For a long time I’ve wanted to build the ultimate snow machine. This fatbike would have an insanely powerful motor and no suspension components whatsoever. I wanted the power to be harnessed with a Nexus 3 speed IGH which would allow it to plow though a foot of heavy snow or go 40+ mph on the road. The most important thing to me was power and weight and I didn’t care that much about the price. What I ended up with after a lot of head banging was the Ba Ba Black Sheep which looks like a cheap fatbike but rides like an ultralight motocross machine. Although the Ascent has not been tested extensively in the snow yet, I expect that it will perform well with the additional waterproofing of the electrical connectors. On the singletrack trails this thing is scary powerful and feels borderline out of control all the time. It is the first build that I’ve had to exercise serious restraint on the throttle with.
I call this build Black Sheep because it really is the Black Sheep of the single track trails. I want to keep all my mountain biking friends and not have them burn my house down in my sleep so I only ride this monster on private land.
Did I really throw a $2100 6000W Ascent mid drive on a craptastic $399 fatbike? You bet your ass I did.
I had been trying to figure out the correct gearing system for this build for a long time. I started with Nuvinci N171 which started to leak the first time I took it out and pumped 4000W into the drive system. It was way too heavy anyway and it felt like I was dragging the back end over everything int he woods. The next thing I tried was a single speed and that worked well when the bike was moving but the top speed sucked . When trying to start from a standstill on an uphill slope the 3220 Astro Flight made a bunch of noises that I know it should not be making that sounded like “Really? You really want me to climb this hill, from a stop without any gears?”. I laced up the rear rim with a Nexus-3 which has proven to be incredibly robust in my other high power mid drive applications. In 2nd gear the 4 pawls lock in place and you can literally dump as much power as you want into it without fear of mashing delicate gears or teeth. I’m not aware of any other IGH which is better suited to this application. As long as you exercise restraint and do not shift under load you should not have problems.
The front rim is mounted with a ghetto tubeless super fat 4.8 Surly Bud
The heart of the Ascent system is the centroid gear reduction. This build uses the 20:1 gear reduction, although it would probably work just as well or better with the 40:1 reduction. When plowing through deep snow you need a lot of torque and the 20:1 reduction does not produce that much power until it starts spinning where the 40:1 seems to produce more power from a standstill. The front tire is mounted with a tubeless Surly Bud which is one of my favorite deep snow tires. I tried mounting a 4.8 Surly Lou in the rear but I could not get it to stop rubbing on the Deadeye Monster frame so instead I opted for the 4.5 Vee Rubber Snow Shoe which fits well and leaves enough room for tire chains.
I found this great cog for the Nexus-3 with a built in chainguard on ebay. It really helps with the wacked-out chainline you get with a 100 BB and a 135mm rear dropout.
I really like the Deadeye Monster fatbike as a donor because it has horizontal dropouts so you can fit an IGH on the rear without a tensioner and it costs less than $400 shipped here. I’m not sure why aluminum framed fatbikes are still so damn expensive, and the brakes and the tires on this bike should be upgraded, but the rest of the bike is equal in build quality to your average $200 Walmart bike, with an aluminum frame rather than steel. The Beast and Dolomite from Walmart both weigh in at about twice what the Deadeye Monster does. I have about 15 fatbikes in my shed and not a single ‘REAL’ brand name fat bike. I’m just too damn cheap.
The CA v3 setup on the Ascent is mildly annoying but a necessary evil to control the Astro
I think for most people it makes more sense to add the Ascent mid drive to a decent full suspension ebike. There are plenty of times on the trail where I feel totally out of control with this bike. It goes way too fast and has an incredible amount of power. I ended up buying a Cane Creek 40/44 headset so I could mount a Bluto fork on the front of this build. I will swap out the Bluto in the winter and go back to a rigid fork as the Bluto has a nasty tendency in cold weather to let air leak into the bottom air chamber.
The Talon controller can support up to 120Amps, but the high voltage cutoff is 60v so it will only work with a 12S Lipo pack or a 14S 18650 pack
I was impressed with the Talon controller which is an upgrade from the incredibly tiny Castle Creek controller on the 3000W Ascent version. I would recommend that you silicone where the phase wires go into the controller as you can actually see the plating on the connectors and if it gets wet & muddy on the connectors the motor will almost certainly stop working properly. I also recommend that you silicone the CA connectors that are closest to the drive unit to protect them from water creeping in.
A Thudbuster LT is needed on any Ascent mounted hardtail and the Snowshoe 4.5 will give excellent rear traction in the snow
You will have to pick a chainwheel/sprocket combination that will work for your application. I was nervous about using a Raceface Narrow\Wide 34T chainring with over 4000W of power but I have to confess that my fears were unfounded. The Narrow\Wide tooth configuration helps the singlespeed KMC chain stay on even with a pretty bad chainline. In the rear I found the CS-S500 18T cog which has a built in chainguard for about $11 online here. The Nexus-3 hub I built up I got from amazon for $78 here but be aware it does not include the shifter (make sure to get one with the cables and bellcrank included) and centerlock adapter.
The 6000W Ascent is the most powerful and lightest mid drive unit I have tested to date
There is a fair bit of discussion on the Endless-Sphere forums about whether gearing is even necessary with high power mid drives. I have to say after a fair bit of experimentation that at the 3000W continuous power level I can say in no uncertain terms that you will be happier with the 184% of range that the Nexus-3 provides. Originally I tested the Nexus-3 extensively with the BBS02, then later with the BBSHD and the Cyclone 3000W drive system and I can say that as long as you’re not shifting under load the Nexus-3 is remarkably strong, especially in 2nd gear where 4 Pawls lock into place and you get a 1:1 power transfer.
Here is a breakdown of the costs I have on this build (minus the battery)
$2100 Ascent 6000W drive system from Tangent (currently not listed on their website but it will be soon)
$399 Deadeye Monster from Bikes Direct
$120 Nexus 3 IGH, shifter & centerlock adapter Amazon/ebay
$45 Snowshoe 4.5 72TPI rear tire
$129 Surly Bud 4.8 120TPI front tire from Treefort bikes
$75 BB7 brakes from ebay seller cycleling in Hong Kong
For a total of $2868
For less than $3000 I got an ebike that literally blows away everything else electric powered that I have ever ridden (and I have ridden a lot). Once you get the feeling of 4000+ watts between your legs the ebikes that your local ebike shop are selling start to feel like a bad joke, that the general underinformed ebike consumer is the butt of.
The cycloidal gear is the heart of what makes the Ascent so special, massive reduction in a very tiny package. 40:1 reduction shown.
While this build is not even remotely street legal the reality is that anything that looks like and ebike and is ridden at less than 30mph on the streets will probably not attract too much attention from the cops. This build easily exceeds 45mph on the road and if you start tooling around town at those speeds you are guaranteed to run into problems. Am I encouraging you to break the law and ride this bike on the street? If you want to ride 30mph up 15 degree grades, then this is probably the ebike for you. If you take this bike on your local trails and don’t exercise a lot of restraint on the throttle then you will almost certainly make enemies with the local mountain bike riders. You will become the Black Sheep of the community. Don’t be that guy.
With great power comes great responsibility.
When there is a foot of snow on the ground then all bets are off. Shred away.
Ride on.