Number of magnets and gear reduction ratio for this motor

[hinxx]

I bought this hub motor: EBike Antrieb Motor hinten Pedelec Elektrofahrrad 36V 250W Hinterrad Zündapp Rad 4250845941839 | eBay.

The seller says that there are 9 magnet poles. Does that make sense? Reading some posts here I learned that the number of magnets should be an even number. I guess the seller means "9 pole pairs"? I'll try to clarify with them..

I also asked for gear reduction ratio and was given this answer: The total gear ratio is 0.29 so 4:7. How to interpret this value?

 

[amberwolf]

How it is "interpreted" depends on what you are doing with the information.

What specifically do you need to know?

 

[hinxx]

I'm trying to use the correct gear ratio and number of poles in the EBiCS code that calculate the speed. It used here EBiCS_Firmware/Src/main.c at 85616c417b49c5ecdf48abf151bfc47b43168226 · EBiCS/EBiCS_Firmware.

I was reading
Programming Ebikeling 750w Geared hub. Cannot find gear reduction ratio value.. Then I tried counting the hall events on one of the phases and counted 50. Now I'm trying to make sense of these numbers I have and somehow they are not adding up..

 

[richj8990]

I'm trying to use the correct gear ratio and number of poles in the EBiCS code that calculate the speed. It used here EBiCS_Firmware/Src/main.c at 85616c417b49c5ecdf48abf151bfc47b43168226 · EBiCS/EBiCS_Firmware.

I was reading
Programming Ebikeling 750w Geared hub. Cannot find gear reduction ratio value.. Then I tried counting the hall events on one of the phases and counted 50. Now I'm trying to make sense of these numbers I have and somehow they are not adding up..

Assume 5:1 internal reduction and see what happens with the calculations.

I also assume the S830 display came with your kit. It's very similar to SW900, S866, etc. I'm going to copy and paste parameter 7 below, and then also paste the manual link and what I typically use for my 500W hub motor (that's going to be very similar to your 750W one). You will NOT need to deal with the # of internal magnets x internal gear reduction ratio with these types of displays.


P07: Range: 1-100 This is 46 for direct drive (1200w and above) motors and 01 for geared (500w - 750W) motors.


S830 Display Manual

1 =3
2 =1
3 = 48
4 = 0
5 = 1
6 = whatever wheel size you have
7 = 1!!!
8 = 50
9 = 0
10 = throttle 1, PAS 2 (I have found that PAS sucks with these, but you can certainly try 2)
11 = 20
12 = 5
13 = PAS magnet (outside of the motor, # of shiny circles on the black plastic disk by your crank pedal) 5, 8, 12
14 = 17 (you can go to 20A or even try 30A but play it safe with the current for now and do 15-17)

 

[hinxx]

I appreciate the input!
Actually I do not have a display; just using UART/SWO as a debug feature. I'm running the opensource EBiCS firmware (more specifically just the FOC motor control) to understand how flux weakening would work. For that to work motor speed is needed which is defined by the time between two hall events, wheel circumference and gear ratio.

 

[hinxx]

I got the response from the seller about the magnet poles when asked if they meant 9 magnet pole pairs and not 9 magnet poles:

The pure number of pole pairs is 6. However, the pole pairs here cannot be imagined as in a three-phase field. Of the 12 poles, 3 are always negative and 3 positive. Three poles always form the empty phase. That is why 3 Hall sensors are installed in the motor winding so that the rotor position can be determined without a doubt at any time.

Seems like actual number of magnet poles is therefore 12.. i don’t understand the rest of the text , though.