Kepler Friction drive comes of age.

[Kepler]

Many here are probably aware of my ongoing love hate affair with friction drives. My latest design has been tested over 5000km of commuting and has been been documented on this thread viewtopic.php?f=6&t=74269

After discussions with US interests, I have continued to refine this design, reducing the parts count and increasing its strength and reliability. My under bottom bracket design has been copied on a number of occasions and even commercialised under the pretences that it is their own unique design. Having always been open with my designs I suppose there is not much I can do about that.

Although this latest design looks to be simplicity personified, it is the culmination of many years of development, trial and error, and real world testing. It has its limitations as with all friction drives but on the right bike, has proven to be an amazing performer.

Precision laser cut from 304 stainless and assembled completely with stainless steel fasteners, this drive is built to last. The design allows for left or right bottom bracket mounting and has a unique end stop adjustment system which makes setup and adjustment very quick and easy. with the drive being so well hidden, powder coating is an unnecessary expense and as such an elegant brushed Stainless Steel finish has been opted for. The low parts count and economical manufacture of parts means the drive can be brought to market at the right price point.

Its not for sale quite yet but watch this space. Here are a few teaser shots.

[spinningmagnets]

Brilliant!

[Dogboy1200]

Brilliant!

Agreed! Simple is very hard to achieve, it's very easy to design an elaborate system to solve a mechanical problem. The real challenge is to chip away at it until it's the irreducible minimum as seen here. Well done!

[2old]

Superb; looks like the years of evolution are culminating in a masterpiece.

[footloose]

Elegant!

[recumpence]

I love the minimalistic approach to this.

The only question I have is about the thickness of the plate. It looks like the torque of the motor could twist the plate. That may be merely due to the angle the picture is taken, however.

You could also make that plate from carbon fiber to save a few grams and look awesome. Then again, I have always been a sucker for high tech materials.

Matt

[Kepler]

Thickness of material is 2.5mm. There is hardly any flex at all with the drive under load. With the drive being mounted on the chainring side of the bottom bracket, it was important to keep the thickness to a minimum so I didn't effect the chain line too much. In stainless, 2.5mm worked out to be the sweet spot. Weight wise, the drive mech excluding the motor is 150 grams (5.3 ounces) so I don't think weight is too much of an issue . With the motor fitted, the weight comes in at 510 grams (18 ounces)

Would love to do a carbon version though, just for the look. I will do some investigations to where I can get hold of some 2.5mm carbon sheet. Not had a lot of experience with cutting carbon sheet though. Can it be water jet cut or does it need toto be done with a CNC mill?

Could call it "The Signature Series".

Worth noting the swing arm doesn't pivot on the 4mm centre bolt you can see in the pictures. That just keeps the assembly sandwiched together. Also the plan is to sell the drives with 4 different length swing arms that can be easily swapped out to match the geometry of the bike.

[waynebergman]

Very nice Kepler. Keep pushing on! I think its so cool to have a super small simple unit like this. Simple in this case meaning highly refined. Its got to be a great feeling to polish this ongoing project in the way you have. I want to say thanks here for the things I have learned from your posts over the years .........wayne

[Kepler]

Thanks all for the words of encouragement. I am really excited about this design and hopefully bring it to market. I have been so close on a number of occasions but I think this time, the design has been nailed.

A quick screen grab from the manual I am putting together. As you can see, the swing arm will be a simple job to change out to a different length item if required.

Hidden Friction Drive exploded5.JPG (28.09 KiB) Viewed 19153 times

[aCeMadMod]

any updates when will it for sale, and show the girls how to make magic skome,

[Driveless]

What is the cable's purpose in picture #2?
Are you opting for cable pressure instead of centripetal force like in previous iterations to climb the wheel and gain traction?

[Mündawg]

I'm glad for the progress they are making. BUT i would NEVER spend money on a new friction drive.

I built a friction drive motorized bike when i was 17, out of my old mongoose BMX bike and my dad's old 32cc weed whacker motor. It was friction drive, built with a galvanized steel pipe roller, with custom grooves cut in with a dremel. It got 25mph top speed, albeit SOO loud when full throttle But in the rain, it was almost useless, after going more than 5 miles, the roller got so hot it would almost melt my tire. There were some other problems as well.

Friction drive just seems like a 17 year olds technology. Good luck to them tho! I do wish them success!

[tomjasz]

Ha! I've been following from my first week here. Ver1 still sits in my projects crate. This looks marvelous!

Early pest discount, or USA field testing. Might work different in the northern hemisphere. <grin>

[tomjasz]

Th
Could call it "The Signature Series".

Would love to do a carbon version though, just for the look. I will do some investigations to where I can get hold of some 2.5mm carbon sheet. Not had a lot of experience with cutting carbon sheet though. Can it be water jet cut or does it need toto be done with a CNC mill?

Worth noting the swing arm doesn't pivot on the 4mm centre bolt you can see in the pictures. That just keeps the assembly sandwiched together. Also the plan is to sell the drives with 4 different length swing arms that can be easily swapped out to match the geometry of the bike.

My brilliant brother has a carbon fiber manufacturing facility. I'm gonna ask. That would be cool too!

[Kepler]

What is the cable's purpose in picture #2?
Are you opting for cable pressure instead of centripetal force like in previous iterations to climb the wheel and gain traction?

The wheel climbing action of the drive is still a key part of the design. I have found though that getting the drive to contact the tire reliably without grip tape on the motor can be an issue. I set the drive up with a cable pull from the front derailleur shifter. The action is very light and is only needed to make light contact with the tire. The wheel climbing action then takes over. This method makes the drive activation very reliable and gives you plenty of scope to make sure you clear the tire when deactivated. Plenty of other ways to bring the drive up the tire also. Any cable pull mech will do. I have also just used a small RC servo to bring the drive into contact.

[Kepler]

I'm glad for the progress they are making. BUT i would NEVER spend money on a new friction drive.

I built a friction drive motorized bike when i was 17, out of my old mongoose BMX bike and my dad's old 32cc weed whacker motor. It was friction drive, built with a galvanized steel pipe roller, with custom grooves cut in with a dremel. It got 25mph top speed, albeit SOO loud when full throttle But in the rain, it was almost useless, after going more than 5 miles, the roller got so hot it would almost melt my tire. There were some other problems as well.

Friction drive just seems like a 17 year olds technology. Good luck to them tho! I do wish them success!

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.

[Kepler]

Ha! I've been following from my first week here. Ver1 still sits in my projects crate. This looks marvelous!

Early pest discount, or USA field testing. Might work different in the northern hemisphere. <grin>

Don't worry Tom, there will be one coming your way at a price that will make you smile

[bigmoose]

It has been a pleasure to watch the refinement of your design over the years. This version is a culmination of design excellence! Best wishes with it in the market. I sense you will do well. Also thanks for sharing your journey, it has been both inspiring and very informative.

[Ykick]

Damn nice refinements!

I've never been drawn much to FD's but this could be a game changer...

[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?

[tomjasz]

Ha! I've been following from my first week here. Ver1 still sits in my projects crate. This looks marvelous!

Early pest discount, or USA field testing. Might work different in the northern hemisphere. <grin>

Don't worry Tom, there will be one coming your way at a price that will make you smile

VVVBG

Brother the CF guy wrote, "the most efficient would be water jet or laser cut."

[tomjasz]

I'm glad for the progress they are making. BUT i would NEVER spend money on a new friction drive.

I built a friction drive motorized bike when i was 17, out of my old mongoose BMX bike and my dad's old 32cc weed whacker motor. It was friction drive, built with a galvanized steel pipe roller, with custom grooves cut in with a dremel. It got 25mph top speed, albeit SOO loud when full throttle But in the rain, it was almost useless, after going more than 5 miles, the roller got so hot it would almost melt my tire. There were some other problems as well.

Friction drive just seems like a 17 year olds technology. Good luck to them tho! I do wish them success!

it's amazing, to me, but one of the most efficient designs for a gas sipping moped was the Motobecane. Valmet engine with friction drive. I used to mix a gallon of gas every few weeks. Essentially a rebranded Solex. So simple and carried us through university. Style? Nah. Fun? Absolutely. Laughably efficient and a precursor to many interesting designs. 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. Ver.1 is quite amazing, Ver 2 never made it to my bench. The simplicity of this version is nothing short of sunning. Kinda reminds me of my first Swiss Army Knife.

[Kepler]

It has been a pleasure to watch the refinement of your design over the years. This version is a culmination of design excellence! Best wishes with it in the market. I sense you will do well. Also thanks for sharing your journey, it has been both inspiring and very informative.

Thanks for stopping by Moose, appriciate the support. I am really excited about the direction the development has taken and am looking forward to finally getting the drive to market with some reasonable volume.

[Kepler]

Damn nice refinements!

I've never been drawn much to FD's but this could be a game changer...

Thanks for that. I think also it is a game changer. Refining the drive to the point where it is now means I can take it market at a price that anyone can afford. Also since the drive mech weighs 150 grams and is basically flat, it can be posted in a padded envelope so shipping costs anywhere in the world will be very small.

Still some more refinement to come though and just waiting on new prototype parts to come back from the laser cutters. Will post some renders in a couple of days with the changes.

[Kepler]

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.