Left side freewheel sprocket question
I'll be "rolling my own" ebike over the next few weeks. Planning to use a 400watt counter-clockwise motor to drive a left side crank sprocket. Rather than messing with a hard to find freewheel crank sprocket, it seems like it would be better to put a freewheel sprocket on the motor instead. It would need to freewheel the opposite direction of a right side sprocket. And it would need left had threads so the torque doesn't unscrew it.
Anyone know if a standard freewheel sprocket can be screwed on from it's outside, as in backwards?
If not, are there left side freewheel sprockets out there?
I'm not sure most people realize how much energy just a chain rolling around a couple sprockets can soak up, especially as we pedal along with our 100 watts or so of muscle power...so for that reason, I would sure try to have a left side freewheel sprocket on the wheel, and not the motor, which I hear are quite easy to get.
The deal is, it's fairly cheap to get a hub motor and controller from Goldenmotors or Electric Rider, it's hardly worth the trouble of building it any other way, unless of course, you already have the other stuff, or you want an outrageous top end.
Last edited by wernmax; 08-28-08 at 02:03 PM.
I don't know much about chains and sprockets from a technical standpoint but all my research so far indicates they are a remarkably efficient way to transfer power, in the high 90% range.
Here is one recitation of such claims:
My plan is to have a 400w motor mounted above or in front of the pedal cranks. It will turn counter-clockwise with the shaft pointing to the left. The shaft will have a small sprocket connected by a chain to a large crank sprocket. This way the motor gets to take advantage of the bike's gears, just like the human does.
What I was hoping to do is to allow the motor to run the bike without the pedals moving but the more I think about it that's not going to happen...
could you not run the motor clockwise and mount it facing the right side of the bike.
By using a double or triple front chain ring you could match the motor to the inner of the 3 (or 2) chain rings.
Then you could use a standard freewheel on the motor sprocket.
A well oiled and aligned chain is about the most efficient drive mechanism there is.
The only thing to note with this set up is that although you can pedal without the motor, you can't motor without pedalling.
For that you will need a freewheeling chainring.
JB imports carries a freewheel triple crank, I have one, it is intended for tandems. I bought mine from hostel shoppe. about $180 I think. You would want the stoker set. It is set up for road gears.
I'm having a hard time finding freewheel cranks or chainrings, maybe I'm looking in the wrong place? I tried JB and Hostel Shoppe.
I'm not opposed to running off the right side, it would allow me to use more standard parts. I'll have to read up some more on how to re-wire the motor for CW operation.
Looks like they might have just what you need here....
Hostel shoppe lists it under cranks and then Sun Bicycle Indepent Pedaling System. You would want the stoker version. I have one if you want photos. It is made for 170 mm road gears but I am pretty sure I will be able to drill it out for 110 mtn bike gearing for a utility bike and the hills around here.
There is a thread on endless sphere about rewiring the motor. If you don't have one yet, Cyclone Taiwan will sell you one that goes CW or CCW.