Using RC motors on E-bikes [Archive]

[Kraeuterbutter]

come with as much as 25 lbs of iron and realistically no one will every be doing mountain bike trick riding or racing with 25 lbs of unsprung weight.

Gruber Assist...

motor + controller + gearing + cables: 900g

here already mounted on an light carbon-frame:
http://www.gruberassist.com/wp-content/carbon.jpg

do you see it ?
or here:
http://www.gruberassist.com/wp-content/grubermtb.JPG
do you see motor or controller ?

here another bike:
http://www.gruberassist.com/wp-content/gewinner_radubergabe1a.jpg
in the background you see how it works

and here a video how it works:
http://www.youtube.com/swf/l.swf?video_id=jmPUze3WBTw&rel=1&eurl=&iurl=http%3A//i.ytimg.com/vi/jmPUze3WBTw/default.jpg&t=OEgsToPDskL5aEeJCmmmNF7vyP7WIZoV

the motor is very small, benefiting of high rpm and gearing

 

[Johnbear]

That is the most stealthy e-bike! I'd love to try one.

 

[safe]

the motor is very small, benefiting of high rpm and gearing

The picture in the link shows a seat tube motor attached to the bottom bracket. Typical pedal rpm is 76 rpm and the maximum is maybe 110 rpm, so the motor (if there is a 3:1 gear ratio) is going to be a maximum of 330 rpm. That's not anywhere near where the RC motors are because they spin in the 10,000 rpm range.

This is simply not a very good idea, so I'll have to respectfully disagree.

Recumpence (and others) seem to have hit on what is the right direction with the RC motors. They are very light weight, efficient and affordable, all that is needed is the right precision machined "Swiss Watch" gearing to make it practical.

 

[Kraeuterbutter]

@SAFE:
watch the video..

the unit is going around 200-250Watt inputpower..

a motor with 31mm diameter and 8cm long motor would not be able to handle that much current at only 330rpm

so this motor IS a fast turning motor, maybe something similar we use in rc-world, maybe even a motor from the rc-world..

however:
whatch the video..

you will see: there is also a planetary gearbox..
from RC-Models i know:
for example a Reisenauer gear has 38mm diameter and 27mm long, can handle 2000Watt and is geard 6:1
a Reisenauer Micro-Edition is only 22mm diameter and 18mm long, can handle 600Watt short and is geared 4:1

so when looking at the Gruber Assist - Homepage:
the Planetary-Gear seems to be 31mm in diameter and about 40mm long

i would say: its a two-stage planetary-gearbox
--> so maybe 6:1 and 6:1 = 36:1
or 7:1 and 7:1 = 50:1
plus the ~2:1 on the 90° gear

so we see over all maybe ~ 70:1 or even 100:1

so at 90rpm pedal-cadenz the motor can already spin with 6300rpm or 9000rpm
much more reasonable..

the clue on that bike:
when driving it without battery mounted its less than 1kg additional weight !
i think most would not notice the difference...
within an light bike you can still have a bike only 11kg light (with installed motor)
because the motor is not powerfull - only ~200Watt input - you can also use small, light battery..
a 1kg light battery is enough for 45min-1.5h of offroading
of course, its not a drive where you feel the g´s when accelerating..
it for the purpose you come to a hill, and need some 100-150watt extra...

its a complete other conzept like most bikes here at endlesssphere, with
HUGE heavy batteries (72Volt, 15Ah, ...),
and huge motors (5kg, 7kg, ...)
these bikes are fine for commuting daily to work, maybe doing nothing with pedals..
but with all that added weight no fun for offroading anymore

 

[Kraeuterbutter]

That's not anywhere near where the RC motors are because they spin in the 10,000 rpm range.

RC Motors in that size (31mm Diameter) are more like 20.000rpm - 60.000rpm

 

[eP]

so we see over all maybe ~ 70:1 or even 100:1

so at 90rpm pedal-cadenz the motor can already spin with 6300rpm or 9000rpm
much more reasonable..

the clue on that bike:
when driving it without battery mounted its less than 1kg additional weight !
i think most would not notice the difference...
within an light bike you can still have a bike only 11kg light (with installed motor)
because the motor is not powerfull - only ~200Watt input - you can also use small, light battery..
a 1kg light battery is enough for 45min-1.5h of offroading
of course, its not a drive where you feel the g´s when accelerating..
it for the purpose you come to a hill, and need some 100-150watt extra...

What is the efficiency at 100 watt extra ? (and what at 50 watt extra)
It is very poor i'm afraid.
The devil is in details.
So what are the details ?
If efficiency is poor so battery cannot be so light.

 

[safe]

Even if they did build in an elaborate "Swiss Watch" type geardown on this thing to give it the efficiency you still are stuck with a through the pedals motor.

Would you REALLY want to be forced to pedal all the time?

I know that for my designs it's absolutely critical to be able to not pedal while the motor is operational. I suppose some are okay with a "pedal at all time" setup but for my uses it's not a good idea.

The three things of importance in my mind are:

RC type high rpm motor for light weight

Motor power and pedal power must be combined and pass through the multiple speed transmission (derailler) of the bike.

Motor power and pedal power need to be able to work independently, but at the same time the peak power rpms of the two sources need to match so that if you want full combined power it's still possible. (this is tricky to do)

 

[John in CR]

But still the problem nr 1 is classic outrunners 50+ mm in stator diameter are still reserved for very very small high power niche. As a result the best of them are really expensive and others (cheap ) are relatively inefficient especially at low load.

Is that at "low load" or low speed? I'm new enough at this stuff that I'm game for anything. Sure the power is appealing, but I obviously don't want something that only performs well at 4-6kw.

I still wonder why nobody want discuss different topologies advantages for e-biking purposes ?

How are these outrunner motors fundamentally different than typical gearless hub motors?

As far as topologies are concerned, wouldn't the the hub motors with the pancake armature be closer to the ideal for a bike motor?

John

 

[Kraeuterbutter]

@SAFE:

your bike, when i see your avatare (you mean this ?)
seems to have lot of batteries, so i assume: also lot of power..
of course: YOU for sure don´t want to pedal when the motor is running..
when the motor would be fix connected with the pedals, and let say have 4000Watt

o dear: i would not want to put my foots on that pedals... it would cut of my legs if i slip of the pedals.. no thank you..

so of course, on your setup pedals must not be connected with the motor..

on the gruber-assists its different:
the motor is not made to drive without pedalling..

the concept is: YOU are driving the bike.. and the motor helps you on hills when you want.. so you are pedaling anyway

on this heavy-high-power bikes there often comes to my mind: "wouldn´t be a motor-bike even more fun ? for cheaper money ?"

the gruber-assists is for me a normal bike, with no disadvantages of an e-bike...
and if i realy want a little bit added power, than it can give me that..

the downside is price... its far to expensive
on the other hand, its made for people who invest 3000-4000Euro into an carbon-bike... for them 1700Euro for the gruber-assist is maybe not that bad...

 

[Kraeuterbutter]

@Safe again:

i would seperate the ebike-scene in 3 ways:

1.) high power
strong motor
big batteries
high weight (30kg or even more)
something like a motorcycle but lighter...
pedaling (200Watt) is ridiculous when you have a motor with over 1000Watt

2.) medium power
weight around 20-25kg
the "e-bikes" you can buy at ebay and co...
so: they are far lighter than an motorcycle..
but for a bicycle sadly heavy
pedaling is ok to improve distance, but its also possible to go on motor allone
power: about the amount a good cyclist can bring to the pedals himself
without power you have not much fun, because you drive some kg of dead weight around
also the cg is often bad (to high), the unsprung weight from an hub-motor in the wheels... no fun..


3.) light power assist
weight: not much more than a normal bike (gruber assists: bikes with 12kg including the battery are possible)
driving is like on a normal bike
its the most sporty class
even without motor or with empty battery you can have a lot of fun because the bike is so light, the components are so light you don´t feel them
power: less then a good cyclist, the motor should only help you (for example on a hill)

 

[Kraeuterbutter]

my dream would be the Gruber Assist...
it would be the best drive system to fit my wishs..
but the price, the price
its far too expensive for me..

so i desided to go with one of the lighter hub-motors (~3.3kg) here in Europe i could get
i will add some light batteries (1 - 1.5kg)

nevertheless: the bike with the componentes mounted feels like the 20year old mountainbike of my dead.. very heavy ;( (~20kg)

 

[eP]

But still the problem nr 1 is classic outrunners 50+ mm in stator diameter are still reserved for very very small high power niche. As a result the best of them are really expensive and others (cheap ) are relatively inefficient especially at low load.

Is that at "low load" or low speed? I'm new enough at this stuff that I'm game for anything. Sure the power is appealing, but I obviously don't want something that only performs well at 4-6kw.

Low load and high rpm this is the area where cheap big RC outrunners are pretty ineficient.

I still wonder why nobody want discuss different topologies advantages for e-biking purposes ?

How are these outrunner motors fundamentally different than typical gearless hub motors?

As far as topologies are concerned, wouldn't the the hub motors with the pancake armature be closer to the ideal for a bike motor?

John

Convetionals hubs are efficient but heavy, light hubs must be geared or are weak (low torque).
Transverse flux motors are able to work at higher load/ low rpm very efficient. But they are more complicate to manufacturing. They have segmented stators and much shorter copper path - lower copper loss.
They could be light, low rpm and powerfull with no compromise as their Rm dont depend on poles/teeth number. The lower rpm more poles - the bigger is their advantage over convetional hubs.

 

[safe]

o dear: i would not want to put my foots on that pedals... it would cut of my legs if i slip of the pedals.. no thank you..

so of course, on your setup pedals must not be connected with the motor....

When the pedals are allowed to freewheel then no matter what power you use it doesn't matter as far as rider safety. Unless you commit to the recumbent design where you are laying nearly on your back (the legs being stretched out to pedal) means that you present an enormous frontal area to the wind. In my very unique, controversial, and sometimes despised :wink: "Electric Bicycle Road Racer" design the rider stays in the tuck while on the high speed sections and then stands up to pedal (making it less aerodynamic) in situations like hill climbs or coming out of slow turns.

The math (and practical experience) shows that a rider in a "tuck" position uses less energy than a rider that is high in an upright seat pedaling full blast.

...so in true "engineering harmony" the most practical and efficient electric bicycle exploits all these things. Only the dedicated recumbent designs can beat it aerodynamically, but they suck when it comes to handling and are not suitable for sport style "Road Racing" riding behavior. No one on a recumbent is going to risk a slide while going at high speed through a sweeper turn, but the "Road Racer" very well could and, in fact, I already do.

I admit though that my "genre" is bizarre and only time will tell if I can manage to make it successful.

For what I have in mind the RC motor is the ideal solution.

 

[John in CR]

But still the problem nr 1 is classic outrunners 50+ mm in stator diameter are still reserved for very very small high power niche. As a result the best of them are really expensive and others (cheap ) are relatively inefficient especially at low load.

Is that at "low load" or low speed? I'm new enough at this stuff that I'm game for anything. Sure the power is appealing, but I obviously don't want something that only performs well at 4-6kw.

Low load and high rpm this is the area where cheap big RC outrunners are pretty ineficient.

Does one of the specs quoted for the big HXT motor tell me this? I see no load amps at 2A, so at 48V I'd be using about 100W before any load. Is that bad? I plan to run at 36V and have 1000Wh of Lifepo's, so it seems like I'd have good range along with hill climbing and speed power if I choose.

I still wonder why nobody want discuss different topologies advantages for e-biking purposes ?

How are these outrunner motors fundamentally different than typical gearless hub motors?

As far as topologies are concerned, wouldn't the the hub motors with the pancake armature be closer to the ideal for a bike motor?

John

Convetionals hubs are efficient but heavy, light hubs must be geared or are weak (low torque).
Transverse flux motors are able to work at higher load/ low rpm very efficient. But they are more complicate to manufacturing. They have segmented stators and much shorter copper path - lower copper loss.
They could be light, low rpm and powerfull with no compromise as their Rm dont depend on poles/teeth number. The lower rpm more poles - the bigger is their advantage over convetional hubs.

I realize that I'm pretty weak on knowledge for effective participation in the Technical forum, but I don't consider weight to be a fundamental difference. Other than how position is determined (hall sensor or back emf) for the controller, don't gearless bicycle hub motors and outrunners work the same? What makes the smaller lighter outrunner capable of so much more power?

It seems to me that what we really need is a crossbreed somewhere in between small gearless hub motors and these big outrunners. Sacrifice a little weight with an extra turn or two in the coils to slow the outrunners down to more useful speeds, and increase the wire diameter to keep resistance low. Then instead of running them at maximum capacity like is needed for RC use, and everyone seems to be doing with hub motors by over volting them, we run them at only a fraction of their potential to achieve durable long life, just like is done with virtually all electric motors used in industry. We use chains and gears to transfer human power to our wheels, so why go to 25lb motors to avoid gearing for a motor to get a kw or 2? Maybe geared hub motors are trying to get to this middleground, but they still seem too big and heavy. It's amazing that it's 2008, and electric motor design seems to still be in its infancy.

John

 

[Mark_A_W]

o dear: i would not want to put my foots on that pedals... it would cut of my legs if i slip of the pedals.. no thank you..

so of course, on your setup pedals must not be connected with the motor....

When the pedals are allowed to freewheel then no matter what power you use it doesn't matter as far as rider safety. Unless you commit to the recumbent design where you are laying nearly on your back (the legs being stretched out to pedal) means that you present an enormous frontal area to the wind. In my very unique, controversial, and sometimes despised :wink: "Electric Bicycle Road Racer" design the rider stays in the tuck while on the high speed sections and then stands up to pedal (making it less aerodynamic) in situations like hill climbs or coming out of slow turns.

The math (and practical experience) shows that a rider in a "tuck" position uses less energy than a rider that is high in an upright seat pedaling full blast.

...so in true "engineering harmony" the most practical and efficient electric bicycle exploits all these things. Only the dedicated recumbent designs can beat it aerodynamically, but they suck when it comes to handling and are not suitable for sport style "Road Racing" riding behavior. No one on a recumbent is going to risk a slide while going at high speed through a sweeper turn, but the "Road Racer" very well could and, in fact, I already do.

I admit though that my "genre" is bizarre and only time will tell if I can manage to make it successful.

For what I have in mind the RC motor is the ideal solution.

You're building electric motorcycles Safe (what's your name anyway?). Most of the rest of us, are building electric bikes, using bicycles as a donor or at least a reference point. Pedalling is important, not ancillary.

A Road Racer is a motorbike.

Your description of "pedalling" is to get around the law. It's an electric motorbike, your posts belong in the electric motorcycle section, not the electric bicycle section. You try and push thread to discuss electric motorcycles, that's why we get knarky with you sometimes.

 

[Kraeuterbutter]

hey..
just found this pic, i made very fast some time ago - just to make some brainstorming..
(befor i desided to use a hub-motor)

i was made some brainstorming what i could do with an Plettenberg Orbit 30-14
and an e-bike..

some data of the motor:
http://www.plettenberg-motoren.com/Datenblaetter/Orbit/Orbit30_14.pdf

the motor is 300g light
47mm diameter and 60mm long

i thought about something like this

the idea was to screw the unit into the frame of my mountainbike..
at last stage there would be a 4:1 gearing from this unit with change to the big teethwheel of the pedals
so in sum it would be around 100:1 gearing motor <-> pedals

for pedals: using the ones from http://www.bike-elektro-antrieb.ch/ with 3 freewheels in the bike
(motor uses the gears of the bike, pedals nevertheless not turning when motor is turning)

well: without the mashines and without the knowlege how to make something like this, i went with an hub-motor..

but from princip it has some similarities to the bike from helimodman (rc-model-motor, 2 stage-beltdrive)

 

[recumpence]

I am liking the Lehner 3080/18

http://www.lehner-motoren.com/ms30.php?la=en

So, you motor experts, how do the specs look for this motor on 48 volts? What I am mainly concerned about is the fact that this is a 2 pole motor. So, startup and low RPM running may be a bit scetchy compared to my 14 pole outrunner.

I like all the specs and it will fit directly into my bike.

Kraeuterbutter,

I spoke with Toshi at length yesterday about this. He is a HUGE fan of Lehner motors and was sure it would be a good choice. (He also said hello to you, by the way).

So, motor gurus, what are your thoughts about this?

Matt

 

[Miles]

Matt,

It looks nice, but where are the specs for it??

 

[safe]

A Road Racer is a motorbike.

Not necessarily.

We are in a new era where the hybrid power of electric and human is being explored. I've found a rather unique niche where I'm actually using the physics of aerodynamics (low frontal area) in a way that creates an "improved" bicycle.

The Tour De France is a bike race, there are many others, it's inevitable that people will demand perfromance and want to race these electric bikes and all I'm doing is seek to create the appropriate racing category for the street.

There will likely be electric mountain bike racing.

There will likely be electric bike road racing.

There is already electric bike "cruising".

...so just because someone seeks performance out of their ride doesn't mean you are creating a motorcycle. Even the electric mountain bikes will demand performance. (and need something like the RC motor)

The rules go:

750 watt motor.
Must have pedals.
20 mph top speed as sold.

...and you can then modify from there.

My new projects are lighter weight than my first prototype.

 

[safe]

How are these outrunner motors fundamentally different than typical gearless hub motors?

The major problem with hub motors is that they usually are only "fixed gear". This is like riding around on a one speed bike. (even if there is some geardown involved) The multiple speed gearing that can be attached to the smaller RC motors allow them to improve their overall power, efficiency and reduce their heat.

It's the combination of micro sized RC motor and multispeed gears that makes this whole concept significant.

...without the multispeed gears there is no difference. So in a sense you were right about that part.

 

[safe]

Built In Air Cooling!

Hey this looks like a very well built motor. I'm a little confused about their power charts though. The air cooling is an add-on product so it's not part of the original motor purchase. (will cost extra)

http://www.lehner-motoren.com/ms30.php?la=en

 

[recumpence]

This is another motor choice. http://www.plettenberg-motoren.com/UK/Motoren/aussen/Terminator/Motor.htm

However, that motor will not fit directly in my bike without doing some machining and it costs (are you sitting down?) $1,100 for the heli version with output shaft and fan!

What are your thoughts on this motor versus the Lehner 2 pole?

For reference, my AXI is a 14 pole motor, the Lehner is a 2 pole motor, and the plettenberg is a 20 pole motor.

Matt

 

[Kraeuterbutter]

for the Lehner with the build in fan:
that fan has become necessary with the arival of lipos..

with Nicd and only 2000, 2400mah the Inrunners were ok... not enough capacity to overheat them that easy..
but with batts with 4000 - 8000mah this has changed...

for that the outrunners are a better choice for helis..
just an example:
a cheaper and lighter ORBIT 15-12 puts out the same/more power than the more heavy and more expensive Lehner 1930-8 in the same heli, AND the outrunner stays cooler..

so: now with the fan this has maybe changed..

(but, recumpence, you know it from rcgroups: how many guys use today inrunners in helis ? 2 years ago there was the idea with that 2:1 gearing so you can run them at 40.000rpm
i didn´t thought that was a good idea at that time...
and meanwhile there is no talk about that way anymore, everybody uses outrunners)

Kontronik as well has introduced a inrunner-series with fan
and i bet, that Hacker will follow as well..

so iam not sure, if the Lehner without this fan would stay cooler than your AXI

Lehner with the fan: maybe..
maybe (probably) it will see higher efficience

in rc-groups there was once a "rule of thumb" (maybe made by GGoodrum) for e-helis:
2-pol-innrunners for best performance: 40.000rpm (if it turns less, don´t expect super performance, if it turns faster, heat becomes more and more a problem)

the Tango-Series from Kontronik: 25000 - 30.000
and outrunner: not more than 20.000rpm for best performance

so: i don´t know how well this motor would performe at only 10000rpm or less
maybe the outrunner is already the best choice
but you described some "shuttering" (Back-EMF) at some special rpms you want to avoid.

 

[Miles]

Plettenberg Terminator:
Kv 215 rpm per V
No load current 3.7 A (@11 V)
Winding resistance ???

Lehner 3080 / 15
Kv 356 rpm per V
No-load current 4 A
Winding resistance 0.009 Ohms

 

[Kraeuterbutter]

for hub-motors vs. rc modell motors..
high weight and low power vs. small size and weight and high power

i think that its mainly the rpm

do you know the "Swiss Flyer", the old F-Series (the old F-Series had an motor they developed by themself, the newer ones have the geard motor from Sanyo or Panasonic which other bikes use as well)

however:
this motor of the F-Series was mounted in the bottom bracket
it was something around 10kg heavy
poweroutput: only 250Watt at max. 90rpm

so: heavy and weak you can say...

BUT: the very same motor with lot higher voltage is able to put out 20kw at something around 6000rpm

so: it comes down to rpm...
the hub-motors used in rc-bikes are all running very slow..
i guess when you take such a motor, and gear it, and let it run with 2000rpm it would also put out some several 1000 Watts
and the weight/power-factor becomes a lot better