Lightweight ME4201 Offroad Build

[Vertigo]

Greetings!

The goal of this project was to cram as much power as possible into a reasonably small and light package. At 50 kg or 110 lbs, it's not exactly a mountain bike, but it's still far from a full sized dirt bike. And after working on my 2 wheeled inline skateboard project, I wanted to stay away from small power dense, high rpm motors that require complicated reduction drives to get useful torque. That meant a large, low rpm torque monster like the ME4201. Sure, I had to remove the rear fan and cover to make it fit my frame, but it hasn't had any overheating issues yet. Pretty sure that's a good excuse to buy a bigger controller and put more power though it!



Link to GrabCAD for 3D model:
https://grabcad.com/library/light-electric-dirt-bike-1

Specs:

Frame- custom water jet cut and machined aluminum (no welding)
Motor- ME4201 (3 phase permanent magnet, axial flux)
Battery- 20S 12P Samsung 25R cells (~72 V ~1.8 kWh)
Controller- Kelly KLS7275D
Throttle: Domino
Variable regen: thumb throttle
Fork- Marzocchi 380 C2R2
Wheels and tires- Shinko SR-241 2.75 x 19 on 1.4" pro wheel rims
Front Hub: Hope Pro 4 20 mm axle
Rear Hub: Hope Pro 4 Fatsno 150 mm length 15 mm axle (no rear mechanical brake)
Reduction- 5:1 #35 roller chain
Total mass ~50kg or 110 lbs

I'm still working on what to use for a seat. Ideally I would just buy something off the shelf that would aesthetically fit my frame and make a bracket for it. That would also give me a location to add a cycle satiator and a BMS to simplify my charging setup. So if you guys have any suggestions definitely let me know!

[AussieJester]

Thats one hell of a build mate hugely impressive! Definitely grab a MX seat perhaps something from 50cc size bike Honda cr50 for example.

KiM

[Aebrennan]

What a work of art. The frame looks top notch.
Are you planning on a product run? If so please advise.
I have a build using the same forks, rims, hubs and tyres on a Qulbix 76r.
Great to see another quality mid drive build. Please post more vids.

Subscribed

[cwah]

The 18650 brackef look nice. Where did you get them? And why did you remove the cells shrink wrap?

[skeetab5780]

Very sick! Subd

[Vertigo]

If nothing else from this project, I learned that there is a reason most bike frames are welded structural tubes. All of the 20 or so water jet cut parts had to have their mating surfaces machined flat and drilled and tapped to match. I spent the better part of a month staying a couple of hours after work each day to finish the machining. It also takes a lot more effort to make a stiff frame when you are working with flat plate as opposed to tube. So, to answer your question, I would not want to go into production with this style frame. It's cool because it's easy to change or modify something, but it was a lot of extra effort that could have been spent actually learning to weld!

The cell spacers were just 3D printed in a layout that made sense to me at the time. The fit ended up being a little tight, and I had to hammer the 2 halves onto the cells. Pulling the wrapper off the 18650's made the fit a little easier. I can add the STL file to the grabcad page if interested. I probably should have just adjusted the scale of the file, but I was impatient.

[Rube]

Congrats that is a great effort, sounds like you learned at lot in during the design and build. Looks pretty cool too

[ScooterMan101]

A few years ago I visited the Tesla Showroom , when it was in Menlo Park, next to Palo Alto.

They had a rolling chassis sitting on the Showroom Floor ( just lower part of the car with wheels , cut away to show where the batteries and motor go. etc.

Looking closely I noticed that there were few, if any , welds, If I remember right there were No .. welds , it looked like one part was inserted to another part then glued/bonded to each other.

I asked the salesperson about this and he confirmed that the chassis was indeed bonded together.

You do not , have , to learn welding. Bonding ( with a few bolts for added piece of mind , make them aircraft bolts ) could and even should work better .

If nothing else from this project, I learned that there is a reason most bike frames are welded structural tubes. All of the 20 or so water jet cut parts had to have their mating surfaces machined flat and drilled and tapped to match. I spent the better part of a month staying a couple of hours after work each day to finish the machining. It also takes a lot more effort to make a stiff frame when you are working with flat plate as opposed to tube. So, to answer your question, I would not want to go into production with this style frame. It's cool because it's easy to change or modify something, but it was a lot of extra effort that could have been spent actually learning to weld!

[Routybouty]

Updates?!?! This thing is awesome!

[macribs]

That is some really nice work dude. Freakin awesome.

[cheapcookie]

did you use specific wire to solder the 18650's ?

[jonnydrive]

Awesome build Vertigo!

I am looking forward to for the new update!

[skeetab5780]

Swingarm looks like it will flex all over! Be careful

it is a definite showroom piece!

[macribs]

Would it be helpful to sandwich the swing arm between layers of carbon fiber and get added strength against flexing?

[Muzza]

Hi Vertigo. That looks sic!
How much torque at the rear wheel do you get with that and at what amps?

[deewreck]

Hey, you got any more pics?

[Rikobonito]

haaaaa and you give us our chance ...

Man ... a big BiG Thanks to you and all your amazing work and sharing all !!! your model is so gorgeous, but now cause of you I will have to make one one day haha (I'm a big fan of LMX ! I just comeback from many yrs of esk8 and e-mtboarding, try e-Dirt Scooter, and biking but all start here around 8 yrs ago more or less, looking for ebike. So now I will start to make my 1st little ebike to train myself in the e-bike world. But I could already think to the futur now)
is the motor extremly noizy or just the wind effect ?
Big Up