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1940s Monark -- BBSHD Conversion

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    1940s Monark -- BBSHD Conversion

    Hi everyone! I am a student at Cal Poly San Luis Obispo in California, and I am studying mechanical engineering. I love Cal Poly because it is a very hands on school. I am in a senior level bike design class, and for my project I am restoring and converting a 1940s bike into a E-Bike to commute to work on when I graduate! Follow along as I document my build.


    For the first post I will show the frame I found and my plans for the build.


    I would like to design a bike that is stable at higher speed than general road riding. The rider should be comfortable, meaning that he or she can see the road ahead in a comfortable position and that there is some sort of suspension to smooth out the ride at high speeds. Safety will be considered for the rider and from electric hazards. I would like to add disk brakes front and rear for adequate stopping power. Finally, I would like to keep as much of the original styling aspects of these bicycles as possible.

    To accomplish this, I will start with a 1940’s Columbia bicycle frame with springer fork and fenders that I found on Craigslist. From here I will modify the geometry of the headtube angle, chainstay, and bottom bracket height for stability at high speed. The desired top speed is 20-30 mph compared to my average road riding pace, 16-17 mph. I will also need to add disk brake mounting tabs to both the front and rear of the bike. The current rear hub spacing is 4 ½ inches, and to accommodate modern hubs at 135mm, I will need to modify the rear end. I expect to make the majority of my geometry changes to the rear of the bike to preserve the aesthetics of the current frame. Since a lot of the required structural changes to the frame are in the rear triangle, this works out well.



    I'll add more to this as I continue!

    #2
    Welcome to the forum! This should be a fun project, can't wait to watch it unfold.

    Comment


      #3
      Welcome to the forum. I look forward to learning the design decisions behind the choices you make in your build.

      Do you have plans to modify the front suspension? The spring by itself will most likely make the handling of the bike worse than a rigid fork. When the front wheel hits something it will start to bounce until the kinetic energy of the impact is converted into heat by the repeated flexing of the spring. All modern suspension systems include some form of dampening in the system to reduce that oscillation.

      Just a heads up that the engineers who designed your suspension didn't consider the possibility of traveling at 30mph. I have a 1930 Dodge which is a joy to cruise around at 30-35mph. By 40mph it is a death trap. The slightest bump causes the front end to bounce uncontrollably.

      Comment


        #4
        Do those handle bars come straight back? I have been noticing classic handlebars in photos and movies like the Legend of Bagger Vance, the kid's bike early in the movie. A bike on American Pickers, a photo of an early Harley and some random movie last summer. They seem to come straight back. I wonder how comfortable they are?

        Comment


          #5
          Originally posted by funwithbikes View Post
          Do you have plans to modify the front suspension? The spring by itself will most likely make the handling of the bike worse than a rigid fork. When the front wheel hits something it will start to bounce until the kinetic energy of the impact is converted into heat by the repeated flexing of the spring. All modern suspension systems include some form of dampening in the system to reduce that oscillation.

          Just a heads up that the engineers who designed your suspension didn't consider the possibility of traveling at 30mph. I have a 1930 Dodge which is a joy to cruise around at 30-35mph. By 40mph it is a death trap. The slightest bump causes the front end to bounce uncontrollably.

          Riding the bike around as is, the fork does not seem to be that bad. The mass of the system and the small amount of suspension travel does not create an overly undamped feel. I will see what happens when I further increase the mass of the system and go from there.

          As for the handling of the bike, my plan is to alter the geometry of the bike by modifying the rear triangle to make the high speed handing more stable. I am using the Patterson Control Model (PCM) as part of my class to measure the properties of the bike and compare them to other bikes that I know ride well. I believe the PCM is available online with a quick Google search.

          Comment


            #6
            Originally posted by calfee20 View Post
            Do those handle bars come straight back? I have been noticing classic handlebars in photos and movies like the Legend of Bagger Vance, the kid's bike early in the movie. A bike on American Pickers, a photo of an early Harley and some random movie last summer. They seem to come straight back. I wonder how comfortable they are?
            They do not come completely straight back (sweep), but are very close (maybe 5-7 degrees or so). Directly straight back would definitely not be comfortable. I really like the look and am not bothered by their shape. I think the very upright positioning helps and rolling the bars so that they are slightly upwards.

            However, likely the biggest issue for me will be their width. If you are familiar with dirt bikes or mountain bikes, they have generally gone with wider bars which increase stability at speed by 'slowing' down steering--a wider bar requires a large rotation of the handle bar for a given turn, therefore it has a less 'twitchy' feeling. I really like the look, so I have found some wider bars with less sweep (don't have exact measurements right now) that I will compare with. They dont look as cool, but they might work better.

            Comment


              #7
              Originally posted by gbelyea View Post
              I am using the Patterson Control Model (PCM) as part of my class to measure the properties of the bike and compare them to other bikes that I know ride well. I believe the PCM is available online with a quick Google search.
              I believe that that Patterson Control Model gbelyea is referring to can be found at http://www.calpoly.edu/~fowen/me441/...gQualities.doc

              Comment


                #8
                Another interesting read is Motorcycle Handling and Chassis Design by Tony Foale. The higher speeds of an ebike might challenge some of the assumptions used in the PCM.

                Comment


                  #9
                  Back in the 60's I had a Whizzer with a cantilever frame and a front fork just like yours. That fork worked great and the bike handled really well. The bike would do around 40 mph and it never felt out of control. The brakes could have been better though. I had a coaster on the back a poor drum brake on the front. My braking was the plan ahead type.

                  Comment


                    #10
                    Originally posted by calfee20 View Post
                    Back in the 60's I had a Whizzer with a cantilever frame and a front fork just like yours. That fork worked great and the bike handled really well.
                    Interesting. Looking forward to gbelyea's analysis.

                    Comment


                      #11
                      You will have to work around that BB, I believe it's an American/English standard. It can be done, but will require a special adapter to be machined and pressed in the BB itself.

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