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    Tandem project

    Hi All,

    I am thinking of fitting an electric motor to a Cannondale MT3000 tandem mountain bike. I'm wondering if anyone out there has had experience adapting either a mid-drive or hub motor to a tandem. My tandem has a 145mm rear spacing and it seems hub motors with that spacing aren't available or I'm looking in the wrong spot. If I was to go the mid-drive route, I was thinking of mounting it up front and running a chain to a chainring on the rear bottom bracket and then have the other chainring power the wheel. I like the hub drive from the point of less drive train wear though. Thoughts?

    #2
    I converted two tandems with e bike kits. One was an aluminum tandem similar to the older 27 speed Cannondale tandems which I installed a BBSHD mid drive on. It had a 160 mm rear hub for some reason- I don't think that was standard (at the time only Santana tandems had that). The build was very challenging, I put the motor at the stoker's BB and used the stock BBSHD chainring plus an additional timing chainring on the BBSHD to link to the front. The front BB used a freewheel adapter on its chainring so the pedals wouldn't be powered with the motor on, an important safety feature. Another freewheel is built into the BBSHD, thus it works for two the same way it would on a single bike conversion. I did away with the stock display with the PAS system and built my own Cycle Analyst type system which allows setting a wattage assist level, or using the thumb throttle, or the throttle to override the wattage setting. The battery is a triangle battery which uses Velcro to fit in the frame. I liked the performance, it could be ridden one person or two. Top speed and climbing speeds are the same as a single bike conversion, you would like it, plus it is very quiet.

    The problem was it was hard to transport without a van. I bought a custom tandem frame from China that has S&S couplers to make it easy to fit in the backseat of a Toyota Camry. So I needed a e bike conversion that could be disassembled easily- the simplest is the front Hub motor, just remove the wheel which you would have to do anyway for transport. I chose the Bafang geared motor. Its installation was easy, although just about everyone has to get their hub wheel re-centered so the rim runs centered in the fork, apparently they don't do that at the factory (costs $35 or so). I used the same triangle battery, and a different than stock controller again with my own Cycle Analyst type setup. It works well, but speed is limited to 20 mph not the 28 mph of the mid drive. It also makes a bit of noise due to internal gearing. A direct drive hub motor wouldn't have that noise, but then again, it might overheat going uphill with 2 people. Be aware the motor provides up to 1000 watts of power, and that will deform your dropouts just like cutting butter. Install a torque reaction bar between the motor and fork to solve the issue.

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      #3
      Hey thanks for taking the time to reply, jbike! I'm going to continue researching and doodling on this project. I'm in no real big hurry to get it done, so I want to take my time and do it right.

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        #4
        Any rear 135mm hub motor I've seen had an axle that was long enough to use with 145mm rear spacing. Our tandem also uses that size and all it took was adding a few washers on the inside of the frame to make it work. I initially used a BBS02 mounted like jbike up above did. I ended up taking it off after 2000 miles. It wore out the chains really fast and it made shifting more awkward. The 1000 watt rear hub motor I installed has worked flawlessly for over 5000 miles so far.

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          #5
          Thanks for the reply, BK! I'd be curious if you'd be willing to share some pics of your tandem. Mostly interested in how you mounted your battery pack and what voltage you're using.

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            #6
            I use both a 48 volt 20 ah and 52 volt 14 ah battery. Mounting on our tandem will be nothing like yours! Our trike has 2 parallel tubes on the top of the frame so it was no big deal to mount the batteries.

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            • Wattsup
              Wattsup commented
              Editing a comment
              That's a nice looking rig you have there! Looks like you have plenty of battery power available.

            #7
            Well, I pulled the trigger the other day. I ordered a front hub and all the fixings from Grin Technologies in Canada. They seem very knowledgeable and I'm looking forward to the build.

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