Custom Pedel Assist build, looking for alternative to V3CA.

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zachleedogg   1 µW

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Custom Pedel Assist build, looking for alternative to V3CA.

Post by zachleedogg » Apr 04 2021 6:52pm

Hey there gang.

I'm working on building a pedal assist bike for my wife (and for myself!). The basic requirement is that I want a minimal build with minimal controls. No throttle, only pedal assist (with torque sensor).

What I have come up with is the following:
So the issue I am running into is how to control the PAS system with a torque sensor AND a PAS sensor. If I use the torque as throttle input, the motor will tend to be jerky and unstable at low speeds. If I use the PAS system only, the ride motor will not react to force, which is what I want.

I see a few options already:
  • Use a Cycle Analyst V3 to do the sensor fusion and send signal to motor. This looks like quality device and a plug and play solution, but I really don't want to have a large screen (or any screen for that matter) attached to this bike.
  • Use the built-in pedal assist function in the Golden Motor. But the documentation on this device is a bit lacking. Does anybody know how the PAS system on the Magic Pie V5 Works? will it work in tandem with a torque sensor? or will it only use the cadence? If this system is designed to work with cadence AND analog voltage Torque Sensor input, I would pay the extra $50 dollars to enable that feature and the issue would be solved.
  • Design a simple micro-controller based solution that takes cadence and torque as inputs, does math, and sends 1V-4V out as a throttle signal. While I have the skills to do this, I'm not really interested in designing a durable, weather-proof product.
So that being said, Does anybody know of such a device that acts like the Cycle Analyst V3 but is in a small "black box" package that can be easily integrated into a bike? Maybe even an open-source project of such a device would be helpful.

Thanks in advance for all your feedback!

-Zach

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amberwolf   100 GW

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Re: Custom Pedel Assist build, looking for alternative to V3CA.

Post by amberwolf » Apr 04 2021 11:30pm

I've never seen anything else that does what the CAv3 does, in this regard (and many others).


If the only thing really stopping you from using the CAv3 is it's size and the screen, you can dismount the actual CA board from the screen, and eliminate any wires you aren't going to use. For instance, if you don't want any kind of limiting, and are only using it to process the torque and cadence PAS sensors into a throttle signal, you could leave off the shunt wires, the ebrake wires, the throttle in wires, the HV jack output wires, temperature sensor wires, aux input (pot) wires, and you could unplug the front panel buttons, either wiring in your own if you need to change presets / etc, or just leave them off entirely if you don't need any functions those buttons can perform.

You'd need to leave the PAS input connector wires, the throttle output wire, and the battery positive and negative wires, and you'd probably want the speedo input wire as some of the PAS functions may depend on a speed input to work in certain ways, and the serial connector wires, as you would need those to read or write settings to the CA from a computer (as it won't have a screen anymore to do it directly).

This is the layout of the actual board inside:
https://ebikes.ca/pub/media/wysiwyg/CA_Pad_Layout.gif
Image

It wouldn't be hard to pot the board up to waterproof it, and then it can go anywhere on the bike that is convenient, even inside the motor controller (since a number of the wires will hook up to the controller anyway (B+ / B-, throttle output, speedo (using a motor hall), and others like PAS cadence and torque inputs could be bundled into the controller harness while you're at it. The serial could be left as a dongly connector hanging out of hte controller with a plug in it to seal water out, or a waterproof connector could be used (3-pin Higo or Julet with a "dead end" plug in it just to cap it off, etc), for access when necessary.



If cost is the issue, then developing your own may be worth doing if you don't consider your free time valuable. ;) Or if it is something you would like to do as open-source; there is a thread here:
viewtopic.php?f=2&t=110497
for potentially doing some of what you want to do, though I don't know how long it'll be before I get beyond defining what's needed and pseudocoding, and then seeing who can convert that into actual code (or learn programming and do it myself, eventually). You're more than welcome to contribute to that thread (it's original design intent is to "fix" some modes of CA operation for my own usage on my SB Cruiser trike, but the stuff in it may be useful for others), or post it in your own thread, etc. :)



Is the jerkiness / instability of the motor at low speeds (under torquePAS only) caused by a sensitivity issue with the Erider TS? Meaning, does the sensor respond too rapidly to input for your needs? An RC (lowpass) filter might help with that, on the signal line. That would also "slow down" it's response at higher speeds as well, though you could make a speedometer-controlled switch (555 timer that is reset by speedo pulses; if it doesn't reset then it doesn't bypass the filter), but that adds complexity quickly, and is probably easier to do in an MCU like an Arduino Nano.


If the GM internal controller has a cadence PAS input, is that PAS input like most, where it simply activates the motor at "full" of whatever PAS level is chosen? (rather than proportionally increasing assist based on cadence, which it seems few controllers do; I haven't had one yet, and is what I use the CAv3 to do).

If it does proportionally increase assist based on cadence, and the Erider outputs a throttle, then does the GM controller "combine" these two or does it have one override the other (the most common way of doing it is the throttle "always" overrides any cadence PAS input; next most common is the PAS always overrides any throttle input, third most common is the PAS is just required to activate the system and throttle then controls the amount of assist; without pedalling throttle is ignored).

zachleedogg   1 µW

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Re: Custom Pedel Assist build, looking for alternative to V3CA.

Post by zachleedogg » Apr 05 2021 11:40am

Hi @Amberwolf,

Thank you for the thoughtful response. I think the idea of modifying the CAv3 is a great idea.

Its unfortunate that I don't know the precise behavior of the GM controller with respect to it own internal PAS system, but i think you are probably correct in assuming that the throttle would over-ride any PAS signals.

I also did not consider the speedometer input consideration, so i will have to factor that in.

Also, it sounds like you are on a similar path with the custom Nano CA. I think I will let you make progress and report back. I think the GTFOOTW mode sounds kind of like a boost-mode. That would be a great feature.

Also to answer your question about jerkiness of the Torque sensor alone, the answer is, I don't know yet. I have not tested any components yet, but I anticipate difficulty in a smooth start from dead stop by putting all your weight on the pedal and the bike rocketing forward. I have never ridden a custom built e-bike so I don't actually know how it would work as-is.

Cheers,

Zach

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amberwolf   100 GW

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Re: Custom Pedel Assist build, looking for alternative to V3CA.

Post by amberwolf » Apr 07 2021 9:24pm

zachleedogg wrote:
Apr 05 2021 11:40am
Also, it sounds like you are on a similar path with the custom Nano CA. I think I will let you make progress and report back. I think the GTFOOTW mode sounds kind of like a boost-mode. That would be a great feature.
It sort of is, in that that is "get the F*** out of the way" (of whatever is coming at me) ;) mode. For my trike and bike, which are normally limited to 20mph, all the mode does is apply full throttle while active. Not something I would hardly ever use, but there has been need for it on a very few occasions--almost always when someone decides to change lanes into the space I occupy, and I can't brake because of cars behind me, and cant' dodge because there's nowhere to go...but because I'm already slower than traffic in front of me, there's plenty of space to zoom forward into. ;) So far this has not happened on the "modern" version of the SB Cruiser, as it is large enough with enough surface area for even SUV drivers to see, and for them to consider it might actually hurt their vehicle a tiny bit to hit it. But it happened on my old Delta Tripper, and on CrazyBike2, and on regular bicycle-style ebikes, as well as all my pedal-only bikes.


Also to answer your question about jerkiness of the Torque sensor alone, the answer is, I don't know yet. I have not tested any components yet, but I anticipate difficulty in a smooth start from dead stop by putting all your weight on the pedal and the bike rocketing forward. I have never ridden a custom built e-bike so I don't actually know how it would work as-is.
Perhaps it is because CrazyBike2 and SB Cruiser are both long (10-11') and heavy (about 400lbs and 500-600lbs respectively, with me on them, no cargo), but even with 4kw available (both rear motors on the trike, in small wheels, front and rear on the bike, one small one large), there isn't any rocketing forward at full throttle from a stop. Acceleration is smooth and easy.

Since the system you link is only at most 1000w, and would presumably be in a large wheel, I don't think that even if you are jockey-light that you'd get unhandleable acceleration, even hitting full throttle from a stop. (regardless of how you input that full throttle into the controller, it's still asking for the maximum the controller can output).

I think you might want to first get the motor/controller/battery system that you know will do the job you want (can handle the work load and provide the range and speed you are after), and then if it does things you don't want it to do, then worry about whether you need to limit it under whatever circumstances those things would be a problem. :)


BTW, the Erider unit already has a PAS cadence sensor built in "This sensor has an 18 pole single wire cadence sensor" according to the grin page, so you don't need a separate one.

HOwever, if you get the Erider from grin, AFAICR it would need 10v to run it as that's how the CA is setup to power it. You'd want to verify that with Grin, but without a CA you'd need a battery-voltage to 10v DC-DC for it (this can be installed inside the battery if there's space). Depending on how much current it needs, you could make a not-all-that-efficient (but very simple to build and very tiny) one with one of the regulators I talk about in that Nano thread.

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stancecoke   100 kW

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Re: Custom Pedel Assist build, looking for alternative to V3CA.

Post by stancecoke » Apr 08 2021 9:54am

zachleedogg wrote:
Apr 04 2021 6:52pm
So the issue I am running into is how to control the PAS system with a torque sensor AND a PAS sensor.
There is a system from Poland that's quite similar to the CA, but uses modern displays :-)
https://bikel.pl/en/mpe-computer-for-e-bike/

Image

If you want a minimalistic solution, you can look at the METOP "Minimal_E-Bike_Torquesensor_Precontroller" based on a Digispark
https://github.com/stancecoke/Minimal_E ... controller

It reads in the PAS and the torque signal from the sensor and calculates the voltage for the throttle line of the E-Bike controller with the logic motor power = Factor * human power.

Image

by the way, the torque sensor can be sourced directly from China, they offer a suitable controller + display for plug & play use also.

regards
stancecoke

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