Kepler Friction drive comes of age.

[MrDude_1]

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

So how often do they call you a cheater?

 

[Kepler]

No cheater comments so far, just looks of disbelief :lol:

 

[Kepler]

New parts are back form the laser cutters. Drive action is smooth and compact giving maximum clearance on the chainring side. Also end stop adjustments are more versatile with independent top end stop and the bottom end stop adjustment.

Will do a bunch of testing of the next few weeks just to make sure operation is 100%. Very pleased with this version. 8)

 

[JTL]

Good work! This may be just what I need to make my wife's bike into an ebike. She doesn't need much power and we are on flat terrain with an occasional need to ride up and over and overpass. It would be helpful if you could give some motor recommendations. What kind of speed are you getting out of this?
John

 

[tomjasz]

Good work! Excited!

 

[docw009]

Looks very nice. If the motor is not included, what motor would one buy for it, Some kind of 50mm outrunner? I know little about RC motors.

 

[telcosteve]

Hi Kepler, I have been following your various builds now for a few years. Fantastic stuff!!!
I was inspired to create a friction drive this summer so I bought an emax motor, 63mm around 210 KV and a castle 90 ESC with a couple zippy 4000mah 6s batteries and a servo tester. plus a decent charger venom 2 channel. (my other hobby is RC planes.
So I tried some different mounts etc.. but realized I have not the talent for that. Sooo I am excited to see this latest invention of yours. do you think it could be use with a 63mm outer diameter out runner motor? If so and your mounts go on sale I am interested.
Thanks,
steve in central IL, USA

 

[Kepler]

I am actually running a 6354 motor on my test bike at the moment. No problems with fit and it works really well, probably better then the 50mm motors I have testing with. Draw back of course is that the motor is visible and it adds 200 grams to the drive. With the can sprayed black, the motor is less visible but does still stand out more then the 50mm motors.

 

[Kepler]

Here are a few motors that are a good for the drive.




This is an older motor but an equivalent to a SK3-6354-260
Nice torque and quieter under load then the 50mm motors. Being a larger diameter, it is more visible and is the heaviest out of the 3


View attachment 1

The second motor is a Turnigy SK3-5065-236
A really good speed match on 7S 18650 cells or 6S LiPo. The longer can gives it a bit more torque but being longer, it is more visible.



Turnigy SK3-5055-280.
Nice and light and compact. can struggle a bit power wise though and gets a bit of a growl up under low rpm load.

 

[telcosteve]

This is fantastic information. I looked this morning. My model is called an eMax BL5335. I did measure diameter and it is 63mm
Looks like the 6354 you have there. I will keep watching for you to your bracket to go up for sale. I think it would be a good match for my road bike trek 2300 with carbon fork. It's a light and quick bike now. With the friction drive it would be a blast.
Thanks!

 

[telcosteve]

Website confirmed my measurements and the speed is 230kv. On my test runs of the motor on a test stand it was very quiet under no load. I don't mind the visibility or sound. I'm really not worried about stealth. I like the idea of it showing a bit. I do like the neatness of your various designs and the hiding of wires etc. I hope to use some of those aspects on my build. Have a good one!

 

[ScooterMan101]

I Thought the Specialized Venge had / has a BB30 ?

How did you get the outboard Shimano Bearings on/to work with that Frame ?

How can I/and other people get your motor bracket to work on my BB30 Framed Road Bike ?

 

[ScooterMan101]

Cost of that 800 gram , gold color motor ?

Cost of all the other parts to put it together ?

You wrote to use a RC Controller , must look into these, however I cannot picture what the throttle looks like, I know of that big box that RC hobbyists use to control direction and speed, but how could a small version be put on the bars ? Especially on the Hoods/Brake Lever ?

Are you using 6s Lipo now ?

You mention 7s 18650's if using them how many in parallel ?

What is / are the Volts , and Amp hour of the pack you are using now ?

Wonder how many watt hour/ volt , amp pack needed to travel 80 Km's or so ?

 

[ScooterMan101]

To Question Above about how you are doing this / or how anyone can do this with a BB30 Frame ...

This ? https://www.praxiscycles.com/conversion-bb/

 

[Kepler]

That is a great solution to BB30 compatibility issue. Thanks for posting that.


In regards to my bike, it is clone frame not a genuine SWorks Venge hence the 68mm BB.

Speed controllers. Options are endless. I use a standard 6FET KU65 bike controller on 7S 18650 but any Sensorless controller should to the trick. I have some SO6P controllers to test over the next few weeks. However the cheap sinewave sensorless controllers dont work with RC style motors
Any 50Amp plus 6S RC style speed controller will do the job and you could probably go up to 10S with the right controller. Motor KV needs to kept as low as possible on 10S though. Under 200kv is preferable.

What I am really excited about is the VESC skateboard controller. Dying to try one of these in FOC mode.

As mentioned before, that gold motor is a SK3-6354-260 equivalent. They cost $60 USD https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6354-260kv-brushless-outrunner-motor.html

In regards to batteries I am using 3.5ah GA cells. 7S3P So 29.4V hot off the charger. This pack is 300 Whrs and gives you about 70 minutes of full time assist. 600 whrs would get 80km if you didn't do any work. I do 80km plus all the time on my bike though with the 300 Whr battery. Just use the assist when I need it. Thats the whole point of the drive.

 

[EDS]

Looks good. Love the simplicity. I've been itching to make one of these ever since I saw yours & Adrian's original posts years ago. I finally decided to start my own build, but if I can buy your kit I may do that instead to save time. We recently bought a 44 year old house that needs lots of work, and my commute takes too long. Priorities . . . .

My bikes are old (18+ yrs). Would this work with old style bottom brackets? I think one is a BB50 cartridge, & the really old one is not even a cartridge. The older one has a big lock ring on one side that may be similar to what you show.

I was planning to build mine into a seatpost-mount bike rack. There are several available which are adjustable length (slide back & forth). It seems like with the ability to raise & lower it on the seatpost, & back & forth with the rack adjustment, I wouldn't need to sweat the design details as much. As long as I got it close, I could adjust it to a decent arrangement after it was built. It seems like this style would be good for someone (like you perhaps) to sell, because it could fit many bikes. Also, you can have the motor, batteries & controller all built in to the same package. Incorporate a wheel sensor somewhere & you wouldn't even need a throttle (I'd still want one though). If you mount the batteries on the bottom, you also get a rack out of the deal (bonus ). Have you considered selling a more complete package? It could also come on & off the bike easily, or even swap it over to another bike. It seems like many more people would be willing to install something like that.

The spring + auto twist-into-place engagement setup was pretty slick. Is it that it never did work well enough, or rather that it is not practical to make it work for a kit that goes on different bikes? If someone is willing to tweak it for their particular bike, can it be made to work well?

With a single swingarm, it seems easy to install & replace a piece of inner tube over the motor can. Is that recommended for some applications?

How much power can you get out of this setup? I recall someone made one with an 80mm motor. That must have been several kW. I was thinking of going with a low kV 63mm, possibly reterminated to wye, with 12s lipo. The SKS motors claim over 2kW. Is that remotely realistic for a friction drive? I don't need to go fast, but I have a big hill.

Thanks & good luck.

 

[Kepler]

The drive is designed specifically for an English 68mm BB with screw in bearing cups. This wont change.

At this stage, I am offering only the drive mechanics and allowing people to buy their own controllers, motors, batteries. This keep the drive at its lowest price point. I may consider a complete package in the future but not for now.

The spring and torque kick engagement works ok but it is fiddly to setup and in general unreliable especially in an under BB design. Grip tape can help here and is one of the reasons why Adde uses grip tape at the expense of ripping up tires. If you want a reliable drive engagement, it needs to have a mechanical engagement assist. This can be a simple cable pull from a shifter, brake lever, or suspension lockout cable assembly. I am experimenting with an RC servo driven engagement at the moment which might prove to be a viable option. Keep in mind the activation action only needs to make the motor touch the tire and friction will do the rest to pull the motor into the tire.

Power wise, I would guarantee 500W but it is extremely robust so probably 1000W wouldn't be out of the question. I have not tested this level of power though. 500W and you peddling will get you up a decent hill.

 

[cwah]

Do you have to do lots of things to make it run properly? I mean is it:
1. Bike is initially disengaged to the motor
2. You start engaging the motor with lever
3. Once engaged, only then you can use the throttle
4. Once acceleration is done, you need to disengage with the lever

Is it like this at the moment? It would be good if engagement would be triggered by the throttle at the same time.

 

[Kepler]

That is a good point and it does sound like you have a lot of things to do use the drive.

My current setup was using the left hand shifter to pull the motor up to make contact at the same time a microswitch was activated that sent a 4V signal to the throttle input using a simple voltage divider. So one click up on the gear shifter activated the drive and one click down deactivated the drive.

I made up an activation mech that attached to the derailleur mount.



This works really well but I can see that many people will want to keep their front derailleur so I am working on a simple RC servo solution to do the drive activation. It will use a servo tester to drive the servo and just have a button to activate both the controller and servo. Should be relatively simple to do.

 

[Kepler]

The test bike has now had a Shimano 105 5800 50-34 chainring fitted. The latest design drive mech clears everything nicely and allows the front derailleur to operate as it would on a standard road-bike.

So this means I need to use a different drive activation system to get the motor to make light contact with wheel so it can then climb the tire under load. Been working on a simple RC servo to bring the motor in light contact with the tire. This has proved to be very straightforward to achieve.

A cheap $10 metal geared mini servo mounted under the bottle cage and a short length of gear cable was installed between the servo output arm and the drive swing arm. To mount the cable on the servo swing arm I just drilled an accurate hole in the servo swing arm and bent a "z bend" in the cable to secure it,

With the drive deactivated, the cable is slack and has no load on the servo. When activated, the pull force is quite light as it is only lifting the motor until it comes in light contact with the tire. The tire climbing action then takes care of business from there again making the cable go slack and taking all load off the servo.

So far i have just used a servo tester to test the activation. I now need to decide on how i am going to start the controller and drive the servo from one end of its travel to the other with a single push button action. A cheap servo tester will no doubt be used as part process, just need to work out the finer details.

Worth mentioning that if you use a standard RC speed controller, you could use a servo tester with a Y harness and drive both the ESC and servo from the same signal at the same time. This would be a very straight forward solution.

 

[neptronix]

I am not a fan of friction drives but i see how refined this is by watching you all of these years. Maybe we could say you've perfected it, or close to. Hats off, man.

 

[telcosteve]

So awesome Kepler. I was just rummaging through my rc stuff and couldn't find my y harness yesterday. I was about to pull apart a plane. Now I read this. You've already proved what I was wondering. Let me know when your selling your brackets. I have my motor servo tester and controller ready. I really like the servo activation idea. Trying to think of best wiring method to move pot. Or just button and leave servo tester as is then dial in speed of motor hmmmmmm.

 

[Samd]

Its possible to engage the servo as well as the rc BLDC using an arduino nano with pushbutton to ramp the throttle


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[telcosteve]

That sounds like a good way to do the combo. I have zero experience with arduino. I have read a little. Do you have any info on how this setup would work? Thanks

 

[Samd]

Actually do it all in the arduino. Use the servo SWEEP program.


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