First E-Bike Build: Surly Karate Monkey, BMC, LiPo, IGH


10 W
May 25, 2011
Seattle, WA, USA
First, I want to thank everyone on this forum for your tireless development work and tomfoolery. This bike would have been lame if I hadn't read the sphere for months as I spec'd it out and built it. THANK YOU!



My goal was to build a 30mph commuter for my 23 mile one-way commute. Charging at work is OK. I went with the front hub motor because I wanted the Internal Geared Hub (IGH) in the back. Disc brakes & IGH should be much cleaner in the winter, than rim grime & exposed sprocket teeth. Also, the bike has to fit in my girlfriend's SUV for the morning carpool.

Quick Summary:
Bike: Surly Karate Monkey 29'er (steel, rigid); Schwalbe Big Apple 700x60 (29 x 2.3) tires; Shimano Alfine 8-speed internally geared hub (45:16); Avid BB-7 disc brakes
Motor: BMC V2S Front from Ilia (ebikessf,
Controller: Crystalyte Analog from Ilia, with Cycle Analyst & Crystalyte cruise control & Tektro e-brake levers
Controls: Shifter and cruise control on the right, thumb throttle on the left.
Battery: 12S4P LiPo, 20AH, ~900WH. Using (8) Turnigy 6S 5AH packs and GGoodrum's 12S4P BMS & single-plug charge setup.
Charger: Hyperion 1420i
Power Supply: Hobbyking 12V 350W POS hair-dryer.


Flickr Photo Set:


I come from the tribe of conventional bicyclists (mountain bike, bmx, trials, cyclocross, commuting, touring, and not much spandex). I worked in bike shops for a few years while in school, but I got tired of the snobbery. I built some racecars in college (Formula SAE), and had a great time in the machine shop. Now I build reusable rockets. Speaking of which, I've got to track down Chalo...

I still commute by bike most of the time, but I recently moved further away from work. My one-way commute is 23 miles now, which was taking me 1:30 to 1:45 each way on the pedal-bike. That's fine when I feel like a bike ride, but not so great as a daily routine.

During all this time in the saddle I meditated on how to speed things up. Better aerodynamics? A recumbent? A fully enclosed recumbent? Nah, 2/3rds of my commute is on pot-holed 40mph roads, I'd be dead in a week.

I test rode a Think e-bike years ago, but it was weaksauce. Then, at work (aerospace) we started playing around with LiPo, and a lightbult went off. I could definitely build something with enough power & range to change the game if I used LiPo. Sure enough, after a few google searches, I found you guys, and the design project began.

I'm a mechanical engineer with very little electrical experience, so the battery harness design & BMS kit soldering was a welcome challenge.

Battery Schematic:

With the current limit set to 20A, it cruises at 28-32mph on the flat in 6th or 7th gear with 45:16 gearing. I only use top gear above 35mph on downhills. I'm using 14-16AH for my ride home (in the mornings I carpool & have a shorter ride). Best of all, my commute time is now 55 minutes, instead of 90-105 minutes. This bike is saving me 45-60 minutes a day round trip!

Plans / Hopes / Dreams:
Set up the current throttle through the Cycle Analyst (tonight?)
Move the battery pack to the frame for better handling, but less of a stealthy look... waffling on this.
Hook up the server power supplies I got off eBay for 24V input to the Hyperion
Thinking of increasing voltage to keep up with traffic. Still getting passed by a few bad apples when I go 32 in a 35. Thinking of going 18S4P, and just charging in two stages - 12S4P (current pack) and 6S4P (new pack which I'll add in series on the bike).
Dreaming of a 72V mountain bike with a rear mounted BMC V2T. And a cargo bike. And a bike for the girlfriend...

After 300 miles I'm smiling more and more - I think I'm hooked on this electric bike thing :) Looking forward to sharing the fun and helping my friends build similar long-haul commuters.
That is some beautiful bike! The engineering is superb. A definite great way to go e-biking.
This is an absolutely awesome job of building and documenting! I've been thinking of a custom build based on a Surly KM myself this winter and this might push me over the edge. Thanks for sharing!
Nice build leading to a very nice bike. Surly frames certainly seem to be tough and should make a durable bike.

I have a somewhat related bike that I also use for everyday commuting. By ES standards it is a rather mild bike. It has a front Ezee hub with 48 volt LiMn battery. It has a low C-rate battery, so only 20 amps for max of about 1 kilowatt. I also have a front disc brake which as you suggest is quite useful for dealing with the wet, dirty conditions of the NW winters. I have been surprised at how fast the drive train components wear, presumably due to effects of the grit that adheres to everything during winter commutes.

I have considered going to higher voltage but have not tried it yet due to concerns about damaging the gears in the hub motor. There certainly are reports in the pages of ES of hubmotor gears reduced to "peanut butter" after running at higher power. What's the max current you are running with the Crystalyte controller? 40 amps? Fresh off the charger that would get into the 2 kilowatt region. It will be interesting to follow your future reports and to hear of your experiences if you increase voltage.

Thanks for the kind words everyone :)

Rich, I set the CA current limit to 20A to preserve range & battery life. I tried a commute at 25A and my top speed was faster but I didn't make it home any faster. I think I'm dropping off the performance curve at that point.

Thanks for the reminder on the gears, I'll do some more research before reconfiguring the pack. Maybe it will be 18S3P, for a total of 9 packs, which would only cost me $50 + one more BMS board.

Here's what the 48V vs. 72V systems look like on the awesome simulator at


No idea on controller settings for this simulator, but it's a start.
From reports of others on ES, it is my understanding that BMC has made substantial improvements in the gears over time. So being at about a kilowatt, you may have considerable room to increase voltage/power. Increasing the current limit should have increased acceleration somewhat and speed going up hills, with little or no effect on top speed. The increase from 20 amps to 25 amps may have a small but measurable effect on your trip time. On the other hand, my own commute has enough variability due to traffic, signals etc. that it would probably obscure any subtle changes.

Probably don't need to say this but as you go faster, be careful out there. As I read from someone else on ES, you should have the attitude that you are invisible to some motorists and have a target painted on you for other motorists. Encounters with 2 ton powerful vehicles can be hazardous. I have had cars drive me into the curb when they cut inside on a curve. A lot of my commute is on a busy 4 lane urban road with most of the traffic at 50 mph plus. Almost everyone I know who regularly commutes by bike has had an accident caused by something beyond their control.

nice looking build - I love that bike you chose id really like to get one myself possibly next year.

Thanks for sharing.
Excellent work. Got to beat my try this, well that don't work, methods.

12s 4p yeah baby.
Thanks again for the support everyone.

Safety is a big concern for me, and I realize I'm getting into motorcycle territory here (almost). I don't want to go faster than traffic, I just want to keep up on certain portions of the road where a few bad apples still squeeze by me when I'm doing 30 in a 35.

Here's the plan for adding one more pack and reconfiguring to 18S3P. I'm ditching the fuse block and running inline fuses from the battery + bullets to terminal bolts or the key switch terminals. I figured the key switch location in the middle would be convenient, though it could really go at the main + or - leads as well. Anybody see any bad ideas here?

How stable is the Karate Monkey at speed?

The reason why I ask is that I did a 13 mile round-trip this morning (40 min. total) at 22-28MPH powered, up to 36MPH on the downhills on my Diamondback Century flat-bar road bike. I *personally* find that compared to the Novara Strada that I had before with drop-bars, the Diamondback is far more "twitchy" at speed in the front end. I feel like I don't want to even take a hand off the bars to signal at that speed.

My gut feeling is that the Karate Monkey with 29's and balloon tires, plus the bars you have installed would be a far more stable platform.

It's super-stable, especially with that short stem. I've taken a hand off at 30 and it does a very small shimmy, but it never gets scary. The panniers wag a little bit when I swerve, so I'm going to work on stiffening that up. But the front end is awesome.

I just swapped the stem out for something longer (the short one was sitting around) and it's slightly less stable, but a better fit.
Denny, I'm live in Lynnwood (Brier) and work in Renton. If you're agreeable, I'd love to meet you to see your KM. I've already had a discussion with someone at Recycled Cycles about doing a custom build...

You should put yourself on the forum map so we can keep track of all of us members from the seattle area!
TonyReynolds said:
This is an absolutely awesome job of building and documenting! !

+1 Outstanding job mate well done, will be very beneficial for future
members wishing to build a bike from scratch...


p.s the rocket is hella cool to you must LOVE your job i bet!
dennyt said:
Power Supply: Hobbyking 12V 350W POS hair-dryer.

Girlfriend says this: "even the worst power supply can help you achieve great volume and lift" :lol: :lol: :lol:

Anyway, nice bike. You should really fit those batteries into the triangle with a crystalyte or falconEV bag if that will work for you. Weight balance will improve greatly. Just a suggestion.

The panniers are not so bad though. Very clean build there.
Nice Job! :D

Hard to beat the efficiency of a geared motor, and nothing is simpler to install than a front hub. 8)

I'm sure that will do very well for you, just be careful, even if you up the speed, there will always be the bad apple that assumes you are slow and must be passed regardless of your actual speed.

I'm willing to bet that even if you were going 40 MPH in that 35, the bad apples would still try to pass you not even paying attention their speed.

Thanks for all the nice pics with such detail! :)

I too love the IGH's especially the NuVinci (I had just decided I was done with derailleurs! :roll: :lol: ) I actually got into using mine as transmission for a mid-drive on a lark, had no idea I would fall in love with the idea. 8)
Well, I missed the 1000 mile mark, so here's the 1147 mile update. Two months in, it's getting colder, and I'm still commuting 4 days a week!

Salsa Gordo rims installed, 35mm wide vs. the old 24's. Much less sidewall flex at 40psi with the big fat 60mm tires, and less fear of tacoing. And they're full black sidewalls, the bike looks much meaner now.

Just found this nasty cut in my tire! For two weeks I've been wondering what that bump in the ride was, but my fender hid the damage. Had to boot the tire from the inside, & filled the gap with silicone, but I think it's new tire time. I've definitely hit mystery debris in the dark at speed...

New Controls: Ditched the left-side thumb-throttle and went with the Magura twist & Oury grips. Love it! I had to bend the Alfine shift levers down to clear the throttle. I'm not using the Cruise Control any more, so that's going to go away. I hooked up the Cycle Analyst "current throttle" option, which works but has poor response (slow, with overshoot...) as documented here:


Battery Pack: Reconfigured from 12S4P to 18S3P, adding one 5AH pack and bringing the pack up to 1026 WH. I've always wanted to put the packs in the frame triangle, but everyone kept commenting on how stealth my bike looks, not like an electric bike at all, so I decided to stick with the pannier approach. The new pack is narrower & taller, which wags the tail less when it's strapped tightly to the rack. A few mods to the rack quieted up all the rattles, now the bike just makes balloon tire noises when I hit bumps!

I ditched the fuse block & went with soldered blade fuses, and located the kill switch between the 12S and 6S packs, and also used it to interrupt the charger plugs. This way, one switch kills power to the controller and charger, should anything go wrong.

(yes the AH numbers at each plug are wrong, should be 15AH)

Two charge plugs & battery switch:

Battery pack in the right pannier:

I've been keeping track of energy usage, on about half of my trips. WH/Mi is at the controller, and MPG-E is at the wall. A lot of the variability is due to winds, and all of the data above 24mph is with the 18S pack.

All photos posted in this flickr set.

30mph is my new minimum cruising speed, with a 10mph headwind. I've had a few good tailwind days & cruised at 36-38, with some short stretches up to 42mph on the flats. This is with 18S and a 20A current limit. I don't have a thermocouple set up yet, otherwise I'd be tempted to keep pushing the amps up. Some cars still pass me, but I keep up with traffic much better than before.

I'm having some wheelspin problems in the rain from a start. Part of this is FWD, and weight distribution, but the most annoying part is the throttle interface. The Current Throttle is better than the standard throttle, but it's just not right. A long delay followed by a surge, it almost put me down at an off-camber stoplight, the wheel spun & took off sideways, I barely got a foot down in time to save it.

Hopes & Dreams:
-Brake light, for playing in traffic. Maybe I'll even do a big LED array like this:

-SpokePOV kits received! Just need to sit down & solder them up, and figure out waterproofing. Stoked!

-Arduino Throttle Interface. Just received my Uno to play with, I'll probably package it all up with a Nano once I know what I'm doing.
-Traction control using hall effect sensors on the brake discs, to get multiple pulses per rev. Lots to learn here! Sure, RWD would eliminate this problem, but I'm having fun with what I've got :)
-Studded tires for the coming ice
-Hand guards for warmth, with integrated turn signals?
Denny, looks good! Sounds like you're definitely enjoying it!
The good:
Over 1500 miles on the bike now. Got my SpokePOV kits assembled and mounted. They're super bright!

The bad:
Got my studded tires mounted... and lost 25% of the studs on the first commute. Schwalbe Marathon Winters, I'll have to call the supplier. I was trying to take it easy, but inevitably spun the wheel now and then.

The ugly:
Throttle connector failure -> trailside repair in the dark -> accidental WOT -> wheel spinning 60mph in the air as I hold up the bike -> front brake -> e-brake cutoff not working (loose connector inside controller) -> reached to turn off controller while motor is stalled at WOT -> POP POP -> oops. Do not pass go, pedal 22 miles home. At least it was a beautiful night!


Glad to find this thread as a repair guide:
Update - after several months avoiding fixing this ("It's ski season! Replacing FETs is hard! I'll just drive to work!") I'm back on the e-bike.

-Ordered FETs, tried replacing them (difficult soldering). Tested it with a known-good throttle and instantly blew the controller again on first application of throttle with the wheel off the ground. Guess I didn't repair it right, or something beyond just FETs was wrong with it. The sparks and smoke were impressive!

-Also blew the fuses in my battery pack during this event. Two of the three parallel strings blew normally, and the last one seems to have sustained arcing across the terminals! Exciting! So yeah, 12V blade fuses aren't robust for a 72V system. But we all knew that.

-Replaced the controller with a new one and fixed the battery fuses. Controller works!

-Tried the Magura throttle that was on the bike at the time of the first incident - no go. It was late so I didn't test it to find the root cause, but I suspect this is what went bad first. So, I swapped the half-twist throttle on to get the bike rolling for now.
*EDIT* - confirmed the Magura is dead. Resistance goes from 0 to 1.5K then back to 0 at full throttle. Damn.

-Had three awesome commutes this week! Made it home faster than my girlfriend yesterday - pouring rain, terrible traffic, passed hundreds of stopped cars. E-bikes are the best!
Just finished up a fabulous summer of commuting. 4700 miles on the odometer, 3200 for the year so far. I freaking love this bike!

I bought a scooter helmet, the HJC IS-33, which is also great. Much quieter and no more blurry eyes the whole way home.

I think I'll take the hub apart once the rain settles in. The bearings are picking up some play, and I want to make sure the gears are happy. The front tire is almost worn out, and I might switch to a non-slotted rotor to quiet it up.

I've been commuting with a GoPro on my handlebars, recording just in case. Hope to find the time to edit a highlights reel soon :)

Viva la e-bike commute!
I like your build. I was just searching ES for reliable builds (revolving around a steel frame) and your bike popped up (lucky me :idea: ). Being the infinitely curious person I am, I started just google searching for all kinds of related shite. I found this: . It's a frame bag designed around most of surlys middle frame. I did remember reading about someone suggesting it to you maybe for an improvement in handling, though you thought your rear pannier setup was adequate. Just throwing it out there (I'm not sure how waterproof the bag is compared to your current setup). Cheers!
Nice work using the surley 29er..

just wondering if you got those leds on the back or front? heres my tail light.. pretty easy to make..
also with that issue you had with the lag on the cycle alalyst current throttle, you must set the minimum throttle out voltage to the minimum voltage you need to make the controller start moving the wheel ( take off .1v so it doesnt move until you throttle) test by pressing left button from main screen and you can see throttle out, take note when wheel starts to move , and thats your value.. throttle out max should be about 3.9v but you can test this with the same method, just see when it stops getting faster. controller may cut out if too high for throttle short protection (geting close to 5v)
you can set the ramp up to 50 to make it ramp up slow to give great efficiency, or 200 is a quick pick up rate.
btw lucky you didnt get a flat with that slashed tyre. thats crazy..
I know it's bad form to resurrect an old thread, but I must say that a bike like this is eerily similar to what I'd build today for a similar use. I've kinda convinced myself to go mid-drive, and a Bafang Ultra at that, and I'm lamenting that there's so few options that have steel frame, disc brakes and an IGH when it just makes so much sense to me.

dennyt said:
I come from the tribe of conventional bicyclists (mountain bike, bmx, trials, cyclocross, commuting, touring, and not much spandex).

All my background is in touring bikes and though it doesn't necessarily make sense to electrify a touring bike for touring purposes, I do think an electric touring-style bike makes a great "one bike" or "do it all" bike, just as a non-electric tourer does.

I just love your build so much, thanks for sharing it. I wonder if it or something similar is still in use.