Messed up CA3 speedometer using Bafang G.020.350.D 10 + Baserunner Z9.

uralik

1 µW
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Apr 20, 2021
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Hey everyone, I've built my first ebike recently from some new and used parts. Long story short is that the speed values I see in CA3 display does not correlate with the reality regardless of what number of poles / wheel circumference I put in.

Now a bit more details:

Motor: I have a bafang G.020.350.D 10 front hub motor which I got used from the bike shop which disassembled a lot of wrongly laced wheel sets and the seller told me that the motor works like new.

Controller: new baserunner z9 from grin

CA: CA3-WP

Battery: EM3EV 14s9p 27ah

1. I have configured the baserunner with autotune by setting Number of pole pairs to 10 (website shows number of poles 20 which i divided by two). I wonder if anyone can confirm that this is the right way to go.
2. I have set the wheel diameter is baserunner to 4 inches: my wheel is 20 inches and reduction ratio of this motor is 1:5.

After these two steps the max unloaded speed showing in the baserunner suite dashboard is ~41kph and max rpm is ~2100. 2100 looks way too much for me, isn't it? its like >30 rotations per second... and the link above shows lower rpm as of ~300.

Now we are getting to the CA3 part:

3. I have set the number of poles in the CA3 speedometer setup to 20 (as I understood here it means the actual number of magnets inside which is 20 given the link above), and the wheel circumference to 303mm (1515mm / 5) since my 20inch wheel is ~1515mm. After this I see the speed goes only up to ~8kmh but wheel is rotating MUCH faster than that. I have tried to change number of poles to 10 and then speed weirdly fluctuates as it can go up to 12 and then instantly show smth like 4 or so.

That's it. Basically the bike itself works really well as I've successfully set up closed loop power throttle and throttle ranges. But I really want this speed thing to be working well so I can enjoy the numbers while climbing uphill.

It feels like I may have (1) issues with the baserunner motor setup (autotune with 10 pole pairs not sure if thats correct value) and (2) the discrepancy between the baserunner and the cycle analyst settings.

Please help me! thanks :D

attaching the pic of my new ebike for daily commute!
photo_2021-04-20_22-18-59.jpg
 
uralik said:
G.020.350.D 10[/url] front hub motor

AFAIK this has a separate speed sensor, usually the white wire. This has six magnets, so you would set the CA to six poles for this sensor. That is what I would recommend doing. You may have to alter your wiring harness between motor and controller or controller and CA so that the CA uses this and not a motor hall sensor.

If you are using a hall sensor, then you'd need to use the number of pole pairs in the motor (probably 10), multiplied by it's gear ratio, which should be 5, so you'd use 50 for the number of poles in the CA speedo, and then set your wheel circumference to whatever it actually is (you can measure that with string or tape measure, or a number of other ways).

However, if you use the hall sensor, then you *ONLY* get the correct speed when the motor is spinning and driving the wheel. As soon as the wheel spins faster than the motor, the speed reading is now only that of the motor, not the wheel, because the motor has a freewheel in it, so the wheel can spin without backdriving the motor.
 
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