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To gear sensor or not to gear sensor - that is the question.

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    To gear sensor or not to gear sensor - that is the question.

    I have ordered one of the new gear sensors from Luna and have been thinking about it. Here are my thoughts:

    With the announcement of gear sensor availability from Luna Cycle we now have options to consider to protect our drive train while shifting. Instead of figuring out how to shift safely under power by finding ways to manually cut the motor, we can add a shift sensor and let it and the BBSxx automatically handle it for us. We are now a step closer to those high-end factory ebikes that are so smooth but unlike our Bafang solutions are under-powered and over-hyped. They do still have one leg up on us though and that is PAS with torque sensing. That takes PAS to a whole new level but is a topic for a future date (are you listening Bafang?).

    If you don't use PAS, you don't need the gear sensor unless you don't want to let off the throttle while shifting gears. To shift safely using the throttle just let off the throttle and shift. If you can't coordinate that then by all means get the gear sensor and it will lay off the throttle for you. Granted there are times riding single track that is hard to lay off the throttle because of the grip you have on the bars. So mountain bikers that are using throttle only could definitely use a gear sensor.

    If you use PAS and pride yourself in saving $50 by learning manual shift techniques like lightly squeezing the brake or back pedaling to cut the motor before shifting, you may not be a candidate for the new shift sensor. If you ever bought a car with a manual transmission for the pure joy of fussing with the controls, pressing in the clutch and moving the shift lever, you may also not be a candidate. Although you will not be doing something natural like pushing a clutch, you will be unnaturally pulling the brake or back pedalling to shift which may not bring the same pure joy.

    However, if you use PAS and like me don't like to do something unnatural like squeeze the brake or backpedal to shift and despite your best attempts to master these techniques find you occasionally shift before the motor cuts out and you hear and feel a hard 750W+ clunk go through your drive train then you are definitely a candidate for the gear sensor. The ability to shift gears just like you always have without worrying about what the motor is doing with the PAS system or whether you can even let off the throttle (think gripping the bars on a hill riding single track) has got to be nice.

    If you use PAS without a gear sensor there is an often glossed over controller programming parameter under "Pedal Assist" called "Time of stop" that can make a huge difference. The "Time of stop" value is multiplied by 10 to get the number of milliseconds after you stop pedaling until the motor stops. Most vendors are setting this to a value of 25 which introduces a full quarter second delay (250ms) between the time you stop pedaling and when the motor actually quits. This is why people use brakes and back pedaling to ensure that power to the motor is cut before shifting. If you set it to 5 (don't set it any lower or PAS will stop working) then it only waits 1/20th of a second (50ms) before cutting the motor so you can just stop pedaling and then shift and the timing works out. Karl Gesslein, in his "Hackers Guide to Programming the BBS02 and BBSHD" makes the statement, "I strongly recommend setting this to 5, especially if you want to use the PAS system without using ebrakes." Curiously, out of 5 vendors and experts with recommendations, all of them but Karl recommend a value of 25. Trust me, changing this to 5 makes a HUGE difference. Unfortunately, a side effect of this setting is that at slow cadences the pulses from the PAS magnetic poles are coming slow enough that there is a greater than 50ms delay between pulses and the motor never engages. If this happens, you are probably in too high of a gear anyway. The solution of course is to shift to a low enough gear that your cadence is high enough that it doesn't time out between PAS pulses. You can play with optimizing this for your own style by playing with numbers between 5 and 25 but it will be a compromise. Alternatively, you can just get the new gear sensor from Luna and not worry about it. That's what I am doing. :)

    Do something that is good for your health, good for your wallet and good for the planet - get an e-bike.

    www.poweredride.com

    #2
    Maybe Bafang's competitors in the DIY mid-drive market will introduce smooth torque sensing and a refined shift sensor? Oh, wait...

    Great summary. This issue has been around a LONG time.

    Comment


    • Louis
      Louis commented
      Editing a comment
      ...and underpowered...

    #3
    That is a really good overview and statement of the issues!

    I thought I wanted a shift sensor at first, but with more experience, I like the brake/clutch technique just fine. If I get a slow shift, I can simply hold the brake lever in a bit longer to keep power from coming on before the shift is finished. I have the brake and sensor tuned so there is enough free play to do this easily, without actually applying the brakes. This is critical, in order for it to work well.

    You are so right about the 'Time of Stop' tuning. I tried several values, and decided I like 50 mS best. I hadn't noticed that it would prevent power at too low a cadence, probably because I try not to do that. But, what a great side benefit! Good observation!!

    With the shift sensor, I suspect that the 'Time of Stop' needs to be set high enough for the shift to complete under all conditions, so tuning that parameter for fast response may not be compatible with the shift sensor. Anybody know for sure?.
    Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

    Comment


      #4
      Thanks JPLabs. Regarding your last question I don't think the shift sensor and 'Time of stop' are related in the way you suggest. 'Time of stop' cuts the motor after a delay timed from the last PAS pulse and the shift sensor cuts the motor independent of that when it senses motion in the shift cable. Since you can pedal right through a shift the 'Time of stop' parameter will never come into play. However, you are right in that there must be an additional delay in the shift sensor circuit due to the fact that the shift doesn't actually complete until some number of milliseconds after the cable stops moving. This would indicate that there is a parameter like 'Max Shift Time' in the controller or sensor that holds off the motor until the worst case shift completes. I don't think this parameter is exposed. It would be nice though since higher-end derailleurs and cogs shift faster and the delay could be shortened. As it is, it must be timed for the slowest and worst case derailleur/cog/chain combination.
      Do something that is good for your health, good for your wallet and good for the planet - get an e-bike.

      www.poweredride.com

      Comment


      • JPLabs
        JPLabs commented
        Editing a comment
        Sure, that makes sense. I was thinking that time of stop was a delay before power was reapplied after the stop signal terminated. Thanks for the correction.

      • Jasdidit
        Jasdidit commented
        Editing a comment
        The controller doesn't need to have a special delay for shift length. It obviously doesn't, since it works equally well for slow and fast shifts. It is what both shifts have in common that the controller uses. Pedal cadence. The pedal speed changes to a different cadence during a shift. Whether it is an upshift or a downshift, the pedal cadence changes, slower or faster, it is the change that the controller uses to time the shift.

      #5
      You could get a n360 CVT, and sat goodbye to; Derailleurs, shift sensors, driveline lash, and noise. And get Smooooth, quiet and simple. Once you try an ebike with one, it's hard to go back to a derailleur!

      Comment


        #6
        N360 spec, Approved for use with 250w motors. What about a 40A BBSHD?

        Comment


          #7
          I know of several people, many on this forum, who are using, even abusing them, with little or no problems. I'm one, Karl, the unofficial destructive testing branch of Luna Cycle R&D Department, is another. If Karl can't kill it, nobody can

          Comment


            #8
            Good point Rix Ryds. Infinite gears without shifting sounds ideal. As for the 250 watt limit, I don't think any bicycle drivetrain manufacturers warrant their drivetrain for the torque generated by 6 or even 4 cyclists. Wisely Nuvinci warrants there's for the torque of 1. Happily, it appears they over-engineered it for that spec. Which is great. KMC now makes chains to take the abuse of ebikes. Perhaps other manufacturers will follow suit.
            Do something that is good for your health, good for your wallet and good for the planet - get an e-bike.

            www.poweredride.com

            Comment


            • retrocycler
              retrocycler commented
              Editing a comment
              Apparently they don't expect the likes of Cavendish to use their hub - he peaks at what? 1600 W when sprinting?
              Track sprint racers can peak at 2 kW and I'd think they would be good candidates for e-bikes, as their endurance is not so good on long rides;-)
              (That being said, those wattages are not indicative of torque, necessarily. Sprinters will generate those watts pedalling upwards of 150 RPM, so the applied torque is not as high as it might sound)

            #9
            So Louis, when are the 40 amp BBSHDs coming? :) Will that just take a new controller from bafang to do that? Don't want an external controller
            Last edited by New Mariner; 03-18-2016, 06:07 AM.

            Comment


              #10
              I like the Gearsensor. I set the time of stop to 5 first before installing, which helped, but shifting with the sensor is way faster.
              Pulling brake levers, or stopping pedaling just to shift is slow and inconvenient for a high performance set-up. I like not having to pause.

              Comment


                #11
                Thanks TBRO. I will be ordering the sensor with my motor

                Comment


                  #12
                  Do the newer BBSHD controllers with the dedicated Gearsensor plug have any addition to the software to work with the new input? Has anyone plugged one of the new controllers into a PC and looked? A new hardwired feature might very well be supported in the software, or is it simply a third brake input and is processed accordingly?

                  Comment


                    #13
                    Unfortunately, Bafang has not exposed the shift delay in the programming software. However, the delay the controller uses for the shift sensor wire is shorter than the brake cut off. This makes for a more seamless shift than when plugging the shift sensor into a brake cut off connector. I have some experience with other mid-drive motors. Focus and Kalkhoff Impulse drives default to 200ms but work well at 100ms. Bosch actually listens to the shift through the frame and is ultra smooth. I don't know the exact timing Bafang uses but it would be nice if they gave us access to the delay parameter. Well lubed and adjusted derailleurs are much faster than the worst case ones I am sure they set it for.
                    Do something that is good for your health, good for your wallet and good for the planet - get an e-bike.

                    www.poweredride.com

                    Comment


                      #14
                      I got the gear sensor and one of the new BBSHD controllers with the separate gear-sensor wire installed. It is exactly what I hoped it would be. Smooth shifting without stopping pedaling or messing with the brakes to get the motor to stop. The motor cuts out as soon as I start to shift and comes back on right after shift completes. Timing is very smooth. Feels like a real pro set-up - sweet.
                      Last edited by PoweredRide; 06-09-2016, 09:41 PM.
                      Do something that is good for your health, good for your wallet and good for the planet - get an e-bike.

                      www.poweredride.com

                      Comment


                        #15
                        While researching gear sensors, I came across this curious DIY. He fitted his bike with BBS02 and tons of bells and whistles. Most interesting of all was his controller mod. Like all his other videos, he doesn't really go into details of how he did it.

                        https://www.youtube.com/watch?v=USGJbRDOxB8

                        'Auto PAS Assist', as explained at 1:02, "automatically adjusts PAS level by calculating the torque of the motor based on grade level, gear level, speed"

                        I would love this functionality if he can refine the aesthetics a bit. Touch screen LCD setup is pretty sweet also.


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