CA3 - Config for equivalent of assist proportional to steepness of hill?

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cloudcover   10 mW

10 mW
Posts: 29
Joined: Sep 09 2009 12:09am

CA3 - Config for equivalent of assist proportional to steepness of hill?

Post by cloudcover » Nov 14 2018 6:41pm


I have a bike with a rear hub motor, which I had been controlling with a half-twist throttle. That's more of a "manual" approach than I'd like -- and it's uncomfortable for longer rides. So I recently bought and installed the following items from Grin: (1) a PAS (cadence) sensor, (2) a Cycle Analyst 3, and (3) a digital two-button switch. But I'm having trouble figuring out how to configure the CA3 to achieve the "feel" that I'd like.

Ideally, I'd like to have zero assist when pedaling on flat ground -- I'm happy to shift gears as necessary to achieve the speed I want (technically, maybe I actually want some small amount of assist to overcome the hub motor's inherent resistance). I mostly want the motor just to add assist when I'm going uphill -- and I'd like the assist to be proportional to the steepness of the hill. The result I'd like to achieve is to always have the same feeling as pedaling on flat ground -- whether the surface actually is flat or whether it's a hill; I'd like the motor to automagically add whatever level of assist is necessary so that my "human effort" remains the same as if I was on flat ground.

Right now, I think I know how to configure the CA3 to increase the level of assist proportionally to my cadence RPM. So if I'm pedaling faster, I get more assist. But that's actually the opposite of what I want. When I'm going uphill, my cadence usually drops...but that's when I want more assist.

I was thinking that maybe one way of doing that would be to have the assist increase in inverse proportion to my cadence RPM. So, for example, suppose I'm pedaling along just fine and dandy on a flat street at 60 RPM. If the street starts becoming uphill, if I don't increase my human effort, my cadence would naturally decline...maybe to 58 RPM, then 56 RPM, and so on until it reached whatever the steady state was for that slope of hill (assuming I don't change gears). If it's a mild hill, maybe it just decreases to 56 RPM. In that case, I'd love it if the controller would add, let's say, 100W of energy (just making up a number for illustration). On the other hand, if it's a bigger hill, maybe my cadence drops to 30 RPM. In that case, I'd want the motor to add let's say 600W of energy. The numbers don't matter -- my thinking was that the level of assist would be inversely proportional to the cadence RPM. At some predefined upper RPM (let's say 60 RPM), the level of assist would be 0%; and at some predefined lower RPM (let's say 20 RPM), it'd be 100%; and between those two points, it'd change linearly.

Is that doable? And even if it is, is that the best way of achieving the result that I'm looking for?

Thanks in advance!

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