Experiment of the lorentz force law using twin toy motors

Abstract

This paper proposes a torque measurement method with two toy motors. The aim is to study the basic principles of electric motors and generators, that is, the Lorentz force law, in a laboratory experiment. The two motors are directly coupled and used as a driver and a generator, respectively. The generator functions as an electric brake and as a rotational speed sensor. Since the experimental setup does not need any torque tester, its handling is very easy. It is confirmed from the demonstration tests that the twin characteristics of the motors on motional electromotive force lead to reasonable results of torque estimation.

Torque measurement method based on the Lorentz force law for miniature DC motor

“…Such an internal configuration is the most popular one in the field of miniature DC motors. Reference has suggested that, since the measurement method is based on the Lorentz force law, the validity for the toy motor with p = 3 can be extended to such a miniature DC motor as shown in Fig. .…”

“…, a pair of filament current paths on the core surface is substituted for each coil from “1” to “5.” The substitution represents the effect of the iron core, i.e. the concentration of the magnetic flux that is yielded by each coil . According to the Lorentz force law, an electromotive force (emf) and a torque emerging in a pair of filament current paths are, respectively, expressed by Here, ω is the rotational angular speed defined by ω = d θ 0 /d t ; q is a serial number for the five coils or the five pairs of current paths; I q is the current of each coil; and Φ q is the flux linkage (per radian) defined by where N is the number of windings per one coil; a and l are the radius and depth of the iron core, respectively; and are the angles of the inflow and return current paths, respectively; B r ( θ , z ) is the radial component of B ( a , θ , z ); and B ( r , θ , z ) is the magnetic flux density yielded by the permanent magnets.…”

“…It is caused by the current making the loop circuit of routes “I” and “II.” In the final analysis, the equivalence VI = Tω is not established, except for the special case treated in Ref. , that is, Φ = Φ I = Φ II . (Note: The same conclusion would be obtained even if an arbitrary choice was made for the brush width.…”

“…Therefore, the back‐to‐back system may give us the most inexpensive and most convenient system. So this paper reviews a method based on the Lorentz force law so as to use the back‐to‐back system for torque measurement but not efficient instrumentation. Concretely, the measurement error is formulated anew through an equivalent circuit analysis of the DC brush motor because the dependability of the method was not verified properly in .…”

“…So this paper reviews a method based on the Lorentz force law so as to use the back‐to‐back system for torque measurement but not efficient instrumentation. Concretely, the measurement error is formulated anew through an equivalent circuit analysis of the DC brush motor because the dependability of the method was not verified properly in . In addition, error evaluation is attempted for two miniature DC motors on the market: the three‐slot core motor MXN13 and the seven‐slot core motor DMN37 .…”