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Bafang PAS as Traction Control!

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    Bafang PAS as Traction Control!

    These last few days, we've had a foot of cold, slippery snow. I've been breaking trails to get them open, and 'groom' them to nice shape with a few passes before they freeze up.

    With snowshoe XLs at a couple PSI on my BBSHD bike, I was still having trouble keeping my momentum on throttle assist in real deep sections and on hills. I was on the verge of losing traction much of the time, so the tiniest bit too much throttle would spin out. As soon as the rear wheel started to slip, the constant torque response of my throttle would spin the rear wheel up too fast, and I'd stop moving and make a divot on the trail.

    I hate making divots, so kept turning around.

    Eventually I figured out that using PAS, the way I have it set up, works much better for snow traction in such conditions. My PAS operates in speed control in such conditions. Meaning plenty of torque, but speed limited. As soon as the wheel speed starts to climb with loss of traction, PAS reduces power, preventing a total spin out! The wheel keeps turning at a constant speed as the bike slows a bit, which works a lot better for me than throttle control. I simply can't react as fast as the controller does. This thing really feels like it has traction control, it's sensing wheel slip and reacting to eliminate it, more or less. It doesn't know if the bike is slowing down or not, so can't help you if you lose momentum too fast, but for holding a steady, low speed it's AWESOME.

    I made it up a couple hills in PAS which I could not climb un-interrupted with throttle, and did way less tire churning on the way up. This at only a few mph, pretty slow, PAS 2-3 for me in granny gear 1:1 ratio. Crawling along, slight but consistent wheel slip.

    I was DELIGHTED to figure this out.

    There was a 1/2 mile straightaway where I gave up and turned around, early in the ride. Every hundred feed I'd slide off my line and have to restart. I went back and tried it in PAS and made the whole stretch with only a couple restarts, instead of spinning and swerving at every tough spot.

    This wouldn't work for a 'constant power' or 'constant torque' PAS setup. The key is using the quick-reacting 'speed limiting' feature of the controller to stop wheel spin out, and PAS needs to be running in speed control mode to do that. But it's way better at sensing and stopping wheel acceleration than my brain/thumb system. Try it if you have opportunity, and suitable PAS settings! Real cool.

    Having throttle set to speed control instead of torque control (current mode) may be better for such conditions, too, I haven't tried it.

    This was an unintended benefit of my tuning for lower PAS speeds. Having a slow, powerful, constant wheel speed to use for snow isn't available with the stock settings, they are too fast even in PAS 1 for this kind of riding. I'd see 1000W at a couple MPH sometimes. I have a 42T granny gear so I'm not lugging the motor too badly. And it's below freezing, so motor staying cool. But I'm working it real hard. Motor melting snow.

    Having a lot of reserve torque is important, too, I think. High max current vs. keep current. Otherwise bike can't hold speed as load changes. I think...haven't tried otherwise, frankly.

    When I refer to throttle, I mean while pedaling. I'm not just throttling like a motorcycle, I'm using it to add torque. I think it's important to use the pedals in general, but especially so in snow. As soon as the rear tire starts to slip, you feel it. I can't ride worth a darned in marginal traction conditions without using my feet to sense this. For anybody having a hard time in snow on throttle only, try pedaling and using throttle for assist, I think you will have much better luck.

    I also ran my tires lower than I ever dared to, before. They were squashed to half their height when riding. Didn't register on my gauge. I couldn't make much progress without doing that, either. Conditions were that tough.

    Anybody else use PAS like this, or have any other suggestions for 'best traction' operating tips regarding motor control in the snow?

    I feel like I found a real neat new capability, after 5000+ miles. I'm still learning new capabilities, and if I hadn't attempted to ride in 'impossible' conditions, I never would have figured it out. Can't wait to go try more today.
    Last edited by JPLabs; 12-16-2017, 09:51 AM.
    Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

    #2
    I'm betting this is pertinent to riding up the sand dunes too... Next time I'm riding them it'll give me something to play with...

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      #3
      I bet it would, sure. Let me know what you think, I'm curious if you find a situation where you think it makes a difference.



      Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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        #4
        Interesting... newbie question; is that something you had to change in the programming? That whole deal seems a little daunting...

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        • AZguy
          AZguy commented
          Editing a comment
          Not so much the programming as it is tweaking the controller configuration parameters. If you haven't played around with them you should and once you get the feel for them it's not so daunting! ;-}

        #5
        Last night I was pushing it harder. PAS at about 8 mph, low gear, driving right through drifts a foot high, and plow banks. Bike slows, settles in at a higher torque and lower cadence, and churns right through. Like a tractor with fixed throttle.

        regular PAS should do this if operated so it is controlling speed. Mine is going to do better since I have high current limits and relatively low PAS speed limits programmed in, with a pretty generous torque reserve. Meaning, it is very torquey and resistant to stalling out.

        Also, same speed, but in higher gears, didn't work as well.
        Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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          #6
          Lots more practice with this, including on a few hills I could not climb. I've settled into a routine of leaving the bike in a low PAS setting, slower than I'm riding, then using throttle to control speed and assist level while I pedal. If I'm riding 5-8 mph I'll have the PAS on 2, which for my build is about 4-5 mph in 2nd gear. If I start to spin the back tire, I just let go of throttle, bike slows to PAS speed, and PAS takes over motor control. Several times, this has let me keep climbing instead of churning and stalling. A big benefit is better rear tire tracking. Spin too much and the rear tire slides out. Spin just a little, as with PAS, and I can keep control and stay on track better. But traction to keep forward progress is better, too.

          Working well for me this way.
          Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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