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.