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.

 

[PeterHc]

Hello,
this is an older thread, but I have still interest for this motor.
You can probably detect the number of poles from outside, using a strong magnet.
This works with this motor and with other motors.
This magnet must have northpole at one end and southpole on the other end.
Point it with one pole closely to the outer rim of the motor.
Then you can feel the attracting and repulsive forces and count the poles.

Then if you apply a DC current to one coil you can possibly also determine the gear ratio if you rotate the motor by hand.
Or measure current frequency and rpm.

I have more interest into this motor Ananda M145.
I want to know, if it has an internal temperature sensor.
If yes, then the temperature level is probably encoded into the amplitude of the speedometer signal.
If somebody knows this or if somebody has good photos of the internal cabling and PCBs, then I would be very happy to know this.

 

[amberwolf]

I have more interest into this motor Ananda M145.
I want to know, if it has an internal temperature sensor.
If yes, then the temperature level is probably encoded into the amplitude of the speedometer signal.

do you already have hte motor? if so, you can test that by checking the voltage of the speedo signal (supplying 5v and ground to the sensor power/ground lines, with no external pullup resistor on the signal line) and seeing if it varies based on temperature. keep the motor inside for a while, measure it's voltage. put it out in the direct sun for an hour or so, measure it's voltage. if it's the same, then it's unlikley to have the multiplexed temperature/speedo signal.

if the voltage of the speedo signal is modulated by the temperature sensor, it's likely that they're doing it by putting the temp sensor as the pullup resistor on the output of the speedo hall sensor. in that event you can skip applying any power or ground to the sensor and just measure resistance from signal to 5v wires on the speedo sensor.

tyipcal temp sensors are ntc 10k types, beta varies, so at room temperature 25c / 72f it will be near 10kohm, and go down as temperature increases, or up as it decreases.

if it's a ptc it'll go down with temp decrease, up with increase.

if they're instead using the temp sensor as part of a voltage divider to supply the pullup to the speedo, it depends on which side of that divider it is on for where you measure the resistance.

if they're using a more complex circuit then the voltage method in the start of this post is easiest to check, as it may not be possible to tell by a simple resistance check.

 

[PeterHc]

Here is the Ananda cataloque 2023.
It lists the motors and their mechanical dimensions much more accurately than the newer cataloque.
Number of magnet poles and reduction ratio and speedometer magnets are listed.
Hopefully you can find your motor there.
https://prosport-group.eu/download/2022/ANANDA Drive System-Catalogue-2023.pdf