First E-bike plan (peer review wanted)

[lawsonuw]

I'm planning on converting my commuter bike, an old mountain bike with a home made "pickup truck" rear rack, to an E-bike. After running the numbers (ebikes.ca's simulator was a great help) I've decided to make a Stokemonkey look alike using parts from ebikes.ca.

I'm planning on using a Crystalyte 408 "project motor" with a home made mounting to chain drive the left crank arm of my bike. Controller will be a Crystalyte 36V-20A unit. Batteries will be recycled sub-c NiCd cells I've got laying around in a 28s4p (33.6v) configuration. Planned gearing is 14 tooth on the motor and 44 tooth on the crank. With this gearing and voltage my crank should spin 79rpm at no load, 57rpm with the 408 loaded to 70% efficiency, and 48rpm when the current limit kicks in. With my bike's gearing I should get ~20mph in top gear and more than 50lbf of push from the motor in the lowest gear.

I'm planning on mounting the motor inside the front triangle about where water bottles usually live. I'm wondering where I can find an inexpensive crank arm and sprocket that'll fit on the left side? Also, Can I buy sprockets that will fit the 1.375in diam by 24 thread per inch thread the motor uses for output?

Batteries I'm planning on putting in a nice wood box and hanging them from the frame above the motor. The Controller will also hide in the battery box. The NiCd sub-c 1900mAh batteries will be organized into 28s strings consisting of four 7s sub packs. Each string will have it's own 30A fuse. I'm then planning on using a 4PDT to connect all four strings in parallel for running or individually to one of four dumb eight hour trickle chargers for charging.

Marty

 

[Miles]

Also, Can I buy sprockets that will fit the 1.375in diam by 24 thread per inch thread the motor uses for output?

Hi Marty,

Yes, this is a standard cycle thread. Try a supplier of parts for trials bikes eg. http://www.webcyclery.com/home.php?cat=415

Miles

 

[Drunkskunk]

Sounds like a good plan. But the high center of gravity would bother me. it might make it hard to keep upright on a normal kickstand. Have you considered mounting the motor below the triangle, infront of the crank?

The battery setup sounds fine, except you realy can't charge Nicad in parallel. You would end up with some under charged, and other packs over charged. You would need some form of BMS to handle it. easier to just charge each pack individualy

As for the controller. it should be fine for now, but 6 months from now, you might decide you want to run higher voltage. You realy aren't losing anything by going with the 72volt controller.

 

[fechter]

I'd go with separate chargers for each string. With 50 ohm resistors, it will take a long time to charge, and they'll get hot, but it would work.

Are you going to put some kind of freewheel on the crank? Otherwise the motor will drive the pedals.

 

[lawsonuw]

@Miles: Thanks for the answer on the sprockets. That's one less part I've got to make. (looks like I can get down to a 12T sprocket! ) Still looking for an appropriate crank for mounting a sprocket on the left side. http://www.webcyclery.com/product.php?productid=17217&cat=305&page=1 looks promising. I also got a $5 junker bike with very similar looking cranks and sprockets. Could I just use the right crank off of the junker as the left crank?

@Drunkskunk: High center of gravity is already a problem with *just* my cargo carrier. I've decided to solve this by getting center stand like in the picture I've attached.

I'm not charging the NiCad's in parallel. The 48v charge supply and individual 50 ohm resistors form four seperate trickle chargers.

Good point on the controller. The 72V-20A controller is only $35 more on Ebikes.ca. If they're back in stock when I buy my motor I'll make that upgrade.

>edit< I've been looking at how far the motor and mounts might have to stick out to one side and it's looking kinda close. So since It looks like my bike has the space, mounting under the front triangle in front of the cranks is an option.


@fechter: My first goal with the charger is to make it cheap and have it integrated into the battery box. Slow charging is fine as I don't expect to have to charge during the day. I do have several high current NiCd peak chargers at my disposal. (two AstroFlight 112D's, but only one works) I'll add an external plug for each string and use a 4PDT switch that is center-off so I can use these guys too.

I'm not planning on putting a free wheel on the crank. With my current plan adding a pedal freewheel would require a lot of work. This is one of the reasons I've decided to gear the motor so low. With the motor only able to drive the cranks at 80rpm, pedaling along with the motor shouldn't be a problem. (this gearing also keeps me "legal")

Good stuff,
Marty

 

[Miles]

I also got a $5 junker bike with very similar looking cranks and sprockets. Could I just use the right crank off of the junker as the left crank?

I'm not planning on putting a free wheel on the crank. With my current plan adding a pedal freewheel would require a lot of work.

Marty,

The only drawback to using a RH crank on the LH side is that the pedal attachment threads can undo in use (if you fix them with Loctite this shouldn't be a problem).

You can't fit a freewheel if you're driving the LH side of the cranks, anyway - well, you can, but it won't isolate the pedals from the motor, which is the whole point....

 

[lawsonuw]

The only drawback to using a RH crank on the LH side is that the pedal attachment threads can undo in use.

http://www.loctite.com/int_henkel/loctite_us/index.cfm?&pageid=111&layout=2

I currently have a bottle of Loctite 638 for just these situations Stuff's bloody strong, but a quick bake at ~400F (data sheet says 250C but 200C should be enough) and disassembly is easy.

Marty

 

[Drunkskunk]

you can overcome the Left hand sprocket problems by using a 3 sprocket freewheel crank, and running the motor to the 3rd sprocket on the right side.

 

[lawsonuw]

huh, something that convenient exists? Do you have any links to one that accepts standard chain rings? (preferably <$150) If I could fit a 50-36-40 tooth set of rings that'd make the install pretty easy, with nearly the same gear range as my current 48-38-28 rings. (the inner 40 tooth would be motor driven)

good stuff,
Marty

 

[Miles]

You can get this system: http://www.hostelshoppe.com/atp_archives/ips_instructions.pdf

Scroll down here: http://www.easystreetrecumbents.com/stuff/drivetrain.html

You'd probably need to swap the freewheel in it for a higher quality one....

I built my own from scratch, using trials bike parts.

 

[fechter]

The second place had an interesting two speed crank. It would be cool if somebody made a crank setup with a freewheel and a gear reduction input so you could run a higher rpm motor.

 

[lawsonuw]

It would be cool if somebody made a crank setup with a freewheel and a gear reduction input so you could run a higher rpm motor.

there's actuall three different versions of this crank I've found. http://shop.cheekytransport.com.au/store/viewItem.shop?idProduct=8 looks like it sells all three.

No freewheel, but the overdrive versions of the geared crank should already be able to emulate this. Say with the 1:1.65 overdrive, drive the rear tire with chain rings 1/1.65 the stock number of teeth, then still use a large 50 tooth sprocket for the motor input. (say 48-38-28 would become about 29-23-17) Same thing would work with the 1:2.5 overdrive, but the chain rings just become tiny.

Marty

 

[Miles]

Here's the website: http://www.schlumpf.ch/schlumpf_engl.htm

 

[fechter]

$750.? Ouch! those are expensive!

Right idea though.