Looking to Add a BB Torque Sensor to Work In Tandem with my Throttle & PAS (I am using the KT25A Sine wave Controller)

[LongRangeRider]

Hi All:

New member here.

Recently started to modify my stock e-bike.

I have swapped out the Bafang display and controller for the KT LCD8S and KT36/48SVPRL-ffF10AL.

I am running a cadence PAS with throttle; however, I would like to add a BB Torque sensor while keeping the throttle.

I once came upon a threat that discussed how to do this, but I cannot locate it again.

I believe that I needed to change the firmware, adjusted (drop) the operational voltage supply to the torque sensor, and solder in a new wire onto the controller at PIN X4.

After that, I cannot recall the finer details.

If anyone could point me in the right direction, you would make my upcoming biking season, better than the last.

Many Thanks,

LongRangeBiker

 

[amberwolf]

There are at least two ways to do it.

One is to use the Cycle Analyst v3 to read the various sensors and generate a throttle signal to run the controller, without modifying the controller in any way. You don't have to put the CA on the handlebars, it can go anywhere on the bike, so it doesn't interfere with your controller's display, etc. It's relatively simple to setup but more expensive.

You don't even necessarily need a torque sensor to make the bike perform more controllably this way--the cadence sensor is enough because unlike the KT OEM firmware, the CA will actually let you use the pedals to directly control the motor system, either it's torque or speed or power. (the KT OEM firmware, like just about every similar controller, only turns the full power of the presently-selected-assist-level on or off based on whether or not it detects that you are or are not pedalling).


Another cheaper more complicated to setup way is to use the Open Source Firmware OSFW discussed here:

KT motor controllers -- Flexible OpenSource firmware for BMSBattery S/Kunteng KT motor controllers (0.25kW up to 5kW)

This OpenSource firmware/embedded software runs on the BMSBattery S/Kunteng KT motor controllers. The main advantages of this controllers are: 1. sine wave/"FOC": motors run silent and very efficient 2. cheap: starting at 20€ 3. widely available: many online shops sell them and ship to worldwide...

endless-sphere.com

GitHub - stancecoke/BMSBattery_S_controllers_firmware: OSEC Open Source E-Bike Controller in a Windows toolchain for a STM8

OSEC Open Source E-Bike Controller in a Windows toolchain for a STM8 - stancecoke/BMSBattery_S_controllers_firmware

github.com

FLEXIBLE OPENSOURCE FIRMWARE

I don't have a direct link to the post(s) regarding torque sensors, but they're in there somewhere. There are probably also other threads about that specific part we can look for if necessary.


Another alternative is to use a torque sensor like Erider that outputs a more throttle-like signal, and make a small op-amp circuit (or arduino) that converts it's voltage output range to that of the throttle input range of the controller, and connect it to your controller's throttle input. If you need both throttle and pedal control at the same time, you can parallel the signals via either small resistors, or an active merger like op-amps, or if you only ever want to use one or the other, a switch to flip between the two.


Note that your actual bike's BB design will determine which BB torque sensor you can use. Which bike do you have?

 

[stancecoke]

I would like to add a BB Torque sensor while keeping the throttle.

I don't have a direct link to the post(s) regarding torque sensors, but they're in there somewhere

There is a wiki page in the german forum:

elektrotechnik:open_source_firmware_fuer_sxxs_ktxx_-controller:drehmomentsensoreinbindung [Wiki Pedelec-Forum]

www.pedelecforum.de

regards
stancecoke

 

[LongRangeRider]

Thank you both for your replies.

In reading through the threads that each of you referenced, I came across a lot of reports of the BB-T-Sensors failing, due predominantly to what is believed to related to the VDC step-down via buck convertors.

Do either of you see a problem with me using plain ole resistors - Question Mark

Here is what I am thinking:

 

[szkuba]

You can use the transil diode at the DC/DC output to short the voltage spikes

 

[LongRangeRider]

You can use the transil diode at the DC/DC output to short the voltage spikes

Very true, however, space always being at a premium, and less parts always being better if they can do the same job, is where my head is at. I have some 2.2 kOhm resistors kicking around, so in that sense they are also free.

I'm looking to confirm that I am not over simplifying things here.

We are talking about very low current, so, what could really be better than a properly valued and tolerance resistor... The Thevenin equivalent almost lands perfectly on a standard value resistor.

Am I missing something

 

[woody27]

Can you elaborate on the reasons why do the eRider fail (in layman's term)?

Is this because the main battery pack (say 36v) will power the device which is, for example for the t17, operating between 5 and 15v?

Thus it mains you need yet another device to reduce the voltage in a stable way (no spike)?

I read also that the "noise" (spikes?) on those brackets can be eliminated by grounded the bike frame.

Thanks for your help