I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "A PM motor does not have a field winding on the stator frame, instead relying on PMs to provide the magnetic field against which the rotor field interacts to produce torque. Compensating windings in series with the armature may be used on large motors to improve commutation under load. Because this field is fixed, it cannot be adjusted for speed control. PM fields (stators) are convenient in miniature motors to eliminate the power consumption of the field winding. Most larger DC motors are of the "dynamo" type, which have stator windings. Historically, PMs could not be made to retain high flux if they were disassembled; field windings were more practical to obtain the needed amount of flux. However, large PMs are costly, as well as dangerous and difficult to assemble; this favors wound fields for large machines."?
What was the downside to big machines?
The given passage talks about two types of motors - permanent magnet (PM) and wound field. PMs have a fixed flux whereas wound fields can be adjusted for speed control. The passage also says that large PMs are costly as well as dangerous to assemble, which favors the use of wound stator windings in big machines because there is no need for power consumption due to absence of winding on the stators. This makes it easier to manufacture and saves costs compared with their counterparts, i.e., large PM's .
So we could ask "What was the downside to big machines?".