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  1. #1
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    Obtaining access to downtube

    See my previous thread on getting batteries into seat tube for more information on where I'm going with this.

    For those of you who read it already: When you may have thought the sabotage was all over---it isn't.

    So I am happy with the steel frame, but I'm not willing to destroy it. UPDATE: looking into bigger, 60cm R1000 frame.


    Since I'm pretty much set at how to tackle the seat tube, I'm now wondering about the other tubes. I would like to start first considering the downtube.

    A complete battery pack is right around 27-28mm in diameter, and a 40-50cm long. The only way I think this will be possible is to drill one 28mm hole in the bottom bracket or headtube, whichever is not going to undermine the frame's structural strength too much. My hope is that with Aluminum this project will be much easier.


    Keep in mind that this is not for a removable battery pack like on most ebikes today. This is a pack that you put in there, assemble the headset and bottom bracket around it, and forget about it for 1000 battery cycles or until check-ups.


    Any guidance is much appreciated.
    Last edited by hillzofvalp; 01-24-11 at 08:55 AM.

  2. #2
    Randomhead
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    I would say that going in through the head tube is out. People have made large vent holes and caused problems there, and the head tube is not where you want to have problems. Going in through the BB may be ok, I don't know how to answer that question other than performing a structural analysis. I'm thinking that having electrical assist will reduce the max loads on the bb shell.

  3. #3
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    Electrical assist would not always be on, so we have to assume that your average 200lb person is going to be pedaling there like normal sometimes.

    Well- would it be okay to put the battery in, wire everything up, and the weld a little piece to cover and support the weakened area around the drillled hole? It might be sloppy, but at least it's not as visible as other modifications.

    Obviously the best way to do this would be to build the frame from the ground up around the batteries. I have access to people who should be able to do it for me.. but they are go-cart and EV people and not framebuilders. I rather not take the bb shell off because that would completely ruin the paint. But I might not care about that if that's the best way.

    Drilling is going to be most attractive technique to me. 28mm isn't all that big of a hole, and aren't aluminum bottom brackets a bit oversized anyways?

    Would a threadless head set give me room imbetween fork post and frame for possible wiring? hmm... that would be nice. I haven only taken apart a threadless headset once and I can't remember exactly how that works.
    Last edited by hillzofvalp; 01-20-11 at 06:43 PM.

  4. #4
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    there is some room in the head tube for wiring, not much though. There is a reasonable amount of room in the bb for wiring. Unfortunately, the heat of welding probably precludes building the batteries in on initial construction of the frame.

    Aluminum is not going to allow for post-insertion welding because it will be weaker without heat treating. I assume your cells will not take the heat of the heat treatment, and it's not economic.

  5. #5
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    How about accessing the top tube via the rear of the seat-tube. Cut a small port in the seat-tube then weld shut. This is probably a safer option than cutting a port in the head-tube because rear-end failure is much less dangerous. If welding is not possible then an epoxy/fibre glass wrap repair may be strong enough. This kind of temp repair has been used on chainstays and BB and remained temporary for many years.
    Note following this advise is probably stupid and will invariably result in death AND injury.

  6. #6
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    I don't think an aluminum bb shell would be the best thing to drill two 27mm holes into, a steel one would probably fare better. But still, it's the thickest part of the frame, a failure wouldn't be dangerous, and you bought the frame to experiment with....so get to drilling!


    As far as building a frame for this purpose, using couplers would be the best way.

  7. #7
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    Quote Originally Posted by Live Wire View Post
    As far as building a frame for this purpose, using couplers would be the best way.
    doh! talk about something staring you in the face and missing it.

    If you have some access to machine tools, it's possible to retrofit the cannondale to be something like a Rene Herse style demountable frame
    Last edited by unterhausen; 01-21-11 at 09:16 AM.

  8. #8
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    DEmountable rear is really cool, but I think that would be better for steel frames. I think this because aluminum frames are much softer, so the coupler might need to be really big (long). I rather just buy a frame prebuilt like that. Would adding couplers be better near the head tube, since the tubing is so wide down by the bottom bracket? I picture a downtube/headtube coupler and a seattube/toptube coupler. Then it would come part easily.

    I'm not sure what you mean by "two" holes, live Wire. I thought that one was already present from the factory. Here's an illustration.

    Last edited by hillzofvalp; 01-21-11 at 11:33 AM.

  9. #9
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    Quote Originally Posted by MichaelW View Post
    How about accessing the top tube via the rear of the seat-tube. Cut a small port in the seat-tube then weld shut.
    We're trying to get to the downtube because it's wider, though the top tube my be a worthy candidate, also. Not sure of the min diameter in there though. I don't know about patching that area.. I think it would look bad too

    Note: I'm not sure if the bike will be RWD or FWD, but likely RWD to avoid fork troubles.
    Last edited by hillzofvalp; 01-21-11 at 12:03 PM.

  10. #10
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    Quote Originally Posted by hillzofvalp View Post
    I'm not sure what you mean by "two" holes, live Wire. I thought that one was already present from the factory. Here's an illustration.

    []
    The pic doesn't show up for me on this comp, but you'd need the hole into the BB from the outside and then the one from the bb into the down tube, wouldn't you?

  11. #11
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    yes, you need two holes since the cannondale doesn't have a 28mm hole into the down tube from the bb

  12. #12
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    Didnt realize that. Alright--couplers. Only possible on Steel/Al frame? might be a nice project for my old bianchi tsx frame. But would batteries make it all the way down the down tube?


    this shop does retrofits, but I am thinking that it isn't possible for aluminum frames, because the parts are usually for titanium or steel frames. Bilenky is asking $550, but I wonder if I negotiate it down if I do all the paint work myself.

    http://www.bilenky.com/retro_prices.html

    Cherry Bicycles is right in town where I'm going to school actually. EDIT: they closed shop 5 years ago

    Only issue with the ability to dismount the frame like this is that I would have to lock my rear triangle and front wheel to insure low chance of theft (for I do have locking pit lock skewers).
    Last edited by hillzofvalp; 01-22-11 at 11:16 AM.

  13. #13
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    bilenky's price is before paint. Is the downtube a constant cross section?

  14. #14
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    what do you mean? The downtube is cut and then shortened a little bit.. I think the couplers take 2-3mm off the tube radius.

    The picture is based off of my limited knowledge of frame construction. I thought there was a hole through bb into down tube (like on steel frames) but I haven't received my cannondale frame to be able to tell.
    Last edited by hillzofvalp; 01-23-11 at 11:15 PM.

  15. #15
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    Can someone comment further on drilling into the bottom bracket? I just don't see it being that big of a problem. I wonder if I could add reinforcement within the bb area, while still allowing the axle to make it through. But a 27-8mm hole to me just doesn't seem like that HUGE of a deal. Though I will probably get up to 30mph more often than this frame was originally intended for, so I want to be safe, too.

    how thick is the wall between bb and downtube? 4mm? what about the bb? same?

  16. #16
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    updated pics in first post with a bigger frame.

  17. #17
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    Quote Originally Posted by hillzofvalp View Post
    Can someone comment further on drilling into the bottom bracket? I just don't see it being that big of a problem. I wonder if I could add reinforcement within the bb area, while still allowing the axle to make it through. But a 27-8mm hole to me just doesn't seem like that HUGE of a deal. Though I will probably get up to 30mph more often than this frame was originally intended for, so I want to be safe, too.

    how thick is the wall between bb and downtube? 4mm? what about the bb? same?
    I wouldn't be willing to hazard a guess if the 28mm hole is going to cause you problems. To give anything like a credible answer would seem to be a fairly complex engineering project. The loads are not known and then the frame would have to be modeled to see if the stresses are within a reasonable range. The fact is that a bb shell is only 37mm diameter. You are taking a significant part of that away. Since the hole needs to be in line with the down tube, I'm visualizing the hole needing to be fairly close to the chain stay attachment. Thus my enthusiasm for the coupler/demountable approach. I see why you don't want to do this, but in that case you are simply left to the obvious step of trying it. I believe that if it fails, it will fail slowly. You need to avoid sharp edges in the hole to lessen the likelihood of fatigue cracks.

    BB shells on a frame like the Cannondale are a constant cross section. So if you can measure the thickness at the bottom, you will know what the thickness is at the down tube interface.

    Reinforcing the bb shell is going to be a bit of a project since welding is not going to help you. You will anneal the bb shell, and re-heat treating will be required to return the shell to its initial strength.

  18. #18
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    Ok..thanks for more input. Looks like around 4-5mm from pictures. Here are some more pictures (I haven't received it yet). Such a big frame.


    Last edited by hillzofvalp; 01-24-11 at 09:18 PM.

  19. #19
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    Is this more than usual or about right? this is a 60cm CAD3 frame from 1998.

  20. #20
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    Do these pictures help you at all with anything, unterhausen?

    Is there any safe way of rigging up some couplers and installing them by a non-framebuilder (but intermediate welder)?

    Alternatively, I wonder what the best method for drilling the hole would be in order to minimize the amount of material being removed. (perfect hole)
    Last edited by hillzofvalp; 01-26-11 at 12:00 AM.

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