Rider63's Ebike/emotocross from scratch. QS205-Sabvoton powered

[rider63]

Hi all , I'm new on this forum.
I'm french, so sorry for my language faults.

First little presentation of me, I am 30 year olds, mechanical enginer, practice as a hobby machining and metal construction since 10 years, I'm new in ebike world, but mountain biking is my passion since 20 years ( downhill, enduro, skatepark and dirt jumping)...

I'm here to share with you my build project.

It's my first build project, and I'm a little empressed to have a first fonctionnal prototype so it will be perfectible and I has to make compromise to reduce the amount of work.
The objective of this bike is to have an offroad ebike for making travel from home to work, riding only in offroad. 20km each travel, 40km go back. It need to be capable of high speed in offroad so long geometrie and big suspension.

Here is some detail of it:
-downhill bike inspired geometry (1260mm wheelbase, 64deg head angle, 480mm reach, 340mm BB heigh.)
-230mm rear suspension travel ( fox dhx2 downhill bike shox)
-200mm front suspension travel ( fox 40 performance elite fork)
-220mm front and rear downhill disc brake
-27.5 inch front/rear wheel
-sabvoton 72150
-QS 205 5T motor
-72V 20S16P li-ion battery
-wheigh around 50-55kg
aluminium 6061 frame, and aluminium 7075 machined part for the rest.

here is some picture of my 3d and what I already have (work in progress, not finished yet)










please let me your impression about it, and any advice. thanks you

 

[COAR]

I wonder if a tubular frame would lighten the weight considerably. the 'illegalbike' posted on here seems to have similar specs as to what you're going for but apparently is nearly 40% lighter than your estimated weight. you could also make a 'modular' battery, i.e. a 20S8P pack that allows you to double the capacity by connecting another one in parallel.

 

[Merlin]

if you wanna do "emotocross" a 17Kg Rearwheel will not be that fun as you may expect.

since surrons crashed the market its very hard to beat any kind of offroad bikes. 4k, ready to go.
any selfbuild ends up equal or more expensive. and if equal it is far away of the "surron package"

IF you ask me.....Only when pedals are involved to pretend beeing a bicyle i would think about those DIY stuff anymore.

If you re riding pegs. all that bomber, qulbix shit is out.

 

[rider63]

I wonder if a tubular frame would lighten the weight considerably. the 'illegalbike' posted on here seems to have similar specs as to what you're going for but apparently is nearly 40% lighter than your estimated weight. you could also make a 'modular' battery, i.e. a 20S8P pack that allows you to double the capacity by connecting another one in parallel.

my frame weight 2.5kg ( the only front tubular part, not swing arm and seat mount )
my 3D is actualy 52.5kg, illegal bike is ligher because he use smaller motor and battery, my motor weigh is 13kg and battery with box 20kg.
for me 50kg weigh is not a problem, it's the weigh of surron. Making two battery mean two BMS, two separate box, and 2x lower current or 2x higher decharge current for each cell. I wan't a big battery for long travel and big power capabalities.

 

[rider63]

if you wanna do "emotocross" a 17Kg Rearwheel will not be that fun as you may expect.

since surrons crashed the market its very hard to beat any kind of offroad bikes. 4k, ready to go.
any selfbuild ends up equal or more expensive. and if equal it is far away of the "surron package"

IF you ask me.....Only when pedals are involved to pretend beeing a bicyle i would think about those DIY stuff anymore.

If you re riding pegs. all that bomber, qulbix shit is out.

thanks you for your advertising, Yes I agree with you, hub motor is not the best for offroad (my rear wheel weighs 15kg), but it's a first prototype and the next will certainnly have mid motor, but if I never test it, I will never be able to judge how better it's. More over, a friens have hub motor on his bike and don't complain about it. I will see. I also like the silence of hub motor compared to mid motor with chain.

I don't really understand why I can't do better than Sur ron, if I have good geometry, godd suspension, and good motor, why it can't be as good or better?
I understand your point of view for people who buy chinese heavy frame with unsuitable geometry and bad suspension, but for me it's different, I design all, I have bigger battery, much more power, much better suspension, a good geometry for my size, big wheel... for the same weight of a surron. But hub motor, I agree.
More over, I don't do that to do it cheaper than surron and save money, I make it for the pleasure of creating my own machine from scratch, learn things and enjoy ride it. Designing, machining... it's also my passion.

 

[rider63]

this evening I started to work on battery box, I wan't to make quick removable battery box in order to keep it and charge it at work, here some pictures:

 

[rider63]

Hi, some news

started working on mechanical resistance of the frame, here is the motor torque resistance test of swing arm, for that I put a false axle on the swing arm and apply 400N.m on it, here is the result:

as you can see it's not perfect, there will be some matting, but I think it will not be too important, more over, ,it's for 400N.m torque, not sure if qs205 can output this. I will also put a screw to tighten the axle.

swing arm will be in 7075T6 aluminium

 

[rider63]

also made some other change:
-put the controler under the seat, it's not the best looking solution, but like that controler is better protected from impact and projection, more over, it will be easyer to acces and protect the wires. I also use the vertical seat mount as a mudgard for protect controler and shock. Theoricaly, tangent projection of mud from the wheel can't reach the shock stanchion

did also some modification on the pivot between swing arm and yoke, and made many improvement on swing arm in order to reduce weigh (around 1.5kg now)

also modify the frame in order to simplify the fabrication and improve resistance.

starting work on the resistance of the entire frame, for that I made a virtual benchmark with false fork, bearing, shock and wheel axle. Charge it on the footrest at vertical force of 8000N (800kg) wich equal to 10G impact for my weight.

the result don't look so bad, I will not have so many work ( objective is not to reduce massively the weigh, but to be sure the frame will not cut in two part on the first jump.

 

[owhite]

How do you plan on constructing parts, like the swingarm?

 

[rider63]

With my DIY CNC mill

You can see a video of it here: https://youtu.be/J2RuAwibGS4

 

[Overclocker]

wow i'd love to have your CAD and aluminum fabrication skills. i built this bike using coreldraw w/ mild steel :lol: but doesn't weight too much at 50kg w/ 204pcs 18650. 8000w

agree w/ Merlin about the hubmotor. to emphasize, the difference in ride quality between DD hub and chain-drive is *not* subtle. it's like night and day. so you really might be wasting all your time and effort w/ a hub motor dirt bike. sorry to be blunt about it

but i don't agree w/ him about the surron because it's a flawed bike in many ways. the belt reduction stage is certainly not going survive all that mud in the pic above. while the chain conversion presents a lot of other problems...

agree w/ your decision to move the controller. the old location is very vulnerable. i once fell into ditch and that spot took a direct hit which would've crushed the controller if it were there. and that's aside from collecting a lot of mud

speaking of mud you might want to increase your tire clearance. also you really should be using a light motorcycle tire for the rear. bicycle tire wears out too quick and would easily pinch flat from the heavy hub

 

[owhite]

With my DIY CNC mill

You can see a video of it here: https://youtu.be/J2RuAwibGS4

That's fantastic work. Also want to give your build log a shoutout:
https://www.usinages.com/threads/cnc-mecanosoudee-type-portique-mobile-pour-laluminium.63531/

 

[rider63]

With my DIY CNC mill

You can see a video of it here: https://youtu.be/J2RuAwibGS4

That's fantastic work. Also want to give your build log a shoutout:
https://www.usinages.com/threads/cnc-mecanosoudee-type-portique-mobile-pour-laluminium.63531/

thanks you I'll make some videos of the machining of the frame

 

[rider63]

IMG_20201220_160527.jpg

IMG_20210926_095414.jpg

wow i'd love to have your CAD and aluminum fabrication skills. i built this bike using coreldraw w/ mild steel :lol: but doesn't weight too much at 50kg w/ 204pcs 18650. 8000w

agree w/ Merlin about the hubmotor. to emphasize, the difference in ride quality between DD hub and chain-drive is *not* subtle. it's like night and day. so you really might be wasting all your time and effort w/ a hub motor dirt bike. sorry to be blunt about it

but i don't agree w/ him about the surron because it's a flawed bike in many ways. the belt reduction stage is certainly not going survive all that mud in the pic above. while the chain conversion presents a lot of other problems...

agree w/ your decision to move the controller. the old location is very vulnerable. i once fell into ditch and that spot took a direct hit which would've crushed the controller if it were there. and that's aside from collecting a lot of mud

speaking of mud you might want to increase your tire clearance. also you really should be using a light motorcycle tire for the rear. bicycle tire wears out too quick and would easily pinch flat from the heavy hub

Hi, thanks you for yours advices, and your build is really nice, I love it and how you build it. I will read attentively your build log.
I agree with all of yours advices, but the goal of my build is not to have the best off road capabalities, it's
before all a dailly offroad vehicule, I need it to make road to work every day, and silence, reliability and maintenance free have also a big place in my design. I don't wan't to have to grease or tighten the chain. And wan't to ride on silence at morning. So I decided to reduce offroad performance in order to gain comfort in other area. This is also why I have a big battery (320 18650 cell) for long distance. Later I will certainnly build another bike with mid motor and no compromise.

About the rear tire, wear is my main fear. I know it will not live long time. But I already have a rim, and will test with bike park special tire, build for long life. More over, I'm working in a big tire compagny, and have oportunnities of have bike tire for free.
Resistance of tire don't affraid me, because today high end tire are very strong, and you can put insert on tire in order to avoid snake bite. I will try, we will see... it will be not so difficult to make the change to a moto rim if needed.

 

[owhite]

thanks you I'll make some videos of the machining of the frame

PLEASE document that process as much as possible! I will be quite fascinated to see it.

 

[mxlemming]

This is looking great. These self build electric mx bikes are always great to see.

Check the torsional stiffness of your swingarm, i reckon it's going to flex a lot like owhite's did. Mx bikes normally get away with this by a process of sheer mass of metal, huge width and huge cross yolks... Your lightweight CNC swingarm is probably going to flex and put a lot of stress on the shock. I rode a bunch of DH MTBs with this design and they all feel wafty.

There are some really robust dh tires. Try intense hard compound 2.7". I ran one for 3 years 2 weeks a year in Morzine downhilling on the back wheel which is brutal on tires. A soft compound maxxis would barely last a week doing this.

I'd love to see someone use a big scooter motor as a mid drive with a 3:1 step down on the belt. Like the illegalbike on this forum but with a better choice of hub motor.

Your CNC is awesome. Rate of material removal quite impressive.

Overclocker's bike looks fantastic as well. I've seen pictures of this elsewhere but never realized it was an endless sphere member.

 

[rider63]

Hi mxlemming,

I will check my swing arm but I think it will be really stiff because The two sides are linked with a tubular geometry and not H machined profile. more over, the width of the pivot is really biger than on any downhill bike.

Yes I agree with you, there are some DH tire who are very strong, I also ride enduro and donwhill bike, and rear tire drift most of the time, with no wear issue. Brake has more torque that any motor so I wan't to try. I'm also convinced that big wheel ( 27.5 inch) will help the suspension to work with the hub motor.

 

[owhite]

I will check my swing arm but I think it will be really stiff because The two sides are linked with a tubular geometry and not H machined profile. more over, the width of the pivot is really biger than on any downhill bike.

You've done a lot of FEA -- but is there a way to model flex in the swing arm? That'd be very interesting.

 

[rider63]

Yes there is a way, but what force apply? What is a good result? I can do simulation but have nothing to compare

 

[rider63]

If you want send me your swing arm cad in igs or step and I can make a comparison

 

[mxlemming]

Yes there is a way, but what force apply? What is a good result? I can do simulation but have nothing to compare

It's pretty wet finger in the wind, but if i grab the rear wheel of my giant trance and put what feels like about 20kg force (extrapolating from picking up gym plates) sideways on the wheel, it deflects less than 1 inch. Holding the saddle with my other hand.

My DH bike, 2013 canyon torque, actually flexes slightly more

I remember a similar experiment with an old commencal meta gave about 2 inches. That's a wafty bike.

On the trance, my inclination is that the frame and wheel contribute similar amounts.

You have a YT dh bike right? Just check what it looks like in FEA compared to the reality of that.

 

[owhite]

racer63 wrote:

Yes there is a way, but what force apply? What is a good result? I can do simulation but have nothing to compare

I see your point. I think if I had the capability that you have with CAD, I would consider creating a CAD version of a "conventional"
swingarm, like:

and seeing if your results were similar or better to your design.

but it does make sense that it doesnt help unless you have something to compare against.

 

[rider63]

Hi,

some update of my project:

-received the 320 cell, liitokala ncr18650B, quality looks good, tested around 30, capacity are around 3350 to 3550 mah, good news. hope it can have good discharge current, seller anounce 20A max, I have 16P so if I wan't 150A peak, 9A for each cell can be enought, we will see.
anybody already use this model?

-received the spokes and mount the wheel, I also start the motor and sabvoton with a 48v 15A power supply, juste for test, it seem to work.

-received the 18650 honeycomb bracket and some other part for battery, still wait for the nickel plate.

-also find and order a very promising tire, schwalbe eddy current 27.5+ x 2.8, a really fat tire, special for powerfull ebike, with motocross inspired tread (update my 3d model with the real dimensions). will mount it in tubeless with cushcore insert, no risk of bit it.
anybody tested it?

there is also another interesting tire if these don't wear enough, this: johnny watts

-continued working on my cad, on the main frame (add some reinforcement on the head tube and rear seat mount), and the seat mount system, also made mud protector for the shock, please let me know your impressions.

 

[Overclocker]

big possibility that those cells are fake. if you really want to know i got a short writeup here:

https://www.endless-sphere.com/forums/viewtopic.php?t=87798

it's the only sure way to check for fake cells. basically i take the discharge curve then match it against a reference. people do all sorts of useless methods like weighing the cell accurately, various ocular methods, all useless :lol:

btw are those button-tops? i.e. with nipples?

 

[rider63]

hi, sorry don't understand what you mean by saying fake cell, do you thinks its rebadged panasonic or that is not really liitokala cell? I will check the nipple but what I am supposed to see? checking capacity is not enough? I don't discharger capable or creating curve. Just measuring capacity.