CVT on a e-bike

Hi All,
I have been looking into this site for a while ( well a couple of weeks ) and I like whats going on here . Just before christmas I thought I would build a E-bike ( mk1 v1) which I did and road it up and down the road about twice but now Im hooked I took mk1 v1 apart to make v2 ( currently doing ) but now I have also bought some bits for mk2 v1 ( the wife is not a happy bunny ) . Anyway my mk1 is a 350w 24v motor and runs through a Derailer on 20" wheels it will will do any hill i can throw at it with ease all be it very slowly :lol: with a top speed of 19mph with no pedalling at all. with my mk2 v1 i would like to get rid of the derailer and use some other form of gearing I was thinking along the lines of what a auto petrol scooter uses i.e a belt drive is there anybody on here that have messed about with such a setup it will be a much more efficient way of doing gears , I have been looking at the Nu-vinchi Hub but not totally sure this will be man enough for what I want to do with my mk2 ( but could be wrong ) has any body had any experience with such hubs ?, The mk2 will also be running 20" wheels but defo will be a off road e-bike 8) but with required top speed of about 20-25mph max on the flat ( I want it geared to be a out and out grunt e-bike ) If anybody got any usefull tips or pointers It will be very happy indeed.

Hi,

gwhy! said:

Hi All,
With my mk2 v1 i would like to get rid of the derailer and use some other form of gearing I was thinking along the lines of what a auto petrol scooter uses i.e a belt drive is there anybody on here that have messed about with such a setup it will be a much more efficient way of doing gears , I have been looking at the Nu-vinchi Hub but not totally sure this will be man enough for what I want to do with my mk2 ( but could be wrong ) has any body had any experience with such hubs ?

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The Nuvinci will be strong enough unless you are running a huge amount of power. Probably fine up to at least 5kw. They are heavy. Quite a few people like them a lot on Ebikes, others not so much. You can search for Nuvinci on the forum and probably find at least two or three users

Nexus 3 speeds and 7 and 8 speeds are also good but probably not strong enough for off-road use.

I have sold about seven to forum members at a very good price. I still have 5 left, new in sealed boxes.

$275 including Priority Mail Shipping with insurance in the U.S. Complete info here:
http://mitchji.home.comcast.net/~mitchji/NuVinci.html

PM me if you are interested.

MitchJi said:

Hi,


The Nuvinci will be strong enough unless you are running a huge amount of power. Probably fine up to at least 5kw. They are heavy. Quite a few people like them a lot on Ebikes, others not so much. You can search for Nuvinci on the forum and probably find at least two or three users

Nexus 3 speeds and 7 and 8 speeds are also good but probably not strong enough for off-road use.

I have sold about seven to forum members at a very good price. I still have 5 left, new in sealed boxes.

$275 including Priority Mail Shipping with insurance in the U.S. Complete info here:
http://mitchji.home.comcast.net/~mitchji/NuVinci.html

PM me if you are interested.

Click to expand...

Thanks for the reply, I will have to put some thought into it and keep it in mind.

Don't rule out the simple humble bicycle derailler and gears. I've gone 5,700+ miles on just regular bicycle gearing.

safe said:

Don't rule out the simple humble bicycle derailler and gears. I've gone 5,700+ miles on just regular bicycle gearing.

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That is one serious looking bit of kit .. I havent ruled it out just think it will get in the way and be problem some for what I intend to use the bike for. The main thing would be I want to be able to change the gears whilst stationary and feetup, I know this may sound a bit odd but I would like to make a bike that I can do some very light trials on.

gwhy! said:

I would like to make a bike that I can do some very light trials on.

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A year or so ago I predicted that one day we will see the first backflip on an ebike... I'm still waiting... (Trick Riding)

Trials Riding and electric power could be really cool. The low end torque of electric motors would be ideal for Trials Riding.

You meant Trials Riding right?



To my knowledge you are the first to think of the idea.

Thats it :wink: , I used to ride moto trials, but then I started doing cycle trials, I also think that the power delivery and control from a electric motor would make it very intresting and fun as long as the drive chain can handle loads of torque but very low speeds. Thats my plan, Scorpa ( mototrials manufacture ) are due to release a BMX size electric trick bike for the summer it looks well cool check this link out http://www.sev-world.com/en/etricks.html Just a bit on the pricey side but this is what have inspired me

You are the pioneer in the sport!

My input would be to tell you about how the electric motor powerband works. (if you don't already know)

Electric motors can produce very high torque at low rpm... at least in theory. However with low rpm torque you also get heat and that can destroy a motor. The controllers are designed with current limits in them so that you can't damage the motor or the battery with too much current.

For your specific application you want to MAXIMIZE low rpm torque and that means you need to gear the bike low (normal for a Trials Bike) and also you need:

A battery that can handle high currents in the 10C range most likely

A controller that allows unlimited current. (no current limit)

...you need to be sure that the battery can hand the "grunts" of low end power and you will likely need to seek out a more expensive motorcycle controller to be able to handle the peak currents.

Finally you will need to realize that if you do all this that the motor will get overheated if you are using it too much in a period of time that is too short. Regular ebikes run into troubles when you are running up a long hill under heavy loads. If you gear the bike low enough I doubt you will have problems, but you might want to have the motors natural "powerband" be set up so that it runs well below your pedaling rpm. This would allow you to pedal in the high rpm areas and then use the motor power for the low rpm. (so it will be important that the pedal speed can exceed the motor... you need a separate freewheelling device to allow independence between the two)

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Just so you know... in the "Electric Bicycle Road Racer" bike I'm building I'll be using the OPPOSITE line of thinking. On my bike it will:

Use a very restrictive current limit to suppress low end torque.

Pedal power is for the low rpm and motor power is for the high rpm.

...so we would in effect be building bikes that serve the opposite purposes.

safe said:

Don't rule out the simple humble bicycle derailler and gears. I've gone 5,700+ miles on just regular bicycle gearing.

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What thread is that bike from?

DeathBlade said:

What thread is that bike from?

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My project threads are here:

http://endless-sphere.com/forums/viewtopic.php?f=6&t=84

http://endless-sphere.com/forums/viewtopic.php?f=6&t=1740

Thanks for the input safe

I havent even thought about maxamizing the torque i.e battery's and controller, But that will come im sure :wink: the main problem is fitting a big motor and batterys onto a very small light weight frame the motor and batterys needs to be as low as poss but with max ground clearance. I have a few ideas and when the time comes i will start a project thread..

gwhy! said:

...the main problem is fitting a big motor and batterys onto a very small light weight frame

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If you have enough $$$ and time it's no problem.

The RC motors weigh about two pounds... LiFePO4 cells could be around 5 - 10 pounds. The technical hurdles to get this together at this level of sophistication are enormous because we are at the pioneering stage of this revolution.

Read some of the RC motor threads in this section... if you have the $$$ you can do this....

However... I've been developing my projects for three years now and every time I make an advance I always feel that I could have improved even more, so the rate of change in these technologies is hard to keep up with. Plus... there is a loooooooooong learning curve to learn all the tricks of the trade.

Are you sure you have what it takes?

Don't expect anything to be easy... I promise you it will not be...

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One year ago the RC motor was largely an abstract concept for ebikes... so that should give you some idea of how fast this is moving.

Hi Safe,
That RC setup looks a very neat and compact, I will defo have a look through the RC motors sections of this forum. What sort of power can a small motor like that produce and rpm ?. I hope I got what it takes :wink: not to sure about the $$ though . I have got one of my old frames (10") that im gonna try and mount everything on. I have a 5" frame but i think that would be near on imposible. Im gonna run with 20" wheels because this will give me enough space ( hopefully :? ) between the wheel and the seat tube to mount the drive train by the bottom bracket. The battery's will run the length of the crossbar from the headset down to the back wheel and any electronics can fit in the triangle of the frame. Thats the plan so far. The bike im working on at the mo is a 14" frame with 20" wheels and using a my?? 350w motor ( cheep option ) just to see if the concept will work (all fit with a initial gear reduction).

gwhy! said:

What sort of power can a small motor like that produce and rpm ?

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Think numbers like 2500 watts. (3.3 hp)

It's just like with other types of racing if you spin the motor really fast it can produce lots of power. So the biggest trick is in being able to gear these fast motors down to something usable.

Notice the red line... heat and torque are directly related so you can imagine the torque you get at low rpm... this is ideal for Trials Riding, so it's a great idea you are thinking about. (actual power is in green) You still want to have really, really low gears so that you can spin the motor more because heat is bad news for motors.



Go here:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=8044&start=30

wow 3 horses from such a small light motor nice... I have had a quick look through the rc motor thread and yes you are quite right if the motor is run at max revs when ever its in use that will be the best performance as seen from the chart. I have put some thought into what you said about no current limiting on the controller and have had a thought about using a time limited ( maybe about 1-3 seconds ) unlimited current before the conventional controller kicks in, in trials its all about the initial kick to launch the bike, with moto trials all the control tends to be through the clutch and the revs held more or less at a constant so maybe having a throttle setup/clutch i.e on/off for current limiting may be a way to go. When I get the 350w motor into the 14" frame that is something that I think may well be worth playing with. I have got a 1kw motor to play with also but it is big and heavy but it will be usefully to try and get some figures..

Hi,

RC Ebike Info:
http://www.wisil.recumbents.com/wisil/shumaker/default.htm
http://endless-sphere.com/forums/viewtopic.php?f=6&t=3904#p57685


http://endless-sphere.com/forums/viewtopic.php?f=3&t=5156
If you check the last few pages you will find out this is geared too high (really slow from 0 to about 25mph, really good from about 25 to 40 mph):
http://endless-sphere.com/forums/viewtopic.php?f=6&t=5168

http://endless-sphere.com/forums/viewtopic.php?f=28&t=7180
http://endless-sphere.com/forums/viewtopic.php?f=28&t=8057

I wish I had found this forum before I bought the motors that I have The RC setups looks like they are just the job Thanks for the links MitchJi some food for thought in that lot.

gwhy! said:

I have put some thought into what you said about no current limiting on the controller and have had a thought about using a time limited ( maybe about 1-3 seconds ) unlimited current before the conventional controller kicks in, in trials its all about the initial kick to launch the bike.

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One idea people have used for current limiting is to run a normally unlimited controller and then place a heat sensor inside the electric motor itself. That way when the motors armature (the wires) start to overheat you can turn down the throttle as an afterthought. For your application that would make a lot of sense and some controller/motors already do such things.

So you might get ten really strong pulls from the motor in a row and then things get hot and you start to get less after that. It would depend on a lot of factors about when the overheating would really happen though... maybe ten pulls... maybe fifty... you would have to try it and find out.

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There are also many different types of motors and for what you are doing you might look into the "Stepper Motor" out of curiousity. (not sure if that's as practical)

You might check some of the motors used in "robot wars" because they tend to need high torque.

It's in interesting project, if you succeed with it you will have broken new ground.

safe said:

One idea people have used for current limiting is to run a normally unlimited controller and then place a heat sensor inside the electric motor itself.

Click to expand...

This sounds a much more elegant solution . The bike im gonna be using for some testing is a 14" jump frame and weighs in at a little under 14kg ( as a complete bike without no electrics or mods ) and I cant see how I can really get any lighter than this unless i use a smaller lighter trials specific frame. Strength is up most important ( I have seen frames, bottom brackets and axles snap without any additional weight attached :? but this is mainley on landing the bike) but on the up side most of the trick riding is done by unweighting the bike totally so in theory the motor/drivetrain would only need to launch the 20-30kg'ish bike. The more I am looking into it the more I think it is gonna be possible to build a competitive e-trials bike a full blown mototrials bike weighs about 80-90kg and produces about 14-18 bhp at the back wheel so looking at some of the RC setups this should be doable 8)

The trick to Trials bikes (I seem to recall) is in getting a motor that spins up really fast... so you want little to no freewheel. The RC motors have almost no inertia to them since they are so light and this would mean you could get them to spin up to higher rpm rapidly.

My guess is that gearing will be the thing that matters. It's not all that important to ride at high speeds but the rate at which the wheel accelerates is all that you care about.

That's why I was suggesting that the motor be geared below the pedal speed so that most of the "grunting" is done with the motor and not the pedals. The pedals are for when you ride home on the street and want to make more speed.

The original idea for a CVT might not be needed if you devote the motor to the "grunts" and the pedals to regular riding. It's almost like having a two speed this way.

I don't know how a CVT thread turned into a Trials thread that requires instant grunt, but I like where you are going with this. Its always nice to get a fresh perspective in here though. Have you seen "recumpence's" build? Study the clutch he designs to take some of the bite off the motor and save the belt. You might do well with something similar, but have a lever on the handlebar to feather the engaging disks. Also, the SRAM 3 speed would be plenty strong enough to handle the 2-3 KW you are talking about. Or get a flip-flop rear hub, left side 2 stage rc drive with a 250 KV motor, some rc pouch batteries, a thumb control throttle, and a Castle Creations HV110 controller. Total price= $1200 Trials E-bike grin= Priceless.

safe said:

The trick to Trials bikes (I seem to recall) is in getting a motor that spins up really fast... so you want little to no freewheel. The RC motors have almost no inertia to them since they are so light and this would mean you could get them to spin up to higher rpm rapidly.

My guess is that gearing will be the thing that matters. It's not all that important to ride at high speeds but the rate at which the wheel accelerates is all that you care about.

That's why I was suggesting that the motor be geared below the pedal speed so that most of the "grunting" is done with the motor and not the pedals. The pedals are for when you ride home on the street and want to make more speed.

The original idea for a CVT might not be needed if you devote the motor to the "grunts" and the pedals to regular riding. It's almost like having a two speed this way.

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Your absolutely right safe, the rate at which the wheel can get up to speed is the trick. Your also right about the original idea (CVT) , the reason I was thinking along the lines of CVT was more from the mototrials side ( more momentum to climb hills ( quarry faces ) it would be nice 8) but not essential for cycle trials. I will be thinking along the lines of gearing the bike as you have suggested initially to see how it goes with the motors i have already, to get a feel for it :wink: but a RC setup would be the way to go maybe later down the line.

etard said:

I don't know how a CVT thread turned into a Trials thread that requires instant grunt, but I like where you are going with this. Its always nice to get a fresh perspective in here though. Have you seen "recumpence's" build? Study the clutch he designs to take some of the bite off the motor and save the belt. You might do well with something similar, but have a lever on the handlebar to feather the engaging disks. Also, the SRAM 3 speed would be plenty strong enough to handle the 2-3 KW you are talking about. Or get a flip-flop rear hub, left side 2 stage rc drive with a 250 KV motor, some rc pouch batteries, a thumb control throttle, and a Castle Creations HV110 controller. Total price= $1200 Trials E-bike grin= Priceless.

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Yes I have seen recumpence's build and it has given me lots of ideas but has also raised some potential major problems Im gonna sell one of my mototrials to help finance the project when I have completed all my home work. I have had a look at the SRAM 3 speed hub and think that may be a big possibility :wink: loads of initial testing to do yet hopefully without spending to much more money :lol:

A Slightly Insane Idea...

You have to take some of my suggestions with a grain of salt because I have a habit (as people here will tell you) of just saying whatever idea I happen to get.

This one is a bit extreme...

What if you eliminated the controller entirely and just used a pushbutton?

Since those trials riding "grunts" (is there a true name for what is done?) are basically going to be a massive surge of energy for a short burst of time with a simple pushbutton (the technical issue of finding the right way to do it still unresolved) all the voltage and current would flow at once to the motor and that would be the maximum you could ever get from it.

You would not want to hold the pushbutton on for long both because of the heat as well as the fact that the bike might take off on you.

It might not be my best idea... but it is cheap and simple.

Are there times when you would want behavior other than full on and full off?

It's kind of a dangerous idea, but if the pushbutton could be blipped very quickly you could just get the kind of twitchy behavior that I think you might be looking for.

As I recall Trials Bikes use special throttles with very little twist to them because you want things to happen really fast.

This would be reaaaaaaaaallllly responsive.

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You could still use the temperature sensor idea and just hook it up so if the temperature is too high the pushbutton will not work. Once the motor cools a bit the pushbutton would start to work again.

Maybe even figure out how to have a premeasured pulse size for each pushing of the button.

No totally insane it is sort of the same idea as I mentioned earlier in this thread the push-button would be on the side where the clutch would be on a moto but this would be the back brake with a switch so when the brake is released unlimited amps will be passed to the motor if the throttle is open/on max but the unlimited amps will only be on for a short burst of pre-set time or until the motor windings heats up to much. But to keep it simple for the time being a simple push-button would be a really go way of testing without designing/testing any electronics 8) . The idea behind the CVT would have been to use a variator setup that can be locked or held in a low gear, I know the 650 suzuki burgman semi-auto scooter uses this system and it is a very efficient and works well , the nice thing about running a variator would be you can keep the motor at its most efficent rpm and the gearing adjusts itself to the load not totally usefull for trials but if it was able to be locked i think it could work well.