Dedicated E-bike Downhill/Freeride frame and build

******* Here is a current picture of the bike********


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I am long time lurker on the board, gathering info and looking for inspiration. Now its time for me to share with the rest of community.

I had originally planed to cut out the top tube and add a battery tray (bonded carbon fiber) to a downhill mountain bike frame.



I now realize that I may not be OK on strength but more importantly the geometry will be incorrect. For an EV bike a longer wheel base and longer “chain stay” length is needed to prevent wheelies. In addition I have switch to A123 pouch cells from 18650′s due to availability of pre-built packs and reliability. I will use batteries, motors and controllers from my friend Paul at EM3EV.

Here are my design priorities

1: easy to make and assemble
2: proper heavy duty frame for “freeride” type of riding with weight of batteries and motors.
3: a low risk EV drivetrain. Reliable is more important than fast for now
4: excellent hill climbing ability on and off-road.
5: Flexible for different motor-controller-battery combinations

Its an unusual frame construction but serves my design priorities. I have been designing many sheet metal parts for my racecar project and I have come to value the cost effectiveness of sheet metal parts. There are severe constraints on which shapes can be cut and folded and it is a huge challenge to develop a light weight and strong structure, but it can be done. I am using a mix of CNC machined aluminum parts (many of the parts are common to reduce cost) and the laser cut folded chrome-moly sheet.

The current design is sized to hold two 50v 20AH A123 battery packs (2000 watt-hours!). This should give me 80-100 km of flat ground use or 30-40 km of steep hills. Of course smaller batteries could be used.



I will add more photos from the test fit this weekend later today.

As shown, your rear triangle will really lack rigidity, I hope you plan to brace it someway. I like the idea of a laser or water cutted Alum frame however.

Just had a look at your blog. that bike is looking fantastic. Congrats.

Looking forward to seeing how the rest will turn out.

Andy

How much do you think it's weight is suspected as? 30#?

bzhwindtalker said:

As shown, your rear triangle will really lack rigidity, I hope you plan to barce it someway. I like the idea of a lazer or water cutted Alum frame however.

Click to expand...

You are right the swingarm does not have the stiffness I would like. I completed analysis again downhill race bike swing arm and my defection is around 9mm vs 3mm for the welded aluminium tube swing arm of the Commencal. I do have design for CNC alum swing arm but its just too expensive. I need to do more work on the swing arm... its good enough for now but have to be better.

Weight with the large battery and 2 hub motors will be around 40kg.

Very nice! I doubt your swing couldn't be any worse than Wei-Yin Chen. He's been out for most of the season, and "the O's" are just shy of division lead. :lol:

I guess the others will just have to step up in his place.

Do you have the parts to cut up the steel frame? I could see water jet work would freaking blow your wallet to smithereens. But the end result would be smooth and sleek.

Here are photos of the test fit of the side panels and the CNC parts



Side plate (this a sample made of carbon steel instead of chrome-moly)


CNC alum parts


One 1/2 assembled


Here is the frame with both sides getting the headset. The side plates will eventually be welded in few stops for addition strength.

No progress on the build today as i have a cold

melodious said:

Very nice! I doubt your swing couldn't be any worse than Wei-Yin Chen. He's been out for most of the season, and "the O's" are just shy of division lead. :lol:

I guess the others will just have to step up in his place.

Do you have the parts to cut up the steel frame? I could see water jet work would freaking blow your wallet to smithereens. But the end result would be smooth and sleek.

Click to expand...

The front end is laser cut but the swingarm is waterjet. I used to manage a waterjet shop 15 years ago so i love to make parts that are waterjet. machined. The swing arm is 10mm 4130/4140 plate and cannot be lasercut (too muchj heat for the thin webs) so i had to turn to the waterject. The cost was not that bad as pressure was gone up on the machines (cutting time is down from the 36,000 psi (when i used them) to 94,000 psi and over!

as a rough estimate, what are you paying ($USD roughly) for the CNC of the alum headset bracket. I've been toying with the idea of a laser cut / water jet cut frame for a while but the CNC parts (ie headset, BB and seat post) are the $$$$$ expensive parts..

Andy

You can purchase those parts already made from different places.

www.cycle-frames.com
www.paragonmachineworks.com


I like that frame!

migueralliart said:

You can purchase those parts already made from different places.

http://www.cycle-frames.com
http://www.paragonmachineworks.com


I like that frame!

Click to expand...

These parts are all my own design. If there is enough interest i may sell the frame but it cannot be assembled by the customer due to the bonding process. The alum parts are bolted and bonded in place with the majority of the strength coming from the bond joint. The high strength adhesive is bit hard to work with and the cleaning process for the parts is not something you want to do at home.

Price for the CNC parts was very high but I was looking for convince and quick turn around instead of the lowest price.

Do you have an estimate?

Subscribed. Look awesome.

Every now and then, someone brings up the idea of an "ideal" bike frame, with many of them stagnating. Looks like you are well on your way to making a very usuable and suitable frame for our needs here. Hopefully you can produce these things at a good price point.

sabongi said:

Do you have an estimate?

Click to expand...

I don't have an estimate for the frame cost, this prototype will cost me more than 1000USD to make. I am able to reuse many parts however as i make new versions to adjust the geometry and handling. (i think an even longer wheelbase might be nice with steeper head angle) This design and construction method is not very cheap (on a unit basis) but it avoids the big mold and tooling charges that a normal welded frame would have. It does have the benefit of a small cross section with allows for massive battery capacity.

In short it is good for a prototype or low volume production. If i were making 10 frames I would likely stick to this method, over that it ends up being cheaper to invest in some tooling and molds (upfront cost) which will reduce the per unit cost.

bzhwindtalker said:

As shown, your rear triangle will really lack rigidity, I hope you plan to barce it someway. I like the idea of a lazer or water cutted Alum frame however.

Click to expand...

Here is some simple analysis on swingarm stiffness. 50kg load applied at the tire surface - paralle to the axel. This is similar to skidding the tire sideways and hitting a curb.
3mm of deflection for a Commencal Downhill Bike


7mm of defection for my 4140 waterjet cut swing arm


5mm of defection for a CNC swingarm i designed but did not make due to high cost (so far)


As you noted and i expected the "real bikes" with they "normal" construction win on the stiffness and weight. Keep in mind my goal was to quickly and easily build a frame with NO TOOLING cost as I will likely build several to get the needed geometry.

Here is an update.

I have most of the frame assembled and picked up the last of the major CNC parts. Since they were late, no time for anodize . Its fine since its just a prototype) but my friends here all have nice looking bikes, i gotta try to keep up.

Here are photos of the rear shock mount and swingarm and frame stiffners.





Here you can see the frame with a few parts test fit. I still need to make the seat tube and to pick up the swing arm and make a few more parts. Keep in mind this only a test frame. The chrome-moly frame was complete but i was feeling sick so i did not pick it up. Now that I am feeling better progress should speed up.

I'm liking those ANSYS workbench plots..

I do that $hit every day man ... it only gets better when you go to classic

Got the swingarm semi-done. The build on the frame is at a bit of a standstill since I don't have the bottom bracket that i need.



It turns out the needed bottom bracket was discontinued about two years ago. I wish i knew that when i specified it for the design. I ordered the needed bottom bracked but have no idea how long international shipping will take. In the mean time i will start on making a new swingarm also.

Tomarrow I am off to my the make the wire harness. First a non-weather sealed wire temporary harness. One of the main differences on my build compared to most will be a fully weather sealed electronics and wiring. I am making my own high amp
(80-100 amp) connectors after spending months looking for and not finding what i needed. In my previous job I was responsible for manufacturing and quality of wire harnesses for electric cars. I learned many hard lessons on what works and what doesn't and became familiar with many different types or harness and connectors. I THINK i have something much better than what typically available at normal prices (i like the Sauriau stuff but its way to expensive and still a bit big for an e-bike)

Stay tuned

Its been a while since I posted an update. I am still testing the prototype frame in both 2wd and rwd configurations. I am pretty comfortable so far with the handling. Shock ratio changes and bit shorter swingarm are next.

Here are a few photos of the bike from a week ago.





I did manage to fall off a few days ago so I am resting for a couple of days. A non e-bike and not even a part i made broke. A failed seatpost bolt cause a relatively low speed crash while I was playing around on my favorite backroads.

Current spec is a prototype EM3EV direct drive motor, 30s1p A123 battery, range is around 100 km and top speed is about 70 kph, this is all on downhill knobbies, it would be a bit better on slicks.

http://www.youtube.com/watch?v=M-hhEjnJG-Y

Its been along time with no updates for you here on the Sphere...I am done with the design and production of the new frame design and I am doing some durability testing now.

This is my new frame design and I may put it into limited production if there is demand. As someone who grew up racing downhill bikes I was looking for a e-bike that could perform like a downhill mountain bike. I did not succeed...Due to the weight the electric bike will never handle like a (modern) downhill race bike but it turns out that is fine because my e-bike is so much more versatile. Modern downhill bike are terrible anywhere except a downhill trail or course. While my e-bike does not match a Commencial or Santa Cruz race bike for speed down a UCI World Cup course it is still pretty good and fun. The big advantage is that it is also fun on flat places. This has changed my riding from focusing only on downhill and mountain trails to finding less crowded spots to have fun. Plus i can use it to commute to and from work.

Here is a short video of some testing, mostly checking on swing arm stiffness, i am trying to feel the FEA results and make sure I have the stiffness i need. So far so good. This is my testing area near my workshop. Btw Meanwell (the power supply company) is just barely visible in the background. I will have to pay them a visit soon.

[youtube]W1e9EL-mCFE[/youtube]

We have a nice BMX track nearby except it is overgrown with grass and is now a lawn with a BMX track under it. No fun on a Mountain bike or BMX (you cant get any speed and there are holes hidden in the grass) and hours of fun on my e-bike. I will take some video from there soon,

subscribed. looking forward to the next vids. and more pics!

New video from todays ride in the mountains. Still a few things to update on the design but it is getting to be alot of fun. I'm not totally happy with the brake feel. I still have not installed the upgraded pads or even switched to the Hope V2's that I have. The Shimano Zee brakes are ok but can fade a bit on long steep downhills. Today I dropped about 1000 vertical feet in less than 7 minutes and they we still OK.

[youtube]ftEQuzwwKu8[/youtube]

looking good Z!

just checking out the build, its looking really good, i like the waterjet, laser cut shapes. Coming from an engineering background i used to do wire erosion and CNC machining, there's alot of machine hours in that puppy.
Did you ever think of aluminium rear swing arm with machined pockets to keep the torsional stiffness yet remove weight?
Well done so far on the build.
I'm interested if you ever got to a finished version for us prospective customers or if there are CAD files for us to build?

The swingarm was designed with topology optimization and I was surpized at the number of windows vs pockets. It is CNC machined form 6061-t6 aluminum.

I have had a few componet failures in vibe testing but hope to be selling frames and complete bikes soon.