Motorcycle Experiment

I recently completed this DIY electric motorcycle.  Weighing in at 125 lbs this one-off prototype is super fun on tight and/or sweeping single track trails.  As of this writing I have about 20 charge cycles on it and next steps are to make it street legal, improve the battery charging procedure, and to keep having fun riding it.

I sold my DRZ400S after doing the Trans America Trail and put those funds into this project. You can check out my trail blog at www.talesfromthetat.wordpress.com if you like.

I’m not the only one who thinks this is area of light weight electric motorcycles is an unfilled niche. Check out the French guys doing LMX and the Sur Ron bike from China too.

This was taken just after the first test ride around the neighborhood. So far so good. It wheelies easily and has plenty of power. Throttle response settings took a little while to get sorted.


Stats:

  • 7500 watts continuous (this is the output it will give all day without melting). That’s about 10 hp which doesn’t seem like much but since it’s electric it is a whole different world from a 10 hp gas motor. Another factor to consider with electric is that most motors will put out double their “continuous” rating for short bursts like 30 seconds (IF your batteries and controller allow). Regardless of the numbers there is a smile inducing sense of ample power. It wheelies with ease – at slower speeds. I do miss having a clutch.
  • 52V – 30Ah battery. Cells are Samsung 30Q
  • Kelly KEB72380 Controller
  • Shimano Saint Brakes – I need to add a larger rotor to the back wheel but overall the brakes are excellent.
  • CR125 seat
  • YZ250 foot pegs
  • 50″ wheel base (downhill bikes are in the 45″-50″ range and modern dirt bikes are around 58″)
  • 35″ seat height (modern dirtbikes are generally 37″)
  • 125 lbs. For reference: downhill bikes ~ 35 lb range, modern gas dirtbikes are at least 220 lbs
  • 67 degree head hangle
  • 13″ ground clearance (similar to modern dirt bikes)
  • Front and rear suspension travel is 7″
  • Range: so far I get about two hours of road riding or three hours on single track trails.

Here I have turned the smaller scale drawing of the frame into a full size on brown paper so that I could verify bend angles on the frame tubes.

Here the main frame is just about ready to weld. I used .063 wall 7/8″ diameter 4130 Chromoly tubing for the main tubes and built a jig to hold all the pieces together during welding. Swing arm pivot tubes and a head tube were machined and mounted to the jig before fitting of the main tubes.
A free program called tubejoin made it possible for me to model the tube joints in 3D and then print the intersection or cut paths so that I could make really tight fits. The way it works is once you print the cut path on paper you then wrap the paper around the metal frame tube and cut away the metal until you reach the line of the cut path. It worked super well as you can see in the photo. Thanks to open source software. Check it out at https://cq.cx/tubejoin.pl
For the primary design work I used the good old pencil and paper. It really would have helped to model it in 3D to really understand some aspects but this is what I had to work with… You can see here that the main frame design is on the page behind the vellum which is where I worked to identify the best leverage ratio for the rear shock placement

One of the things I aimed for with this build was to minimize unsprung weight.  This is a known key to maximized suspension handling.  This photo compares rear tires from three bikes:  at far right is a massive back tire from my CRF450X, in the middle is the one from my current electric motorcycle experiment, which weighs less than half that of the traditional motorcycle rear tire, and at left is the back tire from a Specialized Big Hit – downhill bike, essentially a 24″ bicycle tire.  

Here I’m lacing up the rear wheel for my electric motorcycle experiment using a Pro Wheel 19X1.4 rim, Oset hub and custom SS spokes.  For now I’m leaving the front wheel a regular 26″ downhill bicycle rim with Maxxis tire.  If I end up doing the taco to it or going for DOT approval I’ll switch to something more like this for the front also.

Here the swing arm is being welded together. I used an air cooled Miller Econo-Tig.
In this photo the rear subframe (where the seat is mounted) is being figured out.
Little clip of it being ridden by my friend Travis.
I did the final assembly and wiring in a small Albuquerque broom closet – early winter of 2019.
Headed to Kairos, WV for a ride with a friend and his KTM 200 two stroke. We did a bit of single track in the rain and traded bikes mid ride. When we got back he said he wanted one like mine. I have to admit the KTM was super good. Probably the best traditional woods bike I’ve ridden to date.
After a mud fest at Kairos, WV. Bike did great. Super easy to handle in the tight and slick conditions today. My new fenders did a pretty good job keeping the electronics dry and clean. I made the mud guards of black plastic from a cheap waste basket and some zip ties.