Using RC motors on E-bikes [Archive]

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you don't add add losses you multiply them, and you don't use loss anyway you use efficiency(75% instead of 25%, 93% instead of 7%), 0.75 * 0.93 = 0.697, 1000W * 0.697 = 697W at the wheel.
 
I was doing that "ballpark" thing. :)

To get really serious about this stuff you need to build a spreadsheet or computer program to load all the variables and get down to the nitty gritty.

My point was that 50% is too high a number for losses for a geared bike. If you are being realistic with your numbers you will be more in the 30% range.

50% is too high, but would you agree 30% is in the "ballpark"?

697W / 1000W is roughly 70% efficiency or 30% losses...
 
hey safe, you don´t need to convice me, iam 100% of your opinion when it comes to gears..

for that cheap unitedhobbies-motors lets assume 75%
than 95% for the first belt-stage (5:1)
than 95% for the second belt-stage (3:1)
and 98% for the chain (gearbox-out to lower bracket or how that is called were the pedals are mounted, 3,5:1)

assuming the 400rpm/V motor runs with 14Volt at ~5000rpm
we need ~50:1 reduktion to get our 90rpm cadenz on the pedals
thats reached with the above given numbers..

efficience: 66%
so form the 150Watt only 230Watt would be needed
-> the battery i mentioned would last not 14min but 18min
well well.. 1,5h mountainbike-tour with girlfriend ;)
 
yea you came close, but consider if you used 50% loss, 50 + 50 = 100% loss, thats very wrong, it would be 25% efficiency, or 75% loss. 70% is ok i guess, it would be cool to be a ble to get it higher though.
 
I was thinking that the brushless RC motors had efficiencies that were closer to 90% than the usual 80% for brushed motors.

Using metal gears (ideally planetary gears) like in a Swiss Watch type transmission you should be able to think in terms of at least 90% "out the back" to the rear wheel, so:

0.9 * 0.9 = 0.81 or 81% efficiency to the front sprocket.

Tack on another 0.95% efficiency for the chain and you get:

0.81 * 0.95 = 0.77 or 77% efficiency at best.

Now throw in the fact that even with multispeed gears you sometimes operate above or below your efficiency peak and then I'd figure a final efficiency overall of about 75% would be the best possible on average. For brushed that would be:

0.8 * 0.9 = 0.72
0.72 * 0.95 = 0.68 or 68% efficiency at best.
...but on average that's going to be more like 65%.

So the "ballpark" of 30% would actually be somewhere in between the brushed and brushless motor. You also have to figure what amp rate you are running and whether you use armature current limiting or not because that makes a big difference too.

But if someone asked you on the street:

"Hey, how efficient are ebikes anyway?"

...you could say 70% efficient or 30% losses and be okay.

Hub motor people like to quote the peak efficiency number like they spend all day riding at that speed, (maybe they do :? ) but in reality if they really wanted to use their motor to achieve their top speed (the definition of proper gearing) and rode around town with stops and starts you would get average numbers below the geared numbers. Pure efficiency calculations only apply to velodromes where the speeds are constant and not the real world.
 
i think on some hubmotors you will see efficience (at hills, ...) of less than 50%

for the efficience of RC-motors:
look for example here for this Plettenberg outrunner:
http://www.plettenberg-motoren.com/Datenblaetter/Orbit/Orbit30_14.pdf

specially on low rpms (so voltage not that high, motor around 6000rpm) you see efficiences
in the 80% region

i doubt that this 30 Euro Outrunners from china will be as good or better than this 200 Euro Plettenberg outrunner

90% is possible with BL in that size, but not for all
innerunner are often reaching this value more easily than outrunners..
on the other hand: outrunners are "stiffer" and better on partial load

so i still would calculate with 80% for the motor efficience than with 90%
if it realy comes close in reality use to the 90% -> let us be happy (better this way than other way round)
 
here for example you can see some measured curves for some AXI-outrunners:
http://www.elektromodellflug.de/motoren/axi-bericht.htm
(scroll down)

not close to 90%, even not reaching 80%

Kontronik Micro DANCER (outrunner):
http://www.elektromodellflug.de/motoren/grafik/Micro-Dancer.gif (under 75%)

Kontornik Mini Dancer
http://www.elektromodellflug.de/motoren/grafik/Mini-Dancer.gif (max. = 81%)

Kontronik Maxi Dancer
http://www.elektromodellflug.de/motoren/grafik/Maxi-Dancer.gif (max. = 80%)

Kontronik EVO Dancer
http://www.elektromodellflug.de/motoren/grafik/Evo-Dancer.gif (max. = 83%)

MVVS Outrunner (in an innrunner-housing):
http://www.rc-network.de/magazin/artikel_08/art_08-016/bilder/antr-beispiel.jpg (max. = 82%)

the list is neverending...
so: 90% is something you will not reach that easily (specially not with outrunners)
 
There have to be some brushless RC motors with 90% efficiencies... there just has to be...

If you can barely beat 80% with an RC motor then the brushed motor could beat it and save lot of hassle with gears.

I'm pretty sure there is a range of efficiencies with the RC motors... some much approach 90%... we need a search to find the highest efficiency verses the lowest price intersection point.
 
Neu motors are running 93% efficient for many of their motors.

I do not know who classifies these things, though. Brushed motors ten to run very hot while brushless (even with lower efficiency numbers) run cool. :?

Matt
 
thats impossible, all losses end up as heat. even the mechanical power put out to the wheel ends up as heat, the tire and road heat up, and moving air molecules heats them up.
 
50% is probably a pretty good number, since you guys are still leaving out battery losses (they do generate some heat), plus you've got more wind resistance, and if you're talking about hills then you also have to consider hauling the added weight up the hill. I personally don't really care that much about efficiency (just carry more batts), since a gas engine is only about 30% efficient, and that's just gas to mechanical. You have deduct the significant drive train losses from there. If efficiency is such a big issue with these RC motors, let's see some real world efficiencies of the alternatives, hub motors and others.

I can see that efficiency and weight are huge issues for the RC guys, because they directly affect performance and flying time. I'm attracted to the RC motors because of their small size, which makes them easier to fit, and their high power, which otherwise seems to require a 15-30lb motor of considerably higher cost. As far as gearing is concerned, I'm going for that 130kv motor, so all I need is a small sprocket, a chain, and a large sprocket. Hopefully that motor will be reasonably efficient at small loads, and I'll have tons of power to spare for when I want it. If I have to carry some extra batts, so be it.

John
 
John in CR said:
since a gas engine is only about 30% efficient, and that's just gas to mechanical. You have deduct the significant drive train losses from there. If efficiency is such a big issue with these RC motors, let's see some real world efficiencies of the alternatives, hub motors and others.

I'm attracted to the RC motors because of their small size, which makes them easier to fit, and their high power, which otherwise seems to require a 15-30lb motor of considerably higher cost. As far as gearing is concerned, I'm going for that 130kv motor, so all I need is a small sprocket, a chain, and a large sprocket. Hopefully that motor will be reasonably efficient at small loads, and I'll have tons of power to spare for when I want it. If I have to carry some extra batts, so be it.
Click to expand...

Gas is not a great comparison, as it has huge energy density.

The efficiency of the RC motor or any other is the foundation of the rest of the system: high efficiency and low weight require less batteries, less cooling, resulting in less total weight. All the better if the batteries are light & powerful, the bike is low drag and the system works reliably. Not too different than machines that fly.
 
dirty_d said:
John take some pictures as you do it, ill be interested to see how it all comes out.
Click to expand...

Dirty,

I will, just please don't expect anything at Matt's level of engineering artwork. I'm even considering just going with a friction drive, at least to get some quick results. That way I can get an idea of whether or not these things become just a battery eater when you operate them at only 10% of their potential 90% of the time. Plus, I want to quickly find out just how exciting it is to have 6-8hp at my fingertips on an Ebike.

First things first though. I have to finish versions 1.2 and 2.1 of my electric stand-up paddleboard (version 1 showed enough promise to proceed in 2 directions. I just got my motor and Comet CVT mounted today for my electric motorcycle project. Plus I have less than 3 weeks to finish up hub motored bikes for myself and the kids to bring along on my beach trip in July.

John
 
TylerDurden said:
...The efficiency of the RC motor or any other is the foundation of the rest of the system
Click to expand...

I disagree. While a reasonable degree of efficiency is important for it to function well, a 10-15% swing in efficiency will have virtually no effect on any of my projects.

TylerDurden said:
: high efficiency and low weight require less batteries, less cooling, resulting in less total weight. All the better if the batteries are light & powerful, the bike is low drag and the system works reliably. Not too different than machines that fly.
Click to expand...

Of course I agree, though I'd rank reliability at numero uno.

John
 
I do not know who classifies these things, though. Brushed motors ten to run very hot while brushless (even with lower efficiency numbers) run cool.
Click to expand...

dirty_d: "thats impossible, all losses end up as heat."

i agree with that (physic laws) but will nevertheless second what recumbence said (real-life-experience)

you have ot look at the whole power-band, not only at the peak of max. efficience

EXAMPLE:
rc-slowflyers..
a brushed Permax 280BB has something ~70% efficience
how can it be, that a little brushless outrunner build from an CD-ROM with 75% efficience works nevertheless SO much better ?!?

the efficience curve from the brushed motor is very steep..
he has maybe 70% at 4A, but at 7-8A its under 50% and on more current it will burn
the BL has 75% with 4A, at 7-8A its still in the 70% region.. and you can go even higher with 10-12A staying above 60%

the same with rc-cars and the very varying loads...
if you only look at peak-efficience, the differens between brushed and brushless are only some few %-points..
the clue is: were the brushed falls down to 50% at 30A loads (loosing some 25 %-Points), the Bl only drops by maybe 5 %-points

---------------------------------

another thing to considere:
80% efficience
90% efficience

the differnets seems not to be that great...
but look at the heat !!!

100Watt Input
90% efficience ===> 10Watt heat in the motor
80% efficience ===> 20Watt heat in the motor

so: the difference seems not that great when looking on efficience,
but when looking on the looses you see, that its doubeling the heat in the motor !!
on rc-models which are often build to the limits of electrical compontents (due to weight) this is very essential
 
for the 93% NEUs...

yes, there are some motors, which break the 90% barrier..
but i think less than 1% of rc-model-motors can reach 90% or go even above that

Neu, Lehner, Kontronik, Plettenberg are some candidates which have motors that can do that..
BUT: here we are in the 200$+ range

on the cheap(er) motors i doubt to see anything close 90%

here you have for free a big list of many many motors..
many measured, some only calculated:
http://www.elektromodellflug.de/Uploads/AR-V221_026.zip
(you need MS Excel to run the program, there is also a switch for English mode)

if you don´t have Excel: here a stand-alone application:
http://www.drivecalc.de/

here you can get two very good programs in 30day-trial-versions
with hundrets of different rc-motors meassured:
http://www.geck-elektroantrieb.de/
http://www.motocalc.com/
 
Thank you for clarifying that.

I am talking about real world experience with electric motors in general.

I have heard many people talk about how hot their brushed motors get, but post great efficiency numbers. Hmm, something is amiss here........ My experience with motors shows brushless run far cooler than a brushed motor with similar output.

At any rate, no matter how I run my brushless outrunner, it never gets hot.

Matt
 
I went through this in the PA forum when building my bike. There were a few people who were harping on how these "Tiny" motors must have a very narrow efficiency curves and how they cannot last long with such high power output, etc.

I can say this, I have more than enough power, my motor runs luke warm (about 110 derees) all the time, and it runs cool no matter what RPM it is operating at.

I am shocked at the performance and characteristic of these motors under these conditions. Even with my 3 stage reduction (motor to wheel), I am still averaging 15.69 WH per mile at 20mph average speed. As Tyler pointed out, that may be due to my recumbent layout. I agree with that. I am not sure how much that contributes, though. All I know is, I am hooked on this! :mrgreen:

Matt
 
Brushless suffer no problems at higher rpms, but the brushed motors start to have problems with contact of the brushes above a certain speed. So the brushless can be spun up into the 10,000 rpm range without any problems, but the brushed motors start to break up about about 4,000 rpms. My bike is now reving up to 5,000 rpms and it seems like at the very highest rpms it's coughing and sputtering a little... but I can't say for sure if that's brush related. Right around 4,000, which is the peak power, the motor runs really smooth and perfectly, so I know that at least up to 4,000 rpms a brushed motor is solid.
 
depends on size !!!
you have always have to add this...

there are of course brushed motor which can spin a lot more than 4000rpm...

AND: its also again something which has to do with quality...
maybe its easier to build a cheap (outrunner) brushless motor than a cheap brushed motor

(in fact, the motor for it allown is a lot easier when it is a brushless motor than it is as a brushed motor)

i would suggest to take a look at the plettenberg homepage..
they made and make the maybe best brushed motors in RC-world,
and also one of the best in the brushless-sector, so you can compare this..

example:
BRUSHED:
http://www.plettenberg-motoren.com/Datenblaetter/355_37/HP_355_37_04.PDF
Plettenberg HP 355/37/4 Evo
580g heavy

now compare this with an state-of-the art brushless outrunner:
Plettenberg HP 355/30/B14 P10 (short: Orbit 30/14)
http://www.plettenberg-motoren.com/Datenblaetter/Orbit/Orbit30_14.pdf
305g light

what do we see:
at 30Volt
brushed: (~ 26`000rpm fast)
30A --> 79%
40A --> 84,5%
50A --> 86,9%
60A --> 86,9%

brushless: (~ 15`000rpm fast)
10A --> 75%
20A --> 85%
30A --> 87,6%
40A --> 87%
50A --> 85%

so: this eff.-values are not that far appart..
the brushless is a lot lighter (for exapmle no brushes needed, for smaller at same magnet-material)
(also maybe the outrunner can get off the heat much easier because of design)

EDIT:
searched again, here a
http://www.plettenberg-motoren.com/Datenblaetter/355_25/HP_355_25_08.PDF
the brushed HP 355/25/08 Evolution (about 15`000rpm like the outrunner in my last example)
10A --> 74%
20A --> 86%
30A --> 86%
40A --> 80%

weight of the motor: 450g (so 150g heavier than the outrunner)

you see: efficience values at 30V for both motors at similar rpms are very close
(up to 35A, then the brushed motor starts to fall of with efficience much faster than the brushless)

at least: when you look at an Plettenberg brushed motor and then on an brushless from some other companies: you will see, HOW well build this plettenbergs are...
(some have even auto-timing !!! with an magnetic ring which turns under torque to improve the timing and higher the efficience, something brushless-controllers with hall-sensors for example do not.. (some sensorless controllers can do it, for example JAZZ-series from Kontronik)

picture:
355_25a.jpg

thats how a good brushed motor looks like
 
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