Brushless- actual experience & 'analysis' - Long
LearningCycle
for years along with many others. This is not a new technology. What IS new
is speed controls designed for land based RC (cars, trucks, etc). Novak
announced their system for a summer introduction. Modeltech
(www.modeltech.co.uk) already has been shipping and is, I believe, the very
first company with an ESC truly suitable for land based RC.
Most of my basic technical info on the brushless motors here are primarily to
the credit of Mike Smith of Modeltech. The info on brushed motors, I have
gleaned just by reading and listening to the rest of you. I have no
affiliation with Modeltech other than the fact that Mike was generous in
sharing information. Most of the conclusions, comparisons and applications are
mine by making logical observations, and I hope they are correct or at least in
the ballpark. If they are not, I am solely responsible for the error.
Obviously, please make corrections of any erroneous conclusions.
The brushless system for RC cars are already on the market. I believe
Modeltech (www.modeltech.co.uk) is the first one with a delivered and working
product for land based RC. Aveox does have motors, but not ESC that works well
for RC cars. Here's a quote from one of the owner of RB-RC products. (i.e.
Blue Goo & other RC lubricants.) He is talking about the E-maxx here.
"I had the brushless system set up for my TC3 at our track and my friend had
his E MAX with a bad speed controler, We took out the two motors and replaced
them with my brushless motor system.We only had six cells for power and it
pulled wheelies the whole length of the straight away. Everyone was impressed.
I really think that this is the system for the E Max. If you use twelve cells
you will probley get twenty minuets of run time. This system will really make
you a good driver because this system does not have reverse. Mike can tell you
the correct set up for the I MAX. Sorry for the delay in getting back to you .
My team is getting ready for the nets in
Maryland and I have been working on a new diff lube that seems to work even
better than my current diff lube. Let me know how you made out and keep in
touch. RB
My system has quite a work out. After we tried it in the E MAX at our club race
on Thursday night , carpet that is I let one of my friends use it for the
Friday night stadium truck night. Our track has special jumps built to place on
the carpet for this night. Once my friend got used to the power band of the
system he was having fun with all that power. Remember we only use one motor.
The only complaint was that he now didn't have reverse. It was faster than the
stock set up and you could lift the front end up just by pulling the throttle.
I think he was using 2400. The problem with the E MAX is that the speedo that
comes with the truck is failing. He has many E MAXES in storage waiting for new
speedos. Many of the drivers want to use this system when the outside dirt
track opens up this spring. They plan on putting twelve cells in series and to
run a ten min main like the gas trucks. Right now my other friend is putting
the system in his drag car for testing. He plans on breaking the national
record at the drag nats in May at a track in North Carolina. Hope this helps.
RB"
Just so we get the sticker shock out of the way, a single ESC and single motor
cost over $400 US. This DOES include the speed controller. However, my
conclusion is that the performance more than justify the price, AND will save
one substantial amount of money in the long run. (By the way, I am not
affiliated with Modeltech or any other company..J) However, obviously, you do
NOT need to buy one of these systems to still enjoy your E-maxxes. (The goal
is to have fun right?)
Here are my thoughts on the brushless motor systems for RC cars. I segment
these into three secions. First, are just the conclusions without any
justifications. Second are some basic technical info giving the reasoning
behind the first section. Third are some examples of applications.
One: What a brushless system is my preferred choice over brushed motors
1. Brushless is substantially more efficient. That means for the same run
time as a brushed motor, I can have much more power. Or for the same power, I
can have much longer run times. Or a combination of the two.
2. Brushless has a much wider powerband. That means its power/torque
delivery is much more consistent across the entire motor rpm range. So, the
power keeps on coming no matter what rpms you are spinning at unlike a brushed
system.
3. Brushless is efficient across a great range of voltages. So, the same
motor that runs awesome at 7.2 volts will also run just about as efficiently at
14.4 volts, or some other voltages within the range of the esc. RC car brushed
motors designed for 7.2 volts will wear out very quickly at 14.4 volts.
4. Brushless motor is virtually a ZERO maintenance motor. No brushes,
commutator to replace etc etc. In fact, many systems are sealed and are
supposed to run for many thousands of hours without maintenance.
5. Because of item 3 & 4 above, brushless motor will be much cheaper in
the long run. We can use one motor across a wide range of applications, and it
will last a very long time.
If I had to provide an analogy, this is like going from a purely mechanical
speed control world, into the electrical speed control world. The performance
advantage is drastic.
Two: Technical info, in laymen's terms. (I hope)
1. Brushless is substantially more efficient. By efficiency, we mean how
much of the electrical power going into the motor is actually changed into the
spinning motion of the motor. So, an efficient motor puts more of the power
into moving the car, and looses less into heat/friction. That means for the
same run time as a brushed motor, a brushless motor will give us much more
power. Or for the same power, I can have much longer run times. Or a
combination of the two.
a. Most brushed motors that are put on the E-maxx such as the Trinity
Sapphires, or Chameleons have a peak efficiency of only about 60% stock, and
that is on the upper range. The reality after a few runs is probably more in
the mid 50% range or lower.
b. Maximum efficiency brushed motors are found in the lower turn modified
motors such as the Trinity D4. The D4 in 9 or 11 turns are about 80%
efficiency when new. (p. 102, RCCA, May of 2000)
c. This efficiency drops further as the motor is run due to the
deterioration of the brushes etc.
d. In contrast, brushless motor that Modeltech produces have an efficiency
of about 85-92%. That is a little more than 50% than the regular motors that
most put on the E-maxx. (I don't know of anyone that puts D4 12 turns on the
E-maxxes yet.) In reality, if my point 2 below is correct, it is even much
higher than that.
e. My conclusion:
Therefore, if you run the Modeltech motors for producing the same power, you
could probably get about 50% more run time. Your 3000 mah packs, will now run
as if you had 4500 mah packs. OR, if you strive for the same run time, you
could have 50% more power. (Roughly speaking) This would be as if you added a
THIRD motor to the other two, and still not reduce your runtime. Or you can
get a combination of the two.
f. Given how much money people spend to get a few % more efficiency/power
in their motors, or that extra few seconds of run time in their super high end
matched packs, a 50% increase in efficiency is a PHENOMENAL achievement.
g. Key: No matter how much tweaking you do on a super high quality brushed
motor or super high end matched packs, you could not come close to a 50%
increase in efficiency. To get this done, you need a 'new' paradigm- which is
what the brushless motors are for land based RC.
2. Brushless has a much wider powerband. That means its power/torque
delivery is much more consistent across the entire motor rpm range. So, the
power keeps on coming no matter what rpms you are spinning at.
a. Even if we were using a modified brushed motor (i.e. Trinity D4) with
80% efficiency, it is useful to note that this maximum efficiency exist only at
a particular rpm. The efficiency graph of brushed motors is like an upside
down parabola. (i.e. like a rainbow shape) So, the peak efficiency exist only
at one narrow rpm range. For the Trinity D4 11 turn, the 80% efficiency it is
at about 25,000 to 30,000 rpm. (RCCA, May, 2000) If you are outside the range,
which is most of the time on the E-maxx or any other vehicle, you are not
getting close to the peak efficiency. (i.e. At 9000 rpm, it is 50%. At 12,000
rpm, it is 60%) So, if you are running your car at only one speed, then you
may get 80% efficiency. Obviously we accelerate and decelerate, so our
efficiency is really a whole lot lower with brushed motors.
IF the above is true for a top of the line modified motor with a peak
efficiency of 80%, what about motors most of us use with only about 60% peak
efficiency?
b. In contrast, across the entire rpm range of the Modeltech motors, the
efficiency is 85-92%! The power delivery profile/graph of efficiency is almost
like a flat horizontal line without the drastic dropoff of a brushed motor.
That means no matter what rpm you are at, you will be at least 85% efficiency,
compared to the D4 where you can conceivably drop to a much lower efficiency.
c. KEY: It seems to me that if you average out that supposedly 80%
efficient brushed motor across its entire operating rpm, the efficiency is
actually drastically lower since that 80% exist only at one particular point.
Obviously with 60% efficient brushed motors, which is what most run in their
E-maxx, the same principle apply and we are actually no where close to 60%
efficiency. In contrast, the brushless maintains a minimum of 85% efficiency
and peaks up to 92%. Therefore, compared to the brushed motors, the brushless
motors are actually far more efficient than the numbers indicate when compared
with brushed motors. (My gut level intuition is that overall, it may be up to
100% more efficient?)
Therefore, it seems to me that the brushless motors can easily be twice as
efficient in real terms when the entire operating rpm range is taken into
account.
d. Besides efficiency, the brushless motor with its consistent power band
gives much better CONTROL as it is more predictable, and much better
ACCELERATION as the powerband exist throughout its rpm range. There is no
'flat spot' as in the brushed system. Even without the added efficiency, this
alone is a true performance advantage.
Mike provided a quote from a driver: "In the manual it says the power delivery
is linear - after driving it I can confirm it is exactly that - it really is
very nice to drive."
e. One final note. If you look at the D4 powerband for example, the
MAXIMUM power (233 watts) is at 17000 rpm, but at that rpm, it is only about
70% efficiency, not 80%. At 80% efficiency, it only produces about 190 watts
average. Therefore, the brushed motors do not give you max efficiency and
power at the same time. The brushless remains high in efficiency across its
entire powerband which also remains high across the rpm. (I don't have the
exact numbers as they are currently 'proprietary'.)
3. Brushless is efficient across a great range of voltages. So, the same
motor that runs awesome at 7.2 volts will also run just about as efficiently at
14.4 volts, or some other voltages within the range of the esc. RC car brushed
motors designed for 7.2 volts will wear out very quickly at 14.4 volts.
a. This is a REAL advantage. So, in your E-maxx, you can use six cells by
themselves, two six cells in paralle, or two six cells in series for 14.4
volts. The Modeltech esc is capable of 16 volts by the way. And the motor
will function 'happily' across this entire range of voltages, maintaining its
efficiency and durability all the while. Nothing in the brushed motor world
even comes close. Try running any regular brushed motors at 14.4 volts
(except for the E-maxx type motors) and you'll wear them out in a hurry.
b. So, ONE motor can serve the function of many purpose. You want a long
runtime with good power? Use two 7.2 volts system in parallel. You want super
high power T-maxx beating speed/torque? Use the two packs in series. On motor
does it all, and it does not burn up.
c. We can all see the possibilities. One example is the RC10's 110mph
speed record run which was just reported using high voltage and a brushless
sytem. 110mph!
4. Brushless motor is virtually a ZERO maintenance motor. No brushes,
commutator to replace etc etc. In fact, many systems are sealed and are
supposed to run for many thousands of hours without maintenance. Oil the
bearings and that is it.
a. You can just drop in the motor, and go.
b. Time saved. Money saved.
c. Levels the playing field for those without the funds to buy lathes etc
etc.
I know, this sounds quite idealistic, but that is the promise that many who
know about brushless systems have agreed is accurate.
5. Because of item 3 & 4 above, brushless motor will be much cheaper in
the long run. We can use one motor across a wide range of applications, and it
will last a very long time.
Not much to add here.
OTHER INFO
1. Modeltech, as far as I know, is the ONLY one who is making brushless
ESC suitable for RC cars. There is a top end German company who may be
producing some of these but I've not yet found the info. So, my comments are
about the Modeltech since if you want one now, they are the only game in town.
2. The motors at modeltech are rated to 600 watts at 16 volts. That would
drain TWO of your 3000 mah packs in 3 minutes so there is NO LACK of power.
600 watts is not quite 1 horsepower so these still cannot compete with those
who put in .21 monster motors in the T-maxxes. (Darn! J) This should very
handily beat the stock T-maxxes though. Of course, most people won't come
close to maxing out the 600 watts so runtime will be good.
At 7.2 volts, these motors can do around 270. That is compared to the Trinity
D4 at 230 watts. Obviously factoring in the greater efficiency, the brushless
is MUCH more powerful than the Trinity D4.
3. For example, their second highest rpm motor, the B47S, will run at
96,000 rpm at 16 volts. The ESC is speed limited to 100,000 rpm. Most RC cars
will disintegrate well before that but it is good to know the potential of
these systems, and also knowing that they work very well at a much more sedate
speed.
4. From a couple of field reports I've read, they had significantly longer
run time than using 12X2 brushed motor turns, but are keeping up with people
running brushed 8X2 motors. This figure is going by my memory so factor this
accordingly.
5. The ESCs are capable of 70 amp continuous for the forward only model,
and 60 amp continuous for the forward/reverse model. So, this is PLENTY.
(i.e. 60 amp continuous will drain a 3000 mah pack in 3 minutes or less.) At
600 watt maximum continuous and 16 volts, the current draw is about 39 amps.
6. The ESC with reverse has been announced for delivery starting 2-3 weeks
from now. (Feb. 23rd, 2001)
7. Yes, these are regenerating ESCs, so some of the braking power is used
to charge your batteries for longer run time.
8. The greatest problem with brushless ESC is managing the back current
from braking. Apparently these can easily spike over 100 amp which causes the
ESC to shut down protectively until the spike is over. Apparently the higher
the KV (rpm per volt) the motor, the more prone it is to this problem.
9. Their current motors are the B4x series. They are able to deliver a B5x
series motors that have larger cans and will have more torque. However, it
should also draw more current and give shorter runtime than the B4x. The B5x
were never released because the initial market Modeltech was focusing on
(1/10th scale) could not handle that much power. The B5X are probably no more
efficient than the B4X, so if the B4X is powerful enough for you (and I think
it is), then it is a great choice. Should give you longer run time. Mike, am
I right?
10. Higher rpm is not always your best bet. If you want the max torque at
lower speeds (which is still screamingly fast compared to a brushed motor), you
would choose a lower rpm/volt motor.
11. Novak is coming with their brushless system this summer. No details
except it is forward/brakes/reversing ESC.
12. For further discussion on forums, go to the two links below. They
provide a lot of discussions AND most importantly, review from people ACTUALLY
running the Modeltech setup.
http://www.rctouring.com/rcubb/Forum1/HTML/000824.html
http://forums.about.com/n/main.asp?webtag=ab-rcvehicles&nav=messages&msg=9
144&cof=1&OK=OK
13. This is a posting Mike of Modeltech posted on www.rctouring.com's
board. It helps one select the appropriate motor- a little technical but makes
sense. I quote:
"As already mentioned in a discussion somewhere and on our site, the max rating
for all the motors is approx 600W at max volts, i.e 16v, and the torque curve
closely matches that of the power curve, but has a slight positive bend in it.
For this simple exercise straight lines will suffice…
Now draw a simple x/y plot of the line for Watts, use a simple straight line
,it is fairly close, from zero rpm to max power (watts) at say a nominal 7.2
volts, which is approx 270W nominal.
The slope of the line will actually depend on the Kv value of the motor, so a
B46 motor will peak 270W at approx 50,000 rpm at 7.2v, while a B48 will do the
same at approx 38,000. So the B48 develops a higher absolute shaft torque at a
given rpm than the B46, ok so far, but in use what does that mean!
In reality that 50,000 rpm motor shaft speed it just not useable in our sport,
speed way too high, but if you were to gear it down to say 2:1, the the torque
would be doubled, ok.
Now if you plotted the power line of both the B46 and the B48 on your graph,
take the nominal torque at say 25,000 rpm, measure the 2, now double that of
the B46 (2:1 gearing) which was originally lower, what do you now have? Much
higher drive torque but with a relative higher shaft speed and lower shaft
torque, the torque multiplcation occurs AFTER the motor shaft.
So, the "lower" shaft torque motor now has a higher drive torque, but it also
has a much higher shaft inertia at that rate, approx 4 times (corrected from
double - thanks JesseT) that of the B48, the result is that it will change
shaft speed much faster in its "normal" operating power range than the B48, BUT
the B48 will accelerate from zero, or lower speeds, faster than the B46 since
it goes through a steeper power curve, even with the gearing factor, but as
soon as the 2 curves meet up the B46 becomes the faster, the effects of motor
inertia have come into play, also the B48 changes over a smaller rpm band than
the B46 to get to that cross-over value.
As I have said on a number of occasions to those that keep requesting specific
numbers, in the end its what the driver feels that matters not the numbers. The
B48 produces the same torque but at lower rpm, after suitable gearing it
provides greater low end acceleration compared to the B46, which by comparison
has more mid to top end punch. Although in-appropriate choices of gearing can
and will totally reverse this situation AND really ramp up the current required
to change speed.
By the sounds of the reports we get back, most people pay attention to the
manuals reccommendations and soon get to an optimum gearing that suits them and
the car. Those that don't go by the manual seem to fall into 2 camps, they
break the car (way too highly geared and way too fast) or they can't control it
at the bottom end. The level of power just magnifies the results of incorrect
choice of gearing.
The gearing of a brushless motor, due to the relatively high operating rpm band
is very important on the end result you get. I hope this helps you understand
a little more."
APPLICATIONS - The fun part
1. As seen from the quote at the top of this post, the system is already a
WORKING system. The reverse ESC is coming in 2-3 weeks. If you follow the
suggested links above, you will see postings by others who are also using the
system.
2. The brushless system opens up a lot of possibilities. This is the
ideal setup in my mind for an E-maxx:
A. SUPERMAXX (www.monstermaxx.com) suspension system. I won't belabor the
point except to say this suspension system is supposedly to be a whole
different level of performance. From the report by some, it is almost like the
performance difference between a brushless and brushed motor. The difference
is supposedly that dramatic. Robin Oury, the owner/designer is a great engineer
and perfectionist. (Robin, where's MY system….J) Even at that price, he is
backordered.
However, the supermaxx suspension is 11 ozs heavier than stock setup, which is
daunting in an already almost 10 lbs truck. This has been the main drawback.
That is why almost all the Supermaxx users are also .21 T-maxx people.
B. However, with the power of brushless motors, the Supermaxx suspension
becomes much more viable for the E-maxx.
C. FURTHER, you can save more weight than the suspension system's 11 ozs.
a. Panther Meat Grinder tires are 7.5 ounces lighter than stock. (Larry,
you need to be advertising this fact!)
b. Only ONE MOTOR with the brushless system. Not including the missing
wires, you are already saving over 6.5 ounces on one motor. More if you use
Titan motors as you baseline weight.
c. The one brushless motor is also about 2 ounces lighter though you need
a mounting plate so that probably evens it out.
d. Therefore, with meatgrinders, and only one motor, you are loosing over
14 ounces back!
e. So, with this setup, you will have the ULTIMATE suspension system,
ultimate electric motor system.
f. I believe this setup will beat a stock T-maxx pretty handily.
D. OR, if you don't use the Supermaxx suspension, using Meatgrinders AND
the brushless system will save you almost ONE POUND of weight off the stock
setup! You are now in the T-maxx weight territory. If you run with only one
battery pack, you are now BELOW the T-maxx weight territory and that 8 lbs
E-maxx will have MUCH better handling. Losing more than 15% of the trucks'
weight obviously makes a REAL performance difference, even if you don't factor
in the power of the brushless system. See the implications? Time to eat some
T-maxxes for lunch. (Guys, just kidding here- not trying to be inflamatory.
Take it all in fun please.)
E. The Modeltech motors are much smaller in diameter than the stock 540 or
550 motors. They provide a mounting plate adapter.
I believe the Modeltech motors will indeed take off in the E-maxx community,
not to mention other land based RC.
SO…. there will be the need for a CUSTOM MADE motor mount that is only for
ONE motor, and smaller diameter motor to replace the original E-maxx motor
mount. Such a plate will save considerable weight, lower the center of
gravity, and look great. It will not be expensive to make. Obviously from a
marketing point of view, anyone who invest over $400 for a motor system will
gladly spend that extra few bucks for a custom motor mounting plate. Whoever
gets to the market first with this motor mount should corner the market.
F. Obviously, everything said here applies to the Clodbusters and other
MTs. And even more so for any smaller scale RC cars and trucks which are a
lot lighter than the E-maxx. Have fun! Report back.
G. Finally, there are always those who wants to 'one up' the rest with the
fastest & most powerful etc. These are talking about putting TWO brushless in
the E-maxx to double the power. However, in my opinion, this is erroneous
'brushed motor thinking' in a 'brushless motor world'. Such line of logic, two
motors being better than one on the E-maxx makes sense with brushed motors,
especially when you are talking 7.2 volts Super Rooster type set up. If you ran
those brushed motors at 14.4 volts, you'll wear them out in a hurry. They are
incredibly inefficient at 1.4.4 volts, producing a lot of heat. HOWEVER, with
a brushless, the results are entirely different. A brushless will run just as
happily on 14.4 volts as on 7.2 volts. So, ONE brushless motor with two
battery packs in series providing 14.4 volts will run in the same ballpark, or
a little faster than two 7.2 volts setups with two esc and two motors. The
efficiency stays about the same. Incidentally, you would not want two motors on
14.4 volts as one motor can drain the battery packs in 3 minutes if you run it
at the 600 watt maximum. Hope I saved some of you $400 plus. J
OK, this post is already very long so I'll refrain from adding any more info.
I'll leave you guys to dream up more applications. Thanks guys for all your
help on this board. I hope this returns the favor. Let the discussions
continue!
Blessings,
MT