geared hubmotors and the cycle analyst: setup tips

[voicecoils]

Hi all,

I spent a bit of time playing with my Cycle Analyst (direct plug in model) with my Bafang hubmotor. Since the geared hubmotors have a motor speed higher then the wheel speed, and the Cycle Analyst (CA) determines speed from the hall sensors, extra setup steps are needed to get wheel speed and distance to display correctly.

My motivation for trying to correct this was twofold:

* Firstly speed was being displayed incorrectly (much too high)
* Secondly, the max speed limit I can set is 99kph but the corresponding motor speed was much higher, so the controller was cutting power to the motor above this.

For the Bafang motor, here were the peices of info I needed:
* Gear reduction: 4.3:1 (so if the motor spins 43 full revolutions, the wheel turns 10 times)
* Motor poles: 10 pole pairs (this is set in the CA advanced menu)

I altered wheel size field by dividing my actual wheel circumference by 4.3. My 26" wheel with large tires comes in at 2100mm, so I programed wheel diameter to be 488mm. Now I am getting a noload speed reading of ~62kph at 79-80v. I'll do some riding tomorrow with my GPS and compare speed accuracy.

Another thing to note is that some geared hubmotors have a freewheel (including the Bafang). This means the plug in CA cannot correctly measure distance as distance traveled while the motor freewheels will not be counted. If you use a small bike computer that measures speed and distance, you can use the distance info along with the watt-hours (Wh) consumed on the CA to determine the all important Wh/km or Wh/mi figure.

Anyone have any other CA and geared hubmotor tips?

 

[fechter]

Hmm...

Couldn't you mount a magnet on the wheel and use a bike speedometer pickup to feed the CA?

This way your distance values would not be affected by the freewheel.

 

[voicecoils]

Hmm...

Couldn't you mount a magnet on the wheel and use a bike speedometer pickup to feed the CA?

This way your distance values would not be affected by the freewheel.

Yes I think so, that's how my stand alone CA works. Perhaps it's just a matter of hacking into the CA cable and pulling out the correct wire for speed pickup?

I had a short ride last night and the speed seemed to correlate reasonably well with my GPS.

Are there any other values (advance menu?) that should be altered as well, or is tricking the CA into thinking there's a smaller wheel just the simplest way to go?

 

[geoff57]

hi
this problem of geared motors and the Cycle Analyst has come up in testing the infineon controller, the answer is not so easy but is possable with a bafang If I remember.
the way to make it work is deone in stages :-
1: find the number of poles. in the case of the bafang it is 20 1 magnet = 1 pole
2: find the gear ratio. in the case of the bafang it is 4.8
3: find circumfrence of wheel.
4: a ver 2.0 CA goes up to 14 poles so you shold set the poles to 10, divide the cir. by 2 to correct for this.
5: divide the result by the gear ratio 4.8.
6: feed this into the CA as the cir.


this should give an acurate speed result out of the CA the only problem is that the CA showed signs that it has a clock limmit which I found out about when doing the same thing for a puma motor 32 poles, 5:1 ratio, knuckles in the US did the same thing with a bafang and he was able to get a result, my bafang arrives soon so I can repeat the test.

Geoff