Electric Bicycle Road Racer (R&D)

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Electric Bicycle Road Racer (R&D)

Rather than mix all the stuff that is specific to the development of my latest ebike project (Project #003) into the other threads I'm instead going to move all that stuff here.

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A Silly Mistake

For some reason I have been operating under the mistaken notion that the Sturmey Archer 8 Speed hub was supposed to be adjusted when the bike was in third gear.

That's wrong... it's supposed to be fourth gear.

Once I got that right the shifting all of a sudden became quite good. It does not look (at this point) that the rear hub is a problem.

Cross that off the list...
 
Power and Rpm's Do Not Seem Right

I took the bike down my local downhill and put it into eighth gear and it was able to reach what "appears" to be it's no load speed.

However, the no load with that gearing is supposed to translate into about 58 mph... which I know was not the case.

The speed was closer to 40-45 mph by my estimates. I have not yet hooked up the speedometer, but I have a general idea of how fast each speed should feel.

Also the power seems to be missing up top, but seems okay down low. The no load rpm is 6600 and that might be too high even still. The stock motor is 4500 rpm and maybe that's all that the motor can take... in which case it's going to be hard to get the power out of it that I want.

The other possibility is that my controller is not able to deliver the current that it should be doing. It's rated at only 30 amps and I've modified it internally so that it should be able to pull more. (by overriding the current shunt)

To AussieJesters credit this sort of problem would be easier to resolve with a WattsUp meter because you could find out very quickly what the controller is actually delivering. (verses guessing)
 
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Motor Mount Flex

This was mentioned elsewhere...

The motor mounts flex so much under load that the tiny little 10 tooth motor sprocket is able to get out from under the chain and allow the chain to skip. Now that I've switched to a smaller rear sprocket for the rear wheel the skipping actually seems to be going down a little. But this is a serious design issue that will have to be dealt with.
 
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Ice Cooling

I tried a damp cloth between the Ice Cooler and the shell and that seems to help somewhat. By the end of my ride the ice was all gone and the water was luke warm.

I'm running an "unprotected" motor which means my controller is supposed to be delivering a nearly unlimited amount of amps... but as said before I'm not sure what is happening yet.
 
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Not Enough Room

I was afraid of this...

The 14x2=28 (20 AWG) Rewind is a really tight fit. Though I ground down the sides where the coils needed to fit I didn't grind the outer edges at all. When the motor spun itself up to full speed the wires moved slightly outward due to the centrifugal force and then were worn away as they rubbed against the shell.

I think I can somewhat salvage this rewind by replacing just the top winding layer with another. (I have a spool of 20AWG that has a little left on it) This time I'll wind it as tight as I can (last time was rather loose) and then after some more grinding maybe it will work.

There is a strong possiblity that 28 Turns is going to be difficult to make work out because of the clearance problems with the container and not the actual grooves of the iron core.

In the image you can see that the last set of turns rubbed against the edges and two wires are now exposed. This explains why the power was off from what it should have been. It's possible that the wires ground off very early in the process.
 

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Blown Transmission

< < < Serious big time trouble for this bike. > > >

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The entire rear end of the frame was custom designed (many hours) so as to make the Sturmey Archer 8-Speed operate perfectly. I had all kinds of special things like a clamping dropout for the slotted rear axle.

So today I get the motor together and everything to go with it. I'm running 48 volts and 40 amps so the torque is very impressive... apparently too impressive for the hub. I managed to ride around a little and the bike was doing pretty well, except any time I really torqued the motor the chain was still popping over it.

I stop... return home and place the bike in it's bike stand where the rear wheel can freewheel. In order to simulate some torque I would stop the motor and apply the rear brakes so as to stop the rear wheel. Then I let off the brakes and crank the throttle hoping to see whatever is going on with the chain.

But instead.... POP... the rear axle is broken.

The rear axle broke while the bike was in the bike stand !!!

So the motor had enough torque to actually break the axle. (and I don't have to worry about any other possible cause) The reason is that while the axle and hub look really strong on the outside, you can see that the axle on the inside has all kinds of deep grooves in it that weaken it. (well, the picture is probably not good enough, but take my word for it, the axle has deep grooves for little clicker thingies) The axle would never have survived.

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This means a complete redesign of the rear end. No more internally geared hubs, they are expensive ($125) and fragile and it's hard to get good shifts with them because they require you to let off the power. The derailler can handle all the torque you can throw at it and it can be shifted while under power.

This probably sets me back a month. :sick:

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It's somewhat ironic that when I do get some better power out of the motor that it's the motor that manages to break something else.
 

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wow that is too bad about the hub, have you thought to try the nuvinichi(SP)
 
The moral of the story is:

"Just because something is expensive doesn't mean it's any good."

I'm going to go "back to basics" and return to the proven technology of the standard cassette and derailler. On my other ebike I have 6,500 miles on a standard derailler and it still works great.

I've heard that you can't "speed shift" the NuVinci and that was a major flaw on this Sturmey Archer 8 Speed hub as well. Not being able to shift at rapid speed is a serious disadvantage for any transmission. (it's time lost that could be spent making the bike go faster)

My choice and advice is to stick to deraillers.

Sturmey Archer built a hub that looks really strong from the outside, but once this axle broke and I actually see what they did on the inside it reveals that they really weren't serious about a design that would withstand abuse. A typical low powered bicyclist could probably use the hub for a long time without troubles, but for an ebike it's just too weak. An expensive lesson to learn I guess.

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I actually have a Shimano derailler and most of the things that go with it laying around, so I might be able to get away with just buying a new rear cassette hub with a disc brake capability.

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This was disappointing... however... I went through similiar "suffering" with my other bike. It took SEVEN versions of the "transaxle" component before I finally got it right.

In some ways building the bike the first time is the easy part... the development is where the real work gets done. (refining something takes longer than building it)
 
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New Drivetrain Idea

In order to deal with a dearailler and also cure the chain skipping problem I'm looking to reroute the chain.
 

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