Panasonic System Power Delivery Explanation

[prState]

You know, 4 years with my LaFree the slow pedal cadence has a rather eccentric effect I think when you're topping out speed-wise in final gear, and using a lot of effort.

For instance, as I try to increase my speed, where I'm already maxed out pretty much with muscle power, the bike is reducing the power as I try to increase the power!! -- thus negating the whole point of the effort.

I'm not really complaining, as it's not really a draw back when you're able to pull up the lower gears slack -- only in the top gear, and only when you are at near maximum effort already at the slow pedal cadence. Does that make sense?

It is very much like a speed limiter. Although it does vary on conditions, for instance if conditions warrant that I can move pretty easily in top gear, the pedal cadence reducing power works pretty much the same as the lower gears.

[flecc]

Yes that makes complete sense prState. It just emphasises the utility bike nature of the system, and when you try to speed up by pedalling faster at near the maximum, you're trying to use it in a more sporting manner which it's system is unsuited for.

It would be possible for Panasonic to redesign the electronic and pedelec systems to have two different switchable modes, Utility and Sporting, but as I remarked previously, Japanese law on bikes and e-bikes is so restrictive that wouldn't be worth Panasonic doing, since the home market is where most of their sales are.

Also, as with any system that tries to do two different jobs, the compromise would probably impair the operation of both.
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[nasatir]

Originally Posted by flecc

Hi nasatir

With the Panasonic unit, the greatest saving of energy for hill climbing is to opt for a speed that allows you to climb on Standard power, rather than the slightly faster climb on high power. This is what I said in my Agattu review Extra section:

Reducing speed has a far greater effect than changing power modes. For example, at 7.5 mph on a 14% hill in Standard mode, changing to High Power saved me 32 watts of effort, but cost the motor and battery the same 32 watts extra. Alternatively, slowing very slightly to 6 mph and leaving it in Standard mode saved me 52 watts of effort, saved the motor 52 watts of effort as well and reduced the load on the battery.

So although going slower like that makes the motor run for a longer journey, the fact that it's only a little bit slower but saves so much power will increase the range, as well as being less demanding on you.

However, pedal at or just below the 39 cadence for maximum power, for although that uses a bit more than if you pedalled much faster, it starts to remove the point of having electric assist if you pedal fast just to save a minute bit of power. Much better is to switch off when the going is easy and save in that way without stress to yourself.

In that way I was able to achieve an over 50 mile range equivalent with average hills included at the age of 71, so many would at least equal that. I doubt if many would require such a range though.
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Thanks.

While I have heard that "in theory, there is no difference between theory and practice..." I am always particularly pleased to learn from actual practice as well.

[readingaloud]

I've been thinking, in my own slow and muddled way, about the power phase out issues that flecc so clearly explains, and it seems to me that there's a relatively simple way for manufacturers to deal with the problem.

To oversimplify:

In order to still be considered bicycles for regulatory purposes, bikes cannot offer power assist beyond about 25 kph, and they phase out the assist so that it begins to diminish at about 15 kph. Well and good.

The problem is that the only way the bike knows how fast it's going is by the cadence. The control system doesn't know what gear the bike is in, so it has to assume that the bike is in it's highest gear. That means that it's going to apply stricter limitations to lower gears.

Now, how high a gear should the bike have? If the very highest gear were one that would only go 25 kph when ridden at a reasonable cadence of 70, that would seem a pretty wimpy top gear. So they give you a top gear that yields a respectable (but still not very fast) 25 MILES per hour when ridden at a standard cadence.

But in order to do that, they need to start phasing out the power assist at a much lower cadence. Hence the fact that the phase out begins at a paltry 39 cadence.

Since the only thing the control system knows about the bike's speed is the cadence, it can easily be fooled by changing the sprocket.

Now, as flecc notes, this has a side benefit, at least as far as the manufacturer is concerned, in increasing the range of the bike. Since a cadence of 39 is uncomfortably slow for most cyclists, most of the time, they'll pedal a bit faster than that, and the bike will scale back the motor's contribution accordingly. In a way, the bike is doing automatically what flecc and others recommend for getting longer range out of the bike--turning down, or even off, the power assist except when you really need the help.

But, assuming there are some who would want (or even need) more help, and were willing to live with a shorter range, there would seem to be a much better solution. Why not give the controller better information about bike speed? If the controller "knew" what gear you were in, it could adjust the phase out schedule so that it observed the legal limits, but didn't begin the phase out as low as 39 except when you were in the highest gear. That would make it possible to climb hills better, cranking up to 70, or even 90, for greater efficiency without being penalized by the controller.

Now, this would require some kind of feedback device so that the controller knew what gear you were in, and it would still be possible to fool the system by changing the sprocket size.

So why not go further, and actually measure bike speed? A wireless cycle computer could become part of the standard configuration, and the speed information would be sent both to a display mounted on the bars and to the controller located wherever it is it's now located. It would no longer be possible to fool the controller by changing the sprocket. You could, I suppose, try to fool it by mounting bigger wheels, but that would be much more difficult, and much easier to detect.

Bike computers are so cheap, these days, that the cost increase would be negligible. And how many people buy such an expensive bike without spending a little bit extra for the computer anyway?

Could you fool the system by disabling the wheel sensor? Well, the system could be designed to revert to the present phase-out threshholds if it didn't get a signal. Could you fool it by spoofing the signal from the wheel sensor? Well, I suppose you could (or at least some folks could), but that's still a lot more difficult than simply changing out a sprocket.

The more I think about it, the sillier it seems to have the bike enforce some kind of speed limitation without giving it some way of knowing what the speed is. Surely, with all of the fancy technology that goes into bikes these days, this is a solvable problem!

[flecc]

It definitely is, and there are several ways in which it's achievable, including the way you describe which could easily be implemented.

The reasons it isn't done are not in any way technological though, and are due to the small e-bike market and where most of them are made, and here's some of them:

1) The Chinese are notoriously slow cadence leisurely cyclists, and I'm assured they also avoid cycling up hills and don't understand our obsession with doing that. Therefore they have no interest in doing it for their large home market, the overseas sales being peanuts in comparison and not warranting investment.

2) The Japanese legal restrictions I mention in my article extend to cycling law in general. In many areas bikes are restricted to shared use pavements and not allowed on the roads, with speed strictly limited to 8 mph. In other circumstances speeds are restricted to other degrees, and that's reflected in their view that sports riders travel at 15 mph as I mentioned in the article. So once again there is no home market need.

3) The only impetus for a different design would have to come from outside of the Orient, but once again the small size of the whole e-bike market prevents investment, and that's especially true for a bike that would appeal only to a very restricted sector of that tiny market.

4) High quality systems like the Pansonic one require a huge investment, well beyond viability, and with the evidence of the world's largest cycle firm failing with their Lafree series still fresh in the mind, no-one else is going to be willing to take such a large risk. The only viable way for the present is to use the Panasonic standard system with the odd tweak as five manufacturers have done using six names.
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[readingaloud]

Those reasons make sense, flecc. Let me offer another possibility too:

From one point of view, the present system is just a silly mistake. It governs speed by measuring the rotation of the crank, which is only indirectly related to speed, rather than the rotation of a wheel, which is directly related to speed. If you can do one, you ought to be able to do the other.

But consider that the electrical parts of the bike are made by Panasonic, and the mechanical parts by Kalkhoff, Biketec, or whomever. Perhaps moving the rotation sensor from the crank to the wheel means moving it out of the part of the bike that Panasonic supplies, and on to the part that the bike builder is responsible for. This would complicate matters substantially, and require a closer integration between Panasonic and the bike builder. It's not that it's hard to do--it's just hard for Kalkhoff of Biketec, whose core competence is bicycle mechanics rather than electronics.

When I'm not on my bike, I do product design for a large publishing house. What I do, for the most part, is to mediate between the technology people and the editorial staff. Fortunately, we have lots of expertise in both areas, and so can build products that integrate editorial content with technology in a graceful way. It would be vastly harder to do what needs to be done if I had to source editorial content from one company and technology from another. And so I might find myself doing silly things, like measuring crank rotation rather than wheel rotation.

I still think this is a foolish mistake. If you put flecc, the Panasonic engineers, and the Biketec engineers in the same room, you'd have an elegant solution within an hour or two. The trick, I suppose, is to get them to do it. And to understand why they haven't, you only need to look at flecc's list.

[oldosc]

with all the cheap (and clever ) electronics about what chance of making a cheap(ish) cadence meter, on the handlebars, then look at it from time to time instead of counting...one white hippotimus two white(etc) this to get 1.3 per sec,instead of one per sec we wer trained to do at Cycle class.

[oldosc]

ps I got left behind when Valves went out of fashion

[flecc]

Originally Posted by readingaloud

From one point of view, the present system is just a silly mistake. It governs speed by measuring the rotation of the crank, which is only indirectly related to speed, rather than the rotation of a wheel, which is directly related to speed. If you can do one, you ought to be able to do the other.-------------------------------------------------------------------------------
I still think this is a foolish mistake. If you put flecc, the Panasonic engineers, and the Biketec engineers in the same room, you'd have an elegant solution within an hour or two. The trick, I suppose, is to get them to do it. And to understand why they haven't, you only need to look at flecc's list.

There's another overriding factor in this, Panasonic only made this system for their own domestic market bicycles, no separate unit being available or ever intended.

When the world's largest bike maker, Giant, had failed with their own Lafree 1 electric bike, they begged Panasonic to make the unit separately available to them for the new Lafree, and Panasonic relented. Since that had happened, the Swiss bike manufacturer BikeTech also managed to join in by paying very high prices for the smaller quantities they needed, positioning theirs as up market quality items.

The failure of Giant to make a success of the Lafree underlined to Panasonic that they were right in the first place, but a couple of years later others wanted to take advantage of Panasonic's improved variant so we now have five in all starting to use it. I can understand Panasonic not wanting to get involved in design with any of them, given the history and the tiny potential market. Look at their latest TZ series cameras, already sold in their multi-millions around the world at £200/£300 apiece. Thats Panasonics sort of business, not a few hundreds of bike motors to export markets, peanuts to them and more of a nuisance than anything.
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[flecc]

Originally Posted by oldosc

with all the cheap (and clever ) electronics about what chance of making a cheap(ish) cadence meter, on the handlebars, then look at it from time to time instead of counting...one white hippotimus two white(etc) this to get 1.3 per sec,instead of one per sec we wer trained to do at Cycle class.

It would be quite simple on many e-bikes using a pedelec sensor disc, but that would have to be added on the Panasonic system since it's rotation measurement is from the output shaft by a proxy system and couldn't simply be used. It's surely not worth it though, in use the motor contribution clearly indicates what's needed.

I posted the system explanation in this thread because there was such a demand for that, but frankly everyone gets far too involved in either understanding or wanting to adapt it. I say just use and enjoy for those who it suits as I did for over four years, and for others who it doesn't suit, just buy the bike that does.
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