Direct Drives

Hi

1) About torque:
Motor temperature ( if current is set and all the more so without cooling) is related to motor dimension ( dissipation capability) and so what you are asking for is not an easy task.
If you suppose that you are controlling the current in the best way possible ( so we are free from driver and feedback performance) the torque is caused as a result of stator and rotor magnetic field interaction. So if you want increase torque in a motor ( without increase dimensions) you need to increase these fields or improve the way they interact without increase the nominal current. For a DD rotary motor that means that you can for example:
A) Increase copper in windings ( but this force you to increase dimensions if we suppose that in this moment all motor manufacturer use about the same filling technology to coil them. Probably coil up windings by hand let you gain 5-10% but that's not so cheap...)
B) Use magnets with the highest B as possible ( NdFeB) and with the highest thermal class.
C) Improve the way these fields interact; that's a design issue and it is quite a job ( EM CAD and finite alement method)!
D) If you use high thermal class materials you can go up with temperature and so you can squeeze more torque from the motor without destroy it ( in addition to magnet also epoxy resin, windings wire... must be higher thermal class).
E) It depends also from the application; for example if you only need to increase peak torque, highest thermal class magnets could be suitable for you, in order to decrease dimensions without lose peak performance and without damage magnets induction.

As a last general consideration I say that I see torque values and dimensions very similar in manufacturer catalogues...

2) About the inertia:
If the motor is smaller the inertia too is reduced.
Then is possible to work on shaft materials and on shaft geometry. This too is a design issue and it's quite a job. I suppose that a lot of trick to reduce inertia or so are patented.

best regards