footloose said:
My setup is 20" wheels, Shimano 8-speed IGH.
Just swapped in a new chain and took bike out for a ride in the dark.
Serious hills here in my neighborhood.
Was pedaling up long/steep hill in 3rd gear, all well but felt like it was lagging a bit, so hit the throttle as experiment.
Serious power surge, then an odd sensation. Took me a moment to realize it was because front wheel was off the ground, and I was riding balancing on the rear wheel.
Fun moment for sure, but quite an adrenaline surge! Leaned forward, slacked off throttle, and all was well.
Going to have to be a bit careful with this.
Just so you get this...
1.) Shimano 8-speed IGH if it's the A variety has 308% of range within the following ratios:
1st Gear: 0.527 : 1
2nd Gear: 0.644 : 1
3rd Gear: 0.748 : 1
4th Gear: 0.851: 1
5th Gear: 1:1
6th Gear: 1.223 : 1
7th Gear: 1.419 : 1
8th Gear: 1.615 : 1
Presuming stock Shimano 8 input cog being 25T and a driving Chainring of 48t, the ratio from Chainring to rear (before the IGH gears are applied) is:
48 / 25 = 1.92 : 1
Our new drive ratios become:
1st.) 1.92 * .527 = 1.015529 : 1
2nd.) 1.92 * .644 = 1.2364 : 1
3rd.) 1.92 * .748 = 1.43 : 1
4th.) 1.92 * .851 = 1.62292 : 1
5th.) 1.92 * 1 = 1.92 : 1
6th.) 1.92 * 1.223 = 2.34816 : 1
7th.) 1.92 * 1.419 = 2.72448 : 1
8th.) 1.92 * 1.615 = 3.1008 : 1
Presuming at assist 3, throttle ramp would take about 1.5 seconds to reach Maximum current of 100% - at 100% current is at 26A.
So that 1.5 seconds after going to WIDE OPEN THROTTLE your going to push maximum current while in 3rd gear or 1.43 : 1
Since the rated kV of this motor appears to be 118 at 48v loaded, that should produce a rear wheel RPM of just 168.74 RPM or 10 mph maximum. Such a low
top end combined with a peak of torque and power and sure your gonna feel the surge - I have tested with the same 8 speed internal geared up as you have
and found only a few gears were really of use - always started in 3rd 10 mph, went to 7th @ 19.13 mph and finally 8th for a top speed of mph- unless I was
starting at the base of a mountain and from a dead stop... 8th gear when use-able would give me 21.77 mph at nominal voltage of 48 sustainable.
There are a few solutions to this that I have used, and a few I am working on and will have available shortly:
1.) The first and most useful of the options (quick switch over) is simply to bolt on a new chainring. Since bafang is not stepping up I have a initial batch of 30 rings coming in - 10 x 52 tooth, 10 x 53 tooth, 5 x 56 tooth and even 5 60 tooth for the recumbent crew, I don't have prices per unit yet but will announce them when possible - they are crafted using a dual process of sand cutting rough and lazer finishing as they are 7075 Aircraft aluminum - should do wonders for noise, weight and longevity.
With even just an upgrade to a 52 tooth your ratios would increase dramatically.
2.) Your controller may need to be reprogrammed, it sounds as if instead of 100% throttle with very fine control you have firmware or settings limiting your throttle before reaching pedal assist level 3... could be designed to prevent drive train shock but current monitoring could do a much better job!
3.) With my 750 at 15S (I think at 13S too but I'd have to check) and being logged - without pedal assistance enabled (hardware bypassed), i goosed my throttle (configured with no transitional delay or ramp up other than that which I dial into the throttle, full control. and from 3rd gear I too went up - that pulled no more than 26 Amps using 10 time per second sampling. There are some minor issues between how we (any of us) may want this to work and how each version does indeed work but the US vendors I'm in contact with, the manufacturers and Chinese distributors are aware of what truly are a combination of misunderstandings and what seems to be a lack of understandings of the reps and sales people, who translate complicated specs and reqirements to the engineers and things get lost in translation and vendors end up with firmware which doesn't actually suit their needs exactly. Still great units.
For the gentleman with the "Crappy Brake Pulls", you are indeed right and as most of my bikes have trigger shifting for rapid fire change (derailleur based anyway) may I suggest you remove the junk ones... restore your original or maybe upgrade the pulls to something nicer if possible with your bike - discs are a great asset.
Hope this helps make sense of it all for you!
Regards,
Mike
