I decided to thread-ize build four, the mighty trail slaying dirt machine: The Off-Roader, a full suspension Giant NSR3 paired to a Gen1 GNG mid-drive.
After some experimentation with a magic pie 2 I came to the conclusion that hub motors don't like to be bogged down and I needed a mid-drive for those steep super grind off-roading trails that are common here in Prescott. Thus from the depths of electric bike part land The Off-Roader was born.
Fond memories of ol’ breaky spoke the Magic Pie 2 hard tail
It started honestly enough, a 500watt GNG mid-drive system run at a 500 watt rate, and it could have ended right there, but hey this is the endless-sphere, and if you are familiar with this forum you know about the sickly affinity people have for ramping more and more power through stuff till it blows apart… and maybe even kills someone. This leads me to my main problem with the GNG kit: blown belts.
Chompy the Beltinator strikes again.
The GNG was fun to poke along in at 500 watts, but the fun really begins around 1500. The 1000-1500 watt range gives you the power to pop a wheelie at the flick of a switch and “aint nobody got time” to go around obstacles when you can wheelie up and plow right over the top of them. 1500 watts was powerful enough to climb my 220lb body straight up the side of a mountain, and coincidentally also the wattage it took to shred the heck out of those belts. Ultimately I couldn’t find any way to hold the belts together and ended up doing the chain mod. User: Denisesewa did a great write-on exactly how to do this.
Let’s see you tear through that!
Another grievous shortcoming of the GNG was its pathetic efficiency, and by pathetic I mean my stock no-load (where you lift the tire off the ground and give it full throttle) was measuring in a whopping 230 watts. I blamed the shoddily constructed tensioners for this crazyness, so I got rid of them. I swapped the belt out for a tensioner free chain setup, and soon I was spinning wheels at a much better and slightly less awful 140 watts no-load. I took this one step further, bought a bmx half-link ($2), and made the other side tensioner free too. This didn’t have as big of an impact but dropped the no-load watt draw down to 100 watts at 48 volts and also had the unexpected, but welcome consequence of removing the need for a chain guide.
You’re telling me that all this time I could have increased efficiency, lowered noise, and eliminated the need for a chain guide for a measly $2. Why the heck didn’t I think of this sooner?
Come on 99… come onnnnnn…. DRAT, triple digit wattage draw.
For battery I started with 20ah of 12 cell but ultimately I ended up liking 10ah better as it still was giving me a couple hours of riding and weighed much less. When it came to cranking up the side of steep Arizona trails this really was a case of "less is more". I experimented with a “rain diverter” from the hardware store which worked ok, I found it a bit heavy mounted to the front of the bike, making it hard to wheelie up over rocks. I mounted it to the tail with the batteries hugging the seat but ultimately I ended up liking backpack + coiled electrical wire (like the stuff your landline phone) the best. I chose a sensorless controller due to previous issues with those tiny little hall wires breaking and hall sensors getting fried.
Having your tire get violently assailed by a bazillion thorns is pretty much par for the course around here. For my off-road machine I went with Stans, which is kinda like slime but built specifically for tubeless setups. I did the "getto tubeless tire mod" and now I can run over all kinds of stuff with no ill effect. Shards of glass, nails, thorns, pull em out, leave em in, it doesn’t seem to matter as long as it doesn’t rip a gaping humungous gash in your tire. The problem being that after about 3 months things that puncture your tire start to make the tire leak air again in which case you have to deflate your tire, pull out the “Stan booger” blorp a little more of the overpriced stuff in there in and you are good to go again for a few more months.
The Off-Roader is a tad noisy, it has a low top speed, and is not as efficient as I would like to be, but works nicely as a machine for conquering those hills that are too much for your standard hub motor.
Total price minus batteries (because I share batteries between all my bikes): about $850
$400 GNG kit
$150 Lyen 12 fet sensorless (overkill)
$20 three way toggle switch (makes things nicer)
$40 chain conversion
$10 BVM 8s (to monitor cell voltage)
Battery: 12s 10ah (I tried 18s but my leg cadence is about 100rpm and 18s spins the pedals too fast)
Top Speed: mid 20s mph after chain mod
Update 4/29/13: Well two months in I managed to strip the bottom bracket. For some reason I thought it would be a good idea to "help" the cranks on by hammering them into place first. I JB welded my BB cups back into place but a month later I managed to bend the BB spindle and mangle my sprocket on a rock. I'm not sure if the GNG spindle is cheap or it's just that the impact would have been enough to damage even a quality spindle. I am leaning more towards the flimsy spindle theory.
Update 7/29/13: I finally replaced the bent spindle and mangled sprocket. Sickbikeparts.com had the extra long spindle I was looking for. My JB welded BB cups broke off after a few rides. Not sure how to fix a stripped out BB. I'm afraid to tap the BB because the metal is so thin, I can't weld it because the bearings will die from the heat, clearly it can't be glued, possible fixes include chopping the BB off and welding a new one on or maybe I can drill holes through the bb and rivet the thing on.
Update 9/19: I have pronounced build 4 dead, but it was a fun run the GNG and I. I couldn't figure out how to fix the bb so I made my wife a SWB recumbent. I welded a snowboard to my bike to do this.
The garage floor needed a bit of purple paint too in case you were wondering.