Electric bicycle building

[hzoltaan]

Hi,

I thought I build an elecric bicycle before I jump head on into converting a motorcycle just to see how it works... I decided to have a "blog" here.

I'll try to keep it cheap.

Things I'd like to achieve:
- to go to work.

I live in a city... (well, a few cities built together in a huge industrial area) and I live some 14kms from work. getting to work by bus or train is some 90 minutes, with the bike it could be a little less. I could charge (at least partially) the batteries at work, so they will have to be able to give me some 20-25km range.

So far the idea is:

- bike: a simple Dutch roadster, slim tyres
- motor: 12V power steering motor (because it's cheap and I trust it more than the chinese motors one can find on internet.) the idea is not mine, I stole it from Julian Edgar, I hope he does not mind. ( Browser Warning)

- batteries: 2 x Greensaver 12V 20Ah/2Hr, I found them on internet. They were new/old stock sitting in a warehouse for three years where they were recharged every 6 month. (so the seller claims) they arrived in original packaging with 12.80 v so it does look promising. I hope they are in good shape.

- drivetrain: I was considering friction drive, but If I can manage I'd like something better. The huge ratio between the rpms of the motor and wheel makes a simple chain connection hardly possible. I found somwhere that the gearbox from an angle grinder was used. I checked mine, the ratio is 1:3.08, which could work with a 1:4 - 1:5 chain transmission. I do not know if the angle grinder gears will be able to handle the torque, and also I could not find exact data on steering motor RPM, so I'll have some shooting in the dark here.

- controlling elecrics: copy of Julian Edgar's... I plan to pedal up to a certain speed where I can engage the motor on 12V and we'll see how fast it will be able to go. I think for shorter periods 24V (batteries connected serial) will do no harm. So the bike will be definitely hybrid :Start and acceleration with human power, keeping the speed with electric. I plan to put two small buttons on the handle and a pair of relays by the batteries. Wireing will be simple. I think I will get an ampermeter and voltmeter to check and test the operation at least at the beggining.


Calculations: I used Bicycle Speed (Velocity) And Power Calculator to check what power I need. Assuming, that the steering motor will be able to give me 200-300W, it should give me some 25km/h, which is quite ok. Will see, how it works.

Any Ideas, Recommendations?
(If this works, I might step forward to buy an old palett lift and convert my GS450 which has a half dead engine anyway... )

[hzoltaan]

Ok, here some pictures of the basic parts I've already got:

the battery:

the motor (12V power steering motor (Koyo electrics))







next step is to get an old angle grinder from the fleahmarket and to figure out how to connect the motor, the gearbox and the sprocket on the output shaft.

[drmiller100]

wow! what a great idea on the angle grinder!

and, you certainly seem to have a great project going.

consider using mosfets and your thumb to create a cheapy motor controller - push the button for a few seconds to get a boost. the longer you hold the button down, the faster you go.

also, you could use a capacitor/resistor delay setup like a wiper delay. use an adjustable reostat for variable power.

[Electictracer]

[QUOTE=drmiller100;285551]wow! what a great idea on the angle grinder!
QUOTE]

An angle grinder is very high rpm, I don’t think the gears would hold up long at all. You might want to try something like a Hole-Hog. In the electrical industry we actually use them (with additional gear reduction) as cable pullers. They are incredibly robust and would probably get you closer to the rpm you would need.

[Electictracer]

After looking at a hole hog more carfully, this might be really difficult to adapt....

[Electictracer]

One more thing, I would bet money this is a series wound motor. This is a good thing for you as the torque goes up as the rpm goes down. The only bad thing is they really have no speed limitations, if you don’t put load on them and run the motor, it can over speed some motors.

[hzoltaan]

I finally managed to test the motor and "measure" the RPM.
I pushed the shaft against the rear wheel of the bike and checked the revolutions the rear wheel took under a minute. Seems like with this load (bike off the ground, practically minimal load) the motor spins with 1950 RPM.

Electictracer, I have similar doublts about the angle grinders. Checked RPM/Torque data and found out, that they produce like a 5th of the torque I might use as continous...

I happen to have some leftover parts from a motorbike gearbox, so in theory I can can put together a reduction gear which can do the trick...

the data I have so far:
Motor RPM (minimal load): 1950
Bike wheel RPM @ 20km/h : 160
reduction gear I can make with the gears available: 19/12: 1:1.58

big question: what RPM would the motor have, provding enough torque for a continous motion with the speed of about 20km/h? If no load RPM is 1950, with what RPM would I have to count for the gears?

With this site
Bicycle Speed (Velocity) And Power Calculator
I calculate 100W-s for my humble carcass on the frame, 0% incline.
1%: 180W
2%: 260W
0% - 260W ---> 28km/h

Of course I do not know the accuracy of the site but it gives a good idea. I'll be able to play with the final gear ratios as it will be with stock rear sprockets, so I'll figure it out.

Any ideas about the RPM under load for such a motor?

[drmiller100]

GA7021 7 in. Angle Grinder-GA7021 at The Home Depot

Move up to a 7 inch angle grinder. They are TOUGH.

15 amps at 120 volts is 1800 watts, which is over 2 horsepower.

if you are making over 2 horsepower continuously, you don't need electric assist!!!!!!

[hzoltaan]

Yes, I was considering the same idea. I have an auction on an eurotec 3150W angle grinder. That is a beast. sold as broken as some rubber part is missing. I can't wait to lay eyes upon it!

[Electictracer]

The big grinder would work great. Calculating the rpm under load is tough. You might have to do some sprocket changes. Good luck, I love these electric bike projects.