Using RC motors on E-bikes [Archive]

[John in CR]

I for one am putting my chips on Matts real world results. He has one. He uses it on his bike. Plus he has great follow through and evaluation, not to mention the generosity to share the details from start to finish. If his motor doesn't get hot, that's all the efficiency data I need. Add on top of that less than 16wh/mile at average 20mph, and you know with that kind of power available Matt's not puttering around like some 80's Egeek trying to save a penny getting to work. I'll be happy as a clam if I get to just 80% of what Matt pulled off in style, and I've got my 1kwh+ of lifepo4's just itching for exercise, so I should have more range than I'll ever use.

All the worry about efficiency and range, yet the greatest gains in this regard aren't weight and drivetrain efficiency. Make you and your bike more aerodynamic, yet that's all but ignored except my those few who have done everything else. If efficiency is so important to you, address wind resistance first, and don't just blindly accept upright design and wind resistance as something you can do nothing about.

John

 

[TylerDurden]

No arguments on aero being #1 obstacle. Check the fairings/aerodynamics threads.

 

[safe]

Your brushed motor, not brushed motors in general.... :wink:

Actually it's probably fine... it's just, well you know, when you pass the peak power and drop into the no-load speed the motor isn't doing much of anything anymore.

I suspect that there is some upper limit to the rpms but I have no idea where it might be for my motor. So far it's been smooth and reliable for 3,500 miles or so and it works more efficiently at higher voltage anyway so it's actually better now at the higher rpms than before.

Maybe some day I'll try it at 60 volts or 72 volts just to see if it can handle it...

 

[John in CR]

No arguments on aero being #1 obstacle. Check the fairings/aerodynamics threads.

I realize it's talked about, but only talk. I'd bet less than 5% of us do anything substantial in this area. I plan to try some different things and take full advantage of those previous discussions, but first I need to settle on a bulletproof drivetrain. If I can use that 8hp HXT along with a simple implementation, and it proves reliable and doesn't get very hot with either normal conservative riding or hill climbing, then I should have a performance platform that will satisfy my wants for acceleration and speed. I just don't see anything comparable, though I do have one of Knuckles DD motors in route and will give overvolting a hub motor a go. I should be able to provide some direct yet mostly subjective comparisons before summer is finished, and hopefully include some objective range comparisons using the same set of batteries for some non-subjective data.

 

[recumpence]

I am having so much fun doing this.

One thing I find funny is the mindset that motors this small can't work well or batteries this small cannot handle the load or won't work properly in a bike, etc.

If someone does not want to believe this equipment is up to the task, that is fine. All my findings are true. I make sure to check and double check my numbers before I post anything. Also, I am my own worse critic. If I have a mechanical or electrical issue, I am the first to mention it.

I keep getting people asking me to market something. I hae no interest in manufacturing anything. I have no aex to grind here. I do not mind designing and making something if I had a simple system I could make easily, but, again, that is not my intent. I am not against hub motors or ping packs. I just went a different route.

An, yes, aero is extremely important especially above 25mph.

I want to try 45 or 50mph with my bike and see if it still runs well (and efficient) at 20 or 25mph with that tall gearing. That is the next step for me.

Anyway, this can be debated for a long time. Meanwhile I will enjoy riding my bike and enjoying the fruit of my labor. :wink:

Matt

 

[safe]

I keep getting people asking me to market something. I have no interest in manufacturing anything.

People are desperate and are looking at people like us SOLVING the transportation problems in ways that look like fun and they are at first curious and then envious. They want to see more products on the market because they want one too.

Gas is too expensive... the price went up $5 again today (above $140 a barrel) and so the desperation is oozing out.

In some ways I'm almost feeling like it was more fun a year ago before the real "Oil Crisis" hit so hard. Now it seems like a scene from one of those creepy monster movies where the "undead" are walking around saying:

"Save me"

"Save me"

"Save me"

 

[Kraeuterbutter]

just found on Internet:
price of petrol in US:
about 0.70 Euro per liter

is it realy that cheap for you ?
we pay meanwhile over 1.30 Euro (so nearly double the price you have)

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

8 HP in an electric bicycle ?
is it then a bicycle anymore ?
i mean: for me that sounds more like something of this:
http://www.zeromotorcycles.com/
17000Watt Power
58Volt and 35Ah battery
40miles range
or
http://www.electricmoto.com/
45mph max
18hp
48Volt and 40Ah battery
Reply With Quote

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

airdrag.. yes, with a recumbant or lowrider you can safe mucho energy..
but for a mountainbike with assistance only up to 16-17mph this is not that important

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

funny is the mindset that ........ or batteries this small cannot handle the load or won't work properly in a bike,

two years ago, when i first though of building an electric bike and was in the pedelec.co.uk forum
i was told: NiMh for power, Lipo for range
but on hills, Lipos have too few power..
?????
"how can this be" were my thoughts..
i looked at my heli: 24Volt and 10Ah with my Lipos -> that would be over 3500Watt poweroutput possible from the batteries..
so how can that be too weak for an ebike with legal 250watt (and in peaks on hills maybe 500Watt)
it was, when i learned that in the bike-scene they use - of course - cheap batteries, and this are often only rated for 1-2C

my opinion: because our rc-modells (planes, boats, helis, cars) are generally smaller,
we generally use smaller batteries we can (and do) invest in the best batteries available..
i pay 200 Euro for an 4s 5000mah-Batterie for my heli..
an e-bike-batterie 36V 16Ah would cost 1600 Euro which is too much (for most) electric-bike users (and companies)
we also use a lot of different batteries...
not seldom that there are rc-pilots which dotzends of different batteries from different manufactors and different sizes, buying each year several (different) packs..
so the knowlege-base is much higher than from most e-bike-users which buy only every 2-3 years a new set of batteries for there e-bike
(for example: i have
A123 Fepo4, Konion 1100, Konion1300, Konion1600, different Kokam cells, different Tanic cells, different Thunderpowercells, a Quick, a some noname, a HDHE, a Flightpower, and some more i just not remember
i bet there are not many e-bike users with have used that much different batteries sofar)

 

[Miles]

Get a grip, safe

 

[Toorbough ULL-Zeveigh]

Just to be clear on the matter, I for one am definitely not envious of anything 'safe' has done & have zero interest in emulating anything he's built as it's all very much so behind the times representing nostalgic outdated thinking.
I'm patiently waiting for hub motors to incorporate such modern concepts like phase advance timing & 'electronic gearing' to hit EV mainstream which will make all this mechanical stuf passé.
These are already old concepts that no one save Kraeuterbutter mentioned in passing & nobody so much as noticed cuz it's not even on the radar yet, on this continent anyways.
In fact just higher quality & updated design hub motors on par with the latest RC motors would go a long way towards raising their level of performance.

 

[safe]

Get a grip, safe

American success was built on cheap oil.

Take away the cheap oil and we (Americans) probably will not be as successful anymore.

It's just the price shocks that are causing people to freak out.

...all the more reason to use the RC motor on an ebike.

 

[cerewa]

If efficiency is so important to you, address wind resistance first, and don't just blindly accept upright design and wind resistance as something you can do nothing about.

Idunno about the rest of you, but I (who can't afford a good aerodynamic recumbent) put some cheap aerobars on my upright bike. Definitely makes a difference.

 

[dirty_d]

a hub motor with electronic gearing and phase advance i think would be the best possible thing, as long as you can keep the weight the same. it seems like designing the motor to spin the same speed as the load keeps the losses as low as possible, because there is no gearing. im curious to see exactly how the electronic winding switching would be done. the advantage the RC motor has right now is the low winding resistance because of a low number of turns of thick wire, but this results in a very high rpm, if hub motors could do the same using less turns of thick wire, but use more poles to keep the rpms the same, then you get the same deal. for a given voltage, the max power of a motor is proportional to its winding resistance, for the AXI (48V / 0.027) * 48.0 / 4.0 = 12333W max output power, for crystalyte 5305 with resistance measured by doc, (48.0 / 0.142) * 48.0 / 4.0 = 4056W max output power, now those max powers are at 50% efficiency, so if you want 4056W at the wheel, with the crystalyte you're only getting 50% efficiency, but for the AXI you can get the same 4056W at a much higher efficiency(maybe 80%) by running it at at lower power closer to no load. so if you can get a hub motor with the same power density thats a real good thing.

 

[recumpence]

For me, I don't care if it has be geared (reduction system) or not. I just do not want the weight of a big hub motor.

I agree, the ideal would be a light weight hub motor with a super high pole count.

For now, I am enjoying running equipment that is so different and cutting edge. Though, this equipment is considered old school be RC standards.

My lipo pack is rated at 10C. That is sky high for e-bike standards, but terrible by RC standards. I have packs that are rated at 30C. Heck I have pulled 60C from one RC pack.

But, RC packs are EXPENSIVE!

Matt

 

[John in CR]

Matt,

Are there any deals to be had on obsolete RC batts that we could combine into great bike packs?


Kraeuterbutter,

Yes most of the folks around here consider what I want not to be an ebike, however:

I plan to ride it like a fast ebike, often staying in the 35-40kph range, so it should have similar efficiency.
It will be similar in weight and style as a normal ebike (well maybe not style), so it will handle similarly.
Here in Costa Rica, as long as it has peddles and doesn't have a gas motor > 49cc it is legally a bicycle, with no legislative change in the foreseeable future.
The motor is only $150, so those savings can go toward more batts that I will likely need.

If I can have that kind of power in a 2-3 kg package including the controller, then why not? I'll have power to spare for hill climbing. I can take it on the highway if I chose so. I'll have impressive acceleration that will not only be exciting and fun, but instances will arise where being able to accelerate quickly to maintain separation from other vehicles will give me a much greater margin of safety than a more typical ebike. Did I mention how much more fun it will be than some off the shelf ebike that's similar in weight and cost, yet putts around at 30kph but take 30 seconds to get there. No, I don't want to build a racing ebike like Safe wants, but I do want a sports ebike.


Toorbough ULL-Zeveigh,

I realize that substantial R&D is going into new solutions, especially for hub motors to be used for cars and motorcycles. Can we expect anything soon for ebikes as well? More specifically that is lightweight and super efficient in the 500W range, but is capable of handling 5kw peaks just as well?

John

 

[The7]

the ideal would be a light weight hub motor with a super high pole count.

Against the law of physics!?

 

[Kraeuterbutter]

maybe a "linear motor"
(comparable to the trans-rapid)

on the rim - were normaly the v-brakes are used - there are the magnets..
the coil is left and right, front and rear of the fork...

so.. just like a transrapid, but instead of the transrapid moving, the "rails" will move in form of the rim..

problems what i think about beeing not an electric engineer:
weight, and you have to make sure, that the distance between magnets and coil is very low... maybe not that easy with an rim which makes the whole thing even heavier...

recument: you said you don´t wana use a heavy hub-motor..
you have for sure posted the weight of your whole unit somewere... can you do that again (in kg) for me ?
thx..

(and again my question: how light do you believe could an electric assist with beltdesign as you made it be, when using the gears of the bike as well, and only with 200Watt/400W peak... is it doable with less than 2kg (including the batts)?

 

[recumpence]

My entire electric system, including my lipo pack is under 17 pounds.

It is possible to make a 200 to 400 watt system with (I would say) 5 to 6 pouunds of equipment.

Matt

 

[eP]

(and again my question: how light do you believe could an electric assist with beltdesign as you made it be, when using the gears of the bike as well, and only with 200Watt/400W peak... is it doable with less than 2kg (including the batts)?

All strongly depends on how long range of assistance you need IMO.

If 4s1p 10Ah LiFePO4 (120Wh) config is fine for your needs, so it is doable.
If you need 240Wh at least (LiFePO4 for long life), so it is definitely impossible (these days) as far as we don't know negative mass/weight materials

If you don't care about batteries long life and safety issues than even up to 300 Wh config is doable IMHO.

 

[John in CR]

Kraeuterbutter,

Isn't your real sticking point going to become the noise? A solution approaching the weight you want may be doable, but even with nylon gears it's going to be noisy. I completely understand the appeal of a true peddle assist, but if I rode one I'd want it to be dead silent.

The guys told me in my wheel motor post that the problem with a rim motor is that it will pick up magnetic debris from the road. Don't those mag drive trains use all electro magnets? Then you'd need windings all around your rim, which is likely to get heavy, expensive, and will set you back to requiring brushes.

John

 

[recumpence]

Belts are very silent.

They are also easy to work with.

Matt

 

[Miles]

+ 1

 

[eP]

Isn't your real sticking point going to become the noise? A solution approaching the weight you want may be doable, but even with nylon gears it's going to be noisy. I completely understand the appeal of a true peddle assist, but if I rode one I'd want it to be dead silent.

For 400W power out level you don't need more than 4000 rpm at air gap diameter D=40mm and 25mm stator height.
The larger diameter the lower rpm you need for that power level.

 

[John in CR]

eP,

Are RC motors quiet in the 4krpm range. I'm hoping the big HXT outrunner is, but I was under the impression that they weren't.

 

[recumpence]

You will hear the windings pulsing and belt whine. It is subtle, though.

Matt

 

[eP]

Are RC motors quiet in the 4krpm range. I'm hoping the big HXT outrunner is, but I was under the impression that they weren't.

All depend on quality (bearings, air gap clearence, etc ) i suppose. 4k rpm is a low rotational speed for 40 mm class motors as they are used to work at 10+k rpm range.
Big RC outrunners (80mm class) would work fine at 1500 rpm for 400W output.