Building a 1000 watt mid-drive electric full-suspension folding bike
I'm pretty happy with the way the bike came out, and I've been using it to commute for a whole week without any issues. Huge hills that used to be painful for me on the way home feel just like flat ground. The bike tops out at about 30 mph, which is much faster than I ever want to go. My commute involves multiple segments: biking to the train, riding the train, biking to work, and then back again. I've been riding a Dahon folder for about two years now, so I wanted to keep the ability to bring it with me wherever I go. The finished bike folds to approximately the same size that it did before electrification, so I'm very happy about this. The only real difference in the folding now is that the seatpost is blocked by the motor, but this really isn't an issue in practice.
Folding the bike (video):
The donor bike was a 2008 Dahon Jestream that I've been commuting on for ~2 years now. I previously added an Axiom Journey cargo rack and built a new rear wheel incorporating a Shimano Nexus-7 internally geared hub. Even without a motor this was a fun bike to ride... the suspension works great to smooth out potholes and the occasional curb jump.
My biggest concern with this build was the configuration of the bottom bracket on this bike. As you can see, the seat tube actually exits ahead of the bracket, leading to some slight interference with the motor. I decided not to modify the frame in any way, since in reality - with such a big chainring - the motor clearance is fine.
The chain line is pretty great, and it certainly helps to have the geared hub to play aroung with rear cog tooth number.
I'm running a Surly Singleator chain tensioner in the "push-up" position to add just enough tension to keep the 1/8" chain from slipping off at full throttle.
I've run the gear sensor just behind the chainring, in between the shift cable standoffs. It's really quite stable here and doesn't cause any interference.
The chainstays on this bike are flared out, with a small flat area near the dropouts. This is where I decided to mount the speed sensor, as it allows me to make the most adjustment, and the spoke angular velocity is lower toward the hub so I believe this allows the sensor to function better, and lessens damage to the sensor in the event the magnet collides with the sensor body.
I really lucked out with the battery mount, since the staff at Cambridge Bicycle pointed me to this awesome Blackburn Outpost rack that mounts like a waterbottle cage. The finished mount allows me to fold/unfold the bike easily, and the weight distribution is ideally better than mounting under the seat or on the rear rack. The battery bag that Luna supplies is really well made - seems very watertight, and mounts just fine as a saddlebag as well using the velcro straps.
The rear shift and brake lines run under the monotube through eyelets that are nicely sized and spaced to allow the BBS02 wiring harness to run between them.
Up front there was a bit of wire mess, but after lots of 8mm cable wrap the cables/wires are much easier to deal with.
I really like the new full color DPC-14 display. It's very easy to read outdoors, and the information display is quite useful. I'm not sure the speed is accurate (compared to GPS measurements), but it's close enough. Voltage and amperage displays are helpful as well. The left-side throttle feels good, and integrates well with my right-hand shift controls.
Under the rear rack, but above the fender, I've mounted an Ortlieb micro saddle bag.
The whole bike still folds almost exactly like it did before adding the motor.
There's also plenty of retroflective tape on the bike for visibility.
Bill of materials
|Shimano Nexus-7 hub||$160||Amazon|
|Sunringlé CR-18 rim||$30||Amazon|
|Schwalbe Marathon Winter studded tires||$40 x 2 = $80||Amazon|
|Axiom Journey rack||$40||Amazon|
|Ortlieb Commuter bag||$200||Ortlieb|
|8mm cable wrap||$10||Amazon|
|52v Mighty Mini Cube Ebike Battery Pack Panasonic GA 7ah||$355||Luna Cycle|
|Bafang BBS02 750w Mid Drive kit||$544||Luna Cycle|