Using RC motors on E-bikes [Archive]

[eP]

What about the way Erato handles it? Is the iron loss reduced by 2/3rds by reducing the poles count by 2/3rd for the high speed setting to enable much higher rpms?

Poles count depend on magnets count, so you cannot decrease magnets count by leaving some coils off.
That way is possible to enable much higer rpms for the same voltage, but as your rpms will be higher your iron loss will be higher too.
So it is not an energy efficient solution.

 

[John in CR]

What about the way Erato handles it? Is the iron loss reduced by 2/3rds by reducing the poles count by 2/3rd for the high speed setting to enable much higher rpms?

Poles count depend on magnets count, so you cannot decrease magnets count by leaving some coils off.
That way is possible to enable much higer rpms for the same voltage, but as your rpms will be higher your iron loss will be higher too.
So it is not an energy efficient solution.

But doesn't the fact that you go to most of the magnets being idle as they pass the "off" coils offset this. I don't follow where the efficiency loss increases. It seems like essentially all it does is decrease the turns by 2/3rds to give you higher speed. Then when it's switched to low, the number of turns is tripled, which increases the torque. While in high speed mode, it's not the most efficient use of magnet and copper resources, but does it really affect energy efficiency in a negative way?

 

[Miles]

dirty-d wasn't proposing to "leave coils off".

 

[eP]

Piotrek,

Are you sure you understand what dirty-d was proposing. It seems pretty unlikely that it's feasible but, if it was, I don't understand your (non) argument. Could you explain for us?

Yes i understand that but frakly speaking it is a fool idea. How do you think why nobody wants do that this way ?

You are able to wind the stator for highest kv you want, so if you want low rpm the controller do that for you by PWM. It is much more easy than switchng many separate turnsfor different configurations.

BTW if you rea ready for making high speed multistage gearboxes, water cooling , etc, so instead lets try how to made transverse stator easy way.
Maybe that way all thing will be easier and cooler.

This is the reason why i ask all of you guys for a little bit of patience and deeper investigation of that transverse flux idea.
I have to admit i'm beginer as most of us, but i'm definitely not creazy man and IMHO transverse flux is the most promising idea i was found so far.

Best regards

 

[eP]

dirty-d wasn't proposing to "leave coils off".

Yes i know it was to John, but Dirty-d idea is very similiar in fact.

 

[Miles]

Are you saying that there's no advantage, in efficiency, to changing kV for a given voltage? Won't the peak efficiency point be shifted?

 

[eP]

But doesn't the fact that you go to most of the magnets being idle as they pass the "off" coils offset this. I don't follow where the efficiency loss increases. It seems like essentially all it does is decrease the turns by 2/3rds to give you higher speed. Then when it's switched to low, the number of turns is tripled, which increases the torque. While in high speed mode, it's not the most efficient use of magnet and copper resources, but does it really affect energy efficiency in a negative way?

Moving magnets are never idle regardless they crosing over coils on or off.
Only broken magnets (lost out of the bell) are idle in fact

 

[eP]

Are you saying that there's no advantage, in efficiency, to changing kV for a given voltage? Won't the peak efficiency point be shifted?

For the same rpm and the same load you get the same motor's efficiency.
Only controller's efficiency could change this way. But if you add one extra switch per each turn for flexible configuration purposes this cannot help you improve the controller's efficiency. Keep in mind also power wires losses.

The same current must go from controller to each one turn and go back to switch in controler many times (depend on turn numbers). It almost like one of the Safe ideas

 

[Miles]

As I understood it, the switching would be done in the motor.

 

[Miles]

BTW if you rea ready for making high speed multistage gearboxes, water cooling , etc, so instead lets try how to made transverse stator easy way.
Maybe that way all thing will be easier and cooler.

This is the reason why i ask all of you guys for a little bit of patience and deeper investigation of that transverse flux idea.

Well, I'm interested but it's all a bit above my head....

 

[eP]

As I understood it, the switching would be done in the motor.

Even if the contoller is into the motor's case it still need wire endings between turns and mosfets. Or maybe you know windable mosfets Miles ?

Sorry if i'm laughing to loudly but it is definitely not promising idea.

Well, I'm interested but it's all a bit above my head....

I'm not fluent in English as you Miles, but im trying to read and learn some new concepts to me.
It is matter of patience, all together we are able to do more than alone.

Edit:
If we agree that idea is cool, and someone like Matt would like sacrifice his time for that maybe some of us could contact directly to sciencists who are designing and working with these machines ?

 

[recumpence]

I am not an electrical engineer. I do think I could manage a two speed transmission, though. I will have to look into it a bit more. I like the idea of two separate drive chains or belts in a box with freewheels. One freewheel could be engaged and disengaged giving a two speed system. Actually, RC cars use a similar system with a centrifugal clutch making it effectively an automatic two speed transmission.

I have found, though, that these motors are so efficient and the controllers are so advanced that a multi speed transmission is not "Needed". However, I do agree there are benefits to it.

I need to resolve the motor issues I have (decide if a two pole motor would work or if I should bite the $1,000 bullet and buy the 20 pole Plettenberg). After that, I can begin looking into a decent two speed transmission.

Man, I am thoroughly enjoying this discussion. I must admit, I am lost when you gyus talk about iron losses and what-not. But, I can make pretty much anything (within reason) mechanically. I think that is what is good about these forums; Those with one skill set can get together with those that have other gifts and skills and come up with good solutions.

I haev wanted a two speed since I built my bike. I will begin thinking about the best, most elegent solution.

Matt

 

[Miles]

Matt,

How about something like the "Retro-Direct"? Then you just reverse the motor to change gear... Rotor inertia is so low for this kind of motor, it should work ok.

Or, another approach: http://www.g-boxx.com/videos/G-Boxx-2-general_function.wmv (I guess your RC car set-up is like this..)

 

[dirty_d]

i think miles understood what i was talking about, by being able to change the motors Kv you can change the slope of the motors torque curve, for example a 50Kv motor would be able to produce 10Nm at 1000rpm more efficiently than a 130Kv motor, because 1000rpm would be closer to the 50Kv motors peak efficiency point than the 130Kv motor. it might end up that with all the extra electronics you need might offset any gains you get by being able to change the Kv, i dunno, i was just saying maybe someday.

 

[John in CR]

Matt,
How about something like the "Retro-Direct"? Then you just reverse the motor to change gear... Rotor inertia is so low for this kind of motor, it should work ok.
Or, another approach: http://www.g-boxx.com/videos/G-Boxx-2-general_function.wmv (I guess your RC car set-up is like this..)

Matt,
Thanks, that retro-direct is just too sweet and easy. http://en.wikipedia.org/wiki/Image:Retro-Direct.jpg I have to try this with a motor I already have, to make a hill climbing speedster. Now the only question is how big a gearing ratio do I want. A 3:1 jump seems about right, with max rpm in low turning 12mph for a steep hill and 36mph max in high.

 

[markcycle]

Matt,

How about something like the "Retro-Direct"? Then you just reverse the motor to change gear... Rotor inertia is so low for this kind of motor, it should work ok.

Or, another approach: http://www.g-boxx.com/videos/G-Boxx-2-general_function.wmv (I guess your RC car set-up is like this..)

Man I love the Retro Direct idea had no idea about it but I think it would work great on my motorcycle

Thanks a million

Mark

 

[safe]

Old Arguments

We seem to retrace old arguments now and again about electric motors. One of the recurring arguments is the dream of creating a permanent magnet motor that can vary it's magnetic field with rpm. There are tricks to try to do this such as switching the firing order at a certain rpm, but the results are never very impressive.

The best motor solution is the Tesla motor... the Induction motor... where the magnetic field is variable and generated without the need for permanent magnets. As with everything there's a "catch" which is that the Tesla motor doesn't work very well until you get up to about 100 Kilowatts of power, the sort of thing a car might use, but serious overkill for an electric bike.

So we return (full circle) to the permanent magnet motor and seek to optimize it by increasing it's rpm (RC motor) and giving it a wide multiple speed gearing. Throw in some cooling techniques and you have about the best you can get for our small machines.

I'm at the point of just ACCEPTING that the RC motor plus multiple speed gears and something like armature current limiting is about the best possible. Until someone comes along with some really new thinking (which I'm not seeing) I'm sticking to what appears to be the best of our time.

Nothing really new seems to be emerging... :|

 

[John in CR]

It may be old school, but after one poster said he ran friction drive using the same tire for 10 years, I want to give it a go. Now add in the fact that the shell spins on an outrunner and it may be a match made in heaven from a KISS pov. I don't plan to run my Ebike in the rain anyway.

Another seemingly easy implementation would be a USPD looking install with the RC motor down at the wheel. Put a small planetary gear on the motor shaft and a large one installed with a freewheel on the hub. With planetary gears a step down from 6-10krpms at the motor to 300-400rpms at the wheel in one step seems quite doable. You may even be able to get away with a nylon gear on the wheel to keep the noise down. It's not as elegant as Matt's rig, but give me KISS over elegant any day.

 

[recumpence]

I seem to gravitate toward one of two camps for my projects;

#1 Simple, but effective. Obviously is less costly and easier to make and service.

#2 As radical and high tech as possible. This is far more time consuming and expensive, but generally better performance and cooler looking, though harder to service (sometimes).

My bike was never meant to be simple. It was meant to be as radical as I could make as well as extremely light and compact.

I know very few people have the capability to make this kind of thing. In that respect, my bike is kind of useless as far as furthering our hobby. But, it is cool to push the envelope.

My bike is sort of a Boyd Coddington hotrod e-bike. Most guys here are interested in reliable and innexpensive transportation. That usually precludes radically custom projects. So, my bike is an odd project from that perspective. However, it has been reliable and efficient, though not cheap or easy to design and build.

Matt

 

[safe]

My bike is sort of a Boyd Coddington hotrod e-bike. Most guys here are interested in reliable and innexpensive transportation. That usually precludes radically custom projects. So, my bike is an odd project from that perspective. However, it has been reliable and efficient, though not cheap or easy to design and build.

You have identified a true difference in the motivations of people who post here. I share your interest in "radically custom projects" but I also get a lot of flack from folks that just want to know where to shop and what to buy. Since we are the minority when it comes to ebikes it can be difficult here at times.

Sometimes I think we need to divide the "shoppers" from the "inventors", but usually things work out well enough. Whenever I have a problem with someone in particular I just place them on my "Foes" list and forget about them. Someone might do the same to me. It works better than I thought.

The RC motor is a great idea, but it really was the fact that you built it that made us all realize that is was really possible. It's hard to know if things are possible without someone being a pioneer first.

So I think we all thank you for that. (even those people who have no plans to build one are thankful for seeing it done)

 

[docnjoj]

Thats a 20-25 :1 reduction, JohninCR! You would need a big case and large gears! Aint cheep, especially composite gearing! Good luck on that!
otherDoc
U could use multi-stage gears, but more expensive!

 

[John in CR]

Thats a 20-25 :1 reduction, JohninCR! You would need a big case and large gears! Aint cheep, especially composite gearing! Good luck on that!
otherDoc
U could use multi-stage gears, but more expensive!

Let's work it out. Start with a smaller tire, eg a 20" tire, which is right at 1000 revolutions per mile. Add in the big HXT at 130rpm/V run at 36V, since I already have 36V Ping packs and I don't need the full 8hp anyway. That's 4680rpm at the motor, and 588rpm at the tire for 35mph or 672rpm for 40mph. That's only a 7 or 8:1 reduction. Now I'm thinking just forget the gears and use a chain.

My only question is regarding low speed torque. At an 8:1 gear reduction, 20" tires, and 36V, will this motor provide enough torque to haul 300lbs (rider+bike) up reasonably steep hills.

 

[John in CR]

Matt,

Yes your bent is a work of engineering art, and I believe it's opened up a lot of eyes to the potential of using RC motors. I've even worked a deal for free machinist lessons at my favorite local machine shop, so I can learn to do something similar.

John

 

[Kraeuterbutter]

for friction drive and rc-motor:
look here this video..

its i think an AXI:
http://uk.youtube.com/watch?v=Qxh_cMrIyVI

already one year old, this video..
maybe he realy did the lightest electric-bike with that
(at least motor, battery and controller weight is far less than anything you buy in an ebike-shop)

 

[recumpence]

Sounds good John.

You will be happy to learn some machining skills. Be warned, however, machining is its own hobby and gets quite addicting.

Yes, the motor will have PLENTY of torque for hills. I mean HUGE torque. Too much, in fact.

With my bike geared for (currently) 34mph top speed on 48 volts, I normally cruise at 26mph. There is a steep grade about 1/10 mile long (steep enough to be very difficult to pedal up). When I cruise at 26 mph and leave the throttle steady, the bike only slows down to 24 mph up that hill. So, I have tons of extra torque available. You should have a similar amount.

Matt