...A new one! [low-cost dirt bike] -- second test video

silvocross · Aug 1, 2012

Hi guys,
following the results of my first electric bike (http://endless-sphere.com/forums/viewtopic.php?f=28&t=35694), I'm starting a new improved build.

I'm moving to Trento (italy), it's an alpine city, so I need a bike capable of some good offroad.
As always, my budget is really low, so I'll not use DH components, not many expensive machinings and so on, I'll try to keep it as much homemade as I can.

The main components:

- C80-100 rewinded engine
- Turnigy dlux 160HV controller
- LiPO 12s cells
- Custom throttle interface
- Dirtbike 35mm USD front fork
- Rear shock not chosen yet
- Dirtbike Racetech handlebar
- 26" wheels

The frame is inspired by the awesome work Ratking made with his downhill bike.
Like my first build, I'll use just one final chain to the wheel, combining pedals and motor power on a main shaft. I'll then use a 2 or 3 gears sequential transmission for both pedals and motor.

here a quick concept video, there are many things missing yet:

http://youtu.be/YNuCDhJ16Ts

suggestions are really welcome!

Rodney64 · Aug 1, 2012

Idontwanttopedal · Aug 1, 2012

Very nice have keep eye on this

Byte · Aug 1, 2012

Nice! Will follow this one

silvocross · Aug 1, 2012

Many thanks!

Fork:

silvocross · Aug 3, 2012

I just found out a 4 speed sequential transmission that fits perfectly in the frame (7cm wide)... so good!

crossbreak · Aug 12, 2012

building a case for these gears won't be so easy... mabye it's simpler to use an original gearbox from a honda dax

I like your reduction gearbox on youtube. It's only two stage, so no high rpm and no power with an RC-motor, even if you rewind it, torque will not grow much. Which reduction ratio are you aiming on?

silvocross · Aug 12, 2012

crossbreak said:
building a case for these gears won't be so easy... mabye it's simpler to use an original gearbox from a honda dax

I like your reduction gearbox on youtube. It's only two stage, so no high rpm and no power with an RC-motor, even if you rewind it, torque will not grow much. Which reduction ratio are you aiming on?

I'll definitely use the 4 gear transmission, It's cheaper and a lot smaller then my first 2 gears concept.

I rewinded the motor for about

Code:

kV = 118 rpm/V

primary transmission will be

Code:

i = 0,232

final tranmission

Code:

ii = 22/38

and here the 4 gears ratio and the relative max speed:

Code:

I      10/33   =>  25 km/h
II     15/29   =>  42 km/h
III    19/24   =>  65 km/h
IV     21/22   =>  78 km/h

crossbreak · Aug 12, 2012

that's cool , you do 3-stage 8)

so I guess you get 1/0.232*38/22=7,44 standart gear ratio

reduction ratio would be

I 1:24,55
II 1:14,38
III 1:9,4
IV 1:7,8

If you do 25km/h in the first gear your wheel does ~200rpm. That would be 4933 motor rpm . Lets say the no load rpm are about 1.2 times the load rpm, so you should get 5920 motor-rpm when spinning free in the first gear. Your battery voltage should be about 50 volts then. If you wanna use 12s you just calculated right

how will you build the gearbox? And will there be any pedals?

silvocross · Aug 14, 2012

Ok, I adjusted the project to fit the 4 gears transmission.
The coaxial pinion is unfortunately gone, but I'll save a lot of weight.

The project is almost finished, hope to begin the construction next week!

gwhy!1 · Aug 14, 2012

I will be watching this one, I quite often thought about gearing the peddles to the motor speed, I know it will make it very hard to peddle but who cares, its just to make it 'legal', one thing I would say ( and you may not be able to do anything about it ) the ratios are very close together, I would go for at least double the ratios that you have or you will be forever shifting or you will get lazy and just start using the higher gears which will put undue stress on the controller.

silvocross · Aug 14, 2012

I agree with you, ratios are too much close for an electric motor, and maybe too far for a cyclist. I hope that the truth lies somewhere in between

By the way, I'll set it to only use the first gear for hard climbs, and not for standard roads.

Here the frame plans (A1 sheet):

View attachment telaio parti mediane.PDF
View attachment telaio parte destra.PDF
View attachment 1

and here the steering pivot (A4 sheet):

View attachment cannotto sterzo.PDF

RWP · Aug 14, 2012

silvocross said:
I just found out a 4 speed sequential transmission that fits perfectly in the frame (7cm wide)... so good!

Very cool builds!

My buddies and I have been seriously curious about using a transmission like you are doing. How are you enclosing the gears?

We have looked at 50cc 2-strokes because the transmission is separated from the crankcase. Grinding and or machining away the crankcase and just using the transmission case...is that what you are doing or are you making your own transmission case or???

More pics of this area would be great. <edit> Just saw your new post and pic of the transmission in the frame...are you going to encase the gears in any way?</edit>
Thanks!

silvocross · Aug 14, 2012

RWP said:
<edit> Just saw your new post and pic of the transmission in the frame...are you going to encase the gears in any way?</edit>
Thanks!

The bearings will be mounted, from the outside, in holders soldered in the frame. According to solidworks, I'll have enough space to mount the shafts without covers etc.. :wink:

the transmission comes from a 50cc moped:

crossbreak · Aug 14, 2012

nice pics!

your drive looks very similar to a Herkules Prima 5 drive:

http://board.mofapower.de/board1-al...e-hercules-prima-gt-°-infos-s-6-°/index5.html

silvocross · Aug 16, 2012

Here some parts:

pedals shaft:
View attachment albero pedali.PDF

pedals bearing housing:
View attachment mozzo pedali.PDF

rear fork:
View attachment braccio forcellone.PDF

rear fork mount:
View attachment 5

front wheel hub:
View attachment mozzo ruota anteriore.PDF

rear wheel hub:
View attachment mozzo ruota posteriore.PDF

front wheel shaft:
View attachment perno anteriore.PDF

silvocross · Aug 16, 2012

Ok the bike is almost (software) completed, only the rear shock is missing (it's coming next week).

and this is the shock I ordered:

bandaro · Aug 17, 2012

Awesome, will be keeping a close eye on this. But it brings one problem I have been wondering about for a while to the surface, how strong do the gears need to be to withstand the motor? What pitch, width and material are they made from? If they are from a scooter then they should be strong, I am fiddling about with some design concepts myself but far under-qualified to determine if the gears will hold up, or what ones I need, so if you could tell me what works for you that would be awesome.

Is the frame going to be left open, as in made from a U profile? that would be pretty trippy, just remember to leave some drainage holes. That's a serious looking spring you got there, the bike is going to be so fun...

silvocross · Aug 19, 2012

From my previous calculations I' ve done for the first construction and from the practical experience it's fine to use gears made of c35 steel with a module m=1.5mm and width 17mm. The transmission gears have 1.75mm module, width 9mm and are hardened. However the main problems are not the struggle on tooth but the high speeds so if you want to calculate them you need Hertz law.

crossbreak · Aug 20, 2012

Thanks for posting gear ratios and modules, that helps a lot! Have you seen the pictures about the Herkules Prima gearbox V3 I posted? This may give you some sort of reference, it's an equal configuration.

1. pedal shaft
2. shifter shaft
3. clutch shaft
4+5 crankshaft

silvocross · Aug 21, 2012

crossbreak said:
Thanks for posting gear ratios and modules, that helps a lot! Have you seen the pictures about the Herkules Prima gearbox V3 I posted? This may give you some sort of reference, it's an equal configuration.

that's a really interesting transmission, very compact. I never seen this shifting method before