ELECTRIC MACHINE

1 . A rotor for an electric machine, the rotor comprising:

an annular disk formed of a unitary piece of a material and defining an axis, and having an inner edge and an outer edge;

circumferentially spaced posts extending axially from the annular disk and defining slots between the posts; and

the annular disk defining holes extending radially within the annular disk from the inner edge or outer edge.

2 . The rotor of claim 1 in which the posts are formed of the unitary piece.

3 . The rotor of claim 1 in which the posts are arranged on both sides of the annular disk.

4 . The rotor of claim 3 in which the posts on each side of the disk are aligned with respective posts on an opposite side of the disk as projected onto a plane perpendicular to the axis.

5 . The rotor of claim 1 in which the holes are aligned with the slots as projected onto a plane perpendicular to the axis.

6 . The rotor of claim 4 in which the holes are aligned with the slots as projected onto the plane perpendicular to the axis.

7 . The rotor of claim 1 in which the holes fully extend through the annular disk between the inner edge and the outer edge.

8 . The rotor of claim 1 in which the annular disk defines openings connecting the holes with the slots.

9 . The rotor of claim 1 in which each post extends between the inner edge and the outer edge.

10 . The rotor of claim 9 in which the posts have a first axial height at the inner edge and a second axial height different from the first axial height at the outer edge.

11 . The rotor of claim 10 in which the second axial height is greater than the first axial height.

12 . The rotor of claim 9 in which the posts define straight lines between the inner edge and the outer edge, adjacent posts defining substantially parallel lines.

13 . The rotor of claim 12 in which the posts have an inverse taper of circumferential thickness with axial height for retaining magnets.

14 . An electric machine comprising the rotor of claim 1 and further comprising:

a stator having an array of electromagnetic elements;

the rotor having electromagnetic elements defining magnetic poles, the rotor being arranged to move relative to the stator;

an airgap between the stator and the rotor;

the electromagnetic elements of the stator including stator posts, with slots between the stator posts, one or more electric conductors in each slot, the stator posts having a post height in mm;

the stator and the rotor together defining a size of the electric machine;

the magnetic poles having a pole pitch S in mm;

the size of the motor, pole pitch and post height being selected to fall within a region in a space defined by size, pole pitch and post height, the region being defined by either

1) a first union of:

a) a first surface defined by a first set of inequalities for a first size of electric machine;

b) a second surface defined by a second set of inequalities for a second size of electric machine; and

c) a set defined as containing all points lying on line segments having a first end point on the first surface and a second end point on the second surface;

the first set of inequalities and the second set of inequalities being respectively sets of inequalities A and B, or B and C, or C and D, in which the group of inequalities A is for a size of 25 mm, the group of inequalities B is for a size of 50 mm, the group of inequalities C is for a size of 100 mm, the group of inequalities D is for a size of 200 mm; or

2) a second union of a surface as defined by set of inequalities D and a corresponding set of all points with size greater than the surface but with pole pitch and post height corresponding to points within the surface;

where

A is selected from the group of sets of inequalities consisting of:

Set A1:

Post Height >

−1.070 * S + 2.002

for

0.572 < S < 1.189

 1.175 * S + −0.667

for

1.189 < S < 2.269

13.502 * S − 28.637

for

2.269 < S < 2.500

Post Height <

−5.898 * S + 19.863

for

1.970 < S < 2.500

 0.229 * S + 7.794

for

1.349 < S < 1.970

 7.607 * S − 2.160

for

0.723 < S < 1.349

11.430 * S − 4.924

for

0.572 < S < 0.723

Set A2:

Post Height >

 −1.340 * S + 2.305

for

0.619 < S < 1.120

 1.100 * S − 0.429

for

1.120 < S < 2.074

 3.830 * S − 6.082

for

2.074 < S < 2.269

Post Height <

−69.510 * S + 160.318

for

2.222 < S < 2.269

 −3.430 * S + 13.492

for

1.667 < S < 2.222

 2.830 * S + 3.056

for

1.133 < S < 1.667

 8.650 * S − 3.545

for

0.619 < S < 1.133

Set A3:

Post Height >

 −4.160 * S + 5.032

for

0.723 < S < 0.967

 0.839 * S + 0.198

for

0.967 < S < 1.692

 2.713 * S − 2.973

for

1.692 < S < 1.939

Post Height <

−53.233 * S + 105.506

for

1.879 < S < 1.939

 −1.406 * S + 8.122

for

1.465 < S < 1.879

 3.898 * S + 0.353

for

1.035 < S < 1.465

 7.535 * S − 3.412

for

0.723 < S < 1.035

B is selected from the group of sets of inequalities consisting of:

Set B1:

Post Height >

 0.254 * S + 0.462

for

0.319 < S < 3.667

 2.665 * S + −8.380

for

3.667 < S < 5.000

Post Height <

−18.282 * S + 96.357

for

4.500 < S < 5.000

 −4.663 * S + 35.071

for

2.738 < S < 4.500

 2.585 * S + 15.227

for

1.447 < S < 2.738

 16.013 * S − 4.204

for

0.319 < S < 1.447

Set B2:

Post Height >

 0.269 * S + 0.456

for

0.380 < S < 3.016

 3.051 * S − 7.936

for

3.016 < S < 4.167

Post Height <

−14.766 * S + 66.309

for

3.667 < S < 4.167

 −3.952 * S + 26.654

for

2.315 < S < 3.667

 3.108 * S + 10.310

for

1.278 < S < 2.315

 14.542 * S − 4.303

for

0.389 < S < 1.278

 88.444 * S − 33.051

for

0.380 < S < 0.389

Set B3:

Post Height >

 0.191 * S + 0.626

for

0.472 < S < 2.181

 2.135 * S − 3.613

for

2.181 < S < 3.095

53.475 * S − 162.511

for

3.095 < S < 3.175

Post Height <

−5.095 * S + 23.450

for

2.222 < S < 3.175

 0.805 * S + 10.339

for

1.381 < S < 2.222

10.251 * S − 2.706

for

0.572 < S < 1.381

24.420 * S − 10.810

for

0.472 < S < 0.572

C is selected from the group of sets of inequalities consisting of:

Set C1:

Post Height >

 0.322 * S + 0.359

for

0.233 < S < 6.667

 2.202 * S − 12.179

for

6.667 < S < 8.333

Post Height <

−25.555 * S + 219.122

for

7.778 < S < 8.333

 −5.585 * S + 63.794

for

4.000 < S < 7.778

 3.214 * S + 28.600

for

1.793 < S < 4.000

 21.749 * S − 4.633

for

0.233 < S < 1.793

Set C2:

Post Height >

 0.277 * S + 0.593

for

0.250 < S < 5.182

 2.342 * S − 10.111

for

5.182 < S < 7.222

Post Height <

−13.149 * S + 101.763

for

6.111 < S < 7.222

 −4.885 * S + 51.265

for

3.333 < S < 6.111

 4.291 * S + 20.680

for

1.520 < S < 3.333

 20.788 * S − 4.395

for

0.251 < S < 1.520

161.000 * S − 39.588

for

0.250 < S < 0.251

Set C3:

Post Height >

 0.277 * S + 0.591

for

0.278 < S < 4.425

 1.916 * S − 6.663

for

4.425 < S < 6.111

Post Height <

−21.337 * S + 135.438

for

5.556 < S < 6.111

 −4.985 * S + 44.588

for

3.175 < S < 5.556

 2.749 * S + 20.031

for

1.560 < S < 3.175

 18.321 * S − 4.260

for

0.278 < S < 1.560

and

D is selected from the group of sets of inequalities consisting of:

Set D1:

Post Height >

 0.257 * S + 0.327

for

0.208 < S < 7.778

 1.977 * S − 13.044

for

7.778 < S < 9.444

Post Height <

−36.195 * S + 347.445

for

8.889 < S < 9.444

 −5.777 * S + 77.062

for

4.833 < S < 8.889

 1.950 * S + 39.718

for

2.222 < S < 4.833

 20.301 * S + −1.058

for

0.389 < S < 2.222

 34.481 * S + −6.574

for

0.208 < S < 0.389

Set D2:

Post Height >

 0.322 * S + 0.359

for

0.233 < S < 6.667

 2.202 * S + −12.179

for

6.667 < S < 8.333

Post Height <

−25.555 * S + 219.122

for

7.778 < S < 8.333

 −5.585 * S + 63.794

for

4.000 < S < 7.778

 3.214 * S + 28.600

for

1.793 < S < 4.000

 21.749 * S + −4.633

for

0.233 < S < 1.793

Set D3:

Post Height >

 0.212 * S + 0.600

for

0.264 < S < 4.833

 3.017 * S + −12.960

for

4.833 < S < 6.667

Post Height <

−12.356 * S + 89.531

for

5.556 < S < 6.667

 −4.551 * S + 46.170

for

3.175 < S < 5.556

 3.850 * S + 19.496

for

1.502 < S < 3.175

 19.751 * S + −4.387

for

0.264 < S < 1.502