Kepler Friction drive comes of age.

[Samd]

Just saw this thread mate. Nice.


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[Mündawg]

wow, ya'll need to chill out. I said i was proud of their achievements and i wish them success!

IF you knew diddily about design you'd recognize this isn't your old BMX with a stink box haphazardly hung, and destined to fail.

Who said it was haphazardly hung? I don't remember saying that.

I think you are missing the point by comparing this drive to a weed whacker motor that you strapped to your BMX bike and to quite frank, a little insulting to refer to the design as 17 year old's technology.

If you're insulted that's all on you buddy. I clearly said that to me friction drives (in general) will always seem like 17 yro's technology (Because i was 17 when i built my own). I made no remarks to the craftsmanship or ingenuity of THIS particular design. I didn't say that THIS design was 17yro technology, ya'll must have missed the point. Also the weedwhacker story was just a fun anecdote, i thought people on ES would be more receptive to that creative spirit.

If you accurately read my post you would see that the issues i was pointing out pertain to my experience with friction drives as a whole, had nothing to do with mechanical shortcomings of the weed whacker i used. I never said that THIS friction drive would have the same problems, but since you're all in a huff i clearly hurt ya'lls feelings with my opinion. It wasn't my intention to put down your efforts and work!
Mündawg

 

[Kepler]

No worries, i can actually relate to your original friction drive experience. I too built a rudimentary friction drive when i was about 17 but with a Morris Minor starter motor and a well used car battery. Good for about 5km too.

 

[MrDude_1]

I assume this uses a spring to kick out like your previous one.
When you change out swingarms for longer ones, do you have to change the spring to a stiffer one as well, or can you just preload the spring more?
Or is the spring not important anymore, now that you use cable actuation?

No spring in this design. Just another complication and unnecessary cost. Although the kick spring has its merrett, I have never been happy with how finicky it made the drive setup. Using a cable activation to get the drive to make light contact with the tire is so much more reliable.

I plan to document different methods of adding a simple and cheap cable pull mech. Keep in mind the cable mech is only there to make contact with the tire then the tire climbing action does the rest.

simple is good... and setup should be much simpler without relying on that spring kick.

if there is no spring, what keeps it from bouncing around when it is not engaged, and how does it pull away from the tire when not in use?

 

[Kepler]

All good questions here.

The weight of the motor holds the drive off the tire when not in use. Yes, it can bounce around a bit when disengaged however keeping the motor to tire clearance at a minimum keep this in check. You do get a slight rattle over rougher surfaces but its not much. A cable tie around the bottom stop pin to act as a plastic stop rather then a metal to metal stop would probably reduce any rattle to next to nothing.

 

[tomjasz]

wow, ya'll need to chill out. I said i was proud of their achievements and i wish them success!

IF you knew diddily about design you'd recognize this isn't your old BMX with a stink box haphazardly hung, and destined to fail.

Who said it was haphazardly hung? I don't remember saying that.

I think you are missing the point by comparing this drive to a weed whacker motor that you strapped to your BMX bike and to quite frank, a little insulting to refer to the design as 17 year old's technology.

If you're insulted that's all on you buddy. I clearly said that to me friction drives (in general) will always seem like 17 yro's technology (Because i was 17 when i built my own). I made no remarks to the craftsmanship or ingenuity of THIS particular design. I didn't say that THIS design was 17yro technology, ya'll must have missed the point. Also the weedwhacker story was just a fun anecdote, i thought people on ES would be more receptive to that creative spirit.

If you accurately read my post you would see that the issues i was pointing out pertain to my experience with friction drives as a whole, had nothing to do with mechanical shortcomings of the weed whacker i used. I never said that THIS friction drive would have the same problems, but since you're all in a huff i clearly hurt ya'lls feelings with my opinion. It wasn't my intention to put down your efforts and work!
Mündawg

Intent is I'm[possible to read. My apologies. I've always found this idea fascinating and have had positive experience. Something that seems to be uncommon with this idea.

I apologize.

 

[Mündawg]

Of course. I apologize as well

 

[Driveless]

All good questions here.

The weight of the motor holds the drive off the tire when not in use. Yes, it can bounce around a bit when disengaged however keeping the motor to tire clearance at a minimum keep this in check. You do get a slight rattle over rougher surfaces but its not much. A cable tie around the bottom stop pin to act as a plastic stop rather then a metal to metal stop would probably reduce any rattle to next to nothing.

Athletic supporter included? :lol:

Beauty of this drive is stealth and affordability. Perfect to boldly go beyond the ES audience.
Early adopter incentive price for the initial offering?

Maybe on Facebook, Instagram, Twitter, Pinterest.
http://mashable.com/2013/01/21/online-coupons-business/#2n_gfWZaOkqS

...May be better suited to ES though, economies of scale can be daunting.

 

[Kepler]

Some further refinements just being finalised. I needed to make the profile of the drive slimmer on the chainring side to make sure it would cater for people who wanted to keep multiple chainring and front derailleur setups. For my bikes l was satisfied with a single chainring but as this project has gained momentum, i felt it important to make the fitment more versatile.

Should have new laser cut parts back next week for testing. If all goes to plan, I will begin my first production run of 100 units.

I want this drive to be a no brainer no risk purchase for all my friends here on the forum. Price will be just under $100 USD and will open a for sale thread early in the new year.

Feel free to PM me with expressions of interest.

 

[devo1223]

Is $100 just for the brackets? So we'll need to source are own motor and modify are own KU65 controller?

 

[MrDude_1]

little off topic.. but the VESC is about the same size as that tab coming out.
if you were to mount one on that bracket.. you would have everything except the throttle and battery all in that one tiny unit.

 

[frankly]

Lovely work. Congrats and good luck!

Having almost no experience with fd, I shouldn't comment. (but)

I applaud the notion of affordability and not clunking up the bike too much. If it gets more people riding bikes, any limitations are quickly eclipsed by an overall good.

As I was reading this thread, thoughts came from a perverse need to complicate things.
Humor me?

First pondering had me looking at a specialized tire. Not quite a gear wheel, but heading that way...with a corresponding wrap on the motor drive. This is the cusp of wrong-think and not even wrong-think, I think.

That lead to envisions of wheel rim extensions that the motor engages, as opposed to the tire. Like, with teeth...matching motor teeth.
Has this left the definition of friction drive?
What if that motor engaged the bb chain ring instead of the tire?
What if the motor was mounted to engage a pulley wheel on the inside of an extended bb axle?

Apologies for my inadequate research. I can likely assume that all approaches have been done to death.
Last bit:

Any quantitative analyses of how the friction drive effects tire longevity? Do its fans seek a particular brand of tire?

thankyou

 

[Kepler]

Hi Frankly, welcome to the forum.

Lets not try and re invent the wheel now that it is rolling nicely . Design creep has been one of my greatest short comings when it comes to friction drives and never being completely happy with design. Although there is always room for improvement and innovation, I am in a good place here with this design and believe it is ready for release as it is.

You are correct, what you are proposing means it is no longer a friction drive. Research further and you will soon understand the complexities of using a small RC style motor in a direct drive setup.

In regards to tire wear, this also has been discussed in detail. My current test bike has hit 5000km on the original road tire. This is due to using a smooth metal roller that works perfectly in dry conditions but doesn't work at all in wet conditions. If you want to use your bike in wet conditions, this drive is not for you.

 

[Kepler]

Is $100 just for the brackets? So we'll need to source are own motor and modify are own KU65 controller?

Now that would be a bargain with all included . I am selling the drive mechanism only for this price.

As far as motor / controller / battery combos are concerned, as long as it is a 50mm diam motor, you are looking for a no load motor RPM of around 5000 to 6000 RPM.

A 250kV motor on a 6S liPo and RC style controller will give you about this. I personally prefer 7S 18650 packs these days so a 230 kV motor is the sweet spot for this voltage.

 

[Kepler]

little off topic.. but the VESC is about the same size as that tab coming out.
if you were to mount one on that bracket.. you would have everything except the throttle and battery all in that one tiny unit.

The VESC is a controller i am yet to experiment with but i am keen to test. I believe they are sinewave (correct me if i am wrong). Noise is the only real drawback of this drive. A quite RC style friction drive is the holy grail as far as i am concerned.

 

[MrDude_1]

little off topic.. but the VESC is about the same size as that tab coming out.
if you were to mount one on that bracket.. you would have everything except the throttle and battery all in that one tiny unit.

The VESC is a controller i am yet to experiment with but i am keen to test. I believe they are sinewave (correct me if i am wrong). Noise is the only real drawback of this drive. A quite RC style friction drive is the holy grail as far as i am concerned.

The controller can operate in normal BLDC mode like a common ebike controller or ESC.. but it also has a FOC mode that makes most motors almost silent. I just started to play with them myself, but they have really matured into a kickass controller that is absolutely tiny. For the power size we're looking at with your bracket, I think its a perfect match.

 

[Kepler]

Now you have me really excited.

 

[cwah]

What about running in the rain and the noise?

Would it work on a brompton?

 

[Kepler]

Not for wet weather operation.
Can be noisey under high load and low speed but the noise reduces with speed. Typical RC motor noise.
I have never tried fitting it to a Brompton so l cant tell you.

 

[VINTAGEBASS]

Hi Kepler, first of all thanks for your help sourcing a controller for my friction drive, works a treat but my unstealthy arrangement means your bottom bracket design is a must for me. Will you be shipping to the UK?
Keep up the great work

 

[Kepler]

No problems shipping to the UK or anywhere else in the world for that matter

 

[VINTAGEBASS]

great news, please send me a quote once you are ready to ship

 

[alan]

No spring in this design. Just another complication and unnecessary cost. Although the kick spring has its merrett, I have never been happy with how finicky it made the drive setup. Using a cable activation to get the drive to make light contact with the tire is so much more reliable.

Just an idea... Add a small toothed gear to the motor axle (such gears are readily available for the intended motor output that otherwise is not being used for this drive). Then extend a small tab on the mounting bracket towards the motor axle with linear gear teeth on that edge of the bracket to engage the motor axle gear, but only when the motor is down, away from the tire. Then, powering up the motor could also cause the axle spin to "kick off" the geared tab throwing the motor up to the tire. The tab would need to be low enough in height such that the axle rolled completely off of it before the motor housing made contact with the tire. Only added part is a gear for the motor, and only a small change to the main bracket shape, adding the toothed tab extension.

Should be cheaper, simpler, and easier to use (fully automatic) than either the spring or the cable. However, gearing design may be tricky so as to handle motor lift efficiently, disengagement with motor start and re-engagement with power off, and minimization of the motor being jolted to stop, or being thrown too hard into the bracket stop due to motor spin momentum, while also avoiding bounce back of the motor to the tire from spin down momentum.

Another alternative is to add a U-shaped spring where the above bracket extension describe above is located, such that the spring presses against the motor axle when the motor is stopped away from the tire. Friction between the axle and the spring may be enough to lift the motor into tire contact, while letting enough slip for a more gentle spin down of the motor at power-off that might better avoid bounce-back of the motor towards the tire. This alternative would add a spring and spring attachment screws to your part count, but is still fairly simple.

 

[Kepler]

Sounds good theory. Tried a few similar strategies over the years. Every time its ends up being fiddly to set up and inconsistent in its operation. The cable pull method just works every time and is easy to setup. Appreciate your thoughts though and by all means, if you decide to have a go at one of these drives, see what you can come up with.

 

[Kepler]

Perfect weather for my 27 km commute this morning. Combination of this drive on a carbon bike is just a joy. 50 minutes on bike paths to get to the office this morning. So much fun being the fastest rider out there with every other rider around you thinking they have just been passed by a gun rider

Picking up my latest design parts from the laser cutters tomorrow. All going to plan, will have it on the bike tomorrow evening.