Concept: Custom cruiser-style GRP-build

[Carsten]

Hi,

I was dreaming of building my own bicycle till i was a child and had a ride in an alloy alleweder velomobile. now, grown up (still childish) its time to make it happen. first i thought of welding some kind of short recumbent out of steel but i did not have a shop nor appropriate tools. im also movin to big city during the next 2 months. riding a bent during rushhour is kind of masochistic. so i decided to built a GRP-frame with cruiser-geometrics.

GRP is easy to work with and needs only simple tools. all stressed parts are goin to be sawed/drilled/grinded alloy profiles and tubes. its been built around a positive mold out of foam. then the foam core will be removed, first mechanicly and then melted with acetone.

building start is in about 2 months after my move to big city. im not in a hurry gettin it done but i have to put it out of my head and into discussion before gettin insane

during the last weeks ive done a lot of sketches, improved them, throw away, did it again and so on. atm this is my favorite, but may change till building starts.

actually im doin a CAD drawing to figure out some measurements. (when i teached that damn program to do what i want )

desired specs so far:
- 26" x 2.0 - 3.0 tyres
- nuvinci hub
- discbrakes f&r
- front suspension fork
- 170 kV motor & middrive gear ratio for about 40 km/h top speed and 75-80 pedalling cadence (@max hubgear ratio)
- motor and gears built in motorbox out of alloy inside frame, accessible from bottom. maybe some kind of scoop for cooling purposes
- 36V 15-20Ah lipo or lifepo
- all wiring and cables inside frame, clean and smooth lookin.

thats it for now. you guys here on es are amazing and doin great stuff, i get a lot of inspiration out of ur builds and i want to give something back. maybe someone gets inspired by my project as well.

have a nice day
carsten

 

[Carsten]

ive made some progress in teaching that programm not to fool me , this is the result so far

befor i begin calculating the gears, i have to make a decision for the batteriepack. on this i need some advice.

-during my search for valuable lifepo, i found this http://www.conhismotor.com/ProductShow.asp?id=45 pack. in the dimensions 340x140x75mm it would fit really well (the blue one in the above picture) are there any experiences in using their packs? what kind of bms are they using? is there a lvc signal output?
these are 2c cells, would be good for about 40 Amps.
(330$ + shipping + about 20% taxes & duty, including charger & bms)

-second option would be 8 of these http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=13380 turnigy packs. wired in (2x5s)4p. i want a simple plug & charge solution without disassembling the hole pack, maybe with switch to simply switch between 2x5s4p to 5s8p for charging. so what options do i have for a balancing bms + cheap charger (why are 10s charger so expensive compared to 6s?). how would the wiring look like?
(8 x 49$ in german warehouse, much less shipping, no taxes & duty, without charger & bms, much less warranty trouble)

-im also thinking about a 6s6p economymode with the ability to switch to (2x6s)3p powermode, but then i have to deal with different gear ratios for pedalling. i think it would be a lot of fun, but also adds complexity and costs.

so please tell me what would u choose and why? is lipo really save and foolproof when treated right? i dont want to melt the frame just for one bad cell or something.

just for completion, i decided for that http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7870 motor, here are some stats on different voltages.

btw: EVcalc is a really nice and handy peace of software, thanks for that.

some background infos, in germany is a 25 km/h 250 watt limit. But for a short (not specified) period of time ur allowed to pull more (not specified) watts (some street legal "frock" conversion kits pull up to 1kW with low RPM). so my intention is pulling 1kW (or more) without transforming them to heat
a little more speed is also tolerated by the race management. the goal is pushing street legal limits to the max.

 

[Zoot Katz]

That's a nice looking project you're tackling. Best of luck!
Comparing the sketch to the CAD drawing, I say keep the fenders. They look cool.

 

[Carsten]

thank u, yes i will keep the fenders. i just dont want to build them before the frame is finished. i will rebuild it when the measurements for dropouts and motor/gearbox are clear. i also made a mistake with the steering angle. atm its like a roadbike at about 78 deg, i want a less nervous angle of about 70 deg. as a former roadbike driver i like direkt steering but its not realy comfy.

according to the batterypack ive found the thread about the cellog8 based bms from GGoodrum, i think thats the simple plug and charge solution i was searching for, only appropriate powersupply needed. so i decided for (2x5s)4p lipo and maybe upgrade to (2x6s)Xp later. if the lipos want to burn or something, so what? (anyone remembers Mayor Kong? )

im goin to treat them right so hopefully they wont do me no harm.

ive calculated the gear ratios, for the gearbox its about 16:1 @36V to 20:1 @44V. (calculated with 27" wheeldiameter, 1.75 highest hubgearratio, 50kph topspeed and 1:1 ratio between rearsprocket and gearbox). cranks to gearbox is about 1:3. with the 1:1 its easy to adjust it slightly up and down with different sprocket sizes.
to get a clue about the dimensions i made some drawings of different gearing approaches.

1st stage is always 15:60 T5 16mm wide beltdrive

2nd stage simple cogwheels 20:100 Modul 1, i dont like that, dont know why

2nd stage similar to matt's 2-stage-drive unit, 12:60 #25 chain. nice but huge

2nd stage matex planetary gear, 5:1 75mm dia. nice but would not be easy to build an adapter to attach a freewheel to the output side.

comments and suggestions welcome