Full suspension mountain bike Friction Drive

Discussions related to motors other than hub motors.
This includes R/C motors, botttom bracket, roller and geared drives.
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Kepler   1 GW

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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 02 2018 7:03pm

urga,

Sure, if you can attach the drive to the swingarm, no need for the complication of the pivoting system i have designed here. However most modern mountain bikes have hydroformed swingarms that have complicated shapes that give you little option for mounting. Other consideration is if you mount it to the swingarm, the motor becomes unsprung weight. Probably not an issue with the motor so close to the BB but still a consideration.

I agree a chain driven system with the weight and stealth of this system is the holy grail. Believe me, i am thinking about it. So many negatives though. You cant get away from a reduction system. Even with the lowest kv RC motor and say a 4S battery, you still need a minimum 10:1 reduction. Your thoughts of using a 52 tooth chainring would probably at best be good for a 5:1 reduction. And then you have less ground clearance then i have now. Add a double reduction and you introduce bulk, complication, and noise.<br/>

I find the friction drive path so inviting because it removes all these complications. Sure there are other issues to solve but not too many now.

I thought the tire was going to be a major issue but it has turned out to be fine. Sure, for an extreme rider, its not going to cut it, but extreme riders aren't interested in assist anyway.
I ride reasonably hard and quick and still had all the grip i needed. Bonus was that the bike peddled really well with that tire. Noticeably better then with an aggressive knobby.

I am looking at ways to get the motor tighter up on the swingarm and perhaps going to a 50mm motor. Also have some ideas on reducing the size of the battery/ ESC combo.

So for now my focus is on making this friction drive the best it can be. :)
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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 03 2018 7:37am

So a bit of change of direction (thanks to urga). As much as liked my pivoting design, it did make sense to attach the motor directly to the swingarm. Managed to fab up a funky "J" shaped bracket that wraps around the back of the swingarm and attaches to shock mount. this design keeps the motor permanently in contact with the tire however I have found that the drag is so minimal, you hardly feel it. As a point of reference, the video I posted a few days ago had the motor in permanent contact with the tire.

The permanent tire contact also gives me the opportunity to experiment with with some regen braking which the Vesc does really well.

I am also testing some new hardware with this design. I have gone to a 50-65 270 kv motor mainly to improve ground clearance. The picture below has the new motor actually fitted and sits higher then the chainring now.

Also i have a new mini Vesc to test. This Vesc is half the size of the standard 4.2 Vesc with exactly the same power rating and features. It also has a built in heatsink which should assist with cooling especially in enclosed spaces. This has allowed me to fit the vesc inside the tool bottle together with the battery, Arduino interface, and Bluetooth interface. If I am happy with the overall performance, the plan is to build a second bottle battery with its own vesc built in. So rather then just changing the battery, you change the entire power and control unit. Vesc's are quite cheap now so its not a big investment to double up on controllers.

One other advantage is that this combination strips off a little more weight with the total weight of the drive system now being just 1500 grams.

Will have it ready for the weekend to continue testing.
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Re: Full suspension mountain bike Friction Drive

Post by urga » Oct 03 2018 10:39am

That's spooky because I've just ordered a mini vesc from Flipsky (same one? ) I too am trying to get everything inside a bottle(albeit I'm hoping to custom build the battery from cells) with a socket at the bottom for quick change overs.I imagine the permanent drag is of no consequence on a mtb's fat rubber anyway.Is there any chance you could post a drawing of your mounting method,John? I use Sketchup for my work and could maybe use the pics to draw up a model. The smaller motor seems a good move also as the single chainring doesn't give you as much cover as a 2x.What I love most of your setup is you can hardly tell it's assisted.VERY cool
Scooterman,I'm still tempted to have a go at crank driven setup. I'm not getting why you need a 10:1 reduction on a low KV motor with a 34T to 9T ratio from crank to motor?I also understand that you can limit the throttle settings on the vesc for soft startup and limit the ERPM of the motor. Surely it would be possible to tune the motor to start softly and never go above whatever your natural cadence is? ( mine's 90rpm on the road)I agree though you do need a good bit lower offroad. However,I would be using this for climbing only and asI like to spin up climbs I would be happy with the high cadence. I also think that rather than complicating the design with clutches and gears etc,it would be better to use the assist only where suitable. A bit of a compromise I know ,but I really don't want to just power up climbs as some of the E bikes can.This motor here looks tempting:https://alienpowersystem.com/shop/brush ... 0kv-1700w/
and :https://alienpowersystem.com/shop/brush ... 0kv-1800w/
The latter has huge torque for a 50mm 60KV motor.
If I had more engineering skills...........

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Re: Full suspension mountain bike Friction Drive

Post by urga » Oct 03 2018 10:43am

John,can this Bluetooth module be used ? https://flipsky.net/collections/accesso ... rd-ws82013 ie with the metr app?

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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 03 2018 4:46pm

Not with the Metr app but you can monitor while riding with the Vesc Tool using the Real Time feature in the app. Unfortunately the RT readout isn't optimized for reading stats while riding unless you have really good eyes. I need my reading glasses to see whats going on but I am old :(

There might be another app already available though to use this interface to monitor. You do need to be careful using other apps though. I tried using another app with the Metr Bluetooth interface and it bricked the controller.
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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 03 2018 5:41pm

urga wrote:
Oct 03 2018 10:39am
That's spooky because I've just ordered a mini vesc from Flipsky (same one? ) I too am trying to get everything inside a bottle(albeit I'm hoping to custom build the battery from cells) with a socket at the bottom for quick change overs.I imagine the permanent drag is of no consequence on a mtb's fat rubber anyway.Is there any chance you could post a drawing of your mounting method,John? I use Sketchup for my work and could maybe use the pics to draw up a model. The smaller motor seems a good move also as the single chainring doesn't give you as much cover as a 2x.What I love most of your setup is you can hardly tell it's assisted.VERY cool
Scooterman,I'm still tempted to have a go at crank driven setup. I'm not getting why you need a 10:1 reduction on a low KV motor with a 34T to 9T ratio from crank to motor?I also understand that you can limit the throttle settings on the vesc for soft startup and limit the ERPM of the motor. Surely it would be possible to tune the motor to start softly and never go above whatever your natural cadence is? ( mine's 90rpm on the road)I agree though you do need a good bit lower offroad. However,I would be using this for climbing only and asI like to spin up climbs I would be happy with the high cadence. I also think that rather than complicating the design with clutches and gears etc,it would be better to use the assist only where suitable. A bit of a compromise I know ,but I really don't want to just power up climbs as some of the E bikes can.This motor here looks tempting:https://alienpowersystem.com/shop/brush ... 0kv-1700w/
and :https://alienpowersystem.com/shop/brush ... 0kv-1800w/
The latter has huge torque for a 50mm 60KV motor.
If I had more engineering skills...........
Keep in mind, motor RPM is kV x Voltage so a 200kv motor on 24V = 4800 RPM. We are looking for at best 120 RPM at the crank. So a 34T to 9T is a ratio of 1:3.7 reduction. This brings the RPM down to 1200 RPM. To turn the crank at 120 rpm, we need to run a the speed controller at a duty cycle of 10% and duty cycle of 5% for a more practical 60 rpm. No controller will survive for long pushing usable amps at that duty cycle.

However, all is not lost and perhaps we can do this with a 50kv motor on 24V and single reduction of around 10:1.

So we now have 50kv x 24V = 1200 rpm. then a 10:1 single reduction with 120 rpm now at the crank. The Vesc has no problems at a 50% duty cycle or even a bit lower so no problems tuning the crank at 50 rpm.

And now the engineering.
So the mount is easy and can be mounted up nice tight in a similar position to my latest bracket but using the ISCG-05 mount.
In regards to the drive system, I would consider using a #25 chain and sprocket combo. This will keep the sprocket diameter quite compact and should be plenty strong enough to handle the power output of this motor combo.

Keeping it simple,the motor would be connected direct drive (via reduction) so the cranks will turn on there own with the drive is activated and when free pedaling, the motor will be driven. Not sure how much drag this will place on bike when pedaling but it may well be quite minimal. However, if the drag is too great, I would consider using a sprag clutch on the motor side. This wont stop the pedals turning under power but would remove the drag on the system when free pedaling.

So it looks like there might be another project in my future. :D Best I finish this one first.
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Re: Full suspension mountain bike Friction Drive

Post by Hillhater » Oct 03 2018 8:04pm

My limited experience of "off road" riding tell me you dont get far along a trail befor you have to hop over a log, or rough section of rocks. Inevitably the bottom bracket gets a bashing no matter how careful you are.
Water splash's or crossings are also common, and i am not talking about any serious downhill sillyness !
Your bbracket mounted FD is ideal for stealthy street bikes, especially now you can get battery and controller in a bottle pack, but i might suggest the mountain bike /off road application dictates different requirements
So if you are going to design a new mid/crank drive for a "offroad" /mountain bike, i would strongly suggest you consider siteing the motor inside the triangle or even higher if possible. :wink:
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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 03 2018 10:38pm

Ground clearance on a MTB was a major consideration and one of the reasons I went to a new design that got the drive up closer to the BB. It is now high enough so that chain ring (which is only a 32 tooth) will hit well before the drive gets a knocked. with the ground clearance available on modern mountain bikes, if you are hitting the chain ring, you are on some seriously gnarly terrain. I may add a bash guard also with this design just to make sure the drive stays protected. After all it only take one rouge rock to sneak up on you spoil your day.

Mud and water are not a problem. these motor will run under water and the electronics are now perfectly sealed in the tool bottle. Got to say, I think I am close to having all bases covered :)

With a mid drive design, actually no choice but to mount the motor up high. Looking a bit more closely at the how a mid drive could be laid out it became quickly evident that there wouldn't be enough distance between the chain ring sprocket and the motor sprocket if the motor was mounted under BB.

I have a feeling also that the mid-drive design would be disappointingly noisy. The other day when testing my friction drive off road and coming across the Bosch power MTB, I was really quite surprised how much more quite my drive was compared to the Bosch.
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Re: Full suspension mountain bike Friction Drive

Post by ScooterMan101 » Oct 04 2018 5:56am

Kepler where can we buy this mini Vesc ?

Cost with shipping ?
Kepler wrote:
Oct 03 2018 7:37am

Also i have a new mini Vesc to test. This Vesc is half the size of the standard 4.2 Vesc with exactly the same power rating and features. It also has a built in heatsink which should assist with cooling especially in enclosed spaces. This has allowed me to fit the vesc inside the tool bottle together with the battery, Arduino interface, and Bluetooth interface. If I am happy with the overall performance, the plan is to build a second bottle battery with its own vesc built in.
My first conversion ...

https://endless-sphere.com/forums/viewt ... 1#p1077497

It's 2018 already, lets get some real , improved e-bike / e-velomobile / e-motorcycle designs .

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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 04 2018 6:12am

From here. https://flipsky.net/collections/new-acc ... er-ebike

I have been testing one of these today. So far so good.
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Re: Full suspension mountain bike Friction Drive

Post by ScooterMan101 » Oct 04 2018 6:24am

Kepler,
I also think that when using a RC motor on a Full Suspension Bike for a mid-drive that drives the crankset and thereby also drives the rear cogs on the cassette ,
that
the motor and reduction stage , should be located up in the front triangle of the bike above and a little forward of the crankset.

My idea, is to make the reduction , that is located between the cog on the motor and the crankset, to have that reduction use a standard large chainring, from 42 tooth and up . this would keep the final cost of the drive much lower than the systems that use expensive custom machined parts.
This Mid chaingring can be put on a jack shaft .

Also I wonder about on that jackshaft that has the chainring on it , that a freewheel is on it, the chainring connected to the freewheel. The same freewheel that is used on freewheeling cranksets. Which can be bought from a number of places. like Luna, Sick Bike Parts, Cyclone , etc. What would that do ? and/or is it even necessary ?

But I am ready to just buy the I SIS BB and Freewheeling Crankset that places like Cyclone sells. Until someone can make a more modern crankset freewheeling .

I do not have to worry about noise too much since I will be riding mostly on the road with noisy cars and trucks , Besides the motor can be put in a can, with sound absorbing materiel and a small fan on one side to draw out heat .

I do have a lower cadence than most avid and very fit riders. More like the majority of recreational riders.

I do not have to worry about keeping the speed low, since I will be on roads with traffic going over 60 kph and more. So do not need as much reduction, except for keeping the cadence low. But then a freewheeling crankset would take care of that anyway .

Kepler wrote:
Oct 03 2018 10:38pm

Mud and water are not a problem. these motor will run under water and the electronics are now perfectly sealed in the tool bottle. Got to say, I think I am close to having all bases covered :)

With a mid drive design, actually no choice but to mount the motor up high. Looking a bit more closely at the how a mid drive could be laid out it became quickly evident that there wouldn't be enough distance between the chain ring sprocket and the motor sprocket if the motor was mounted under BB.

I have a feeling also that the mid-drive design would be disappointingly noisy. The other day when testing my friction drive off road and coming across the Bosch power MTB, I was really quite surprised how much more quite my drive was compared to the Bosch.
My first conversion ...

https://endless-sphere.com/forums/viewt ... 1#p1077497

It's 2018 already, lets get some real , improved e-bike / e-velomobile / e-motorcycle designs .

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Re: Full suspension mountain bike Friction Drive

Post by urga » Oct 04 2018 11:47am

Googles 'Sprag clutch' :?
I was thinking of modifying a single speed freehub,but these are much better!
Scooterman, is this the kind of thing your thinking of? http://www.chainreactioncycles.com/hxr- ... d|575489UK
John,just so I'm clear.......14.8V 4S cell on 50KV giving 740RPM with a 1:3.7777 reduction(34T:9T) giving 196rpm at the cranks.Running the Vesc @ maybe 40% duty cycle should have my wee legs spinning @78 rpm ? I could live with that cadence,but can the Vesc live with a 40% duty cycle ? The cell mentioned above is off the shelf from HK and I can go up to 16000mAh but would probably use the 8000mAh one,because it's a little more bijou.
Just hoping I can avoid reduction and therefore simply introduce a cog directly connected to the motor mounted ,as you say, via the ISCG-05 mount and driving the chain after the crank. I'm also thinking I would need to introduce the chain keep back into the mix as well. I wouldn't want a dropped chain with this setup.
Just thinking last night that in some ways pedal assist seems to suit mtbing more(albeit with more engineering challenges) as a lot of younger guys hate the climbs and love the descents.I'm old school and don't mind pedaling up, but ,a little assit may help prevent me from blowing out of the wrong orifice.

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Re: Full suspension mountain bike Friction Drive

Post by ScooterMan101 » Oct 04 2018 12:59pm

No that is not the freewheeling crankset I was think of, however that is a good find, I like that there is an option to the Square Taper, and I SIS type of BB/Cranksets.
At that price of $ 432 I would just buy a freewheeling crankset from a vendor,
here are a few parts to make your own from SBParts

http://sickbikeparts.com/bottom-bracket ... 48mm-isis/

http://sickbikeparts.com/cranks-freewhe ... crank-set/

http://sickbikeparts.com/freewheel-spider-5-arm-130-mm/
or
http://sickbikeparts.com/freewheel-spider-5-arm-110-mm/

http://sickbikeparts.com/front-freewheel-heavy-duty/
or
http://sickbikeparts.com/front-freewhee ... eavy-duty/

This is how most DIY , use a freewheel crankset on their mid-drives.

When the price of the one , or others like it , that you link to comes down then that will become more common .

urga wrote:
Oct 04 2018 11:47am
Googles 'Sprag clutch' :?
I was thinking of modifying a single speed freehub,but these are much better!
Scooterman, is this the kind of thing your thinking of? http://www.chainreactioncycles.com/hxr- ... d|575489UK
My first conversion ...

https://endless-sphere.com/forums/viewt ... 1#p1077497

It's 2018 already, lets get some real , improved e-bike / e-velomobile / e-motorcycle designs .

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Re: Full suspension mountain bike Friction Drive

Post by Hillhater » Oct 04 2018 6:12pm

urga wrote:
Oct 04 2018 11:47am
.......14.8V 4S cell on 50KV giving 740RPM with a 1:3.7777 reduction(34T:9T) giving 196rpm at the cranks.Running the Vesc @ maybe 40% duty cycle should have my wee legs spinning @78 rpm ? I could live with that cadence,but can the Vesc live with a 40% duty cycle ? .....
Hmm, 78 rpm @ 1:3.77 would have the motor under 300rpm at max speed !
(100-200rpm "normal" running ?)
Without knowing the details of that motor, i would suspect that rpm is way out of its efficiency band, probably generating more heat than power. ?
There is a reason why most of the commercial mid drives have reductions of between 20:1 and 40:1 ..even when they are using custom designed, motors..
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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 04 2018 7:42pm

I agree, need more reduction for any chance of efficiency.

My selection would be a 6355 60kv motor
https://alienpowersystem.com/shop/brush ... 0kv-1700w/

I would use a #25 9 tooth on the motor and an 80 tooth on the chainring. Lots of cheap #25 running gear option out there including freewheel adapters and idler sprockets to use as a tensioner.

I would go 5S. With an 8.9:1 reduction, we are now down to 120 rpm at the crank at 100% duty.

This would be my personal starting point. No idea how well it would work but I think there is potential there. :)
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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 04 2018 8:25pm

Up date on on the friction drive setup.

The 5065 motor was a disaster. So noisy even when not under power. So back to the 6355 motor. So much better. Luckily I left enough meat on the bracket to fit the bigger motor.

The bigger motor it mounted up nice and tight and has great ground clearance. Drag on the bike when not powered is minimal and hardly noticeable. This setup is ultra robust and will need very little maintenance.

The bottle battery with the built in Mini Vesc, Ardunio interface, and bluetooth interface I think is keeper also. I like the idea of rather then carrying a spare battery, I will have a spare power unit with me as a backup. I needed a long skinny battery for this setup and has an old 5S 5800 mah Zippy Compact laying around so the power unit was built using this battery. I can fit a 6S 6200 mah Zippy Compact in the bottle with the rest of the geat and now have one of these packs on order. Total weight of the unit is 750 grams which is the same weight as if the bottle was filled with water. Motor and bracket came in at 650 grams for a total conversion weight of 1400 grams. Total weight of this bike is 16.5 kg (36lb)

Commuted to work today on this bike. 27 km, used 90% of the battery, and average a comfortable 28 kph. No super fast but still quicker then most of the commuters out there. I forgot how comfortable it is to commute on a big dual suspension mountain bike.


Capture.PNG


Some interesting observation running 5S.

With the 6355 190 kv motor, max speed at full assist amps (set at 10A) was around 32kph. Above this, the assist would start to taper off and the amps would reduce. at 35kph, the assist amps halved. Still enough to maintain speed with a bit of effort.
When going down hill and heading towards 40kph plus, with the throttle activated, the system would go into regen unto a max of 10A. I had never seen this before as I always used 6s or 7s with higher kv motors and never reached a speed threshold above 100% before. Also I would always deactivate the drive if going down hill at high speed.
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Re: Full suspension mountain bike Friction Drive

Post by urga » Oct 07 2018 9:39am

Interesting. Could that regen threshold be modified via the vesc,or it's inherrent to the KV of the motor and V input?
The more I begin to understand about using outrunners the more I can appreciate why you pursued the FD method. The 11:1 reduction circumnavigates the main problem I'm having getting my rpm down. The more I look at using gears etc the more I'm put off . I like the FD system because of it's 'simplicity' and lack of clutter on the bike. It gives me more than enough assist( done a 42 miler with a cat 2 climb @18mph ave with 3850ft climbing ,and still had juice left in a 8AH battery!) for my needs and the bike hasn't taken on the frankenstein look of most of the mid drive/geared systems I've seen.
So although I've given up before I started,I still might be converting my gravel bike to a FD.The terrain I ride on this would suit the FD perfectly.Can I ask whether you have any intensions of producing the mounting bracket with a larger dia for us poor BB30 chaps out there?
No big deal but it would save a bit of time with the Dremel.

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Re: Full suspension mountain bike Friction Drive

Post by ScooterMan101 » Oct 07 2018 12:32pm

Andre did this on his 2013 Specialized Secteur Expert ,

on page 14 , about 20% down the page look closely at the picture of the BB, notice how he made a great looking thin clamp that bolts around the BB shell of the bike. That the plate is then bolted onto with three bolts/allen machine screws.
not in the picture because the plate is hiding it is , probably , a second bolt so the clamp is in two crescent shapes with one side larger than the other . From an Engineering standpoint I wonder if that makes a stronger clamp ?

viewtopic.php?f=28&t=84905&start=325


urga wrote:
Oct 07 2018 9:39am


Can I ask whether you have any intensions of producing the mounting bracket with a larger dia for us poor BB30 chaps out there?
No big deal but it would save a bit of time with the Dremel.
My first conversion ...

https://endless-sphere.com/forums/viewt ... 1#p1077497

It's 2018 already, lets get some real , improved e-bike / e-velomobile / e-motorcycle designs .

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Re: Full suspension mountain bike Friction Drive

Post by urga » Oct 07 2018 1:47pm

Yes,I seen that post. I was worried that this wouldn't be suitable on a carbon frameset as they advise against clamping forces here.I loved what he did with the rest of his setup.I used Kepler's mounting bracket which worked fine after some machining,albeit I now have a creaking BB,which ,ironically it never did before fitting the convertor! I didn't use Loctite initialy as I had to mess about with the settings quite a bit,but once I was happy I marked it up and refitted it with Loctite. Stills creaks but hey ho.....it's an old framset so there may be some wear in the interface.

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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 07 2018 7:52pm

urga wrote:
Oct 07 2018 9:39am
Interesting. Could that regen threshold be modified via the vesc,or it's inherrent to the KV of the motor and V input?
The more I begin to understand about using outrunners the more I can appreciate why you pursued the FD method. The 11:1 reduction circumnavigates the main problem I'm having getting my rpm down. The more I look at using gears etc the more I'm put off . I like the FD system because of it's 'simplicity' and lack of clutter on the bike. It gives me more than enough assist( done a 42 miler with a cat 2 climb @18mph ave with 3850ft climbing ,and still had juice left in a 8AH battery!) for my needs and the bike hasn't taken on the frankenstein look of most of the mid drive/geared systems I've seen.
So although I've given up before I started,I still might be converting my gravel bike to a FD.The terrain I ride on this would suit the FD perfectly.Can I ask whether you have any intensions of producing the mounting bracket with a larger dia for us poor BB30 chaps out there?
No big deal but it would save a bit of time with the Dremel.
The regen is dependent on the kV of the motor and the set voltage. If I was using a 6S battery or a higher kV motor, I wouldn't have seen the regen happen. You can of course can set the the max regen in the Vesc with the regen then being variable via the ppm signal input.

I think regen may have some potential with this setup especially off road when doing lots of decent. Still thinking on how I would control it. A micro on the brake lever might be an option or a second button on the opposite grip to the button throttle.

Glad you get why I have persevered with FD for so long. I think for low powered applications, the positives well out weigh the negatives now compared to other available systems.

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 :D (Clue, the motor sees the tire as the road)
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Kepler   1 GW

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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 07 2018 8:12pm

urga wrote:
Oct 07 2018 1:47pm
Yes,I seen that post. I was worried that this wouldn't be suitable on a carbon frameset as they advise against clamping forces here.I loved what he did with the rest of his setup.I used Kepler's mounting bracket which worked fine after some machining,albeit I now have a creaking BB,which ,ironically it never did before fitting the convertor! I didn't use Loctite initialy as I had to mess about with the settings quite a bit,but once I was happy I marked it up and refitted it with Loctite. Stills creaks but hey ho.....it's an old framset so there may be some wear in the interface.
A use a similar clamping method on my carbon road bikes. Trek use a BB90 bottom bracket. The clamp is against the carbon outer of BB however the crushing force of the clamp is distributed through the carbon fibre to the bottom bracket bearing so it not actually putting much load on the outer shell of the BB.

Unfortunately this bracket is very hard to make as the carbon BB outer shell has a slight taper and the taper varies around the the circumference of the BB. So the clamp is first machined then hand filed and fitted to suit the varying taper. Very much a one off custom process.
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urga   10 mW

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Re: Full suspension mountain bike Friction Drive

Post by urga » Oct 08 2018 5:36am

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


To my non engineering mind it is EFFECTIVELY a reduction via rear wheel dia/cog and crank and then ultimately my leg speed ?
Let's say the 63mm motor is running at 5940rpm(22V @ 270kV) the 700mm rear wheel will be running at 534.6rpm on the road. The motor would then cover 1.17km/min linearly and the rear wheel would also cover 1.17km/min This is irrespective of the wheel size since the motor's 1.17km/min will always be realised via whatever rear wheel size it's contacting ie a 20" wheel would also cover 1 .17km.It's rpm would be higher though , and thus I would regard this as a lesser 'reduction'.
From a cyclist's point of view, the small motor driving the larger rear wheel is the same as a small cog driving a larger cog.
No doubt I'll get my knuckles rapped for this :oops:
I can undertand what you mean with the carbon BB as they all are moulded and lack any kind of flat surface on which to purchase against. I would also be worried about overtightening and binding the bearings,or worse still stress factures. They are overbuilt though because of all the forces that are transmitted through them.

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Kepler   1 GW

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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 08 2018 6:40am

Basically right. Easiest way to think about it, a 63mm diam motor will roll out approx 200mm for each revolution. So anything that motor is pressed up against will also move 200mm for each motor revolution. :)
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Re: Full suspension mountain bike Friction Drive

Post by Kepler » Oct 09 2018 7:58pm

I received the new 6.2ah Zippy compact and have fitted this into the tool bottle. It was a tight fit and didn't leave much room for the Vesc. To get the vesc to fit, I re configured the board layout so that the large capacitors now sit on top of the circuit board rather then in line. Also trimmed off the mounting lugs on circuit board and round the corners. A tight fit, but managed to get everything in.

20181010_111158.jpg

Also blinged up the motor mounting bracket with some fake carbon fibre. I think I will just paint it mat black or get it anodized as it is less noticeable now that it is a dark colour.

20181010_064743.jpg

Rode the bike to work again today. Performed so well. You can't even hear the drive above the noise of the knoby front tire. Used about 80% of the new battery for 27km and averaged 29kph.

20181010_074629.jpg

I am completely satisfied with the motor mount. I redesigned it with a larger diameter at the motor attachment point so that the motor is now more protected from ground strikes. It mounts with a single 8mm extension bolt from lower rear shock mount and can be removed from the bike in about 20 seconds if not needed..

I still want to refine my tool bottle battery setup but I think the concept is sound.

Next thing to experiment with is regen. I will have this up and running tonight.
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falcongsr   1 mW

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Re: Full suspension mountain bike Friction Drive

Post by falcongsr » Oct 09 2018 10:54pm

Nice work! Are you charging at work for the ride home with that supply on your desk? Are you using any kind of balance circuit?

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