Electric Bicycle Road Racer (R&D)

Discussion in 'Electric Bicycles' started by safe, Jun 12, 2009.

  1. safe

    safe Active Member

    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.

    [​IMG]
     

  2. safe

    safe Active Member

    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...
     
  3. safe

    safe Active Member

    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)
     
    Last edited: Jun 12, 2009
  4. safe

    safe Active Member

    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.
     
    Last edited: Jun 12, 2009
  5. safe

    safe Active Member

    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.
     
    Last edited: Jun 12, 2009
  6. safe

    safe Active Member

    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.
     

    Attached Files:

    Last edited: Jun 12, 2009
  7. safe

    safe Active Member

    Blown Transmission

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

    [​IMG]

    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.

    ----------------------------------

    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. :ack2:

    ----------------------------------

    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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    Last edited: Jun 14, 2009
  8. nadroj

    nadroj Member

    wow that is too bad about the hub, have you thought to try the nuvinichi(SP)
     
  9. safe

    safe Active Member

    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.

    ----------------------------------

    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.

    ----------------------------------

    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)
     
    Last edited: Jun 15, 2009
  10. safe

    safe Active Member

    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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  11. safe

    safe Active Member

    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)

    [​IMG]

    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...
     
  12. woody

    woody New Member

    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
     

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  13. safe

    safe Active Member

    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.

    ---------------------------------

    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.

    ---------------------------------

    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...
     
    Last edited: Jun 17, 2009
  14. woody

    woody New Member

    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.
     
  15. woody

    woody New Member

    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.
     
  16. safe

    safe Active Member

    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... :rambo:
     
    Last edited: Jun 17, 2009
  17. duivendyk

    duivendyk Guest

    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.
     
  18. safe

    safe Active Member

    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.
     
  19. safe

    safe Active Member

    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)
     
    Last edited: Jun 24, 2009
  20. safe

    safe Active Member

    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.

    --------------------------

    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)
     
    Last edited: Jul 20, 2009
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