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Power Functions Motors Compared to old 9V Motor
Article and Graphics by Phillipe Hurbain
 | We compare here PF motors only with regular 9V mini-motor in its two versions: the 71427 produced from 1997 to 2002 and the 43362 motor produced from 2002 to 2006. Externally these motors are identical but differ mainly in the weight, 43362 motor is much lighter.
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| PF regular has a weight comparable to 9V motors. XL is much more heavy, something to expect from such a powerful thing. |
| Volume of the bounding box of the motor. |
| PF XL turns slowly, giving it an impressive torque. Once again, PF regular is similar to 9V motors. |
| A weak point of PF motors: their no-load current is high, denoting internal friction. They are not well suited to low power applications such as solar panel supply. The 71427 was exceptionally good for that. |
| Maximum torque delivered by the motors (motor is blocked). PF regular provides twice the torque of 9V motors, while PF XL outdoes its rivals with an axle twisting torque! |
| High torque comes with a price, current consumption. Note that the high stalled current of XL motor exceeds maximum current delivered by the PF remote receiver (800mA) and of its own internal protection. Maximum torque is only obtained with direct battery connexion for a short time. |
| Maximum mechanical power is delivered when load halves its no-load rotation speed. PF motors easily outdo their elders here but with a reduced efficiency. |
| Efficiency is the ratio between delivered mechanical power and electrical power provided. Note that the best efficiency is obtained when load decreases rotation speed by one quarter. |
| Ratio of mechanical power by motor weight. |
| Ratio of mechanical power by motor volume. |
Conclusions are clear: PF motors outperform their elders in all respect except energy efficiency, sometimes with huge difference.
PF motors power curves when connected to IR remote receiver
Since the motor driver inside remote receiver has some dropout and current limitation, the charts above don't tell the whole story. The two curves below show the mechanical power of PF motors driven by the remote receiver. These characteristics were measured at 9V (alkaline batteries voltage) and 7.2V (NiMH rechargeable batteries voltage).
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