regulator shuts down, there is
no voltage output and hence, no voltage to operate the radio - need I say more? However,
all is not doom and gloom, for most regulators in regular BEC use are rated at 1 Amp or
more. With the maximum number of servos attached to the BEC system (normally 4), this
limit is likely to be exceeded only when large demands are placed upon several servos at
once and is likely to be only of a transient nature. Therefore, if you are using a BEC
system with the maximum number of servos, be aware that unusual glitching of the system
may be caused by the current limiter operating.</p>
<p><strong>d) Thermal protection</strong> - The regulators incorporate a thermal
protective which will shut the device down completely when a certain temperature is
exceeded. Now you may be thinking, why would the thing get hot in the first place? Well,
the linear regulator operates by ‘dumping’ the excess voltage that it
doesn’t need. This voltage appears as heat. Also, the greater the current drawn from
it, the greater the heat produced. The combination of these two parameters may be
sufficient to cause your regulator to shut down just when you least expect it.</p>
</blockquote>
<p>As stated above, the amount of heat produced by the regulator is a function of its
input voltage and the load on it. The greater the number of cells and/or the greater the
load, the larger the amount of heat produced in the voltage conversion process. Some
recent tests carried out by the author on a typical regulator show that at an input
voltage of 7.5 Volts (7 cells), the regulator was capable of supplying 800mA (0.8A)
continuously without shutting down. With an input voltage of 11 Volts (10 cells) it could
only maintain 400mA without shutting down. Note that these current levels have nothing
whatsoever to do with the published current ratings for the regulators - the published
figures assume an almost infinite heatsink is attached to the regulator, which is not the
case when it is used in a model. A regulator whose published rating is 3 Amps will still
shut down at a similar figure to one rated at 1 Amp if the heatsinking arrangements are
the same.</p>
<p>[Some manufacturers use clever design to increase the BEC’s capabilities, such as
the doubled regulators in the Astro Flight 215D featured last month. - BC]</p>
<p><strong>What do the above figures mean in practice?</strong></p>
<p>Above all else, stick to the speed control manufacturers’ recommendations with
respect to number of cells used and number of servos used. If in doubt, play safe and use
servo/cell combinations as shown here.<ul>
<li>6 to 7 cells - up to 4 servos</li>
<li>8 to 9 cells - up to 3 servos</li>
<li>10 cells - up to 2 servos.</li>
</ul>
<p>Be extremely suspicious of any manufacturer who claims that their BEC system is OK for
use on anything above the given figures. I have noted, in particular, of late, that one or
two manufacturers are starting to rate their speed controls for use with BEC on up to 14
cells. I would just ask why would you want to take the risk of using such a setup? Surely,
if the model is capable of carrying a battery pack of 14 cells, then an additional 2
ounces for a small receiver pack will hardly be noticed? Keep BEC systems for those models
that really need it and fit a receiver battery to those that don’t.</p>
<p>[See my comments after the end of Gordon’s article – BC.]</p>
<p><strong>What can I do to make my BEC system safer? </strong></p>
<p>Ensure that all wiring in the model is in first class condition - the system is only as
reliable as it’s weakest link. If running the speed control near to its current limit
or at part throttle for extended periods, it would pay to ensure that it has some cooling
air - every little helps. Remember, too, that a system running close to the limits when
you complete that new model in mid-winter, may well be over those limits on a hot
summer’s day. </p>
<p>Beware, too, of end-to-end soldered battery packs - it is easy to crack the solder
joint between two cells in a heavy landing or just by handling the pack roughly. You will
probably never notice this defect as the shrink sleeve will hold the pack together and it
will be quite capable of supplying motor current. One day, that bad joint WILL let go and
I'm sure you don't need me to tell you the likely result! Side-by-side battery packs with
soldered straps are much safer and easier to inspect when using BEC.</p>
<p><strong>Can I use a fuse with my BEC?</strong></p>
<p>Yes, with certain constraints. The main one is that the fuse must be connected into the
circuit between the speed control and the motor. That way, if it blows in flight, the
supply to the radio is safeguarded. Don’t even dream of fitting the fuse on the
battery side of the speed control unless you like free-flight models! With a fuse fitted
in the correct place in the circuit, you are preventing a burn-up in the event of a
stalled motor or similar event occurring. The fuse cannot protect against a speed
controller fault. </p>
<p>[Since you cannot fuse a brushless motor properly by using a fuse in only one of the
three wires which go between the motor and the controller, using BEC in a brushless system
means you can’t fuse at all unless there is a separate way for the controller to get
power, bypassing the fuse. Only the MaxCim (and MEC) brushless controller is set up this
way as far as I know. - BC]</p>
<p><strong>Can I use a receiver battery with my BEC speed control? </strong></p>
<p>This practice is not recommended and will not make the system any safer or more
fault-tolerant than either being used in isolation. If you need to use a receiver battery,
it is best if the BEC system is isolated. This can be done by removing the contact of the
positive wire on the lead which connects the speed control to the receiver. It’s best
not to cut this wire, as you may need to reinstate the BEC for use in another model at a
later date.</p>
<p><strong>My BEC speed control does not have a receiver switch fitted - can I fit one? </strong></p>
<p>Manufacturers of speed controls have very good reason for not fitting such a switch -
customers might assume that the system is safe if switched off. Nothing could be further
from the truth! By not fitting a switch, they ensure that the battery is unplugged after
each flight - the safest option. If you do need to fit such a switch for a certain model,
it is not recommended that you fit one yourself - simply cutting the red lead to the
receiver and inserting a switch may seem like the right way to go about things, but could
result in the motor bursting into life unexpectedly. </p>
<p>Some speed controls come with an option to fit a switch - a loop of wire or somewhere
else to connect your own switch in. Others are supplied as standard with a switch - these
are your best option if you require a switch for certain models.</p>
<p>If you do use a speed control with a switch, it must always be remembered that the only
safe model is one with the battery removed or totally disconnected. Do NOT rely on that
little receiver switch to keep you safe! </p>
<p><strong>My motor cuts out as soon as I open the throttle - why?</strong></p>
<p>If you are using the correct number of cells with the speed controller, then the BEC
system is almost certainly 'seeing' a low voltage and doing its job to protect the
receiver supply by cutting the motor. There are many reasons that it will 'see' a low
voltage with a fully charged battery pack, but they include - bad cell in the pack,
unsuitable connectors, bad solder joint(s), too thin wiring, cells unsuitable for high
currents, motor drawing too much current (measure it!). The same faults can also be the
cause of shorter than expected motor runs.</p>
<p>[Some of the now-available micro sized servos, such as the FMA S-90/Cirrus CS-21 are
known to have very high current draws when they first move, as much as one amp! This can
cause a regulator to drop out or a low voltage cutoff to engage when you move the
controls. If you are using these servos, check the current rating of your
controller’s BEC and test for this condition before that first flight hand launch!
– BC]</p>
<p><strong>Conclusions</strong></p>
<p>BEC systems are either loved or hated - the up side is that you can save a small amount
of weight and bulk on those models which most need it and, of course, there is no receiver
battery to charge (or maintain) before a flying session. Use it in those models where you
really do need to save either the space or the weight. However, maintain a realistic
outlook on things, because that 60" aerobatic model with 10 cells and three or four
servos really will not notice the extra weight of a small receiver battery and the model
will be that much safer because of it. Providing, of course, that you remember to charge
the receiver pack!</p>
<p align="center"> </td>
</tr>
</table>
</center></div><p>Thanks again, Gordon, for sharing this with us! For those of you who
don’t know, Gordon is the man behind the Micro-Star line of ESCs, made in the UK,
among other things!</p>
<p>One of the reasons I personally use BEC/cutoff systems is not just to save weight, but
because it is so convenient. Not having to maintain the receiver battery, as Gordon put
it, is a BIG item for me, as I seldom have lots of time to go flying and often only on
short notice. Over the years I have had one crash and several near crashes due to receiver
batteries running down, but have not (yet, anyway) had a loss of control due to a
BEC/cutoff failure. This consideration leads me to use BEC systems in models that are
large enough to not need the weight saving, such as my much discussed Kadet LT-25. I
think, too, this is why the MaxCim brushless controller is set up to provide radio power
via a BEC system on more that the usual 10 cells. This controller is encased in aluminum
heatsinks, however, and therefore has a place for the extra heat to go safely.</p>
<div align="center"><center><table border="1" width="65%" bgcolor="#E5E5E5">
<tr>
<td width="50%"><p align="center"><a href="/articles/ezonemag/1999/oct/control/3escs1.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/3escs1_small.jpg" alt="3escs1.jpg (22768 bytes)" WIDTH="97" HEIGHT="100"></a></td>
<td width="50%"><p align="center"><a href="/articles/ezonemag/1999/oct/control/2escs1.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/2escs1_small.jpg" alt="2escs1.jpg (18117 bytes)" WIDTH="100" HEIGHT="100"></a></td>
</tr>
<tr>
<td width="50%">Three different examples of BEC-equipped controls. From top to bottom:
Viper Models LD-21, Tarling Micro-Star 20, and MaxCim brushless.</td>
<td width="50%">Two other examples of BEC-equipped controls. From top to bottom: JETI JES
350 and Aveox L60 brushless.</td>
</tr>
</table>
</center></div><p>One other aspect of BECs which Gordon didn’t mention was radio
interference. By its very nature, using a BEC system means that your radio system and your
power system share a common ground path – they are electrically connected together. A
good BEC speed control designer will use filtering or other means to prevent this from
being a problem for the radio system. Still, as the motor system power goes up, remember
that the power system and the control system CANNOT be completely electrically isolated
from one another. Beware of anyone who tells you that his controller has a BEC function
and is also optically isolated. At best it can only be partially isolated with an
optocoupler if the BEC is used.</p>
<p>There are all sorts of fascinating little details in the implementation of the
BEC/cutoff function, such as how the cutoff voltage is set, and variations on what the
control actually does when the motor battery reaches that voltage. Perhaps I’ll
expound on those next time.</p>
<p>Our featured review unit this month, the JMP7 indoor/slowfly controller, has one of the
less common approaches to this feature, and is definitely aimed at models which NEED the
weight reduction that comes from eliminating a receiver battery. In fact, such planes
often use motor batteries that are smaller than most dedicated radio batteries….</p>
<p> </p>
</blockquote>
<p><big>JMP7 Micro Speed Control – a quick review</big></p>
<blockquote>
<p>Jean-Marie Piednoir, who makes tiny ESCs for the German firm WES-Technik, sent me an
example of his JMP7 controller to try out, then write about. The JMP7 is one of a family
of ESCs intended for the slowflyer/indoor market, and as such it is extremely small (as
you can see in the pictures) and light. Nevertheless it is a full featured controller
which functions like much larger units.</p>
<p>As supplied, it is a tiny, heat-shrink covered lump of components on a double-sided
circuit board, with 6 inch long, flexible leads (about 22 guage, I think) for battery and
motor, and a standard JR/Hitec receiver lead of similar length. (He notes in his letter to
me that the units he supplies to WES-Technik have shorter, lighter wires and a JST
connector, for a total weight of 1.6 g.) As you can see in the pictures, it is barely
larger than a receiver plug.</p>
<p>On the test stand, I hooked it up to a Titanic Airlines GD-280 (actually the
motor/gearbox out of my Slowmowatt), and powered it with both 7X350 and 8X270 packs. Once
I got the receiver plug in the right way round (always problem when mixing up equipment),
it behaved quite well.</p>
<p>The JMP7 is self-adjusting for both endpoints and range. It assumes that the initial
throttle stick position as the "off" point. If the throttle is above a certain
point, however, the controller will not arm at all. (I haven’t had a chance to
measure that point yet.)</p>
<p>Advancing the throttle from there has it reaching full throttle somewhat before the top
of the stick throw on my old Airtronics Tx. However, about 1.5 seconds after the stick is
at the full power position, it rescales the range and uses the actual high throttle stick
position as "full throttle". Consequently, from then on, you have full use of
the throttle stick's range.</p>
<p>It should be noted that unlike the Viper controls which continue to recalibrate the
entire time the system is on, the JMP7 only does this once. So, any additional changes in
high or low points you might make by, say, moving the throttle trim, are ignored.</p>
<p>It is very responsive, having only a bit of delay in throttle stick motion being
translated into motor speed changes. </p>
<p>It has a fairly unusual approach to the motor cutoff function, one I haven't seen since
the old Airtronics MA-3 frame rate control of about 10 years ago. Rather than shutting the
motor off when flight battery voltage drops below a certain point, it instead
automatically reduces the throttle so that flight battery voltage remains above 5V. In use
this "feels" just like flying a control which has no cutoff at all, allowing you
to use just about every last bit of energy in the battery. It just automatically maintains
the voltage needed to keep the Rx and servos running. Near the end of the charge, moving a
servo will cause the motor to slow or momentarily stop. In an indoor application, where
the plane is not ever very high or far away, and has rather high drag, this is a very
useable approach. Such a plane will be back on the ground quite soon motor battery starts
to go flat. It makes more sense in this application than did the MA-3 in a 2 meter
motorglider (though I never managed to get into trouble with that setup either).</p>
<p>For flight tests I installed the JMP7 in my Slowmowatt. It is so small I made no
attempt to mount it. I just let it dangle from the wiring. My Slowmowatt has a geared
Speed 280, and the rest of the radio is an FMA Micro 2000 receiver and two S-80's. </p>
<p>Unfortunately, the combination of available time and suitable weather for flight tests
did not come together well enough for me to finish flight tests before my deadline for
this column. I will have to report on the flight test of this little unit next time.</p>
<p>It should be available from any dealer of WES-Technik equipment.</p>
<p> </p>
<div align="center"><center><table border="1" width="65%" bgcolor="#E6E6E6">
<tr>
<td width="100%" align="left"><p align="center"><a href="/articles/ezonemag/1999/oct/control/jmp7_1.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/jmp7_1_small.jpg" alt="jmp7_1.jpg (7597 bytes)" WIDTH="117" HEIGHT="100"></a> <a href="/articles/ezonemag/1999/oct/control/jmp7_2.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/jmp7_2_small.jpg" alt="jmp7_2.jpg (8539 bytes)" WIDTH="128" HEIGHT="100"></a> <a href="/articles/ezonemag/1999/oct/control/jmp7_3.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/jmp7_3_small.jpg" alt="jmp7_3.jpg (7557 bytes)" WIDTH="120" HEIGHT="100"></a></td>
</tr>
<tr>
<td width="100%" align="left"><p align="center"><strong><br>
<big>WES-Technik JMP7 Specifications</big></strong></p>
<u><p><strong>Physical</strong></u><ul>
<li>Dimensions: 0.8 X 0.3 X 0.2 inches</li>
<li>Weight as supplied*: 5.5 g</li>
<li>Weight, ready to use**: 6.5 g</li>
<li>Rx connector supplied?: Yes, JR/Hitec</li>
<li>Power connectors supplied?: No</li>
</ul>
<u><p><strong>Throttle Function</strong></u><ul>
<li>Microprocessor controlled</li>
<li>Cell count range: 5 to 9</li>
<li>Rated continuous current: 4 Amps</li>
<li>Setup method: Self adjusting range and endpoints</li>
<li>High rate switching?: 2.5 kHz to 10 kHz, depending on transmitter throttle range</li>
</ul>
<u><p><strong>Brake Function</strong></u><ul>
<li>Brake?: No</li>
</ul>
<u><p><strong>Battery Eliminator/Cutoff Function</strong></u><ul>
<li>BEC?: Yes, rated at 0.7 Amps</li>
<li>Radio on/off switch? No</li>
<li>Cutoff: at 5.1 V, progressive(see text)</li>
<li>Motor Restart?: N/A: power to motor is progressively reduced to maintain Rx voltage</li>
</ul>
<p><u><strong>Price</strong></u><ul>
<li>List Price 99DM. US price, approximately $50</li>
</ul>
<p>*Includes 6 inches of 22 gauge wire for motor and for battery hookups, Rx lead and
connector</p>
<p>**Includes above, plus three pin Deans plug on battery lead only.</p>
<p> </td>
</tr>
</table>
</center></div><p> </p>
<p>As I said last month, let me know if you’re finding this sort of information
useful, and what aspect of electronic speed controls you’d like me to look into. Or,
if you’d like to suggest a particular control to be featured, I’d like to know
that, too. My home e-mail is <a href="http://rcgroups.com/shared/nospam.php?u=ab_cawley&d=compuserve.com">ab_cawley(at)compuserve.com</a>.</p>
<p> </p>
</blockquote>
<p> </p>
<p>I’d like to start out this month by thanking those of you who have contacted me so
far for the encouragement and suggestions. I expect to be taking you up on many of them
over the next couple of installments.</p>
<p>An update item: Last month I neglected to give a price for the Astro Flight 215D
controller. The list price is US$79.95, but Astro Flight sells it over the Internet for
$60. Tower Hobbies lists it at $47.99 for the Futaba connector version, but they are out
of stock as of this writing.</p>
<p>This month’s topic is the battery eliminator/motor cutoff function of ESCs –
a subject that is often a source of lively discussion on the Eflight mailing list. For our
mini-review, we will be looking at the JMP7 micro speed control, made in France by
Jean-Marie Piednoir, and sold by WES-Technik. </p>
<p> </p>
</blockquote>
<p><big>A BEC Q&A, and more</big></p>
<blockquote>
<p>Gordon Tarling wrote a great BEC question and answer article for the most recent issue
of the British Electric Flight Association’s magazine, Electric Flight U.K. It is the
best balanced look at this function of ESCs I have read, so I asked him if I could share
it with you, and he has graciously agreed. After Gordon’s article I’ll add a few
thoughts of my own, then we’ll get to the JMP7 review.</p>
<p>Now, over to Gordon. I’ve added a few comments in [square brackets].</p>
<div align="center"><center><table border="1" width="85%" bgcolor="#E6E6E6">
<tr>
<td width="100%" align="left"><p align="center"> </p>
<p align="center"><big><u><strong>BEC - Q&A</strong></u></big><br>
By Gordon Tarling</p>
<p>BEC systems are frequently the cause of much controversy and misunderstanding in
electric flight circles. There are those who swear by it, those who would never consider
using it and those who don’t really understand it, but just use it because it is
there. Hopefully, this article will help to answer some of those oft-asked questions and,
maybe, help you to understand it a little more.</p>
<p><strong>What is a BEC?</strong></p>
<p>The acronym ‘BEC’ stands for ‘Battery Eliminator Circuit’ and
refers to a method of deriving power for the receiver and servos from the flight, or
motor, battery. This enables the receiver battery to be dispensed with, thus saving some
weight and bulk. Technically, there is no such thing as ‘a BEC’. It should
rightfully be called a BEC system, for it should incorporate some safety devices as well
as a means of deriving the required voltage. </p>
<p><strong>Where can I buy a BEC?</strong></p>
<p>Normally, you just can’t go out and buy ‘a BEC’. A BEC system is
normally incorporated into some models of speed control and will form an integral part of
that controller. There are certain safety functions which must be present in a BEC system
for aircraft - the power to the motor must be reduced or cut if the battery voltage gets
low, for instance - and these functions must be designed in as part of the speed control.</p>
<p><strong>How does a BEC system work?</strong></p>
<p>The flight battery voltage is normally higher than that required for supply directly to
the receiver and servos, so it must be reduced in some way. As well as being reduced, it
must also be maintained within certain limits. The lowest cost and most compact way of
achieving this is to use a device known as a linear regulator. The flight battery voltage
is applied to the input side of the regulator and it will normally give us a constant five
volts output.</p>
<p>Note that the regulator is only able to give a constant output of five volts while its
input voltage exceeds five volts by some margin. This margin varies between regulator
types, but is typically around 0.8 Volts for those normally used. Thus, as soon as the
flight battery voltage drops below 5.8 volts, the regulator will no longer be able to
maintain the five volts output which we need and it is said to have ‘dropped
out’. This situation must not normally be permitted to occur, or we should endanger
our valuable radio link, so it is arranged for the power to the motor to be reduced or cut
completely as soon as the battery voltage nears this level.</p>
<p>Apart from the linear regulator, there are other methods of obtaining the required five
volts, but they are not normally used because they are either more complicated and bulky,
less reliable, or will create more radio ‘noise’ to interfere with our
receivers. </p>
<p>The linear regulators which are used for our BEC systems are normally very reliable as
they are designed for use in other pieces of electronic equipment, not exclusively for our
speed controls. Because of this fact, they also have their limitations, of which we must
be aware.</p>
<p><strong>What are the limitations of a BEC system?</strong></p>
<p>As mentioned above, we are ‘borrowing’ regulators for our own purposes which
are normally designed for other applications. Because of this, most of the regulators have
some protective functions built in which will prevent these regulators from destroying
themselves under fault conditions. It is these very protective functions which can cause
us problems. In no particular order of priority, they are:-</p>
<blockquote>
<p><strong>a) Reverse polarity protection</strong> - no real problem here, this function
can actually do us a favour, for I have seen several burnt-out speed controls where the
regulator was the only major component to have survived!</p>
<p><strong>b) Overvoltage protection</strong> - again, no real problem here, you are never
likely to encounter this function as long as you are only using commercial speed controls
and stick to the recommended number of cells.</p>
<p><strong>c) Overcurrent protection</strong> - this is one of the two major protective
functions which is quite capable of giving us a problem. Every regulator has a maximum
output current specified by the manufacturer - exceed this limit and the regulator shuts
down in order to protect itself from burning out. When the regulator shuts down, there is
no voltage output and hence, no voltage to operate the radio - need I say more? However,
all is not doom and gloom, for most regulators in regular BEC use are rated at 1 Amp or
more. With the maximum number of servos attached to the BEC system (normally 4), this
limit is likely to be exceeded only when large demands are placed upon several servos at
once and is likely to be only of a transient nature. Therefore, if you are using a BEC
system with the maximum number of servos, be aware that unusual glitching of the system
may be caused by the current limiter operating.</p>
<p><strong>d) Thermal protection</strong> - The regulators incorporate a thermal
protective which will shut the device down completely when a certain temperature is
exceeded. Now you may be thinking, why would the thing get hot in the first place? Well,
the linear regulator operates by ‘dumping’ the excess voltage that it
doesn’t need. This voltage appears as heat. Also, the greater the current drawn from
it, the greater the heat produced. The combination of these two parameters may be
sufficient to cause your regulator to shut down just when you least expect it.</p>
</blockquote>
<p>As stated above, the amount of heat produced by the regulator is a function of its
input voltage and the load on it. The greater the number of cells and/or the greater the
load, the larger the amount of heat produced in the voltage conversion process. Some
recent tests carried out by the author on a typical regulator show that at an input
voltage of 7.5 Volts (7 cells), the regulator was capable of supplying 800mA (0.8A)
continuously without shutting down. With an input voltage of 11 Volts (10 cells) it could
only maintain 400mA without shutting down. Note that these current levels have nothing
whatsoever to do with the published current ratings for the regulators - the published
figures assume an almost infinite heatsink is attached to the regulator, which is not the
case when it is used in a model. A regulator whose published rating is 3 Amps will still
shut down at a similar figure to one rated at 1 Amp if the heatsinking arrangements are
the same.</p>
<p>[Some manufacturers use clever design to increase the BEC’s capabilities, such as
the doubled regulators in the Astro Flight 215D featured last month. - BC]</p>
<p><strong>What do the above figures mean in practice?</strong></p>
<p>Above all else, stick to the speed control manufacturers’ recommendations with
respect to number of cells used and number of servos used. If in doubt, play safe and use
servo/cell combinations as shown here.<ul>
<li>6 to 7 cells - up to 4 servos</li>
<li>8 to 9 cells - up to 3 servos</li>
<li>10 cells - up to 2 servos.</li>
</ul>
<p>Be extremely suspicious of any manufacturer who claims that their BEC system is OK for
use on anything above the given figures. I have noted, in particular, of late, that one or
two manufacturers are starting to rate their speed controls for use with BEC on up to 14
cells. I would just ask why would you want to take the risk of using such a setup? Surely,
if the model is capable of carrying a battery pack of 14 cells, then an additional 2
ounces for a small receiver pack will hardly be noticed? Keep BEC systems for those models
that really need it and fit a receiver battery to those that don’t.</p>
<p>[See my comments after the end of Gordon’s article – BC.]</p>
<p><strong>What can I do to make my BEC system safer? </strong></p>
<p>Ensure that all wiring in the model is in first class condition - the system is only as
reliable as it’s weakest link. If running the speed control near to its current limit
or at part throttle for extended periods, it would pay to ensure that it has some cooling
air - every little helps. Remember, too, that a system running close to the limits when
you complete that new model in mid-winter, may well be over those limits on a hot
summer’s day. </p>
<p>Beware, too, of end-to-end soldered battery packs - it is easy to crack the solder
joint between two cells in a heavy landing or just by handling the pack roughly. You will
probably never notice this defect as the shrink sleeve will hold the pack together and it
will be quite capable of supplying motor current. One day, that bad joint WILL let go and
I'm sure you don't need me to tell you the likely result! Side-by-side battery packs with
soldered straps are much safer and easier to inspect when using BEC.</p>
<p><strong>Can I use a fuse with my BEC?</strong></p>
<p>Yes, with certain constraints. The main one is that the fuse must be connected into the
circuit between the speed control and the motor. That way, if it blows in flight, the
supply to the radio is safeguarded. Don’t even dream of fitting the fuse on the
battery side of the speed control unless you like free-flight models! With a fuse fitted
in the correct place in the circuit, you are preventing a burn-up in the event of a
stalled motor or similar event occurring. The fuse cannot protect against a speed
controller fault. </p>
<p>[Since you cannot fuse a brushless motor properly by using a fuse in only one of the
three wires which go between the motor and the controller, using BEC in a brushless system
means you can’t fuse at all unless there is a separate way for the controller to get
power, bypassing the fuse. Only the MaxCim (and MEC) brushless controller is set up this
way as far as I know. - BC]</p>
<p><strong>Can I use a receiver battery with my BEC speed control? </strong></p>
<p>This practice is not recommended and will not make the system any safer or more
fault-tolerant than either being used in isolation. If you need to use a receiver battery,
it is best if the BEC system is isolated. This can be done by removing the contact of the
positive wire on the lead which connects the speed control to the receiver. It’s best
not to cut this wire, as you may need to reinstate the BEC for use in another model at a
later date.</p>
<p><strong>My BEC speed control does not have a receiver switch fitted - can I fit one? </strong></p>
<p>Manufacturers of speed controls have very good reason for not fitting such a switch -
customers might assume that the system is safe if switched off. Nothing could be further
from the truth! By not fitting a switch, they ensure that the battery is unplugged after
each flight - the safest option. If you do need to fit such a switch for a certain model,
it is not recommended that you fit one yourself - simply cutting the red lead to the
receiver and inserting a switch may seem like the right way to go about things, but could
result in the motor bursting into life unexpectedly. </p>
<p>Some speed controls come with an option to fit a switch - a loop of wire or somewhere
else to connect your own switch in. Others are supplied as standard with a switch - these
are your best option if you require a switch for certain models.</p>
<p>If you do use a speed control with a switch, it must always be remembered that the only
safe model is one with the battery removed or totally disconnected. Do NOT rely on that
little receiver switch to keep you safe! </p>
<p><strong>My motor cuts out as soon as I open the throttle - why?</strong></p>
<p>If you are using the correct number of cells with the speed controller, then the BEC
system is almost certainly 'seeing' a low voltage and doing its job to protect the
receiver supply by cutting the motor. There are many reasons that it will 'see' a low
voltage with a fully charged battery pack, but they include - bad cell in the pack,
unsuitable connectors, bad solder joint(s), too thin wiring, cells unsuitable for high
currents, motor drawing too much current (measure it!). The same faults can also be the
cause of shorter than expected motor runs.</p>
<p>[Some of the now-available micro sized servos, such as the FMA S-90/Cirrus CS-21 are
known to have very high current draws when they first move, as much as one amp! This can
cause a regulator to drop out or a low voltage cutoff to engage when you move the
controls. If you are using these servos, check the current rating of your
controller’s BEC and test for this condition before that first flight hand launch!
– BC]</p>
<p><strong>Conclusions</strong></p>
<p>BEC systems are either loved or hated - the up side is that you can save a small amount
of weight and bulk on those models which most need it and, of course, there is no receiver
battery to charge (or maintain) before a flying session. Use it in those models where you
really do need to save either the space or the weight. However, maintain a realistic
outlook on things, because that 60" aerobatic model with 10 cells and three or four
servos really will not notice the extra weight of a small receiver battery and the model
will be that much safer because of it. Providing, of course, that you remember to charge
the receiver pack!</p>
<p align="center"> </td>
</tr>
</table>
</center></div><p>Thanks again, Gordon, for sharing this with us! For those of you who
don’t know, Gordon is the man behind the Micro-Star line of ESCs, made in the UK,
among other things!</p>
<p>One of the reasons I personally use BEC/cutoff systems is not just to save weight, but
because it is so convenient. Not having to maintain the receiver battery, as Gordon put
it, is a BIG item for me, as I seldom have lots of time to go flying and often only on
short notice. Over the years I have had one crash and several near crashes due to receiver
batteries running down, but have not (yet, anyway) had a loss of control due to a
BEC/cutoff failure. This consideration leads me to use BEC systems in models that are
large enough to not need the weight saving, such as my much discussed Kadet LT-25. I
think, too, this is why the MaxCim brushless controller is set up to provide radio power
via a BEC system on more that the usual 10 cells. This controller is encased in aluminum
heatsinks, however, and therefore has a place for the extra heat to go safely.</p>
<div align="center"><center><table border="1" width="65%" bgcolor="#E5E5E5">
<tr>
<td width="50%"><p align="center"><a href="/articles/ezonemag/1999/oct/control/3escs1.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/3escs1_small.jpg" alt="3escs1.jpg (22768 bytes)" WIDTH="97" HEIGHT="100"></a></td>
<td width="50%"><p align="center"><a href="/articles/ezonemag/1999/oct/control/2escs1.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/2escs1_small.jpg" alt="2escs1.jpg (18117 bytes)" WIDTH="100" HEIGHT="100"></a></td>
</tr>
<tr>
<td width="50%">Three different examples of BEC-equipped controls. From top to bottom:
Viper Models LD-21, Tarling Micro-Star 20, and MaxCim brushless.</td>
<td width="50%">Two other examples of BEC-equipped controls. From top to bottom: JETI JES
350 and Aveox L60 brushless.</td>
</tr>
</table>
</center></div><p>One other aspect of BECs which Gordon didn’t mention was radio
interference. By its very nature, using a BEC system means that your radio system and your
power system share a common ground path – they are electrically connected together. A
good BEC speed control designer will use filtering or other means to prevent this from
being a problem for the radio system. Still, as the motor system power goes up, remember
that the power system and the control system CANNOT be completely electrically isolated
from one another. Beware of anyone who tells you that his controller has a BEC function
and is also optically isolated. At best it can only be partially isolated with an
optocoupler if the BEC is used.</p>
<p>There are all sorts of fascinating little details in the implementation of the
BEC/cutoff function, such as how the cutoff voltage is set, and variations on what the
control actually does when the motor battery reaches that voltage. Perhaps I’ll
expound on those next time.</p>
<p>Our featured review unit this month, the JMP7 indoor/slowfly controller, has one of the
less common approaches to this feature, and is definitely aimed at models which NEED the
weight reduction that comes from eliminating a receiver battery. In fact, such planes
often use motor batteries that are smaller than most dedicated radio batteries….</p>
<p> </p>
</blockquote>
<p><big>JMP7 Micro Speed Control – a quick review</big></p>
<blockquote>
<p>Jean-Marie Piednoir, who makes tiny ESCs for the German firm WES-Technik, sent me an
example of his JMP7 controller to try out, then write about. The JMP7 is one of a family
of ESCs intended for the slowflyer/indoor market, and as such it is extremely small (as
you can see in the pictures) and light. Nevertheless it is a full featured controller
which functions like much larger units.</p>
<p>As supplied, it is a tiny, heat-shrink covered lump of components on a double-sided
circuit board, with 6 inch long, flexible leads (about 22 guage, I think) for battery and
motor, and a standard JR/Hitec receiver lead of similar length. (He notes in his letter to
me that the units he supplies to WES-Technik have shorter, lighter wires and a JST
connector, for a total weight of 1.6 g.) As you can see in the pictures, it is barely
larger than a receiver plug.</p>
<p>On the test stand, I hooked it up to a Titanic Airlines GD-280 (actually the
motor/gearbox out of my Slowmowatt), and powered it with both 7X350 and 8X270 packs. Once
I got the receiver plug in the right way round (always problem when mixing up equipment),
it behaved quite well.</p>
<p>The JMP7 is self-adjusting for both endpoints and range. It assumes that the initial
throttle stick position as the "off" point. If the throttle is above a certain
point, however, the controller will not arm at all. (I haven’t had a chance to
measure that point yet.)</p>
<p>Advancing the throttle from there has it reaching full throttle somewhat before the top
of the stick throw on my old Airtronics Tx. However, about 1.5 seconds after the stick is
at the full power position, it rescales the range and uses the actual high throttle stick
position as "full throttle". Consequently, from then on, you have full use of
the throttle stick's range.</p>
<p>It should be noted that unlike the Viper controls which continue to recalibrate the
entire time the system is on, the JMP7 only does this once. So, any additional changes in
high or low points you might make by, say, moving the throttle trim, are ignored.</p>
<p>It is very responsive, having only a bit of delay in throttle stick motion being
translated into motor speed changes. </p>
<p>It has a fairly unusual approach to the motor cutoff function, one I haven't seen since
the old Airtronics MA-3 frame rate control of about 10 years ago. Rather than shutting the
motor off when flight battery voltage drops below a certain point, it instead
automatically reduces the throttle so that flight battery voltage remains above 5V. In use
this "feels" just like flying a control which has no cutoff at all, allowing you
to use just about every last bit of energy in the battery. It just automatically maintains
the voltage needed to keep the Rx and servos running. Near the end of the charge, moving a
servo will cause the motor to slow or momentarily stop. In an indoor application, where
the plane is not ever very high or far away, and has rather high drag, this is a very
useable approach. Such a plane will be back on the ground quite soon motor battery starts
to go flat. It makes more sense in this application than did the MA-3 in a 2 meter
motorglider (though I never managed to get into trouble with that setup either).</p>
<p>For flight tests I installed the JMP7 in my Slowmowatt. It is so small I made no
attempt to mount it. I just let it dangle from the wiring. My Slowmowatt has a geared
Speed 280, and the rest of the radio is an FMA Micro 2000 receiver and two S-80's. </p>
<p>Unfortunately, the combination of available time and suitable weather for flight tests
did not come together well enough for me to finish flight tests before my deadline for
this column. I will have to report on the flight test of this little unit next time.</p>
<p>It should be available from any dealer of WES-Technik equipment.</p>
<p> </p>
<div align="center"><center><table border="1" width="65%" bgcolor="#E6E6E6">
<tr>
<td width="100%" align="left"><p align="center"><a href="/articles/ezonemag/1999/oct/control/jmp7_1.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/jmp7_1_small.jpg" alt="jmp7_1.jpg (7597 bytes)" WIDTH="117" HEIGHT="100"></a> <a href="/articles/ezonemag/1999/oct/control/jmp7_2.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/jmp7_2_small.jpg" alt="jmp7_2.jpg (8539 bytes)" WIDTH="128" HEIGHT="100"></a> <a href="/articles/ezonemag/1999/oct/control/jmp7_3.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1999/oct/control/jmp7_3_small.jpg" alt="jmp7_3.jpg (7557 bytes)" WIDTH="120" HEIGHT="100"></a></td>
</tr>
<tr>
<td width="100%" align="left"><p align="center"><strong><br>
<big>WES-Technik JMP7 Specifications</big></strong></p>
<u><p><strong>Physical</strong></u><ul>
<li>Dimensions: 0.8 X 0.3 X 0.2 inches</li>
<li>Weight as supplied*: 5.5 g</li>
<li>Weight, ready to use**: 6.5 g</li>
<li>Rx connector supplied?: Yes, JR/Hitec</li>
<li>Power connectors supplied?: No</li>
</ul>
<u><p><strong>Throttle Function</strong></u><ul>
<li>Microprocessor controlled</li>
<li>Cell count range: 5 to 9</li>
<li>Rated continuous current: 4 Amps</li>
<li>Setup method: Self adjusting range and endpoints</li>
<li>High rate switching?: 2.5 kHz to 10 kHz, depending on transmitter throttle range</li>
</ul>
<u><p><strong>Brake Function</strong></u><ul>
<li>Brake?: No</li>
</ul>
<u><p><strong>Battery Eliminator/Cutoff Function</strong></u><ul>
<li>BEC?: Yes, rated at 0.7 Amps</li>
<li>Radio on/off switch? No</li>
<li>Cutoff: at 5.1 V, progressive(see text)</li>
<li>Motor Restart?: N/A: power to motor is progressively reduced to maintain Rx voltage</li>
</ul>
<p><u><strong>Price</strong></u><ul>
<li>List Price 99DM. US price, approximately $50</li>
</ul>
<p>*Includes 6 inches of 22 gauge wire for motor and for battery hookups, Rx lead and
connector</p>
<p>**Includes above, plus three pin Deans plug on battery lead only.</p>
<p> </td>
</tr>
</table>
</center></div><p> </p>
<p>As I said last month, let me know if you’re finding this sort of information
useful, and what aspect of electronic speed controls you’d like me to look into. Or,
if you’d like to suggest a particular control to be featured, I’d like to know
that, too. My home e-mail is <a href="http://rcgroups.com/shared/nospam.php?u=ab_cawley&d=compuserve.com">ab_cawley(at)compuserve.com</a>.</p>
<p> </p>
</blockquote>