Welcome Juan,
Thanks for the kind words.
I have been testing a wide range of motors recently, including some of the SK3 motors. The 8mm shaft should be fine as the skirt bearing takes a lot of the load off this shaft.
Here are some of my notes from the SK3's
- bearing quality was good
- fit and finish good
- relatively low levels of flux leakage
- motor diameters smaller than the old orange turnigy 6374-200kv
- a bit noisier on the bike with higher frequency tone than the old orange turnigy 6374-200kv
- cooling holes in the can may be an issue, as they closely align to the edge of the tire on the commuter booster, therefore may allow sand etc picked up by the tyre to enter motor.
- greater radial clearance is required on motor swing arm to accomodate shaft retention clip of SK3 motor
The 149kv motor on 6s LiPo should have a no load speed of ~40kph, so you will end up cruise on the flat at ~35-36kph. If you want faster go for the 168 or 192kV motors.
As for the ESC you linked to, I have never tried it so can't comment. But generally picking one that can accomodate high voltage & higher current than you expect is always a good.
General comment on selecting an ESC based on my preferences are:
- I like them with an on/off switch, so I don't have to disonnect the main battery cables very often. That is the main reason I like the
Turnigy Brushless ESC 85A w/ 5A SBEC.
- the friction drives prefer to have the throttle slowly increased. Some ESCs have a soft start option that can do this well. Others don't. I have ended up designing and manufacturing a custom throttle interface/bike computer that does this among other things. But a simple solution is to use one of these which can adjsut the ramp up speeds,
Turnigy 3 Channel Servo Speed/Direction Regulator- the ESCs also don't like low speed, high torque situations, so be careful use the drive a slower than walking pace.
Finally the friction drives in general work best when power is restricted, so either be careful with how you apply the throttle, or expect lower efficiency or tire wear.
Batteries capacity. This really depends on a lot of factors. I personally do most of my riding with the commuter booster on a good road bike, and like to pedal. I generally cruise at ~40kph, and usually see efficiencies of 6-7wh/km. But if I didn't pedal much and was on a mountain bike, I would likely see up around 10-12wh/km for similar speeds. So unless you like to pedal quite a bit, and don't mind running your battery flat every ride, I would recommend a larger battery if you plan on 50km trips regularly.
Another battery consideration is how you plan to put them on the bike. I actually prefer to use four 5s5Ah batteries, as I can fit them in my Topeak Aerowedge saddle bag. But I can only fit three 6s5Ah batteries in the same bag, which does not give me as much battery capacity. This means I typically would use the 190-200kv 63mm motor to get the speed I like, where as if I had the 6s batteries I could probably use a 170kv 63mm motor instead. So make sure you have a plan on how you will mount the batteries to your bike before you buy them.
All the best,
Adrian.
P.S. I will be posting soon about my next manufacturing run of both Commuter Booster Drives, and my new electronics interface that will soon be for sale.
Latest varients are both non-SD versions. One with a 8x2LCD with uC all in the same enclosure, but with an additional momentary button on the side. Thinking was to use it for all the display options, and leave the throttle to just be a throttle. This will make swapping to an analog throttle much easier. It also frees up some much needed memory to implement a few things, and make a switch to a 16x2 LCDLCD easy.
actual plan is a poor mans dyno. It will allow me to compare motors more accurately. 
Not everything works first time, and some things never work, but you have to try ideas else you stagnate. 
Unless you feel like carrying an allen key and taking the drive on and off each time you fold.
