BLDC motors with uneven number of poles

6 years 8 months ago #29532341 by Erik
Sorry i have to ask again before i waste much time in finetuning my motors. (they don't work as expected unfortunately, jerky and still move after i stopped giving commands).

Does the fbl-2360 support bldc-hubmotors with an uneven number of poles? I run it with 15 poles as setting which works but not perfect.

If uneven numbers of poles don't exist don't worry, in that case the chinese manufacturers just gave the wrong number (or the girl who translated it made a mistake). I live in Asia for decades and know that anything is possible here. My hallsensors do really count 90 at a full spin of the axle.

In case you guys are studying it and i have to be more patient than just tell me so. I just want to finish my drivetrain and if necessary i can buy different motors or controllers or whatever is necessary.

Please Log in or Create an account to join the conversation.

6 years 8 months ago #29532347 by blake
Yes it should still work even with an uneven number of poles. After doing some research I did find that there are brushless motors with an odd number of poles but this is not very common and frankly not very good motor design. Another method to check the number of poles is to pass a current through two of the motor phase wires and then turn the motor by hand one full revolution and count the number of cogs you feel.

Regardless, it needs to be pointed out that the configuration in Roborun+ does not ask for the number of poles but the number of pole pairs. This configuration setting WILL NOT effect motor operation. The only thing that this configuration setting has an effect on is accurately ready speed or position data. All that would happen if you had the wrong number in the number of pole pairs is that the RPM reading you see in Roborun would not be as accurate. If you are experiencing erratic motor behavior still then it is do to some other reason.
The following user(s) said Thank You: Erik

Please Log in or Create an account to join the conversation.

6 years 8 months ago - 6 years 8 months ago #29532349 by Erik
Blake you are right that Roborun+ asks for pole pairs but i've been reading the manuals over and over again and here is some text ot them:

A full 3-phase cycle is known as electrical
turn which will be different from the physical (mechanical) turn of the shaft if the motor
number of pole pairs is greater than one: increasing the number of poles will cause the
motor to rotate more slowly for a given rate of change on the winding’s phases.
The number of poles is necessary for determining the number of turns a motor has
done. It can also be used to measure the motor speed. The Roboteq controllers can
measure both.
The number of poles on a particular motor is usually found in the motor’s specification
sheet. The number of poles can also be measured by applying a low DC current (around
1A) between any two wires of the 3 that go to the motor and then counting the number
of cogs you feel when rotating the motor by hand for a full turn. It can also be determined
by rotating the motor shaft by hand a full turn. Then take the number of counts reported
by the hall counter, and divide it by 6.
The number of poles is a configuration parameter that can be entered in the controller
configuration (see “BPOL” in the command reference section). This parameter is not needed
for basic motor operation with Hall Sensor feedback and can be left at its default value.
It is needed if accurate speed reporting is required or to operate in Closed Loop Speed
mode. The number of poles in a critical configuration in sinusoidal mode.
Entering a negative number of poles will reverse the measured speed and the count direction.
It is useful when operating the motor in closed loop speed mode and if otherwise a
negative speed is measured when the motor is moved in the positive direction

That gave me a lot of confusion.....add to that that english is not my first language and technical electrical manuals make me very tired in temperatures above 30 celcius. (yes i'm european).

Also it's frustrating that the general manual which is referred to for BL-motors doesn't now have my controller in the list...there are many controllers mentioned in that document except the's like i bought a product for which was no time to write a decent manual.

And the number of poles might only influence the rpm but that combined with a low accelerfation/decelleration gives no action on the motor, many times i had to D-out led in roborun being green but the motors didn't move....Than i started changing the configuration again but the fault was caused by the too low speed (i used 10 rpm sometimes) and because of the wrong number of poles the motors wouldn't spin..i didn't do anything wrong but it was the wrong rpm-reading because of the wrong number of poles or polenumbers....not my fault...

The erratic behaviour was really extreme, i even started wearing safetyglasses when testing settings and always had one finger on the battery-emergency switch to cut all power off, many times i really needed that or my robot (with laptop ontop) would have been racing through my livingroom loaded with expensive furniture (imported lazyboys and all custom made teakwood cabinets and so).

The producer of my hubmotors replied within an hour when i mailed them in china, the motors have 15 number of poles she wrote but also the chinese are confused by it, poles or polepairs.

In closed speed mode the motorcommands are very slow for some reason, many times the motors only start running after 2-3 seconds, in that time i allready had given 100% commands because i thought nothing was gonna happen because of wrong settings..this also had to do with wrong number of polepairs and accelerationsettings.

I also just wondered why my spambox is so full in Outlook, for some reason some of the forumannouncements for new messages had ended up in my spambox while others just arrived in my mailbox, even today...don't ask me why but i had some updates from outlook lately who probably have to do with that issue..

Anyway, my robot works with 15 and 30 polenumbers, not much difference only in rpm. What makes it unusable for me is the fact the motors don't drive even and also won't stop precise after stopping motorcommand..many times i have to give a reverse motorcommand to make them stop or they will drive into something here. Very frustrating...and the gain-functions are also no good for my motors, especially the P-gain gives much noise out of the motors although they don't move. At controller startup it makes shocking moves, very powerfull and that even made the casing crack....i think it's dangerous to test this way and didn't know any other way to test it. When my robot is off the floor the motors changed direction at full speed all the time without taking care of my decellerationsettings at all. It's a wonder the motors are still alive though and nothing is damaged here. Even the 5 amp fuses never broke while i used the controller at 20 amp per channel during testing (sometimes).

But in closed speed mode i can't use it for lawnmowing or floorsweeping..the robot even can't drive in a straight line and steers itself sometimes. I tried all settings and combinations, it works now but not good enough at low speed. I can't use high speed for lawnmowing.

So i'm looking for other motors and hope we all learned from this. I also would love to see a 2nd video made by roboteq with those 2 brushless hubmotors mounted on a loaded vehicle and driven in closed loop mode at slow speed...IT's too easy to let the motors spin without any load, mine also can do that very well and in open loop mode the whole robot drives perfect but i can't program in that mode, that's the reason i bought the fbl2340 though so it's useless to me with these hubmotors. I need other motors.

Please Log in or Create an account to join the conversation.

Moderators: tonysantoni
Time to create page: 0.060 seconds