perryscope said:buba said:Rafe said:Buba
Im still having a problem getting my head around cadence mode, surely there is more than a cadence input from the way it is behaving.
I'm running on a Nexus 8 speed hub gear and 48v motor, 52 volt battery Max 18 amps and 800 watts set. To get any decent response I need the cadence assist set at 90 and more. Go up a gentle slope near my home at 10mph in 3rd gear it starts off with decent assist and soon settles to about 11 watts assist and then I change gear to 6 or 8 and suddenly I've nearly got 300 watts assist and to maintain 10mph I am ghost pedalling. Going back down the slope everything seems normal in any gear with hardly any assist. Then as I turn into the rutted lane up to my place pedalling very slowly in gear 8 the assist is suddenly 500 watts or more (which I don't want). Is there also a wheel speed and torque input into this mode?
Hmm... So when you configure an assist level multiplier in Cadence Assist it will actually set the target rotational speed of the motor. If the motor rotates slower it will increase power until the rotational speed increases. If the motor rotates faster it will lower the power. So if you change gears this will upset the ratio and you need to change assist level accordingly. The system does not know that the ratio has changed.
Just thought that this implementation works fine on direct drive motors as the ratio is fixed (hub motor) but is maybe not as optimal where the ratio changes with gear shifts. How does the Bafang compare when shifting gears? Have never tried cadence only assist on a mid drive before. How do you configure the Bafang and how does it react when removing the wheel speed sensor? Does it work the same with and without the wheel speed sensor?
We are only looking at cadence in Cadence Assist but I understand why you were surprised by the difference in assistance!
The bafang motor is somewhat different in how it feels to ride. the Assist levels are set to fix the maximum power and set cadence speed to run at, so as you move up the assistance levels you are increasing the cadence in set amounts.
Its nice for cruising but you do tend to use the assist levels with the gears more, change up gears and sometimes you have to drop the assist level to lower the cadence to suite.
If you remove the speed sensor it makes no difference at all to how the motor reacts, I know this for sure at i had to ride over 200KM with no speed sensor the other week after my tyre melted the speed cable sensor wire right through!
changing gear is somewhat vicious! and a gear sensor really helps to calm this down, or using the gentle ebrake method to activate the ebrake when changing gear without pulling the lever enough to actually brake.
all in the bafang rides in a very constant fashion, providing a set amount of power continuously as long as you pedal, but if you want to change cadence you have to increase the assist level or you will be pushing against the motor.
These are my settings in the bafang config tool on my towing bike running a BBS 02 (350W motor running up to 20A so 720W peak but does not feel as powerful at the TSDZ2 at 500W)
you can see how I have changed the cadence speed to increase with the power.
Wow! This just goes to show how something as simple as assist enabled by cadence can get complicated and is not as trivial as one would assume. I really do appreciate your detailed post explaining how it works and what you think of it.
The very first implementation of Cadence Assist I did was a simple power level selector. You simply selected the assist level and it constantly maintained the power configured in that assist level. So if you had assist level 4 set to 200 W of power it constantly assisted you that much. No matter what speed you were at.
But during startups I thought that users needed more assistance. Something we solve by applying slightly more torque in the torque based modes. But this is obviously not possible with Cadence Assist. Later on, when up to speed, the assistance was too strong. The feeling was very constant. So, less assistance at speed is preferable.
So what is the natural implementation of this? The motor duty cycle target. With that implementation it will naturally assist more at startups, when you need more assistance, and assist less when at speed. But again, the problem is that if we shift gears it offsets everything. Something we are experiencing now.