Friction Drive New Kepler carbon build

[Kepler]

So as discussed prior, the front derailleur shifter and shifter cable are used to pull the drive onto the tire. A micro switch wired though one of the controller's brake switches then activates the drive once the swing arm goes through about 50% of its range. Also there is a throttle potentiometer just under the seat to set the amount of assist.

This all seemed like a good idea at the time however what actually happens is that once the drive activates the motor gets drawn right up to its end stop. Releasing the cable has little effect on dropping the motor off the tire when under load so effectively you are left with the drive pushing you along with the only way to drop the motor off the tire being to pedal like hell and overtake the motor speed and torque or reach down and wind off the throttle potentiometer. Both very undesirable and completely unacceptable.

Time for plan B

The micro switch has been removed from the drive and will be wired to a push button under the seat as an emergency cut-off.
The throttle potentiometer will be moved from under the seat and down to the derailleur assembly where it will be rotated by converting the linear movement of the shifter cable to a rotational movement to adjust the throttle. The idea being that the front derailleur shifter becomes a combination throttle and positive swing arm activation device.

Not so easy converting a linear movement to rotary and making it rotate enough to be effective while at the same time keeping the movement accurate. I have gone to a 10K pot as opposed to a 5K pot to shorten up the range of movement and will using a ball link and pushrod from my vast array of RC helicopter parts to make up linkages. The plan is coming together but not 100% confident with how successful this will be. However, if it works as planned, it should be exactly what I am looking for in term of drive control.

This is where I am up to at the moment.

 

[Kepler]

The throttle system off the shifter cable is a success. 8)

Put together a short Youtube walkaround of the bike showing the drive in action.

[youtube]Miy1V0YjwBQ[/youtube]

 

[IanM]

Awesome build Kepler you have taken friction drive to a really good place. Such an elegant and simple design. You are in my book an ebike pioneer. Nice work

 

[dbaker]

Beautiful work, Kepler I noted you said the bike was a clone. Can you share the source? Did you have to convert the bottom bracket to threaded to mount the drive?

 

[fesanand]

Excellent job, as Kepler accustoms us :wink: ; probably the best relation between weight, max speed and electric system price.

Sorry, I can't help tp ask, I love data :

The nominal assistance is much lower than in your last carbon build. Either you're going slower or you are pushing harder(sport riding) or the light friction drive is extremely efficient (??????)
When you talk about 200Watt, what is your nominal speed?

Friction drives are not the best climbers, even pedaling hard.
I'd like to ask if you already tackled any serious hill >8% ? and in that case, below what speed would you think is a hazard for the motor?

 

[Leebolectric]

incredibly creative, love the derailleur mod.
props!

 

[oatnet]

That throttle solution is elegant. 8) But then, so is the whole build, as well as being the lightest I have come across. Kudo's on yet another incredible stealth build Kepler!

-JD

 

[Kepler]

Awesome build Kepler you have taken friction drive to a really good place. Such an elegant and simple design. You are in my book an ebike pioneer. Nice work

Thank you for your kind words. Frictions drive certainly are not for everyone but i firmly believe they have significant place in the ebike world.

Excellent job, as Kepler accustoms us :wink: ; probably the best relation between weight, max speed and electric system price.

Sorry, I can't help tp ask, I love data :

The nominal assistance is much lower than in your last carbon build. Either you're going slower or you are pushing harder(sport riding) or the light friction drive is extremely efficient (??????)
When you talk about 200Watt, what is your nominal speed?

Combination of things. The bike is lighter and rolls better than my last carbon build. I am a stronger rider now and need less assist. 200W adds 5kph to 10kph on my normal unassisted speed. I have no problems maintaining 30kph on flat roads non assisted on my road bike. 200W through the friction drive takes me up to 35kph to 40kph very comfortably.

incredibly creative, love the derailleur mod.
props!

Thank you. I am really pleased with the derailleur mod. Got it to operate just the way I wanted.

That throttle solution is elegant. 8) But then, so is the whole build, as well as being the lightest I have come across. Kudo's on yet another incredible stealth build Kepler!

-JD

Thanks JD. Much appreciated. I think I may well have edged out the first place holder in this comparison. https://www.electricbike.com/10-light-electric-bikes/

 

[Kepler]

Beautiful work, Kepler I noted you said the bike was a clone. Can you share the source? Did you have to convert the bottom bracket to threaded to mount the drive?

Thanks for that. The frame came from here http://www.aliexpress.com/store/1984031 With the weak AUD, it landed for $730 AUD. Took 5 days to get to Australia and arrived well packed and in perfect condition. The frame is amazing quality for the price. You can buy the frames with a BB30 or English BB68. I of course opted for the English BB68

 

[Samd]

Lovely!

 

[oatnet]

That throttle solution is elegant. 8) But then, so is the whole build, as well as being the lightest I have come across. Kudo's on yet another incredible stealth build Kepler!

-JD

Thanks JD. Much appreciated. I think I may well have edged out the first place holder in this comparison. https://www.electricbike.com/10-light-electric-bikes/

Time to call Guinness! 8)

-JD

 

[Kepler]

Did my first serious commute on this bike today. Really pleased with the way the bike performed however I think the battery is too big. My commute is 28km each way. On the ride to work I used the drive fairly sparingly but still lifted my average speed for my commute in by 5kph compared to my road bike. Charged the pack at work and was shocked to have used only 40 Whrs out of the 200Whrs available.

So on the way home I used the assist far less sparingly and ran the drive for around 70% of the trip. Thinking l would have used the majority of the pack, I was pleasantly surprised to find on this leg I had only used 80 Whrs. This means I am only using around 100W of assist to keep the bike at speed I am after. I actually found I was getting pushed to fast much of the time and needed to constantly back off on the level of assist which no doubt contributed to the excellent economy.

 

[Mikebergy]

On my normal weekend rides, my avg watts output to maintain ~20mph is right around 200w. What speed are you maintaining with the drive engaged? 23-25mph?

Edit: just to clarify, my legs are producing 200w, on my regular bike.

 

[Teh Stork]

Inspiring Kepler, makes me want to build one myself.

How is the sound? Compared to a Bafang BBS for example?

 

[Kepler]

Thanks Teh Stork.

The sound is like all RC friction drives, moderatly loud and nothing like a whisper quite BBS mid drive. Unfortunatly one of the compromises with running this type of assist. It might be stealthy to look at but you are not kidding anyone when you pass someone under power.

That being said, under light load, the noise is about as loud as geared hub motor. Under load its twice that. I tend to get a bit odf a run up when I go to over take people and shut the drive down as i pass them. Once passed i then apply assist if needed.

 

[Kepler]

On my normal weekend rides, my avg watts output to maintain ~20mph is right around 200w. What speed are you maintaining with the drive engaged? 23-25mph?

Edit: just to clarify, my legs are producing 200w, on my regular bike.

I am about same in regards to leg power Watts and average speed, maybe just a little less then you. Adding the extra 100W of assist is allowing me to mainain around 35kph on flat road.

Below is a speed graph taken on my road bike (no assist) last Saturday.



I find the big diference is on assents. and find i am 5kph to 10kph quicker then my road bike. Still work just as hard but it is nice to reach the end of the assent more quickly.

 

[Teh Stork]

Thanks Teh Stork.

The sound is like all RC friction drives, moderatly loud and nothing like a whisper quite BBS mid drive. Unfortunatly one of the compromises with running this type of assist. It might be stealthy to look at but you are not kidding anyone when you pass someone under power.

That being said, under light load, the noise is about as loud as geared hub motor. Under load its twice that. I tend to get a bit odf a run up when I go to over take people and shut the drive down as i pass them. Once passed i then apply assist if needed.

I think the noise could be significantly reduced if the motor is ran with a sinusoidal waveform, but you've probably already considered that.

If I were to go down the sinusoidal/FOC controller route - I'd buy the vedder ESC and tinker with that (up to 2kW able). Or I'd use more time with Texas Instruments's Instastpin FOC line of dev-boards. They have a small one on around 24V 10A (~200W) if memory serves me right. Or I'd just test some of the RC ESC's with FOC that has recently hit the market.

 

[Kepler]

I have tried a few of the cheap Sine Wave controllers with RC motors but unfortunately they don't work. The kU65 and S06 controllers have been quite successful though, just noisy in there operation. With their cheap price point and current limiting capabilities compared to an RC controller, they have been a good option to date.

Thanks for the heads up some other FOC esc options though. The only real drawback with this current build is the noise. If I could improve on this it would take the project to a completely new level.

 

[Samd]

Having ridden with Kep on a few occasions I feel obliged to say I've found the noise glorious. Like a teeny supercharger. I'm odd like that.
I'm tipping six fets and compact form would be your ideal FOC John?

 

[Tats]

Elegance personified kep - very very impressive

 

[Kepler]

Having ridden with Kep on a few occasions I feel obliged to say I've found the noise glorious. Like a teeny supercharger. I'm odd like that.
I'm tipping six fets and compact form would be your ideal FOC John?

Exactly what I am after. Do you know of such a unit that will work sensorless with an RC motor that I can buy off the shelf?

So far I haven't found an ebike FOC controller that will do it. The development FOC controllers suggested by Teh Stork look interesting but are outside my current skill set to assemble being all surface mount componentry.

 

[Samd]

I've got a FOC supplier in China doing a 12 FET for me. I've sent them a message about six.

 

[Allex]

What if you used sensored rc motor. Any downsides with it? About battery, maybe you can go with 1p 3Ah high drain cell, this way cut the weight and use a smaller bag, or even go with 1p 10A 3.5ah cells?

 

[Kepler]

I've got a FOC supplier in China doing a 12 FET for me. I've sent them a message about six.

Cool. And can you check if they are compatible with high pole count RC motors.

 

[Kepler]

What if you used sensored rc motor. Any downsides with it? About battery, maybe you can go with 1p 3Ah high drain cell, this way cut the weight and use a smaller bag, or even go with 1p 10A 3.5ah cells?

Sensored would be a pain. Also I would need to run 5 more wires though the frame. Doable but not prefered.

I am looking at my options in relation to a smaller more compact pack. Reducing the size of the even getting both the controller and batteries into a drink bottle package would be cool too.