The following table lists the primary performance parameters for the dc motors used in ELEC 201: maximum no-load rotational speed, stall torque, and stall current. These values were measured at the 12V design voltage. The mechanical power output of a motor is the product of its speed and torque, and the maximum generally occurs at one-half the maximum speed and torque. The final column calculates this number, and is a general figure of merit for ranking the various motors. A graph of these parameters over the full operating range is given for Johnson motor 31348 in this pdf document; the operating curves of the other motors are similar but with different scales.

Motor	Max Speed rpm	Torque mN-m	Stall Current Amps	Max Power Out: Watts
Mabuchi	4,740	12.6	0.42	2.5
flat Johnson	8,000	17.8	0.81	3.7
Johnson 3520	10,500	26.2	2.3	7.2
Johnson 31348	8,800	21.6	1.7	5.0
Johnson 30029	4,000	33.6	1.3	3.5
Nichibo MDS-1855	12,500	30.7	2.7	9.6

Most of these motors were bought from surplus or discount electronic dealers at various times, and model numbers, specifications, and additional supplies are not always available. The Mabuchi motor was used early in the course; we still have a large supply, but they are not in demand because of their low output. The flat Johnson motor is considerably smaller than the others, easier to mount in some cases, and reasonably powerful. The Johnson 3520 motor is very powerful; in fact, the stall current slightly exceeds the current specification of our motor driver chips. Apparently this motor is no longer available, and our supply is limited to used units, which sometimes no longer have full function. The Johnson 31348 motor was bought directly from Johnson Electric, Inc. ($2.25 in quantity in 2001), and has the maximum performance consistent with our motor drivers. The Johnson 30029 motor was purchased in 2001 from Jameco ($0.65). In addition to its economic appeal, it has interesting characteristics. Its very high torque and low speed means less gear reduction and thus less friction, which may compensate for its lower power output. The new Nichibo motors are the most powerful, and push the motor driver chips to their limit, but we haven't blown one yet. (See the Quick Link discussing gear ratios.)

The Johnson 3520 and 31348 have the same mechanical outline, given in this pdf document. The Mabuchi and Johnson 30029 are very similar, only somewhat longer. All the motors have threaded mounting holes that match the 8mm Fundamental LEGO horizontal spacing. Other Quick Link pages summarize mounting techniques.