Recommendations for Carbon MTB Conversion

[skelinger]

Hi all this is my first post here on the forums but I have been visiting the forum for fair while as its a great source of ebike technical info.

Last year I started the first stage of my build by putting together a carbon hardtail 29er.


I since moved to Norway from Australia and have just had it shipped, so time to continue the build.
My main goal with this build was keeping the bike as light as I could while not sacrificing too much on the sturdiness as I like my trails. Frame is generic chinese carbon LTk023 / FM056 you all probably know the one. 10 to 1 SRAM drive train and some nice hard sun ringle rims running tubeless.The whole bike is sitting at about 10.2 kg at the moment.

My initial plan was to set this up with small hub motors front and rear. The idea behind this was instead of one single larger (heavier) hub on the rear I would split the torque over both wheels. I'll be riding this in winter here in Norway and having increased traction on both wheels will greatly assist me through ice and snow and steep climbs on trails as well. Another benefit would be a more balanced weight distribution.

I have been on the look out for over a year now for the lightest hubs motors I could find, but its been difficult matching motors with the right controllers and just choosing the right type of motors to begin with.
I'm a programmer by trade so I'd like to think i'm fairly technically minded and i'm also good with electronics too. Thus putting together a fairly customized setup is not out of the question, but available time to dedicate to this could be problem.

Things I would like from this build:
* All components must be water tight (Lots of snow)
* Hubs and controller must be as light weight as possible
* Hubs must allow for disk breaks.
* Toque over speed is preference
* Left hand throttle (I have a gripshift on the right)
* Prefer to have freewheel over regen but if there is a way of achieving both id really happy.
* Id like to have a way of toggling between peddle assisted and fully powered modes.
* Anyone know of a throttle that I can trigger regen from pushing the throttle to a forward position.
* Compact battery (A lower capacity bottle shaped one maybe?) I don't require huge ranges, ill be running pedal assisted almost always.

I would really appreciate some recommendations based on these dream requirements of mine. Let me know any concerns you have with my ideas, problems i'm over looking . Any input is greatly appreciated!

I'm planning on this build to be done within the next 3 months if I can. I'm sure you'll all see me asking questions on this forum a lot from now on!

 

[Drunkskunk]

Almost every hubmotor uses a freewheel, where you have built that to use a CST, so your choices are extrtemely limited. I think Bafang makes a CST, and the Andana Cute Q140, which is also the lightest option. they are geared motors, so no regen.

You can't have a freewheel motor and regen. If the wheel is spinning free of the motor, then it can't be turning the motor to regenerate power.

Torque costs weight with hub motors (big motors, powerfull batteries), but there aren't any good torquey options for CST drivetrains, so thats a moot point.

A front motor on a carbon fork is like playing Russian Roulett with an automatic. The dropouts and legs were never designed for the twisting forces the axle will place on them. Get a steel fork if you want a front motor. The lightest hub motor is 3.5KG, so adding 100 extra grams for a far stronger front fork will cost you nothing you will ever notice.

Those motors can accept disk brakes.

 

[skelinger]

Thanks for fast reply! Sorry should have mentioned by forks are alloy, Rockshocks Reba RL. Everything else is carbon.

I also I understand regen and freewheel cannot coexist, what I was referring too was the possibility of a clutch allowing the hub to toggle between a freewheel and regen state. I have read about such a setup at a few places but have no real knowledge of a particular product to back that idea up. It was along shot... I know.. That kind of setup would require a lot of re-engineering to the wheel increasing the width making it most likely incompatible with standard drive trains.

I've looked into the Bafang CST previously, but found it to be heavier than id like. Also specs say it supports 8 and 9 speed cassette, i'm not sure how meaning full this is as a 10 speed should still fit if the 9 does. Any advice on that would be great as I really want to hang on to my 10 speed.

I've seen the cute motors around as well but not anything matching Q140 model number though.

 

[MadRhino]

With this carbon frame, I suggest building a mid drive.
It will not survive the forces from torque and regen of a hub motor, unless it is very low power.
Building low power and to want torque, keeping weight as light as possible, means you want to use the gears.

Another solution would be to build friction drive, why not front and rear if you want 2wd.

If you really want to build torque with hub motors, use another frame.

 

[hjns]

I would also be very careful about the rear dropouts. Usually with carbon frames, the dropouts are steel that is fixated with only the human power in mind to apply forces using the chain. The dropouts in a carbon frame are definitely NOT enough for the torque of any hubmotor over 250W. The carbon tubes are also NOT designed to withstand forces from a regular torque arm that we would usually put into place to keep the axle from a hubmotor from rotating within the dropouts. This all speaks for a midmotor or GNG design.

However, if you want to stick to the near noise-less low-weight hubmotor version, there is nothing that would stop you from putting the smallest hubmotors in the front and in the rear, taking into account that the carbon may brake. For the front, two torque arms should keep the axle in place in that magnesium fork. And for the rear, two torque arms that push against a small steel plate over the full length of the carbon tubes should allow you to use a rear hubmotor as well. The two hubmotors combined would weight about 7kg and would be able to get you up any hill that can be conquered by 500W motors with your weight.

I like light weight carbon, and I like hubmotors. Forget about the clutch, regen is useless on technical trails because you can not vary the amount of braking, and it will gain you only 10-15% extra in terms of energy. Note that if you are going to do any jumping, you may find you are damaging the internal gears of your motors.... then again, I would hesitate to make jumps on a carbon bike anyway, unless it is a real FS DH frame.

 

[skelinger]

More great advise guys! Thanks a million.

As for using hub on the rear I was only ever planning on using maximum 250w hubs. I understand the strength is not there. I don't suspect ill be taking large jumps on this, the most I ever drop down is foot or so.
As for the motors I'm really trying to avoid going over the 5kg mark. I'm currently looking at the Cute Q-R-85SX & 100SX they weigh in at 1.6kg / 2kg, running at 100w - 200w / 150w - 350w.
1.6kg is definitely the ball park i'm aiming for but i'm not sure about quality of these, i'll check out the forum for more info I think. I don't expect ill be aiming to run them at full power either around the 180w mark each would be nice.

As for the torque arms I've already designed my own set in CAD specifically for this frame, they include two arms each side to support the axle. I'll be getting these CNC cut from alloy.

Any advise in regard these hub motors and keeping my frame in one piece would be great. Thanks again for the advise you guys have given already!

 

[-dg]

As for the motors I'm really trying to avoid going over the 5kg mark. I'm currently looking at the Cute Q-R-85SX & 100SX they weigh in at 1.6kg / 2kg, running at 100w - 200w / 150w - 350w.
1.6kg is definitely the ball park i'm aiming for but i'm not sure about quality of these, i'll check out the forum for more info I think.

I have directly weighed and measured the speed of four of the common small motors.

Bafang/8-FUN SWXK 2.9 kg - quiet under light load, growls under high load. I'm running 21 A in 700c with 12s lipo it gets about 23 mph with light pedaling and climbs well enough. I am very happy with this motor.

Bafang/8-Fun SWXH - 2.9 kg - same weight, speed, and sound as the SWXK. I have not ridden this, just bench checked it.

Bafang/8-FUN SWXU 2.3 kg - slightly noisier regardless of load. With the slow wind, 14A, 14s lipo and 20" wheels it is ... adequate ... for my folding bike. It goes about 18-20 mph with moderate pedaling depending on the state of charge. It is no where near as strong as the SWXK and is slightly louder as well.

Q100 2.3 kg - I have weighed this and no load tested it, but not ridden it. It is slightly slower than the slow wind SWXU and about as loud, but sounds higher pitched.

Note that the SWXU and Q100 claim to be 1.9 or 2.1 kg, but both are heavier than the spec at 2.3 kg. The SWXK and SWXH are both claimed at 3.0 kg or higher but are actually lighter then spec at 2.9 kg.

If the SWXU was in a 700c wheel it would be unusably wimpy for my application. It is acceptable in a 20" wheel. The SWXK (and I assume the SWXH) is much stronger. I got the SWXU specifically to do a lightweight folding bike to carry up and down the train station stairs. The bike works for the purpose, but if I were doing it over I would gladly accept the extra 0.6 kg and use the SWXK instead. It is far more capable.

 

[d8veh]

Keyde have exactly the system you're after apart from regen. At the Shanghai show, Annad had a bike with 2WD Keyde motors. They have a battery that goes inside the frame tube plus a tiny bottle battery. The motors are tiny, but pack a fair punch for their size, and the rear one comes with cassette gear spline, so you can keep your present gears. The controllers are integrated inside the motors. IIRC, the optional throttle only works when pedalling for EU compliance. The Keyde website seems to be down at the moment, but here's a re-seller:
http://www.electricbicyclegroup.com.au/#!keyde-ebike-kits/ccj
You can buy direct from Keyde. The kit is not too expensive.
Have a look at the MTBs on the Annad site for ideas - ultimate stealth and lightness:
http://www.annad.net/products-id=1.php.htm
You can see the 2WD system with two batteries in the stepthrough here. IIRC weight was anout 18kg all up.

 

[Tinto]

On a carbon frame I'd suggest mid drive too, although my GNG v1 is far from light.
But im using a heavy bike to start with.

Perhaps the lower power bafang drive may suit and you can work with your gearing for torque.
http://endless-sphere.com/forums/viewtopic.php?f=28&t=50104

Or (if you're will to compromise on weight and get some decent grunt) there's the updated GNG v 1.x with chain drive -
http://endless-sphere.com/forums/viewtopic.php?f=28&t=52865

There's also the GNG gen 2,
http://endless-sphere.com/forums/viewtopic.php?f=28&t=45740

With the bafang my concern would be what impact their slip in style bottom bracket mount could have on a carbon frame.
Do they put a threaded metal insert into the carbon frame BBs?

 

[crossbreak]

I'm trying the same with my commuter, sadly it has 12.5kg... at least I paid only 25bucks and it drives just perfect..it will be below 15kg after conversion, so I can add only 2500g.
I had mixed experience with the Keyde friction planetary motors. One one hand they are almost silent, on the other they have very limited power and quite low efficiency :? Does not matter so much at this low speed.

Cute Q75 is only 1.2kg. S06P controller, controller housing (waterproof) and S-LCD with PAS sensor are together 504g (just measured with LONG wires), so your drive should come in with less than 1700g, since you save some weight for the front hub you throw out. But no one has a Q75 yet, be the first It has 13:1 reduction and should be be quite efficient (thin laminations, high speed, helical geared I hope). Let's see how it does... mine will hopefully be shipped next week. With these added 1700g, I have only 800g left for fenders I calced 20mph for my built, using 36V/201rpm motor in 26"rim and 12s lipo 45V battery, Input power is 630W max. will post some link here as soon as I start to built if you want

For the battery: 2x6s Zippy 5ah lipo and a SmartBMS are 1500g with some duck tape. But that does not matter if you have it in your backpack anyway.

A simple place to hide the the controller is below the seat, put the battery into the backpack, connect it by XT60 plugs (they are just perfect for this job) like my friction drive built:

 

[Samd]

I think you are worrying too much about the weight of the frame, compared to the rest of the build.
If you are adding more than 200 watts, who cares about a frame that weighs 4 or 5 kilos less. Even ten.

The weight of the rider never comes into question. Why worry about the frame then? Use a good material with nice vibration characteristics instead.

Skelinger, which part of Australia are you in now. If you update your signature to reflect your area we can find you some locals maybe to help out.

Cheers.

 

[skelinger]

Long overdue update.

I went with a mid-drive kit. GNG 48v chain drive.
I'm running a 11.6ah newer sleek bottle style battery w/ Pana cells.

I had to modify the bracketing kit for the GNG motor a little to fit the frame, which might have weakened it a little.
I'll be getting some tougher custom brackets laser cut before I begin being too rough on the trails.

I'll post pics soon.

 

[John Bozi]

Hey,

I have a hardtail carbon merida looks very much the same as your bike, and it's been sitting collecting dust for almost a year. I wanted to electrify it ages ago and went through the whole same thing - not made for power, so gave up.

I also looked at a mid drive for it, but was told by kepler the bafang 750w wouldn't fit.

So now I am scratching my head for the details of exactly what you did to mount yours, would love pics and the details please!

cheers

this is me & the bike
[youtube]BrKt-vjbeoE[/youtube]