Full suspension mountain bike Friction Drive

[Kepler]

With regards to ratios, you mentioned 11:1 with a friction drive which sounds logical. However reduction ratios have no bearing on friction drives. A bike with a 20" wheel will go at the same speed for a given motor rpm and as bike with 700c wheel. And would go at the same speed for a given RPM if the motor was contacting the ground directly. However, the actual diameter of the motor does have bearing on the speed of the bike for a given motor RPM

Ponder that thought for a moment (Clue, the motor sees the tire as the road)

That's true! If we think about two gears separated by an idler then the size of the idler gear has no bearing to the the final gear ratio. The back wheel is just an idler gear between the motor and the road.

I was not thinking of it that way until I read this.

Peace,
Ifishtoo

The wheel in effect being an idler gear is a good analogy. I will remember that one next time I am explaining this.

 

[vreppeto]

I am considering the possibility of gear reduction for a setup similar to yours. I need 5500 to 7000 rpms on my 1996 EV Warrior in order to do about 30kph. These stock brushed motors do this on 24v. According to the following document they are rated at 229kv. http://www.enigmaindustries.com/Motors/Bosch_EV_Warrior.htm . These motors are geared down so to speak since the drive shaft connects to a 32.39 mm drive roller.

I just upgraded my battery to 48v. (15ah and I have it configured for 8s2p 'cause I don't want to hurt these brushed motors.) So when I replace these motors with brushless motors I can run them at 14k to 16k and gear them down for more torque. I do not want to get smaller than 25mm or so for the drive roller because the contact patch between the drive roller and the tire is already so small!!

I don't know. Maybe it is not necessary. How does your setup do climbing hills?

 

[ElectricGod]

This is a cool build!
Totally stealth too.
Probably 90% of people just looking at your bike standing still would ever know it has a motor under the BB and that your "bottle" is small battery pack.

I didn't read the thread...just looked at the pics. I think I'd try to incorporate it somehow into the bike chain instead so that sand paper to tire was not generating loss of rubber and loss of grip between them. Otherwise...I love it!

 

[Kepler]

Thanks,

Most people have no idea the bike is assisted. Noise level is low also so that doesn't give anything away.

With regards the grip material, sound brutal on the tire but with the low power levels I use (up to 300W) the wear is minimal. Trick is to make sure the motor is hard enough on the tire so that there is no slip but not so hard that is caused excessive drag. Current rear tire is at 1500km and will do 2000km easy before replacement is needed.

With regards to using a chain mid drive with a similar motor , controller and battery design , check this thread out.
https://www.endless-sphere.com/forums/viewtopic.php?f=28&t=96769

 

[Kepler]

Made some changes to the motor control so I thought I best document it as part of this thread.

I have been riding with a push button throttle that simply activates the drive at full throttle when held down and deactivates the drive when released. Also have the hall sensors on each brake lever which provide 50% regen each brake lever. This has been working really well but thought I would change it up a bit.

It does get tiresome holding down the button throttle all the time (my poor aching thumb ) so I decided to make it latching. Now holding the button for half a second will latch the throttle on and any short push will deactivate the throttle. To further enhance this, touching any of the brake levers suppresses the throttle to zero but at the same time still provides 50% / 50% regen on each brake lever. As soon as you release both brake levers, throttle is returned.

With the low level of assist offered by this drive, having it activated most of the time feels very natural. In fact it just feels like the bike is very light rather then electrically assisted. I can come to a dead stop using the brakes then thanks to the Vesc's amazing low motor rpm capabilities, take back off as if I was on my 7kg road bike.

Also found that I am creating more regen opportunities with this arrangement. 20% regen is pretty easy to achieve with this setup.

This bike is now doing plenty of commuting duties mixed in with some offload entertainment. Clocked up just over 2000 km on the original friction drive tire which has surpassed expectations considering all these kms are with grip tape on the motor.

Not much to fault with this setup. Sure, it would be nice to have a bit more rear grip on loose stuff but most of the time the hybrid tire works fine off road. Commuting, I am not the fastest but close to it. Only occasionally overtaken by a really quick roadie.

This setup is so nice, I am considering selling my commuting road bike and using this bike as my main commuter.

 

[BenMoore]

Love yr work, as always mate!

 

[Kepler]

A couple of months have passed and I have been using this bike most days. Finally wore out my first tire after 2500km. Although happy with this, I think I would have got more out of the tire if I had set the motor to tire contact more firmly so as to avoid any slip.

I have been debating the pros and cons with using a permanent coupled drive or a disengaging drive. For a mountain bike where brakes are used often, I think the opportunity for regen can not be ignored. For a road bike, I think a disengaging drive makes more sense as the rolling efficiency is so much greater then a mountain bike and you really want to maximize this rolling efficiency as much as you can.

So to the discussion of regen. As previously documented, I have regen activating 50/50 through my brake levers. This has worked well and has given me a usable amount of regen on most rides but I could see I was missing some regen opportunities as the regen is set quite light through the brake levers so my braking action stays smooth. Additional braking is then taken up by the mechanical brakes.

To utilize close to 100% of the braking energy available on a ride I have now retrofitted a dedicated ebrake that provides fully variable regenerative braking sufficient for close to 100% of the bike's braking needs. The mechanical brakes are now only used for emergency braking or braking on technical trails. Even under emergency or technical trail braking, around 50% of the bikes braking energy is captured by the regen.

The ebrake is just an inverted thumb throttle. The normal button throttle is still used which latches either 50% assist or 100% assist (200W or 400W). With the throttle latched on, the ebrake proportionally reduces the amount of assist with 50% ebrake giving zero assist and 100% ebrake giving full regen.

View attachment 2

This gives me lots of opportunities to feather the amount of assist and go into light regen say when coming up to slower riders or when entering a corner. Full regen provides significant braking force, enough for all but emergency braking events.

My 28km commute that I do on fairly flat road normally gave me 15Wh regen (using brake lever activated regen) With a 180Wh battery. That works out to around 8% improvement in range. With the ebrake setup, I have basically doubled this to 15% improvement in range. On top of this, using the ebrake to feather the assist means less power is drawn from the battery for a given ride. Other bonus is that the brake pads now hardy touch the discs.

View attachment 1



On flat roads, range using my 180Wh battery has increased from around 40km to 45km. Keep in mind, the assist is switched on from the time I start the ride to the time i finish the ride so there are no "drive off" periods included in these figures.

 

[espresso]

A build like this is definitely in my future!
Kepler, I know that you said earlier that you didn't like the idea of a drive off the sidewalls of the tyre, but what you have made is basically a flat belt drive. In industrial applications, V pulleys and belts are dominant. I would suggest that a V drive pulley where you are driving off 2 surfaces and you are getting the performance plus of the wedging action may be better?

It would also allow the use of almost any tyre.

 

[Kepler]

Been a while since I have updated this thread.

I am clocking up heaps of kms on this bike as I now use it as my main commuter. Now done just under 6000km on the bike with this current set up. Still on the second tire also.

I have gone away from grip tape completely now and find that the drive will work adequately in wet weather without the need for grip tape. The trick is set the contract to the tire quite firmly and run a reduced power profile when the weather is wet. I can use up to 150W of power in wet weather before I start to see some slip. This is still plenty to take the edge of the ride in relation to pedaling effort.

So the big negative with this system is that you cant use an aggressive knobby tire. This is fine for dry off-road and basically any commuting duties. I love this bike as a commuter. It is super comfortable, completely stealth, and still quick enough to keep up with all but the fastest roadies.

I so want to solve the issue of not being able to run an aggressive knobby on the back of this bike. Also the firm tire pressures required for a friction drive are not ideal out on the tracks.

Currently developing a special roller that will hopefully work with a specific aggressive knobby tire and effectively turn the roller and tire into a gear reduction rather then a friction drive. Still very early stages on this one. I have 3D printed a few protypes with varying degrees of success (and failure). I wont go as far to say that it looks promissing however I do see enough potential in this concept to continue with the development.

 

[tentman]

Hello Kepler - I have been avidly following FZBobs drive along with yours. You guys are inspirational!

How does your drive feel for torque?? I'm a mechanical dunce but is there any multiplication of the motor torque - if so how would one calculate it??

Finally for you last idea, how about splitting the drive cog into two pieces - one each side so it "cups" the tire on both shoulders - this is where the biggest knobs are (although often full of mud but cunning design might enable self clearing) ??

Cheers
Foster

 

[aCeMadMod]

Hi its about time i add my 5 cent

I love work you done over the years


Would be able to share 3d print for new roller wheel ?

Or for a low cost
I like to see made in Ti wheel i think that the key
It grip gpod


Much thank for Au Es work

 

[Howiep]

Hi Kepler,

I've been inspired by this thread for a while as I build up a friction drive for my Scott Spark.

I've been grappling with the tyre issue myself.

First I bought a wide (2.4'') knobby intending to grind away the rubber in the centre and replace with a band of thick inner tubing. This way I'd get a wide tyre with mostly knobs. For anyone thinking about it - grinding/cutting off tread knobs is really messy, hard, and difficult to do accurately. Best I could manage was a bald tire instead of a neatly removed centre section.

I'm really keen to know if your special roller creates much extra noise and vibration? I know from experience it's hard to achieve smooth running unless using perfect volute gear profiles.

Finally, I wonder whether anybody here has considered trying a knobby tyre without intermediate knobs, like this -

. If you made a special roller to go in the groove between the side and centre knobs it could work nicely.

This will be the next thing I try once I sort out some issues with torque sensing. Just putting it out there now in case anybody already has, or wants to beat me to it.

 

[Kepler]

Hi Howiep,

Thanks for joining the discussion. Your knobby removal idea was one of the things I was going to try but based on your experience, I think I will give it a miss and stick with the hybrid tire that i have been using at least for commuting duties.

I have printed the toothed roller and fitted the matching tire to the bike. Unfortunately the tire is too wide for the current mount that I have been using so just in the process of building another mount.

I have selected a very similar tire to what you have shown which also has the clear groves on each side of the knobbys also. This will be plan C.

I should have some testing information to share on the toothed roller method by the weekend. I think it will work but no idea how well. Got a feeling if it does work, it will be unacceptably loud. Still worth a try though.

 

[Kepler]

Howiep,

Noticed also you have made mount that is attached to the swing arm. Can you share some more detail on this?

 

[Howiep]

Thanks Kepler,

I wouldn't have have been able to build mine if it weren't for this thread, so glad I've now made enough progress to add to it a little bit.

For the record I think it would be possible (but still very messy) to abrade a specific section of tyre tread, but not holding the tool by hand. I think you'd need to set up a grinding wheel and bike wheel both on a sturdy jig and treat it like a machining process. But the alternative ideas seem easier, so I look forward to seeing how your testing goes - what a coincidence you have a suitable tyre.


As for the mount - funnily enough I had a Trek EX, but snapped it last year. The geometry of my Scott Spark doesn't afford such good mounting points, and is very complex - not a single straight or constant section of tube. Also my brother-in-law has a delicate all-carbon version, and I want to make one for him too.

So I decided I needed to design a mounting that sits gently over a wide area to prevent any localised crushing/twisting forces on the frame - it gets enough abuse already over at Mt Coo-tha. Luckily I have a friend who can borrow a 3D scanner from work, and access to various 3D printers. This is the resulting scan and first prototype mount I cooked up.



I'm still making revisions - the three brackets are very difficult to get 100% correct to shape even with the scanned data, but it's close and works for now. I'm printing these from thick ABS on a cheap FDM printer. I'll print a final version from nylon using SLS. Someone with a more robust frame could probably make a similar "three point" mounting by fabricating from aluminium and attaching with hose clamps.

 

[Kepler]

That is a complex bracket but looks to be a good solution. I have a new Specialized Stumpjumper Carbon Comp with a similar complicated carbon swing arm. The exciting thing about this bike is that it has a storage system within the carbon frame. You basically have full access to the space within the down tube. Plenty of room for batteries and controller.

This bike is non assist for now but if I can get the knobby drive working, it may become a candidate for future conversion.

 

[Kepler]

Been a while since I have updated this thread.

I am clocking up heaps of kms on this bike as I now use it as my main commuter. Now done just under 6000km on the bike with this current set up. Still on the second tire also.

I have gone away from grip tape completely now and find that the drive will work adequately in wet weather without the need for grip tape. The trick is set the contract to the tire quite firmly and run a reduced power profile when the weather is wet. I can use up to 150W of power in wet weather before I start to see some slip. This is still plenty to take the edge of the ride in relation to pedaling effort.

So the big negative with this system is that you cant use an aggressive knobby tire. This is fine for dry off-road and basically any commuting duties. I love this bike as a commuter. It is super comfortable, completely stealth, and still quick enough to keep up with all but the fastest roadies.

I so want to solve the issue of not being able to run an aggressive knobby on the back of this bike. Also the firm tire pressures required for a friction drive are not ideal out on the tracks.

Currently developing a special roller that will hopefully work with a specific aggressive knobby tire and effectively turn the roller and tire into a gear reduction rather then a friction drive. Still very early stages on this one. I have 3D printed a few protypes with varying degrees of success (and failure). I wont go as far to say that it looks promissing however I do see enough potential in this concept to continue with the development.

Toothed Roller.JPG

Well the toothed roller was big fail. Sounded like a jet taking off. Back to previous setup for now (which works beautifully) and back to the drawing board.

 

[Howiep]

Shame to hear the notched roller was a bust.

Just food for thought - in other gearing applications chevron or helical gears are used to reduce noise, as they provide a constant rolling contact. Reminds me of a few front specific MTB tyres such as the Specialized Fast Trak.

A roller designed around this tyre that makes constant/rolling/overlapping contact with the knobs could be much smoother. I might have a crack when I have some time in a week or so.

 

[briangv99]

Well the toothed roller was big fail. Sounded like a jet taking off. Back to previous setup for now (which works beautifully) and back to the drawing board.

Just an idea Kep, how about cutting out a section of knobby tread with some scissors and bonding it to the motor. Imagine it'd still make a bit of noise, but an improvement over the toothed roller.

Or just run the sand paper with a tyre with wider shorter knobs

 

[Kepler]

Thanks for the input guys, really appreciate the ideas being put forward.

Well, I think I have solved the problem of wide knobby with aggressive side knobbys and slick centre 8)

A while back, I purchased a 2.3 x 29 Maxis Minion tire as I thought it had good potential due to small closely packed knobbys in the centre of the tire.





I then thought of stretching a rubber ring around the tire to act like a retread. So what to use for this rubber ring? Just so happens I have changed the 700 x 32mm slicks on my road bike. Still plenty of meat on them but after 5000km on the roadbike I felt they were up for replacement. Fished them out of the bin and proceeded to cut off the side walls.





I already had this tire fitted to the front wheel of my MTB, so I though I would first use the front wheel as a test bench. Deflated the tire and rolled the modified road tire over it. A bit of effort similar to fitting a tight tire on a rim. Straighten the tire up and inflated to 35psi. The tire inflated nicely without and deformation and the slick outer tire stretched and formed to shape slick centre surface.





Rather then placing it on the back of the bike ready for friction dire duties, I have left it on the front to see how the tire rides and responds. Did my normal 30km commute to work with the modified front tire. The tire worked flawlessly in fact I would go one step further and would say it improved the bike. The bike was quieter and rolled really well. No movement at all of the slick upper tire even through hard cornering.





I am really excited about this and am looking forward to placing the tire on the back wheel for friction drive duties tomorrow.
I am confident this is going to work really well however the unexpected bonus is how well it works on the front tire. When using the bike for commuting duties, adding the sick tire over the top of main tire has the following benefits:
1>Allows the bike to roll faster
2>Makes the bike quieter
3> Save you wearing out your fast wearing knobby tires. Then just remove the slick section for when you are going off road.
4> Better puncture protection due to the double layer of tire.

This is going to open up a bunch of new tire possibilities I would say. 8)

This the tire I am using https://www.chainreactioncycles.com/maxxis-minion-ss-mtb-tyre-exo-tr/rp-prod144796

 

[Howiep]

Sweet idea! Well now I feel pretty silly for spending an hour making a mess ‘balding’ my back tyre with a sander. I had a perfectly good tyre and tube sitting sitting there looking at me the whole time!

But I’m glad to say the side channel roller works beautifully for the few laps of the block I’ve done so far. No slippage or increased noise even at 500w. Hopefully it stays working.

I’m using a Specialized Slaughter 2.3 tyre. I had to cut the very corners off the inside knobs with some wire clippers, but no other modifications.

It’s fiddly to set up, I’d definitely recommend making the roller in one piece instead of two as I did. I also expect you’d know pretty fast if you’ve got a warped wheel.

Still, I was pleasantly surprised, as there’s only about 7mm of contact overall. You could increase this if you Kepler’d the groove with some rubber.

 

[Kepler]

Great work. No off road performance compromise with that roller setup. I agree, a one piece roller would be easier to setup and not too difficult to make. The small contact area on a part of the tire that isn't designed for road contact might wear out the tire prematurely however lets test this first before jumping to conclusions. As you mentioned, a strip of rubber in each groove like my last idea might be a worthwhile future addition.

In regards to my last setup, this was 50% successful. No problems with drive or performance however noise was an issue as the profile of the small knobbys under the slick centre still gets partially transmitted to the roller.

So removing the centre knobbys is still required if you want it to be as quite as possible. Thinking of a few simple ways of doing this. One thought is to fit a stationary roller with sandpaper attached where the motor usually goes and then just ride the bike around the block. Adjust the contact pressure and repeat until the centre knobbys are removed. Can also make the stationary roller concave in shape to match the profile of the tire.

I am liking that we now have some new options for the much maligned and under estimated friction drive.

 

[NateTN]

I'm curious how loud your knobbies really are compared to the tire I'm running as I find mine acceptable (its a Kenda Konniption for around town shenanigans).

Here are some pictures of my current setup in testing (6384 120kv motor, waterjet bracket, vesc/battery water bottle holder).








I'm very happy with this setup so far, I've mostly been riding with it set to 250w but this ride was at 750w. Thats using the wattage limit in the vesc tool and a current setting of 40/-20 motor and 40/-20 battery. I'm running the batteries in series for 2650 mah in 8s. I was initially concerned about the limited capacity but its actually been great, it forces the rider to focus on consumption which can be very entertain, and with the 750w setting you can still blast around if you need to.

Currently, if the throttle is under about 10% its in constant regen, so there's no completely off which has a learning curve, but... Everyone I've let ride it has tried to buy it so I guess thats saying something.

I've one friend thats interested in this as added resistance for training (pedal against the regen to charge a small battery) and then a boost home, I never would have thought of that!

Also, It hasn't changed the feel of the bike at all, picking it up and carrying it feels the same.

As for the between the tread rollers, I had some similar ideas that I haven't drawn up yet, I'll do that and report back. I'm concerned about accelerated wear but that could be tolerable. I'll just have to print something off, slap the dirt tires on and see I guess!

Oh and Kepler, I believe you were curious about my comparison of this and the single chain reduction setup. I'll be writing up a reply to FZbob's thread but I will say this, they're completely different animals and I'll be sticking with the friction drive for now.

I have some ideas for an extremely compact belt setup but I'll post about that once I start making parts.

I'm also working on a handlebar control with a tiny oled display, I'll post about that when I've made more progress.

cheers and good work guys!

Nate

 

[Kepler]

Very nice setup. So i presume you are using a normal ebike throttle or thumb throttle then? That's a good way of ensuring you make the most of the available regen. This is the only ebike setup I have used that has a usable amount of regen capability. You are achieving 25% regen which is really useful when using such a small battery. I typically regen about 15% but have managed up to 50% on really hilly rides.

What App is that by the way?

With regards to tires, I think the key to quiet operation is to have no tread gaps for the roller to fall into. If that tire you are using is quiet on the roller, I would say the above would be the case.

I think this setup has so many positives and very few negatives which is why I have been persevering all this time with this system. At this stage, for me, improving tire choice is really the last big hurdle. However, with our collective efforts, I think we are close to have this issue solved also.

And regen, what a bonus this has been for this system. Great having the extra range but also practically no wear to brake pads anymore.

 

[Kepler]

Meanest Hybrid tire ever







Ended up removing the centre knobbys with a file sander. This made the job nice a quick. With the slick over the top, the drive is nice a quite again.




Tire has great grip when cornering on loose stuff. Perfect for road gravel, and relatively dry single track.