Electric Bicycle Road Racer (R&D)

[safe]

Well. I've ordered the parts that I think I'll need and it only has set me back about $80 so far. I'm starting to see some way out of this without doing too many changes.

One good thing is that a standard solid axle and a typical quick release axle use the same threads in most cases. (they share the same size) What I can do is use a solid slotted axle and a cassette hub and then it will be possible to use my existing frame without having to cut it up. (the clamping mechanism is mostly unneeded... but you never know... it might have some value eventually)

With the chain rerouted (see above) the motor sprocket will have the chain wrapped all the way around it so that's going to solve the chain skipping problem. I'm also going to add an extra freewheel so that will solve the problem of the pedals being linked to the motor all the time when all you want to do is just pedal. (the reverse... motor power without pedal power already is working okay)

So there does seem to be some light at the end of the tunnel after all...

 

[woody]

Derailleurs have their own issues.

Don't write off geared hubs straightaway.

I have destroyed derailleurs, rear cassettes, and chains testing various set-ups.

I once had a chain whip into the lower sprocket of a derailleur and jam under big load. Chain sheared with a huge bang and whipped again and seared a nice scar on my calf which I haven't disgusted everyone with a photo of. I will be happy to show you live if you are ever in Chch. I still have the holy jeans, and I don't mean Jesus wore them.

Anyway, I think derailleurs and geared hubs both have their place. It is just getting the right one for the right set-up.

Have you seen the Rohloff hubs?

BR

Woody

 

[safe]

The Rohloff hubs are known to be very strong. (but with a big $$$)

The whole concept of having a small motor sprocket attached to a chain the way I was doing it ended up being wrong. The reason that it didn't work is that the tiny motor sprocket always wants to find the path of least resistance and that means it will always try to skip the chain so that when under heavy torque it doesn't have to pull the chain with it's teeth. (the sprocket wants to avoid the chain)

I had just completed an upgrade where I took the motor mount flex out of the motor with an extra support bracket. Now the motor is completely solid and when the sprocket gets to the point where it used to skip the stronger mount tends to forcefully resist it.

What actually broke the axle (I think) is the torque started to force the motor to flex, which was resisted by the new motor mount. The chain all of a sudden it tightened up to a level where it had a few choices:

One: Flex the motor mount enough to get the chain to skip. (no longer possible)

Two: Break the chain. (it was a strong chain)

Three: Break the axle.

...in some ways the flexible motor mounts were acting as a "safety valve" so when the chain skipped it didn't break anything.

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The nice thing about a derailler is that it provides it's own chain tensioner. This means that you aren't in a battle trying to maintain the perfect tension with the chain.

By rerouting the chain (as pictured above) I'm hoping to avoid the skipping behavior because the chain will be completely wrapped around the motor sprocket. I'm also going to jump from 10 teeth to a 16 tooth freewheel which matches the gear ratio change that was needed when I go to the other 13-30 cassette hub. The cassette is something I already own and I'm also open to the idea of other gearing possiblities.

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The "bottom line" is that the motor torque alone broke the axle... but it was because of the tendency for the chain to skip that the extra tension came about. If the design were done so that chain tension was not an issue then I think there might be hope for internally geared hubs on ebikes.

Let's not forget that deraillers LOVE to be shifted fast. (deraillers hate slow shifts)

That's the one thing that the internally geared hubs don't seem to do well all the time and some have these scary areas between shifts where they freewheel on you. That's really bad news when you have 750 watts of power driving the chain...

 

[woody]

Personally I don't like very small sprockets.

What is the smallest sprocket Shimano sell?

Any less than 11 equals trouble with a capital T, Mr T.

 

[woody]

Not all derailleurs like to be shifted fast. Choose an IG. HG is pretty good but IG is way better.

Here is a snippet from my website.

If breaking/connecting to a modern bike you may find the chain is a Shimano HG or IG. This is clearly marked on the chain. These are Hyper-Glide or Interglide. Basically the chain and headset are specially designed so that the chain engages two gears simultaneously whilst shifting. These chains are especially strong, and extra care must be used when breaking/installing. You can use any chain tool but an HG compatible tool such as the Park CT-3 or the Shimano TL-CN31 is recommended. Always lube the pin prior to install.

 

[safe]

I already own the Hyper-Glide cassette 13-30.

Maybe later (after I test this out) I can start fooling around with different gearing setups.

All I know is that my last Shimano (old style freewheel 14-28) has worked great for 6,500 miles and can be shifted while the throttle is wide open.

And that's wide open at 1400 watts peak...

 

[duivendyk]

You also have to pay attention to the teeth profile of the rear sprockets,the derailer type have a more rectangular shape instead of a pointy triangular shape used with fixed chains. This DOES matter when you'r dealing with a derailleur type slack return chain situation.The chain tends to ride up on these pointy teeth if there is enough chain slack,result is skipping.I ran into that with my NV hub (I tried to keep the front derailleur).The only thing that sort of worked was to increase the chain tension a lot,which made shifting the front derailleur difficult once under way.

 

[safe]

Deraillers shift very poorly when the chain speed is low. The faster the chain speed the better the shifts. (trying to shift a derailler when the bike is stationary is impossible)

On the EBRR bike the motor speed will be slightly higher than the pedal speed at peak (by about 20%) so the actual chain speed on average will be equivalent to about a 100-140 rpm pedaling pace.

That "should" make for very rapid shifts once you get going.

You ideally want to shift just when the power from the motor passes it's peak rpm and starts to fall off... that throws the bike forward with a little extra momentum and creates a high speed chain but with a lightly loaded chain.

Deraillers - High Chain Speed, Low Load or High Load okay

Internally Geared Hubs - No Loading of the chain, Any Chain Speed okay

...at least that's how I see it.

 

[safe]

Update

I've laced up the wheel with the new hub and managed to grind down a new axle so that it's slotted. So at this point the rear wheel is already back together and on the bike.

There's a bunch to do, but I am working on it.

At this point in time I have something like 10 individual tasks (between two bikes) that are going on at the same time, so I work on one, then when I'm bored or tired I move on to the next.

After another 20-40 hours of labor the bike will likely be running again.

(it will take a long time before I will have ridden the bike more than it took to build it... a long time)

 

[safe]

I've been distracted in getting my old bike to work (still am) but one of the things I need to finish on this bike before winter comes is to build a fiberglass front fender that will assist the front fairing in keeping the air out of the little pocket between the front wheel and the forks.

So later this week it's supposed to get warm again and it's always easier to work on the fiberglass on the hot days because each later cures more quickly will less catalyst.

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The motor on this bike already has serious issues and I think I'm going to need to redo the timing because this is another one of those Unite motors without timing advance built in. Like with any overvolting situation, rewinding makes the motor rev higher and that means you need to advance the timing or else face breakdowns.

This bike has been ridden... but not much and I'm hoping to get it to be together again by the end of summer. (I always try to be optimistic)

Looks like any testing I'll be doing will be late summer. (we are in the middle of summer now)