72V Mini funbike

[steam25]

hello crew,
as so many people asking me in emails what the hell i am doing with these small bike in the background all the time i think i just open a new topic for it.

the idea is simple: make a cheap, tiny 20" wheel bike which can fit in a car, bus or train, is light enough to carry it around in a bag (rear wheel stick out and just roll it like luggage) looks not like crap, and enough power to have some real fun also in difficult terrain. and not just like all other 36V folding bikes which are nice to go from A to B but they are slowly and most times a little ugly. but thats just my 2 cents.

so i start to grab a small frame, change parts to make a stable base, throw some electric parts on and the result is more than i expected.



as the box arrived i put it together and get a first look.
well... my first impression was: "its green, weldings looking good" and thats it.

View attachment 19
i throw following things directly in the trash: plastik pedals, handlebar and stem, grips, gear stuff, seat and started to search for better parts to improve the basic bike a little.
also solder some LED lights together, made them waterproof and install all on the bike. later a DC adapter will make a 12V source for LEDs, USB charger and headlight.


i bought the same fat knobby tires from the blue bike and order a 2014 9c motor in 20" rim and 9x7 for highest torque.



motor arrived and looking awesome! more light than i expected.


decide battery shape. it will be a 72V 20s 9p pack good for 180A continuous





nice 180mm discs in neon green fitting to the frame and green aluminium pedals. LOVE IT!

i bought a spinner front air fork with remote lock in white and start install discs to the motor after got the right adapters.
View attachment 9





result until now is this.






i also got a second bike and start make a ultra light version with 200W geared motor like in the video and tiny 8Ah 72V pack and 25A controller



here we tested the small 200W geared motor. pushed it far over the limits but as you see in video it seems to stand the 2000W and i used my 3500W mid drive. cant get close to him most of time. these small bikes are a ton of fun and we had a blast in this park.
[youtube]V5WYOoQs8-A[/youtube]

THINGS TO DO:
i will make some small torque arms soon. a custom battery bag with some extra zippers for small stuff on the side. battery, controller (sabvoton 80A) and rest stuff will be inside the frame.
because i dont need a cycle analyst on this small thing i make a little plastik box for the DC-DC converter and put a display inside which can calculate AH and show charging voltage. also got some space left for 2 switches and the USB charger.
the plastic box is round on the botton and fit perfectly on the upper tube of a bike frame.
battery will be ready tomorrow and controller should also come in 2-3 days.
fork also arrive tomorrow and i will install it.
if anybody is interested i will make a video when i use 4000-5000W on that 9c motor and test the small bike a in the park

of course this is just a little toy to fool around and play. its cheap and small but hopefully will do the job.
suggestions are welcome. have a nice day

 

[fesanand]

Nice and tidy build so far. But for me too fast for that tiny wheels and without suspension. Which DC/DC converter did you use? Do you have the link? Thanks.

 

[steam25]

there will be a good front fork and the fat tires on 20psi do the rest to have a comfortable ride. DC converters i have tons of here. what power you need?

 

[fesanand]

72v to 12v

 

[friendly1uk]

Nice looking bike. I have all the bits here to do something similar, but have given up on finding a good bike to build around in the UK. Picked up a Rock Hopper instead and told a mate he can have it all.

Be interesting to see it shift when it is done.

Why are the tree's painted white?

 

[cwah]

look nice. but bike can't fold?

 

[Hyena]

Cool bike. Tell us more about that meter, I've not seen those before. Do the bar segments measure the amp hours used ?? Presumably it'd have to be programmable for that to be the case ? If so that's pretty cool for a minimalistic and basic battery gauge when you don't want to go with a larger watt meter (and limited to ~60v) or a full blown CA. For a little bike like this, or for many noobs that's all you need.

 

[steam25]

72V --->12V how many amps? smallest here are around 8-10A. but i have one with 30A. another with 50A.
depents what power you need later. light it up like a racing christmas tree? or just small front light?

no it cant fold yet. because folding bikes are pretty wobbley and weak here. i tested them before. not a optimal base to put some thousand watts on...

white painted trees: well...when i learned 1 thing in china it would be "dont ask chinese WHY they do things" because they also dont know. i can give you million examples about crazy things like that you would NEVER belive. haha

the power meter:
the bar elements show rest capacity. there is a simple 1 button menu you can basicly set everything. press and hold it to go in a kind of menu. set your battery type. in my case lithium 4,2V each cell.
then set cells in series (20s)
after that set AH (18Ah in my case)
and then you can choose what the thing show you. after let the button go for some seconds, it blinks to confirm the setting and VOILA, the bars changed to half full (because i just connect a random 72V battery laying around and show me the rest capacitiy in AH!
all that for like 2$ or so.
while charging you can let it show voltage which i like more. so i set it to show voltage and the bars show me rest capacity.
a small simple funbike dont need a full cycle analyst now. and just a voltmeter isnt enough for noobs to see, what time they need to charge. now i have both and its pretty accurate for a simple "guessing meter"

oh boy! postman just ring and the sabvoton controller arrived! gotta go

 

[steam25]

i opend the box. my god the sabvoton is huuuuuge! how can it fit in this tiny bike?!

 

[Hyena]

the power meter:
the bar elements show rest capacity. there is a simple 1 button menu you can basicly set everything. press and hold it to go in a kind of menu. set your battery type. in my case lithium 4,2V each cell.
then set cells in series (20s)
after that set AH (18Ah in my case)
and then you can choose what the thing show you. after let the button go for some seconds, it blinks to confirm the setting and VOILA, the bars changed to half full (because i just connect a random 72V battery laying around and show me the rest capacitiy in AH!

Sounds interesting, but unless it has a shunt or other current measuring method it can't actually display amp hour, especially if you just connect it up it can't say you've used 50%. I assume it just has 2 wires on it to the battery ? It sounds like it's actually progammed with set voltage points corresponding to the bars for different cell count batteries. Eg for a 20S pack it considers 84v 100%, 77v say 60% etc. It can't really be too accurate as the discharge curves vary alot between 2 cells different cells only identified by a 4.2v full charge ( eg high C rate lipo vs say a 2C 18650 cell)

Still, for a simple gauge it's better than nothing. Disregard the above if it DOES have some sort of current measuring system and it just defaulted to 50% charge because it detected a lower resting voltage at power up. If it does do this, put me down for a dozen

i opend the box. my god the sabvoton is huuuuuge! how can it fit in this tiny bike?!

haha I think I warned you that the sabby would be overkill on that bike!
A decent 12 fet 4110 controller will suffice, this is what I used to use on my 9C motors up to 4kw, and with the slow wind motor and 20" rim I doubt you'll even spike the power that high.

 

[steam25]

exactly jay.
it measures voltages and have a programmed curve to see the battery level. you can choose between different cells types but in fact its nothing more as a "guessing meter" like i said.
a shint would be perfect of course. but come on... for 2$ we cant expect those fancy features. i will test it a while and tell you its crap or kind of useful thought.

yes i send the sabvoton 80A back. get a 150A version and pay the difference. use it later for my bike or so. thanks for the tip. i ordered a 12Fet infinion. should do the job!

 

[steam25]

well,
today i made a first testrun with the new mini green bike and 9C motor.
first impression: "holy crap!"


i set current to 40A but the poor old test battery was a real bottleneck. peaked out at 3400W but even on that it is a ton of fun! cant get the frontwheel on the ground.

front fork is too soft and need adjusting with harder spring inside. brakes are great and i am happy to use 180mm front and rear.
top speed is around 50km/h because the battery pack sagged down from 84V to 65V. i think with the new high powqer battery with 20s 18Ah and 180A continuous current we will hit the 5000-6000W and topspeed should be 55-60km/h.

after i went crazy with alot of full throttle starts the motor outside temp was 60C°


i charged the battery full once again and go out with my friend together. her bike is limited to 1200W now and have nearly same top speed. after we ride around all evening and had absolute blast, just made some photos and went back home.




the small battery meter is pretty accurate and i love it. it does the job and for 1$ i cant complain.


after a little more finetuning it should be good enough to work as battery gage and charging control display.



my overall impression: mini bikes are hell of fun and i definitely want one too. torque is unreal and steep grass hills are absolute no problem. its fast enough for the city, small and light enough to throw it in car or bus, and powerful enough to have fun in parks or urban areas. fat knobby tires make a cool noise and the "WHOOOOP" from motor make me grin everytime while accelerating!

made a short video in my underground garage and load it up if you guys want see it.

cheers!°

 

[BikeFanatic]

made a short video in my underground garage and load it up if you guys want see it.

cheers!°

Yes i want to see it. You make good video most people just shoot by themselves so you only see the scenery.
Love the shot of the bikes together with the LED lighting. I bet they look cool at night or in a dark parking garage. The torque on that bike is impressive.
do you have any links to the meter and the accent lights?

 

[steam25]

https://m.youtube.com/watch?v=Sl4UgHUsHc4

 

[IRON DOG]

Nice little thing , can you post a link for that nice voltmetre .

Please thanks

 

[cwah]

Why not get the adapto controller? It's very small and the mini does 3000W. Or the normal allows up to 10KW. And it's small as well

 

[steam25]

hi guys,
sorry for delay.
i had a pretty bad accident yesterday and spend my evening in hospital.
stupid car driver here man... he cut me off and i crashed hard at about 45km/h while testing the new green mini on the street.
driver run away. no licence plate and no camera near that street.

the small voltage meter i get direct´from factory. so no link. but i think it should be easy to find. and it cost me 1$ or something.


i dont use adaptto because its freaking expensive and this bike should be cheap and small.

 

[steam25]

battery is here and i just shrinked it in PVC.
factory destroyed my fancy BMS so i got a new one. it have LEDs on so you can see balancing. charging now. later photos

 

[hydro-one]

comeon how about some pics of your "friend" did you build her bike too? they look very similar

Very nice build, i also like the idea of a small all purpose city bike that can be stowed with minimal hassle. the big thing for me is the batterys. using a safer pack of 18650 minimises the risk but its still risky bringing ANY ebike on a bus or train in my opinion. and i have experinaced first hand the violence of a large lipo fire indoors. i know its minimal risk but the outcome could be very bad if somone burns lipo in a bus. many deaths could result in under 30 seconds. hey its just imo plus, thats why ebikes are great, you shouldnt need the bus anymore ,but in reality i think they need to work together.....

Seems like your having a run of bad luck with crashes, just keep getting back on that horse and someday crashing will be nothing but a distant memory.. your riding skill will improve to the level where crashing due to someone elses mistake will be impossible. you must calculate every possible mistake when interacting with others. and leave yourself a way out.

Mike_Freerider

 

[steam25]

jo mike,
i am using 18650 cells for these bikes.
yes i build the small purple light bike too.
photos of her?? haha

i am not crying around. 5 seconds later i was on that bike again. shit happens. and i can assure, you would have crashed too at this point. he came out of nowhere. no turn signal, no sign of slowing down. and i was sure he saw me because looked directly to me, then made his turn and i slammed the brakes half second before because i know chinese drivers meanwhile. they just give a damn... made a highsider. impossible to stand that one.
yes i could have avoid that crash if i ride 15km/h all time every day. but come on who do that? you got a bike can go 50, and you will go 50 in traffic.
lost some skin, got a couple of bruises. pain like hell but in 2 weeks its gone. (as usual)

EDIT: by the way the bike was totally fine! bendet a crankarm and have 2 scratches on brake lever. these small bikes are really nice to crash.

today the other 18650 battery arrived. brand new high power 18Ah pack with 20s 8p and that new fancy BMS with LEDs on. its charging beside me now and i cant wait to get the battery full and see all the gizmos coming on

 

[steam25]

woooooooooooooooooooooooooh!!!

that is one nice looking BMS!
i love it. and finally i can see the acttive balancing.

 

[steam25]

well,
i am just back from a testride in the park. i reduced the power to half and let her make some take off tests.
even after 20 times she wasnt able to go full throttle from start. definetly end up in a spectacular auto backflip.
[youtube]ATm2yzqPpz4[/youtube]
settings for this ride was 140A phase - 40A battery

after we made the new 18Ah battery nearly empty i went home to charge and change settings so the new profile is now:

290A phase - 65A battery current

i tested this setting on a empty battery in my living room. before i could go full throttle from zero if i lean forward.
THAT SEEMS TO BE NOT POSSIBLE ANYMORE!
oh boy i cant wait to go down and test that.

if the bike act fine i will go up to:

320A phase - 80A battery current (i just modify torque arms and change to big anderson plugs 8) )

 

[Hyena]

after we made the new 18Ah battery nearly empty i went home to charge and change settings so the new profile is now:
290A phase - 65A battery current
if the bike act fine i will go up to:
320A phase - 80A battery current(i just modify torque arms and change to big anderson plugs 8) )

Dude, that's waaaaay too much for a stock xie chang. I hope you like picking pieces of mosfets out of your legs :lol:
I'd recommend not going over 60A battery and 150A phase current

 

[steam25]

shit! and i was so happy to nearly backflipped in my livingroom

so lets go seriously: 65A and 150A phase.