2 or 4 Pole motor?

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2 or 4 Pole motor?

Postby Burgerman » 09 Sep 2018, 11:58

Got an email asking why 4 pole is better since it draws more amps, and 2 pole motors are more common. Rather than reply by eMail I thought it better to do it here and link to it. Since its going to be an essay...

In the typical cases when ordering a chair there are options on the prescription form, a 2 pole motor is the "standard" option included on most 4 or 6 mph chairs. Thats 6 to 10kph chairs. And a 4 pole motor is a more expensive option. (***And a 4 pole HD 4mph motor is sometimes offered too). Should you tick this 4 pole box? Well in most situations, and for most users the answer is yes. ESPECIALY on rear drive chairs or front drive chairs. And especially so if you are heavy. It may not make a lot of difference, or be worth while, or even superior if you are a skinny 7 stone 13 year old ballerina in a mid drive chair.

Whats the acual difference?
In most cases the gearbox, and motor, and brake are absolutely identical The ONLY difference is that instead of 2 magnets in the motor there are 4. And instead of one pair of motor brushes, there are two pairs (with the extra ones sitting 90 degrees apart from the first set). All the other motor parts are usually pretty much identical. (Although this isnt always the case, but its easier to understand if we presume it is for now).

In operation, the 4 pole motor has 2 sets of magnets, and 2 sets of brushes, and 2 sets of motor coils energised at all times. So all else being equal it will pull DOUBLE the motor amps. And make DOUBLE the torque, at any given voltage. This means that provided the chairs POWER MODULE can provide enough amps, the 4 pole motor will make nearly double the amount of TORQUE that the 2 pole motor can. Although its not quite that simple. Why do we need TORQUE? Because to turn on the spot, or to dig yourself out of a hole, or to climb a threshhold, we need enough "push" from the motor to do this.

Its important to understand that AMPS = TORQUE or "PUSHING POWER" from a motor.
A typical 2 pole motor takes say 80A when stalled. A typical 4 pole motor, takes 2x this, so 160A when stalled. Since 2 sets of coils and two sets of brushes are powered up. Both these 2 and 4 pole motors will take far less Amps as they begin to rotate. So the 2 pole motor may drop down to 50A at 1mph. And less at 2mph

So if you only have a 70A controller, say a VR2?, then both motors will make the SAME max torque due to the 70A limit. But the 4 pole motor will make more torque at 1 or 2 mph. Aiding steering or ramp climbing etc. But if you also add a more powerful controller as well, like say the 120A r-net, (tick the box!) then the 4 pole motor can make 120A worth of stall torque! So it will now curb climb, turn on the spot, ignore which way a caster faces, and climb a threshhold for eg, much more easily, and with greater control. And it can do this above stall speeds better too.

This matters more on rear or front drive chairs. As they take more torque to turn on the spot. And this is made worse by users that like the odd burger. The downside of a 4 pole? Not many. But at maximum speed, as you drive long distance they are less efficient, and so use a little more battery power. At lower speeds they are usually considerably more efficient. The other thing is that a 2 pole motor puts a lot of amps through two tiny brushes which fail much sooner. So inevitably less reliable.

So unless a mid drive chair, and a lightweight user, it is always best to go for the 120A controller where possible, and the 4 pole motor option if available if you want it to work properly! And it matters! Why dont stock chairs have this as the default order? COST! Its not cheap. It can add a lot of extra cost. But really it is essential. Especially if you program it to steer properly...

***A HD motor is simply a lower geared (slower) 4 or 5mph 4pole motor. So it has extra torque because of gearbox (speed reduction)! For overweight people so the chair still steers.
And you will never find an 8.5mph 2 pole motor I think, because they NEED to be 4 pole or exeptionally low impedance to have the required torque to steer at all.
Because the taller gearbox ration needed for the higher speed reduces torque proportionally.
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Re: 2 or 4 Pole motor?

Postby zagam » 28 Sep 2018, 03:11

4 pole is better if the motor has an iron core, but it needs to be larger to produce more torque. There is less loss in the reduction gears.

Permanent magnet motors with iron-less stators can go much faster and when matched with planetary reduction they're compact and efficient. They have many poles and are driven by brushless electronics. They operate at large current low speed or high Voltage high speed. The conversion of battery Voltage is done by the drive electronics.

Use Li-Ion batteries and iron-less motors of this century in any new design.

One of the problems with power chairs is their weight. This should be fixed.

Even though my shoulders are damaged I still drive a manual chair as it is easier to load and unload from the car.

Did electronic communications, but built plants with lost of VVVF driven induction motors. Also used modern servo motors on some plants.

drunk2 beer
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Re: 2 or 4 Pole motor?

Postby Burgerman » 28 Sep 2018, 10:13

Not sure what to make of that disjointed confused post! Even is some of it is correct. Initially it looked to me like a spam bot post. But its not.
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Re: 2 or 4 Pole motor?

Postby steves1977uk » 29 Sep 2018, 10:45

That post by zagam looks like confused writing! :?

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Re: 2 or 4 Pole motor?

Postby Burgerman » 29 Sep 2018, 11:02

The beer smilies may have been imprtant and meanuingful...
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Re: 2 or 4 Pole motor?

Postby FourLions » 29 Sep 2018, 11:51

i have seen this type of calligraphy induced by a toxin that goes by the name J D drunk2
Loving my Quickie F55s every day i use it :)
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Re: 2 or 4 Pole motor?

Postby Burgerman » 29 Sep 2018, 11:56

That will do it. Of course it may be disability related. And some peoples posts just are a bit confusing anyway. Or all 3...
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Re: 2 or 4 Pole motor?

Postby FourLions » 29 Sep 2018, 12:20

People need to know as much as they can from your site John it has helpt me so much , i use to paint cars for moste of my life didnt have a clue about elecric wheelchairs :thumbup:
Loving my Quickie F55s every day i use it :)
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Re: 2 or 4 Pole motor?

Postby MichaelB » 30 Sep 2018, 17:47

A useful post, I asked for 4 pole motors when I ordered my Ottobock without knowing exactly why, now I do :) As it happens the Ottobock is supplied as standard with 4 pole, 120A R net for the 10 kph model I ordered according to the rep, he said that they had so many requests for 4 pole and 120A they just do it on every chair. Don't know how accurate that is but he subsequently confirmed that was what my chair would have although I don't know if there is any obvious way to tell.
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Re: 2 or 4 Pole motor?

Postby LROBBINS » 30 Sep 2018, 19:53

If you can see the motor, and if it has external brush caps - which most do, there will be 4 caps on a 4-pole motor.
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Re: 2 or 4 Pole motor?

Postby Burgerman » 30 Sep 2018, 20:09

And a programmer will show you if its a 70, 90, or 120A r-net power module. The most common one seems to be the 90Amp one since its cheaper as it has all in one built in actuator outputs etc. So going for the 120A one ends up a lot more expensive. Given that the permobil prices are about double the average I would expect it to have the 120A one...
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Re: 2 or 4 Pole motor?

Postby Burgerman » 30 Sep 2018, 20:18

Postby LROBBINS » Sun Sep 30, 2018 6:53 pm
If you can see the motor, and if it has external brush caps - which most do, there will be 4 caps on a 4-pole motor.


Even though covered by a rubber weather band, you can see 4 brush holders here on the motors. Old chair!

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Re: 2 or 4 Pole motor?

Postby Burgerman » 30 Sep 2018, 20:22

TWO pole, 2 brushes:

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Re: 2 or 4 Pole motor?

Postby MichaelB » 01 Oct 2018, 15:52

It is difficult for me to see anything at wheelchair base height, won't have alead to connect a programmer. It looks like one of my support workers will be taking a look.

For the price Permobil charge I'd expect 4 pole and 120A but it all looked overpriced hence going for the Ottobock with just the options that I needed, the 4 pole and 120A as standard was an added bonus.
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Re: 2 or 4 Pole motor?

Postby Burgerman » 01 Oct 2018, 17:00

For what its worth, 120A adds about 100 to the price, but then you need the seperate seating module. And 4 pole motors adds about the same. Both are actually essential if you want it to function correctly.
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Re: 2 or 4 Pole motor?

Postby MichaelB » 01 Oct 2018, 17:35

So not too expensive to make it a standard spec as Ottobock have done. I've only gone for tilt in space no power recline or legs, figured that I would keep it as simple as possible main criteria was that it drove well and was comfortable, given that chin steering isn't very precise because of the joystick mounting issues.
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