gearing

[kisshu]

i would like to a mount motor on the frame with a seperate chain to a three speed hub and then another chain from the cranks with front delaileur. does anyone have experience with this? any examples
i can see - any people or sites to stear me to - i don't see much info here.

also do they make hubs that can be run on the left side - or can they be modified - that would be interesting too.

thanks

 

[Miles]

Just do a forum search for "ebikemaui" or hang around here

 

[kisshu]

yes i already searched that - there must be other people on this forum who know about frame mounted motors and gearing? i'll check the bike forum in the meantime

 

[Miles]

Yes, you can get hubs that can be driven on both sides and hubs that have left-hand drive only.

Have a look here: http://www.staton-inc.com/default.asp

 

[Lowell]

Yes, you can get hubs that can be driven on both sides and hubs that have left-hand drive only.

Have a look here: http://www.staton-inc.com/default.asp

Hummer with Subaru power... :lol:

http://www.staton-inc.com/Details.asp?ProductID=3186

Some pretty cool engine powered bikes on that site.

 

[kisshu]

i mean an internal greared hub that runs/shifts from the left side instead of the right side

 

[Miles]

i mean an internal greared hub that runs/shifts from the left side instead of the right side

Oh, right. No, not to my knowledge.

The DualDrive is the only option for combining hub gear and derailleur AFAIK.

 

[Lowell]

I'd like to see some more implementations of the Dual Drive hub to prove or disprove their worth for ebike use. The fact that pedal power alone (inculding tandems and bents) can break them would make me a little hesitant to rely on one.

 

[Miles]

I'd like to see some more implementations of the Dual Drive hub to prove or disprove their worth for ebike use. The fact that pedal power alone (inculding tandems and bents) can break them would make me a little hesitant to rely on one.

It's a question of finding the limits, I guess.

My intention is to use one in a 20" wheel, which will give an extra 25% safety margin, everything else being equal.

 

[safe]

You need to do the calculations to make sure your normal pedal rpms match your geared down motor rpms. Figure a human pedal speed is about 60 - 100 rpm and that a typical motor is 3000 rpm max. You need to make a geardown or a gearup before you blend the two power sources. Even at a 10 to 1 gear reduction you still will get 300 rpms from the motor. So you might want to consider this... I've thought of doing something like this myself on my bike... from the motor you geardown (how about 11 tooth 90 tooth #25 scooter chain) to the three speed hub which operates like a separate axle. (transaxle) Then from there you go to the rear wheel. In parallel you have a chain from your bottom bracket to your three speed hub.

3000 * 11 / 90 = 366 rpm.

But your peak power is probably more like 2500 rpm so:

2500 * 11 / 90 = 305 rpm.

Assuming a pedal speed of 80 rpm you get:

305 rpm / 80 rpm = 3.8 to one gear ratio needed to balance.

So:

14 tooth freewheel (connected to three speed alongside the motor gear that is directly attached to the hub... this will involve some fancy machine work) and on the bottom bracket you use a 52 tooth sprocket.

14 * 3.8 = 52 (or 53)

That way you have a three speed that does not carry your pedal loads (can't break) and also will carry both the pedal and motor power before it's geared down. This means the torque is lower.

Complex? Yeah.... but it's doable if you are pretty skilled in the machining/welding/fabricating department.

Starting with a hub motor makes things a lot easier because the starting rpms are closer to human rpms.

 

[Miles]

So you might want to consider this... I've thought of doing something like this myself on my bike... from the motor you geardown (how about 11 tooth 90 tooth #25 scooter chain) to the three speed hub which operates like a separate axle. (transaxle) Then from there you go to the rear wheel. In parallel you have a chain from your bottom bracket to your three speed hub.

This is pretty much how my second project will be, but for other reasons.

My motor has a peak efficiency speed of circa 1800 rpm so, with a 20" wheel, a single reduction is easily do-able.

Running the 3 speed hub at higher than wheel speed is an advantage in terms of lowering the torque passing through it, sure, but a disadvantage in that it also lowers the efficiency...

 

[safe]

This is pretty much how my second project will be, but for other reasons.

My motor has a peak efficiency speed of circa 1800 rpm so, with a 20" wheel, a single reduction is easily do-able.

Running the 3 speed hub at higher than wheel speed is an advantage in terms of lowering the torque passing through it, sure, but a disadvantage in that it also lowers the efficiency...

Why would it lower the efficiency? Seems to me that you would be running the same hub at higher speed and less torque. Other than the possibility of the lubrication breaking down (which you can remedy with a thicker lubrication) you should be placing less torque on the hub. Less torque means less friction per revolution, but more revolutions, so you still get more heat, but not as much as you might think in a linear way. The gears would have less force applied to them. So I would figure that it should mostly balance out and you would get no difference or maybe even better efficiency at the higher speed.

Starting with a 1800 rpm motor will make gearing much easier...

 

[Miles]

So I would figure that it should mostly balance out and you would get no difference or maybe even better efficiency at the higher speed.

I was going along with the conclusions of tests, reported in Chapter 9 of "Bicycling Science", D.G. Wilson, 3rd Ed. Hope to do my own tests, in the future.

I realise that, for you, pedal power is mostly a way to avoid the hassles of licensing, tax etc. but, for me, it is the primary drive. With that in mind, a pedal drive with bi-directional gearing, 2 stages and a, possibly, less efficient transfer through the hub gear, is not so attractive.