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Minimum setup for adding torque sensor to rear hub

maladroit

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Apr 27, 2022
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Hello, and apologies if this is the wrong place to ask!

I am looking at two similar cargo bikes -- one has a Bafang 250w rear hub motor and a Lishui controller (I don't know the exact model numbers), the other a Bafang M400 mid-drive motor. I like the idea of the rear hub because it seems easier to maintain/replace down the road, but it does not have a torque sensor. The rear hub bike is also significantly less expensive.

This would be my first ebike, and I am definitely looking for a torque sensor ride -- I love biking but for car replacement I need more reliability and endurance than my legs can provide alone. I see that I can get aftermarket torque sensors, but I'm not sure what I need to connect it up. The Cycle Analyst method adds another device, meaning more money and more wires to deal with.

My questions: Is it possible to program the torque sensor into the existing controller, or a replacement controller? Am I right to be concerned about a built-in mid drive frame becoming obsolete in a few years?

I should add that I am not experienced with this kind of DIY electronic project, but I'm ok at following instructions.

Thanks for any advice!
 
If you already have an existing controller, then the CA is likely to be the most economical option with the least amount of rewiring, for adding a torque sensor.
 
maladroit said:
This would be my first ebike, and I am definitely looking for a torque sensor ride -- I love biking but for car replacement I need more reliability and endurance than my legs can provide alone.
Torque sensing is useful, but there are times when it doesn't operate the way you might need it to...so I recommend also having either a throttle, or at least a "get-going" button wired to the throttle input on the controller, so you can still get started in a situation the torque sensor just isn't doing the job.

My SB Cruiser trike is (well, all my bikes have been) my car-replacements; never had a car for transportation. I have used torque-sensing, but at the time the way it worked didn't activate at zero-speed so it wasn't useful to me (taht is the time I *really* need it to work), so I set up using just cadence control via the CA, and it works very well...except that at startup I often have to use the throttle as a get-going button and don't really want to. Thankfully the new 3.2 version of CA firmware now supports it from zero speed/zero cadence, so when I get time I'll be setting that up on the trike to try out with the TDCM sensor I have.


I see that I can get aftermarket torque sensors, but I'm not sure what I need to connect it up. The Cycle Analyst method adds another device, meaning more money and more wires to deal with.
I think the Erider TS has at least one version that outputs a standard throttle-range signal that could be directly connected to a throttle input of a generic controller, instead of the throttle.

If that version isn't available, then another version of the erider could be used, though it might require a tiny bit of electronics (op-amp) to scale the output voltage range so that it fits within the standard throttle input range of a controller.

The CA does add more stuff/cost, but it doesn't have to go on the handlebars so you can put it with the controller and trim all the wiring to minimum to reach just where you need it. You also have to do all the setup of the CA (unless you buy from Grin Tech and have them do it for you), to make sure it's settings match your needs and equipment. It's not hard, but it is a bit complex, and takes some time.

Is it possible to program the torque sensor into the existing controller, or a replacement controller?
Using the Cycle Analyst v3.x, you'd basically be doing that. But it does add another device, rather than directly doing it into the controller.

If you are handy with MCU programming, and either flashing controllers (that have reprogrammable MCUs; they don't all, those you'd have to solder in a new MCU) you could write your own controller program, but you would be starting without any of the original programming code as that's not readable back out of the MCU in most cases.

There are some controller types (KT, Lishui, etc) that have open-source firmware replacements that support things like this. See the Casainho, Stancoke, etc threads about it here on ES or their projects on Github, etc.


Am I right to be concerned about a built-in mid drive frame becoming obsolete in a few years?
If it still does what you want it to do, does it matter if it is obsolete to everyone else? ;)
 
Thanks to you both; I think the consensus is the CA3 package would make the most sense!

amberwolf said:
Am I right to be concerned about a built-in mid drive frame becoming obsolete in a few years?
If it still does what you want it to do, does it matter if it is obsolete to everyone else? ;)

I guess what I am concerned about is when the motor breaks, I won't be able to do anything with that M400-shaped hole in the frame. Integrated motors don't seem to be standard sized. A good bike should last as long as you care for it, but electronics don't.
 
maladroit said:
Thanks to you both; I think the consensus is the CA3 package would make the most sense!
It's the most versatile. :) BTW, if you need access to change levels or presets etc in the CA while riding, you can use handlebar controls plugged into it even if it is hidden away somewhere else.

The "simplest" is the KT controllers with the OSFW installed instead of the OEM FW, in that it doesn't require the separate CA to do the torque sensing...but it may still require it's own display to change settings or levels on a ride, etc.

I guess what I am concerned about is when the motor breaks, I won't be able to do anything with that M400-shaped hole in the frame. Integrated motors don't seem to be standard sized. A good bike should last as long as you care for it, but electronics don't.

That's certainly true. I end up custom-building or rebuilding many things because either what I want isn't made by anyone, or I have one of what I want that doesn't work anymore and I have to fix or rebuild it because it isn't made by anyone anymore. :lol:
 
amberwolf said:
Torque sensing is useful, but there are times when it doesn't operate the way you might need it to...so I recommend also having either a throttle, or at least a "get-going" button wired to the throttle input on the controller, so you can still get started in a situation the torque sensor just isn't doing the job.

This . Amb is totally right: cargo and torque sensors are two pairs of shoes. Had it, and swapped for a simple pas, because the sensor could not account for the huge changes in weight when loaded or unloaded.
 
maladroit said:
... and a Lishui controller ... My questions: Is it possible to program the torque sensor into the existing controller, or a replacement controller?
If you have a "normal" bottom bracket, there are several bottom bracket torquesensors available.
There is our open source firmware for the Lishui-Controllers. But it only works with a FOC controller, look for the "F" in your product number (that will be totally different from the one in the picture ;)).
With the usual KM5s protocol, you can set each assist level individually from 0 to 100%, so you can define e.g. level 1-5 for ridings with light load and level 6-9 for ride with heavy load, when you configure the display to 9 levels.

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regads
stancecoke

Kingmeter PAS levels.PNG
 
stancecoke said:
maladroit said:
... and a Lishui controller ... My questions: Is it possible to program the torque sensor into the existing controller, or a replacement controller?
If you have a "normal" bottom bracket, there are several bottom bracket torquesensors available.
There is our open source firmware for the Lishui-Controllers. But it only works with a FOC controller, look for the "F" in your product number (that will be totally different from the one in the picture ;)).

A belated thank you! This sounds like the lowest cost solution for my question, and also for a ground-up conversion with a torque sensor.
 
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